EPA Ambient Water Quality Criteria for Chromium

DISCLAIMER

This report has been reviewed by the Environmental Criteria and

Assessment Office, U.S. Environmental Protection Agency, and approved

for publication. Mention of trade names or commercial products does not

constitute endorsement or recommendation for use.

AVAILABILITY NOTICE

This document is available to the public through the National

Technical Information Service, (NTIS), Springfield, Virginia 22161.

ii

FOREWORD

Section 304 (a)(1) of the Clean Water Act of 1977 (P.L. 95-217),

requires the Administrator of the Environmental Protection Agency to

publish criteria for water quality accurately reflecting the latest

scientific knowledge on the kind and extent of all identifiable effects

on health and welfare which may be expected from the presence of

pollutants in any body of water, including ground water. Proposed water

quality criteria for the 65 toxic pollutants listed under section 307

(a)(l) of the Clean Water Act were developed and a notice of their

availability was published for public comment on March 15, 1979 (44 FR

15926), July 25, 1979 (44 FR 43660), and October 1, 1979 (44 FR 56628).

This document is a revision of those proposed criteria based upon a

consideration of comments received from other Federal Agencies, State

agencies, special interest groups, and individual scientists. The

criteria contained in this document replace any previously published EPA

criteria for the 65 pollutants. This criterion document is also

published in satisfaction of paragraph 11 of the Settlement Agreement

in Natural Resources Defense Council, et. al. vs. Train, 8 ERC 2120

(D.D.C. 1976), modified, 12 ERC 1833 (D.D.C. 1979).

The term "water quality criteria" is used in two sections of the

Clean Water Act, section 304 (a)(I) and section 303 (c)(2). The term has

a different program impact in each section. In section 304, the term

represents a non-regulatory, scientific assessment of ecological effects.

The criteria presented in this publication are such scientific

assessments. Such water quality criteria associated with specific

stream uses when adopted as State water quality standards under section

303 become enforceable maximum acceptable levels of a pollutant in

ambient waters. The water quality criteria adopted in the State water

quality standards could have the same numerical limits as the criteria

developed under section 304. However, in many situations States may want

to adjust water quality criteria developed under section 304 to reflect

local environmental conditions and human exposure patterns before

incorporation into water quality standards. It is not until their

adoption as part of the State water quality standards that the criteria

become regulatory.

Guidelines to assist the States in the modification of criteria

presented in this document, in the development of water quality

standards, and in other water-related programs of this Agency, are being

developed by EPA.

STEVEN SCHATZOW

Deputy Assistant Administrator

Office of Water Regulations and Standards

iii

ACKNOWLEDGEMENTS

Aquatic Life Toxicology:

Charles E. Stephan, ERL-Duluth John H. Gentile, ERL-Narragansett

U.S. Environmental Protection Agency U.S. Environmental Protection Agency

Mammalian Toxicology and Human Health Effects:

Ernest Foulkes (author)

University of Cincinnati

Michael L. Dourson (doc. mgr.)

ECAO-Cin

U.S. Environmental Protection Agency

Bonnie Smith (doc. mgr.) ECAO-Cin

U.S. Environmental Protection Agency

Christopher T. DeRosa

University of Virginia

Alfred D. Garvin

University of Cincinnati

Charalingayya Hiremath, CAG

U.S. Environmental Protection Agency

Curt Klaassen

University of Kansas Medical Center

Steven D. Lutkenhoff, ECAO-Cin

U.S. Environmental Protection Agency

T.C. Siewicki

National Marine Fisheries Service

Jerry F. Stara, ECAO-Cin

U.S. Environmental Protection Agency

Anna M. Baetjer

Johns Hopkins School of Hygiene

J. Peter Bercz, HERL-Cin

U.S. Environmental Protection Agency

Kirk Biddle

U.S. Food and Drug Administration

Patrick Durkin

Syracuse Research Corp.

Warren S. Ferguson

Allied Chemical Corp.

Carl L. Giannetta

U.S. Food and Drug Administration

Rolf Hartung

University of Michigan

S. Roy Koirtyohann

University of Missouri

Debdas Mukerjee, ECAO-Cin

U.S. Environmental Protection Agency

Wayne Wolf

U.S. Department of Agriculture

Roy E. Albert, CAG*

U.S. Environmental Protection Agency

Technical Support Services Staff: D.J. Reisman, M.A. Garlough, B.L. Zwayer,

P.A. Daunt, K.S. Edwards, T.A. Scandura, A.T. Pressley, C.A. Cooper,

M.M. Denessen.

Clerical Staff: C.A. Haynes, S.J. Faehr, L.A. Wade, D. Jones, B.J. Bordicks,

B.J. Quesnell, P. Gray, B. Gardiner, R. Swantack.

*CAG Participating Members: Elizabeth L. Anderson, Larry Anderson, Ralph Arnicar,

Steven Bayard, David L. Bayliss, Chao W. Chen, John R. Fowle III, Bernard Haberman,

Charalingayya Hiremath, Chang S. Lao, Robert McGaughy, Jeffrey Rosenblatt,

Dharm V. Singh, and Todd W. Thorslund.

iv

TABLE OF CONTENTS

Criteria Summary

Introduction

Aquatic Life Toxicology

Introduction

Effects

Acute Toxicity

Chronic Toxicity

Plant Effects

Residues

Miscellaneous

Summary

Criteria

References

Mammalian Toxicology and Human Health Effects

Introduction

Exposure

Ingestion from Water and Food

Inhalation

Dermal

Pharmacokinetics

Absorption, Distribution, Metabolism and Excretion

Effects

Acute, Subacute, and C

Teratogenicity

Mutagenicity

Carcinogenicity

Criterion Formulation

Chronic Toxicity

Current Levels of Exposure

Special Groups at Risk

Basis and Derivation of Criterion

References

Appendix

Page

A-1

B-1

B-1

B-3

B-3

B-7

B-9

B-10

B-12

B-13

B-14

B-45

C-1

C-1

C-6

C-6

C-8

C-10

C-11

C-11

C-16

C-16

C-21

C-21

C-23

C-29

C-29

C-29

C-31

C-31

C-37

C-47

V

CRITERIA

CRITERIA DOCUMENT

CHROMIUM

Aquatic Life

For total recoverable hexavalent chromium the criterion to

protect freshwater aquatic life as derived using the Guidelines is

0.29 µg/l as a 24-hour average and the concentration should not

exceed 21 µg/l at any time.

For freshwater aquatic life the concentration (in µg/l) of

total recoverable trivalent chromium should not exceed the numerical

value given by e (1.08[ln(hardness)l+3.48) at any time. For

example, at hardnesses of 50, 100, and 200 mg/l as CaCO3 the concentration

of total recoverable trivalent chromium should not exceed

2,200, 4,700, and 9,900 µg/l, respectively, at any time. The

available data indicate that chronic toxicity to freshwater aquatic

life occurs at concentrations as low as 44 µg/l and would occur at

lower concentrations among species that are more sensitive than

those tested.

protect saltwater aquatic life as derived using the Guidelines is

18 µg/l as a 24-hour average and the concentration should not exceed

1,260 µg/l at any time.

For total recoverable trivalent chromium, the available data

indicate that acute toxicity to saltwater aquatic life occurs at

concentrations as low as 10,300 µg/l, and would occur at lower concentrations

among species that are more sensitive than those tested.

No data are available concerning the chronic toxicity of trivalent

chromium to sensitive saltwater aquatic life.

vi

Human Health

For the protection of human health from the toxic properties

of chromium (III) ingested through water and contaminated aquatic

organisms, the ambient water criterion is determined to be

mg/l.

For the protection of human health from the toxic properties

of chromium (III) ingested through contaminated aquatic organisms

alone, the ambient water criterion is determined to be 1,200 mg/l.

The ambient water quality criterion for chromium (VI) is

recommended to be identical to the existing water standard for

total chromium which is 50 µg/l. Analysis of the toxic effects

data resulted in a calculated level which is protective of human

health against the ingestion of contaminated water and contaminated

aquatic organisms. The calculated value is comparable to the present

standard. For this reason a selective criterion based on exposure

solely from consumption of 6.5 grams of aquatic organisms was

not derived.

vii

INTRODUCTION

Chromium is a metallic element which can exist in several

valence states. However, in the aquatic environment it virtually

is always found in valence states +3 or +6. Hexavalent chromium is

a strong oxidizing agent which reacts readily with reducing agents

such as sulfur dioxide to give trivalent chromium. Cr (III) oxidizes

slowly to Cr (VI), the rate increasing with temperature.

Oxidation progresses rapidly when Cr (III) adsorbs to MnO, but is

interfered with by Ca (II) and Mg (II) ions. Thus, accumulation

would probably occur in sediments where chemical equilibria favor

the formation of Cr (III), while Cr (VI), if favored, would presumably

dissipate in soluble forms. Hexavalent chromium exists in

solution as a component of an anion, rather than a cation, and

therefore, does not precipitate from alkaline solution. The three

important anions are: hydrochromate, chromate, and dichromate.

The proportion of hexavalent chromium present in each of these

forms depends on pH. In strongly basic and neutral solutions the

chromate form predominates. As pH is lowered, the hydrochromate

concentration increases. At very low pH the dichromate species

predominates. In the pH ranges encountered in natural waters the

proportion of dichromate ions is relatively low. In the acid portion

of the environmental range, the predominant form is hydrochromate

ion (63.6 percent at pH 6.0 to 6.2) (Trama and Benoit, 1960).

In the alkaline portion of the range, the predominant form is chromate

ion (95.7 percent at pH 8.5 to 7.8) (Trama and Benoit, 1960).

A-l

Trivalent chromium in solution forms numerous types of hexacoordinate

complexes (Cotton and Wilkinson, 1962). The best known

and one of the most stable of these is the amine class (complexes

include aquo- ions, acido- complexes (which are anionic), and polynuclear

complexes. Complex formation can prevent precipitation of

the hydrous oxide or other insoluble forms at pH values at which it

would otherwise occur.

Chromium salts are used extensively in the metal finishing

industry as electroplating,* cleaning agents, and as mordants in the

textile industry. They also are used in cooling waters, in the

leather tanning industry, in catalytic manufacture, in pigments and

primer paints, and in fungicides and wood preservatives. Kopp

(1969) reported a mean surface water concentration in the United

States of 9.7 µg/l, based on 1,577 samples. Trivalent chromium is

recognized as a essential trace element for humans. Hexavalent

chromium in the workplace is suspected of being carcinogenic.

A-2

REFERENCES

Cotton, F.A. and G. Wilkinson. 1962. Advanced Inorganic Chemistry.

Interscience Publishers, John Wiley and Sons, Inc., New York.

Kopp, J.F. 1969. The Occurrence of Trace Elements in Water. In: -

D. Hemphill (ea.), Trace Substances in Environmental Health III.

University of Missouri, Columbia. p. 59.

Trama, F.B. and R.J. Benoit. 1960. Toxicity of hexavalent chromium

to bluegills. Jour. Water Pollut. Control Fed. 32: 868.

A-3

Aquatic Life Toxicology*

INTRODUCTION

Chromium is a chemically complex metal which occurs in valence states

ranging from -2 to +6. The hexavalent and trivalent chromium compounds are

the biologically and environmentally significant forms of the element, but

they have very different chemical characteristics. Hexavalent chromium is

very soluble in natural water. Although it is a strong oxidizing agent in

acidic solutions, hexavalent chromium is relatively stable in most natural

waters. Trivalent chromium tends to form stable complexes with negatively

charged organic or inorganic species and thus its solubility and toxicity

vary with water quality characteristics such as hardness and alkalinity.

Most of the trivalent chromium species are either cationic or neutral and

the hexavalent species are anionic.

Information on the toxic effects of chromium on freshwater organisms is

relatively extensive, but the data base for hexavalent chromium is greater

than that for trivalent chromium. The data indicate that water hardness has

an insignificant influence on the toxicity of hexavalent chromium in fresh

water; thus, it is not necessary to develop a criterion as a function of

water quality. On the other hand, the freshwater data indicate that water

hardness has a significant influence on the acute toxicity of trivalent

chromium.

Most of the saltwater acute and chronic toxicity data are for hexavalent

chromium. Only a few studies have been conducted on the effects of triva

*The reader is referred to the Guidelines for Deriving Water Quality Criteria

for the Protection of Aquatic Life and Its Uses in order to better understand

the following discussion and recommendation. The following tables

contain the appropriate data that were found in the literature, and at the

bottom of each table are calculations for deriving various measures of toxicity

as described in the Guidelines.

B-l

lent chromium on saltwater organisms, probably because of the low solubility

of trivalent chromium in saltwater. The kinetics of precipitation of trivalent

chromium in saltwater systems are complex but regardless of its form,

trivalent chromium may still be ingested and bioconcentrated by filter or

deposit feeding bivalve mollusc and polychaete species.

Of the analytical measurements currently available, water quality criteria

for trivalent chromium and for hexavalent chromium are probably best

stated in terms of total recoverable trivalent chromium and total recoverable

hexavalent chromium, respectively, because of the variety of forms of

chromium that can exist in bodies of water and the various chemical and toxicological

properties of these forms. The forms of chromium that are commonly

found in bodies of water and are not measured by the total recoverable

procedure, such as the chromium that is a part of minerals, clays, and sand,

probably are forms that are less toxic to aquatic life and probably will not

be converted to the more toxic forms very readily under natural conditions.

On the other hand, forms of chromium that are commonly found in bodies of

water and are measured by the total recoverable procedure, such as the free

ion, and the hydroxide, carbonate, and sulfate salts, probably are forms

that are more toxic to aquatic life or can be converted to the more toxic

forms under natural conditions. Because the criterion is derived on the

basis of tests conducted on soluble inorganic salts of chromium, total chromium

and total recoverable chromium concentrations in the tests will probably

be about the same and a variety of analytical procedures will produce

about the same results. Except as noted, all concentrations reported herein

are expected to be essentially equivalent to total recoverable trivalent or

hexavalent chromium concentrations. All concentrations are expressed as

chromium, not as the compound.

B-2

EFFECTS

Acute Toxicity

Hexavalent Chromium

As shown in Table 1, the freshwater data base available for hexavalent

chromium has numerous acute values for thirteen species from ten different

families. Acute values have been reported for six freshwater invertebrate

species from five families. These acute values range from 67 11g/1

for a scud to 59,900 ug/l for a midge. The scud Gammarus pseudolimnaeus was

by far the most sensitive species tested with an LC50 value about onefiftieth

of the next lower acute value. Invertebrate species are generally

more sensitive to hexavalent chromium than fish species. As shown in Table

3, the species mean acute values for five of the six invertebrate species

are less than that of any fish species. The rotifer Philodina roseola was

about three times as sensitive to chromium at 35°C as at 5'C (Schaffer and

Pipes, 1973).

Table I also lists acute values for seven freshwater fish species,

of which more than 70 percent of the values are for the goldfish and fathead

minnow. The 96-hour LC5G Values range from 17,600 pg/l for the fathead

minnow to 249,000 vg/l for the goldfish. Static tests with unmeasured concentrations

and flow-through tests with measured concentrations gave similar

Wallen, et al. (1957) studied the toxicity of hexavalent chromium

to mosquitofish in turbid water using potassium and sodium salts of both dichromate

and chromate (Table 6). Based on chromium, both dichromate salts

were more toxic than the chromate salts. The geometric means of the two

values were 95,000 pg/l and 120,000 pg/l for the dichromate and chromate,

respectively. Trama and Benoit (1960) studied the toxicity of chromium to

B-3

the bluegill using potassium dichromate and potassium chromate. The 96-hour

the chromate salt. They attributed the lower LC50 value of the dichromate

lower pH values.

The toxicity of hexavalent chromium to the bluegill in soft and

hard water was tested at 18°C and 3O'C (Academy of Natural Sciences of Philadelphia,

1960). At 18'C the 96-hour LCso values were 113,000 pg/l in

soft water and 135,000 pg/l in hard water. Similar results were obtained at

3O'C with the 96-hour LC50 values being 113,000 pg/l in soft water and

130,000 ,,g/l in hard water.

to the fathead minnow and bluegill in soft and hard water. The

96-hour LC50 values for the fathead minnow in soft and hard water were

17,600 and 27,300 ug/l, respectively. The corresponding values for the

bluegill were 118,000 pg/l and 133,000 ug/l.

The data from Adelman and Smith (1976) shown in Tables 1 and 6 indicate

that the threshold lethal concentration for hexavalent chromium does

not occur within 96 hours. They found that for 16 tests, the average ratio

goldfish.

The Freshwater Final Acute Value for hexavalent chromium, derived

from the species mean acute values listed in Table 3 using the calculation

procedures described in the Guidelines, is 21.2 vg/l.

Acute toxicity data for hexavalent chromium and twenty saltwater

fish and invertebrate species have been reported (Table 1). Acute toxicity

values ranged from 2,000 ug/l for a polychaete worm and mysid shrimp to

B-4

105,000 ,,g/l for the mud snail. The LC50 values for fish species range

from 12,400 vg/l for the Atlantic silverside to 91,000 vg/l for the murmichog.

The most sensitive species were the polychaete annelids (2,000-8,000

ug/l), the mysid shrimp (2,000-4,400 pg/l), and two copepods (3,650 and

6,600 pg/l). The LC50 values for hexavalent chromium and bivalve molluscs

range from 57,000 ug/l for the soft shell clam to 14,000 pg/l for the brackish

water clam. The sensitivity of the latter was salinity dependent with

acute toxicity values of 35,000 pg/l and 14,000 pg/l at salinities of 22

g/kg and 5.5 g/kg, respectively. Adult starfish were insensitive with an

LC5o value of 32,000 pg/l. A Saltwater Final Acute Value of 1,260 ug/l

was obtained for hexavalent chromium using the species mean acute values in

Table 3 and the calculation procedures described in the Guidelines.

Trivalent Chromium

As shown in Table 1, the data base for acute toxicity of trivalent

chromium to freshwater organisms includes 28 values for 19 animal species

from 14 different families. Although the total number of values is smaller,

more species have been tested with trivalent chromium than with hexavalent

chromium.

Thirteen acute values for trivalent chromium have been reported for

eight invertebrate species (Table 1). These values range from 2,000 ug/l

for Daphnia magna and the mayfly to 64,000 pg/l for the caddisfly, all three

of which were determined in soft water. Chapman, et al. (Manuscript) studied

the effects of three levels of water hardness on the toxicity of trivalent

chromium to Oaphnia magna. They reported 48-hour acute values that

ranged from 16,800 pg/l in soft water to 58,700 ug/l in hard water.

Table 1 also includes data for the acute toxicity of trivalent

chromium to freshwater fish species. Fifteen 96-hour LC50 values have

B-5

been reported for 11 fish species from eight families. These values ranged

from 3,330 ,,g/l for the guppy in soft water to 71,900 pg/l for the bluegill

in hard water. There are comparative data on the influence of water hardness

on toxicity for the fathead minnow and the bluegill. The 96-hour

LC50 values for the fathead minnow tested in soft and hard water are 5,070

and 67,400 ug/l, respectively. The corresponding values for the bluegill

are 7,460 and 71,900 pgll.

The comparative data from Pickering and Henderson (1966) indicate

that in soft water trivalent was more toxic than hexavalent chromium to four

fish species. In hard water trivalent chromium was less toxic to the fathead

minnow and more toxic to the bluegill than hexavalent chromium.

An exponential equation was used to describe the observed relationship

of the acute toxicity of trivalent chromium to hardness in fresh water.

A least square regression of the natural logarithms of the acute values on

the natural logarithms of hardness produced slopes of 1.64, 0.83, and 0.78,

respectively, for Daphnia magna, fathead minnow, and bluegill (Table 1).

The first two slopes were significant, but the last could not be tested because

only two values were available. The arithmetic mean slope (1.08) was

used with the geometric mean toxicity value and hardness for each species to

obtain a logarithmic intercept for each of the nineteen freshwater species

for which acute values are available for trivalent chromium. The species

mean acute intercept, calculated as the exponential of the logarithmic intercept,

was used to compare the relative acute sensitivities (Table 3).

Both the most sensitive and the least sensitive species are invertebrates.

A freshwater final acute intercept of 32.3 pg/l was obtained for trivalent

B-6

chromium using the species mean acute intercepts listed in Table 3 and the

calculation procedures described in the Guidelines. Thus, the Final Acute

Equation is e (1.08[ln(hardness)]+3.48).

The few data that are available on the toxicity of trivalent chromium

to saltwater species (Table 1) indicate that, probably because of precipitation,

a large amount of trivalent chromium must be added to saltwater

to kill aquatic organisms.

Chronic Toxicity

Hexavalent Chromium

The chronic data base for hexavalent chromium and freshwater species

(Table 2) contains data for three fish species. Benoit (1976) studied

the effects of hexavalent chromium in the chronic tests with brook trout and

rainbow trout. The limits of 200 and 350 ug/l, with a chronic value of 265

ugil, were established on the basis of survival for both species. Growth in

weight during the first eight months was retarded at all test concentrations.

However, this was a temporary effect on growth and was not used to

establish the chronic limits.

Sauter, et al. (1976) also used the rainbow trout in a chronic

study. The limits for this early life stage exposure were 51 and 105 ,,g/l

with a chronic value Of 73 pg/l. These values were established on the basis

of a reduction of growth after 60 days post-hatch exposure. This chronic

value of 73 ug/l was about one-fourth of the chronic value of 265 vg/l from

the chronic test reported by 8enoit (1976).

The acute-chronic ratios for brook trout and rainbow trout, calculated

from the data of BenOft (1976) are 220 and 260, respectively (Table

to ca?cu?ate acute-chronic ratios.

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The limits of 1,000 and 3,950 ug/l in a life-cycle test with the

fathead minnow (Pickering, 1980) were based on survival. In this exposure

also an early retardation of growth was only temporary. The chronic value

of 1,990 lrg/l is much higher than that for the trout but the acute-chronic

ratio of 19 is much lower.

No chronic values are available for hexavalent chromium with any

freshwater invertebrate species.

Results of life-cycle studies with the saltwater polychaete, Neanthes

arenaceodentata, and the mysid shrimp Mysidopsis bahia are reported in

Table 2. Other life cycle data on the polychaetes, Capitella capitata and

Ophryotrocha*diadema, (Table 6) were not included here because exposure concentrations

were not adequately defined. Hexavalent chromium was chronically

toxic to the polychaete at 25 ug/l and to the mysid at 132 pg/l and both

of these species were among the most acutely saensitive to hexavalent chromium

(Table 1). The acute-chronic ratios were 120 for the polychaete and 15

for the mysid. These ratios, while quite different, are consistent with

those for freshwater fish species.

The geometric mean of the five acute-chronic ratios for three

freshwater fish species and two saltwater invertebrate species is 72. The

Freshwater Final Acute Value of 21.2 ug/l divided by the acute-chronic ratio

of 72 results in a Freshwater Final Chronic Value for hexavalent chromium of

0.29 ug/l. Similarly, the Saltwater Final Chronic Value for hexavalent

chromium is 17.5 ug/l.

Trivalent Chromium

The freshwater chronic data base for trivalent chromium (Table 2)

contains data for a life-cycle test with Daphnia magna in soft water and a

life-cycle test with the fathead minnow in hard water. In hard water the

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chronic value of 1,020 ug/l for the fathead minnow is greater than the

chronic value of 66 ugll for Daphnia magna. Trivalent chromium appeared to

be more toxic to Daphnia magna in hard water than in soft water. The

chronic value in soft water was 66 ug/l (Table 2), but in hard water the

lowest tested concentration (44 11911) inhibited reproduction (Table 6).

Chapman, et al , (Manuscript) speculated that ingested precipitated chromium

contributed to the toxicity in hard water. Biesinger and Christensen (1972)

also conducted a life-cycle test with Daphnia magna but the test concentrations

ratio is 27 for the fish and 250 for Daphnia magna.

No data on the chronic effects of trivalent chromium on saltwater

species are available.

Plant Effects

Hexavalent Chromium

The data for four species of freshwater algae and Eurasian watermilfoil

(Table 4) indicate that algae are sensitive to hexavalent chromium.

The effect concentrations of chromium range from 10 vg/l for reduction in

growth of a green alga to 1,900 ug/l for root weight inhibition of Eurasian

watermilfoil. Growth of the green alga, Chlamydomonas reinhardi, was reduced

at a concentration of 10 ug/l in BOLD's basal medium.

Toxicity of hexavalent chromium to the diatom, Navicula seminulum,

was tested at three temperatures in both soft and hard waters (Academy of

Natural Sciences of Philadelphia, 1960). The geometric mean of the concentrations

causing a 50 percent reduction in growth was 245 ug/l in soft

waters and 335 pg/l in hard water. The diatom was more sensitive to chromium

at 22'C than at 30°C.

B-9

chromium. However, chromium concentrations were not measured in any of

the exposures listed in Table 4, so a Freshwater Final Plant Value is not

available for hexavalent chromium.

Toxicity studies were performed with the saltwater macroalga, Macrocystis

pyrifera, to investigate the effect of hexavalent chromium on photosynthesis

(Table 4). The 96-hour EC50 reported by Clendenning and North

days at 1,000 ug/l (Bernhard and Zattera, 1975).

the plants were among the most sensitive species

cause no chromium concentrations were measured,

Value can be stated.

Trivalent Chromium

These data indicate that

to chromium. Again, beno

Saltwater Final Plant

Toxicity data are available for only one freshwater plant species

(Table 4). Root weight was inhibited at a trivalent chromium concentration

so a Freshwater Final Plant Value for trivalent chromium is not available.

No saltwater plant species have been tested with trivalent chromium.

Residues

Hexavalent Chromium

Data are available from two studies with the rainbow trout and hexavalent

chromium, and the bioconcentration factor is about one (Table 5).

Data on bioconcentration of hexavalent chromium and saltwater species is

limited to one polychaete species and the oyster and blue mussel (Table 4).

The bioconcentration factors are in the range of 125 to 200.

B-10

Trivalent Chromium

Data are not available concerning the bioconcentration of trivalent

chromium by freshwater organisms.

Uptake of trivalent chromium by the blue mussel, soft shell clam,

and oyster has been studied and the bioconcentration factors range from 86

to 153 (Table 5). These results are similar to those for hexavalent

chromium.

Miscellaneous

Hexavalent Chromium

Table 6 includes data for other effects on freshwater species that

were not included in the first five tables. The data base for hexavalent

chromium is more extensive than that for trivalent chromium.

The data in this table indicate that Daphnia magna is a very sensitive

species. Debalka (1975) reported 72-hour EC5D values that ranged

from 31 to 81 ugil. In addition, Trabalka and Gehrs (1977) studied the

chronic toxicity of hexavalent chromium to Daphnia magna. They found a significant

effect on both life span and fecundity at all test concentrations

this datum is included in Table 6 instead of Table 2. This value certainly

supports the Final Chronic Value.

Algae also appear to be sensitive to chromium. Zarafonetis and

Hampton (1974) reported inhibition of photosynthesis of a natural population

Data in Table 6 also indicate that low concentrations of hexavalent

chromium have a deleterious effect on the growth of fishes. Olson and

Foster (1956) reported a statistically significant effect on growth of chinook

salmon at 16 pg/l and on rainbow trout at 21 ,,g/l. At these concentra-

B-11

tions, growth in weight was reduced about ten percent. As noted earlier,

Benoit (1976) and Pickering (1980) also reported effects on growth of fishes

exposed to low concentrations. However, in these life-cycle tests the effect

was temporary and was not used to establish chronic limits.

Chronic mortality of the saltwater polychaete, Neanthes arenaceodentata,

resulted in 59-day EC50 value for hexavalent chromium of 200 ug/l

compared to the 96-hour LC50 of 3,100 ug/l and the chronic value of 25

building at 79 ug/l.

Holland, et al. (1960) reported toxicity to silver salmon at a concentration

(Table 1) reported for the speckled sanddab (30,500) but twice as high as

The effect of salinity and temperature on hexavalent chromium toxicity

and 20 g/kg toxicity increased with increasing temperature between 10 to

Trivalent Chromium

Embryos of a freshwater snail are rather insensitive to trivalent

chromium (Table 6).

Mearns, et al. (1976) were able to kill a saltwater polychaete worm

with trivalent chromium by adding 50,400 ug/l, probably because the pH

dropped to 4.5 due to the extensive precipitation. When the pH was raised

to about 7.9 by adding sodium hydroxide, the worms not only survived for at

least 160 days, but also reproduced (Table 6).

B-12

Summary

Hexavalent Chromium

Acute data for hexavalent chromium are available for thirteen

freshwater animal species from ten different families which include a wide

variety of animals that perform a spectrum of ecological functions. Data

indicate that water hardness has an insignificant influence on toxicity.

Most invertebrate species are more sensitive than most fish, and a scud is

the most acutely sensitive species.

Long-term tests with brook trout and rainbow trout both gave

chronic values of 265 ugil which are much lower than the chronic value of

1,990 ug/l for the fathead minnow. No chronic values are available for

freshwater invertebrate species.

The data for freshwater plants indicate that green algae are sensitive

to hexavalent chromium and the bioconcentration factor for rainbow

trout is about one.

Other data reveal more sensitive effects. The growth of chinook

salmon was reduced at a measured concentration of 16 ug/l. In chronic tests

with brook trout, rainbow trout, and fathead minnows a temporary adverse

affect on growth occurred at low concentrations. In a life-cycle test with

Daphnia magna the lowest test concentration of 10 ug/l reduced life span and

fecundity.

The acute toxicity of hexavalent chromium to twenty saltwater vertebrate

and invertebrate species ranges from 2,000 ug/l for polychaete annelids

and a mysid shrimp, to 105,000 ug/l for the mud snail. Polychaetes

and microcrustaceans are the most acutely sensitive taxa. The chronic

values for polychaetes and a mysid shrimp are 25 and 132 ug/l, respectively,

and the acute-chronic ratios are 120 and 15, respectively. Toxicity to

macroalgae was reported at 1,000 and 5,000 ug/l.

8-13

Data for bioconcentration factors for hexavalent chromium range

from 125 to 200 for bivalves and polychaetes.

Trivalent Chromium

Acute data for trivalent chromium are available for 19 freshwater

animal species from 14 different families. The data indicate that water

hardness has a significant influence on toxicity, with trivalent chromium

being more toxic in soft water. In soft water the sensitivity of fish and

invertebrate species is comparable.

One life-cycle test with Daphnia magna in soft water gave a chronic

value of 66 ugil, but another gave a chronic value of 445 ug/l. In a

chronic test in hard water the lowest test concentration of 44 ug/l inhibited

reproduction of Daphnia magna, but this effect may have been due to

ingested precipitated chromium. In a life-cycle test with the fathead

minnow in hard water the chronic value was 1,020 ugll. Toxicity data are

available for only one freshwater plant species. A concentraton of 9,900

ug/l inhibited growth of roots of Eurasian watermilfoil. No bioconcentration

factors are available for trivalent chromium and freshwater organisms.

The available acute values for trivalent chromium in saltwater are

both above 10,000 11911, probably because trivalent chromium has a low solubility

in saltwater. Bioconcentration factors for saltwater organisms and

trivalent chromium range from 86 to 153. This is similar to the bioconcentration

factors for hexavalent chromium and saltwater species.

CRITERIA

For total recoverable hexavalent chromium the criterion to protect

freshwater aquatic life as derived using the Guidelines is 0.29 pg/l as a

24-hour average and the concentration should not exceed 21 ug/l at any time.

B-14

For freshwater aauatic life the concentration (in pg/l) of total recoverable

trivalent chromium should not exceed the numerical value given by

e(1*a8[1n(hardness)l+3048) at any time. For example, at hardnesses of 50,

100, and 200 mg/l as CaC03 the concentration of total recoverable trivalent

chromium should not exceed 2,200, 4,700, and 9,900 ug/l, respectively,

at any time. The available data indicate that chronic toxicity to freshwater

aquatic life occurs at concentrations as low as 44 ug/l and would

occur at lower concentrations among species that are more sensitive than

those tested.

For total recoverable hexavalent chromium the criterion to protect saltwater

aquatic life as derived using the Guidelines is 18 ug/l as a 24-hour

average and the concentration should not exceed 1,260 pg/l at any time.

For total recoverable trivalent chromium, the available data indicate

that acute toxicity to saltwater aquatic life occurs at concentrations as

that are more sensitive than those tested. No data are available concerning

the chronic toxicity of trivalent chromium to sensitive saltwater aquatic

life.

B-15

I

v;

5

L

(0 rC

ii,

CO --

+-

BP’

!!I cl

5:

2% OL +C

OV

Qw

I I I I I I

v)

_I w

I I I I I I I I I I I I

I I I I

1 I I

I I I I I I I I I I I I I

0

I

u;

I

v;

I 3

9 9

VJ *

ml -I

I I I I I

8

0

m 8

O-

9

x

E

I

II

I

0’

.2

II

L

%

.

‘;;

l

t

I

c

r-

N

0

-I

0

t

2

s

%

9

Q 9

w

I I I

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I 82, I I I

8

Table 3. (Continued)

Rank*

2

I

19

18

17

16

15

14

13

12

11

IO

9

8

Spacles

Rotlfer,

Philodina acuticornis

Speclas Mean

Acute Va I ue

(pq/1)

3,100

Spaclas Mean

Acute-clwon I c

Ratio

Scud,

Gammarus pseudolinmaeus

61

SALTWATER SPECIES

Mud snail,

Nassar lus obsoletus

Blue crab,

Calllnectes sapfdus

Mummlchog,

Fundulus heteroclltus

Soft she1 I clam,

& arenar la

Starf Ish,

Asterlas forbesi

Speck led sanddab,

Citharichthys stigmaeus

Brackish water clam,

cuneata Rangia

Copepod,

Tlgrlopus japonicus

Atlantic silverside,

Menidla menidia --

Her-ml t crab,

Pagurus longicarpus

Polychaete worm,

Ophryotrocha diadema

Cow@,

Acartla clausi --

to5,ooo

93,000

91,000

57,000

32,000

30,500

22,000

17,200

15,000

10,000

7,500

6,600

B-30

Table 3. (Continued)

Rank’

7

Species

Polychaete worm,

Capitella capltata

6 Mysid shrimp,

Mysidopsis biqeloui

Ctenodrilus serratus

4 CoPePod,

Pseudodiaptomus coranatus

3 PO I ychaete worm,

Neanthes arenaceodentata

2 Mysid shrinp,

Wysidopsis bahia

1 Polychaete worm,

Nereis vlrens --

Species Mean Species Meen

Acute Value Acut~hronlc

QlQ/i) Ratio

6,300

4,400

4,300

3,650

3,100

2,@33

2,000

Rank* Species

Species Mean

Acute I nteccept

(W/i)

Trivalent Chrcunium

FRESHWATER SPECIES

I8 Caddlsf ly,

Hydropsyche betten I

1,075

17 Caddlsf ly,

Unidentified

728

16 Oamself ly,

Unidentified

633

15 Str 1 ped bass,

Morone saxatilis

233

120

I5

Species Mean

Acute-Chrcmlc

Ratlo

B-31

Table 3. Kant inued)

RankB

14

I3

I2

11

IO

9

8

7

6

Species

Pumpkinseed,

J’bbOSUS LepOtIIlS

American eel,

Anguiiia rostrata

Randed klilifish,

Fundulus dlaphanus

Bluegl I I,

Lepomis macrochirus

Wh I te perch,

Morone amaricana

Carp,

Cyprinus carp10

Goldfish,

Carrasius auratus

Ciadoceran,

Daphnia magna

Annei id,

Nais sp.

CrJPPV,

Poeciila retlcuiata

Snal I,

Amnicoia sp.

Fathead minnow,

Pimephales pfomeias

Scud,

Gammarus sp.

224

224

224

I91

191

189

I61

I38

136

132

I23

118

47

Species Mean

ACUh-ClUOniC

Ratio

B-32

Table 3. (Continued)

Species Mean species HemI

Acute intercept Acute-Chronic

Rank* species erg/i 1 Ratio

I hYf IY, 33.4

Ephemerela subvaria

acute value or intercept.

Hexava lent Chromium

Freshwater Flnai Acute Value = 21.2 Rg/l

Saltwater Final Acute Value = 1,260 ug/i

Final AcuteChronic Ratio = 72 (see text)

Freshwater Ffnal Chronic Value = 121.2 ug/ff/72 = 0.29 ug/f

Saltwater Final Chronic Value = (1,260 ug/ff/72 = 17.5 ug/i

Trivalent Chromium - Freshwater

Finaf Acute Intercept = 32.3 ug/i

Natural logarithm of 32.3 = 3.48

Acute slope = I.08 (see Table if

B-33

I

.

.

a

t

ff

m

4

4

i

f

W

m

A

&d I

m

m

.

K- Is:

I I I

I I I

I I I I I I

.

n,

f t

REFERENCES

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aquatic life to certain chemicals commonly found in industrial wastes.

Final Report: U.S. PHS Grant RG-3965 (CZRl).

Adelman, I.R. and L.L. Smith. 1976. Standard test fish development.

Part 1. Fathead minnows (Pimephales promelas) and goldfish (Carrassius auratus)

as standard fish in bioassays and their reaction to potential reference

toxicants. U.S. Environ. Prot. Agency, EPA 600/3-76-061a, Duluth, Minnesota.

Anderson, B.G. 1948. The apparent thresholds of toxicity to Daphnia magna

for chlorides of various metals when added to Lake Erie water. Trans. Am.

Fish. Sot. 78: 96.

Benoit, D.A. 1976. Chronic effects of hexavalent chromium on brook trout

(Salvelinus fontinalis) and rainbow trout (Salmo gairdneri). Water Res.

10: 497.

Bernhard, M. and A. Zattera. 1975. Major Pollutants in the Marine Environment.

In: Marine Pollution and Marine Waste Disposal. Pergamon Press, New -

York. p. 195.

survival, growth, reproduction, and metabolism of Daphnia magna. Jour.

B-45

Bills, T.D., et al. 1977. Effects of residues of the polychlorinated biphenyl

Aroclor 1254 on the sensitivity of rainbow trout to selected environmental

contaminants. Prog. Fish. Cult. 39: 150.

Birge, W.J., et al. 1978. Embryo-larval Bioassays on Inorganic Coal Elements

and in situ Biomonitoring of Coal-waste Effluents. In: Proc. of a -- -

Symposium. Surface Mining and Fish/Wildlife Needs in the Eastern United

States. FWSIOBS-78-81. p. 97.

binary mixtrues of cyanide and hexavalent chromium, zinc, or ammonia to the

fathead minnow (Pimephales promelas) and rainbow trout (Salmo gairdneri).

Jour. Fish. Res. Board Can. 36: 164.

Buhler, D.R., et al. 1977. Tissue accumulation and enzymatic effects of

hexavalent chromium in rainbow trout (Salmo gairdneri). Jour. Fish Res.

Board Can. 34: 9.

(Rotifera) as a bioassay organisms for heavy metals. Water Resour. Bul.,

Am. Water Res. Assoc. 10: 648.

exposure to acutely sublethal concentrations of chemicals. Arch.

Hydrobiol. 77: 164.

B-46

Calabrese, A., et al. 1973. The toxicity of heavy metals to embryos of the

American oyster Crassostrea virginica. Marine Biol. 18: 162.

Rates and Metabolic Activity of Mytilus edulis L. and Mya arenaria L. In: -

Physiological Responses of Marine Biota to Pollutants. Academic Press, New

York. p. 225.

Chapman, G.A., et al. Effects of water hardness on the toxicity of metals

to Daphnia magna. Status Report, January 1980. (Manuscript)

Kelp, Macrocystis pyrifera. a: Proc. 1st Conf. Waste Disposal Marine Environ.,

Berkeley, California. 82.

cadmium to Daphnia magna. Thesis, Miami Univ., Oxford, Ohio.

certain animals. Jour. Water Pollut. Con. Fed. 37: 1308.

Toxicol. 6: 315.

macrochirus: Hyperactivity induced by sublethal concentrations of cadmium,

chromium, and zinc. Jour. Fish Biol. 1: 19.

B-47

Fales, R.R. 1978. The influence of temperature and salinity on the toxicity

of hexavalent chromium to the grass shrimp Palaemonetes pugio (Holthius).

Bull. Environ. Contam. Toxicol. 20: 447.

Frank, P.M. and P.B. Robertson. 1979.

ity of cadmium and chromium to the b

Environ. Contam. Toxicol. 21(1-Z): 74.

The influence of sa 1 inity on toxiclue

crab, Callinectes Bull. sapidus.

Fromm, P.O. and R.H. Schiffman. 1958. Toxic action of hexavalent chromium

on largemouth bass. Jour. Wildl. Manage. 22: 40.

by trout. Jour. Water Pollut. Con. Fed. 34: 1151.

Toxicol. 17: 66.

Hill, C.W. and P.O. From. 1968. Response of the interrenal gland of rainbow

Holland, G.A., et al. 1960. Toxic effects of organic and inorganic pollutants

on young salmon and trout. Wash. Dept. Fish. Res. Bull. 5.

B-48

larvae and fingerlings to nine chemicals used in pond culture. Proc. 24th

Annu. Conf., Southeastern Assoc. Game Fish Comm., 1970. p. 431.

Kuhnert, P.M., et al. 1976. The effect of in vivo chromium exposure on --

Na/K- and Mg-ATPase activity in several tissues of the rainbow trout (Salmo

gairdneri). Bull. Environ. Contam. Toxicol. 15: 383.

Mearns, A.J. and D.R. Young. 1977. Chromium in the Southern California

Marine Environment. In: C.S. Giam (ed.), Pollutant Effects on Marine Organisms.

D.C. Heath and Co., Lexington, Massachusetts. p. 125.

bivalves. Bull. Tokaj. Regional Fish. Res. Lab. 32: 131.

mercury copper, and chromium for Rangia cuneata (Pelecypoda, Mactridae).

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Hanford Biol. Res. Annu. Rep. for 1957. HW-53500: 215.

B-49

Olson, P.A. and R.F. Foster. 1956. Effect of chronic exposure to sodium

dichromate on young chinook salmon and rainbow trout. Hanford Biol. Res.

Annu. Rep. for 1955. HW-41500: 35.

Oshida, P.S. 1978. A safe level of hexavalent chromium for a marine polychaete.

S. Calif. Coastal Water Res. Proj., El Segundo, Caifornia. Ann.

Rep. p. 169.

Oshida, P.S. and D.J. Reish. 1975. Effects of chromium on reproduction in

polychaetes. S. Calif. Coastal Water Res. Proj., El Segundo, California.

Ann. Rep. 55.

Oshida, P.S. and J.L. Wright. 1978. Effects of hexavalent chromium on sea

urchin embryo and brittle stars. S. Calif. Coastal Water Res. Proj., El

Segundo, California. Ann. Rep. 181.

Oshida, P.S., et al. 1976. The effects of hexavalent and trivalent chromium

on Neanthes arenaceodentata (Polychaeta: Annelida). S. Calif. Coastal

Water Res. Proj., El Segundo, California. TM225: 58.

Patrick, R., et al. 1975. The role of trace elements in management of

nuisance growth. EPA 660/Z-75-008. U.S. Environ. Prot. Agency, Corvallis,

Oregon.

Pickering, O.H. 1980. Chronic toxicity of hexavalent chromium to the fathead

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B-50

Pickering, Q.H. Chronic toxicity of trivalent chromium to the fathead minnow,

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B-51

Reish, D.J., et al. 1976. The effect of heavy metals on laboratory populations

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Duluth, Minnesota.

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B-52

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B-53

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B-54

Mammalian Toxicology and Human Health Effects

INTRODUCTION

Chromium (Cr) is a common element, present in low concentrations

throughout nature. Its toxicity has long been recognized,

but detailed analysis of toxic effects is complicated by the occurrence

of many different compounds of the metal; these may contain

Cr in different valence states and are distinguished by their chemical,

physical, and toxicological properties.

This document considers relevant chemical and physical properties

of Cr compounds to which man may be exposed, and attempts to

evaluate possible health hazards associated with such exposures.

The general area of environmental effects of chromium compounds was

recently reviewed by the U.S. Environmental Protection Agency (U.S.

EPA, 1978); a valuable discussion of the medical and biological

effects of Cr in the environment is found also in a volume published

by the National Academy of Sciences (NAS, 1974). Occupational

hazards of chromium were assessed in a Criteria Document

prepared in 1975 [National Institute for Occupational Safety and

Health (NIOSH), 1975]. Mertz (1969) provided a valuable survey of

the biochemical properties of Cr compounds. A general review of

the occurrence, metabolism, and effects of chromium has been presented

by the NAS (1977).

To avoid unnecessary duplication, previously reviewed material

will not be considered at great length except when it impinges

directly on present critical considerations. Detailed documentation

for most of the available information can be found in the earlier

reviews.

C-l

There is little need to discuss here the detailed chemistry of

chromium, as this subject has been adequately reviewed in the recent

past (U.S. EPA, 1978). However, an evaluation of the significance

of various routes of exposure to compounds containing Cr, and

of the factors determining rates of uptake and toxicity of such

compounds, requires an understanding of their physical properties

and of their chemical and biochemical reactions.

The metallic element Cr belongs to the first series of transition

elements, and occurs in nature primarily as compounds of its

trivalent [Cr (III)] form. Generally speaking, the hexavalent compounds

are relatively water-soluble and readily reduced to the more

insoluble and stable forms of Cr (III) by reaction with organic reducing

matter. Because large amounts of Cr (VI) are produced and

utilized in industry (primarily as chromates and dichromates), and

because of their ready solubility, traces of such compounds are

frequently found in natural waters.

As pointed out, Cr (VI) is rapidly reduced when in contact with

biological material. The reverse reaction is not known to occur in

the human body. Trivalent Cr forms stable hexacoordinate complexes

with many molecules of biochemical interest. Interaction of Cr (III)

with such compounds may involve binding to carboxy- groups of proteins

or smaller metabolites, coordination with certain amino

acids, and binding to nucleic acids and nucleoproteins. This last

reaction is of special significance in the consideration of the

carcinogenic potential of Cr compounds. The field was reviewed by

Mertz (1969) and it suffices here to emphasize the stability of

these Cr complexes, and the fact that the element is found combined

C-2

with both RNA and DNA. An effect of Cr on the tertiary structure of

nucleic acids is clearly indicated. In general, it may be concluded

that reduction of Cr (VI) to Cr (III) and its subsequent coordination

to organic molecules of biochemical interest explain in

large measure the biological reactivity of Cr compounds. Thus, the

well-known reaction of Cr with skin proteins (i.e., the tanning

process) involves coordination sites of Cr (III). For reasons of

solubility, however, uptake of compounds of Cr (VI) by the living

organism generally exceeds that of Cr (III) compounds (see Acute,

Subacute, and Chronic Toxicity section).

A good illustration of the behavior of Cr compounds in biological

systems is furnished by the reaction of Cr with erythrocytes

(Gray and Sterling, 1950). These cells do not react to any significant

extent with Cr (III): in contrast, they rapidly take up anions

of hexavalent Cr compounds, presumably utilizing the broadly

specific anion transport facilitation in erythrocytes reviewed by

Fortes (1977). Thus, we may invoke as a likely explanation for the

greater toxicity of Cr (VI) than of Cr (III) compounds their more

rapid uptake by tissues due to their solubility and to the facilitation

of their translocation across biological membranes. Once

within cells, the Cr (VI) is likely to be reduced to the trivalent

state before reacting with cell constituents such as proteins and

nucleic acids. In the case of red cells, it is such an intracellular

reaction of Cr (III) with hemoglobin which explains the essentially

irreversible uptake of the metal and permits use of chromium-

51 as red cell marker.

C-3

Stable and soluble compounds of Cr (III) are found in many

factor (GTF) (Mertz, 1969), a compound of unknown structure

whose absence is believed responsible for symptoms of chromium

deficiency. In the form of GTF and perhaps of other similar complexes

ease; thus it is readily absorbed from the intestine in this form

(Doisy, et al. 1971). One may recall in this connection the general

importance of metal ligands in determining movement of heavy

metals within the body (Collins, et al. 1961; Foulkes, 1974). It

is not surprising therefore that distribution of Cr in the body

1969).

Chromium plays a role in human nutrition. Because of this

might lead to overt Cr deficiency must be avoided. Indeed, effects

of Cr deficiency in man and experimental animals have been described

(Mertz, 1969). Levels of Cr compounds required for optimal

nutrition fall greatly below those which have been reported to

cause toxic effects (see Acute, Subacute, and Chronic Toxicity section):

therefore normal nutritional levels need not be considered

Sources of chromium in the environment have been recently

reviewed (U.S. EPA, 1978). Although Cr is widely distributed, with

an average concentration in the continental crust of 125 mq/kg, it

is rarely found in significant concentrations in natural waters.

C-4

and may be as low as 5 pg/m3. Much of the detectable Cr in air and

water is presumably derived from industrial orocesses, which in

1972 utilized 320,000 metric tons of the metal in the United States

alone. A significant fraction of this amount entered the environment:

additional amounts are contributed by combustion of coal and

other industrial processes (U.S. EPA, 1974). As a result, levels

of Cr in air exceeding 0.010 us/m3 have been reported from 59 of 186

urban areas examined (U.S. EPA, 1973). Mean concentrations of Cr

in 1,577 samples of surface water were reported as 9.7 ug/l (Kopp,

1969). The significance of 9.7 uq/l as a mean value is questionable

because only 25 percent of the samples tested contained any

detectable Cr. Ckcasional values of total Cr [Cr (III) and Cr

(VI)] exceeded 50 pg/l, a fact which must be noted in relation to

the recommended standard for domestic water supplies (see Existing

Guidelines and Standards section).

It is important to reemphasize at this time the analytical

difficulties attending estimation of low concentrations of Cr,

especially in biological materials. Additionally, the different

chemical species of Cr which may be present often cannot be clearly

separated. Considerable uncertainty attaches to the significance

of some results, particularly those obtained with some of the older

techniques. This tonic was considered in detail recently (U.S.

EPA, 1978).

c-5

EXPOSURE

Ingestion from Water and Food

At an average concentration of approximately 10 ug Cr/l drinking

water (Kopp, 1969), and a daily water consumption of 2 1, about

20 pg Cr would be ingested in water per day compared to about 50 to

100 ug/day in the American diet (Tipton, 1960). Dietary Cr intake

on a hospital diet averaged about 100 ug/day, while an estimate for

self-selected diets is 280 ug/day (NAS, 1974). Fractional absorption

of such an oral load from the intestine depends on the chemical

form in which the element is presented (see Introduction section).

In addition, even though mechanisms involved in the movement

of Cr compounds across intestinal epithelial barriers are not

understood, it is likely that the extent of this absorption will be

greatly influenced by the presence of other dietary constituents in

the intestinal lumen (MacKenzie, et al. 1958), as has frequently

been observed in the case of other ingested metals.

For a variety of reasons, therefore, net fractional absorotion

of Cr from the intestine is low and may amount to only a few percent

or even less (Yertz, 1969), depending especially on the chemical

form in which the element is ingested. Intake of Cr from the air

normally amounts to less than 1 ug/day (see Inhalation section),

and thus does not contribute significantly to normal Cr balance.

Average urinary excretion of Cr has been reported as 5 to 10 uq per

day (Volkl, 1971); recent work suggests that because of analytical

difficulties, actual values may be somewhat lower (C-uthrie, et al.

1979). In any case, it follows that the American diet may become

marginally deficient in this element, unable to provide the optimum

C-6

level required for normal function (see Introduction section).

This conclusion is supported by the finding that Cr levels in tissues

generally decrease with age (Yertz, 1969). The situation is

not greatly altered by application of Cr-containing fertilizers or

sewage sludges to agricultural land. Indeed, uptake of Cr by

plants from soil is generally low.

A bioconcentration factor (BCF) relates the concentration of a

chemical in aquatic animals to the concentration in the water in

which they live. An appropriate BCF can be used with data concerning

food intake to calculate the amount of chromium which might be

ingested from the consumption of fish and shellfish. Residue data

for a variety of inorganic compounds indicate that bioconcentration

factors for the edible portion of most aquatic animals is similar,

except that for some compounds bivalve molluscs (clams, oysters,

scallops, and mussels) should be considered a separate group. An

analysis (U.S. EPA, 1980a) of data from a food survey was used to

estimate that the per capita consumption of freshwater and estuarine

fish and shellfish is 6.5 g/day (Stephan, 1980). The per

capita consumption of bivalve molluscs is 0.8 g/day and that of all

other freshwater and estuarine fish and shellfish is 5.7 g/day.

The BCF for hexavalent chromium in fish muscle appears to be

values of 125 and 192 were obtained for oyster and blue mussel,

of 116, 153, and 86 were obtained with the American oyster (Shuster

and Pringle, 1969) and soft shell clam and blue mussel (Cappuzzo

and Sasner, 1977), respectively. It appears that the two valence

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states of chromium have about the same RCF values and that the qeometric

mean of 130 can be used for bivalve molluscs. If the values

average bioconcentration factor for chromium and the edible portion

of all freshwater and estuarine aquatic organisms consumed by Americans

is calculated to be 16.

Inhalation

Levels of Cr in air have been carefully monitored. In the

United States in 1964, an average value of 0.015 ug/m3 was reported,

with a maximum of 0.35 ug/m3. wore recent values show levels below

1973); yearly averages exceeded 0.01 ug/m3 in only 59 of 186 urban

areas.

The chemical form of Cr in air will vary, depending primarily

on its source. There is little information on the size distribution

of the particles, but it is safe to assume that a significant

on the aerodynamic diameter of the particles. Assuming both

uptake would only amount to approximately 0.2 ug/day. Additional

Cr could also be deposited in the upoer respiratory passages

and contribute ultimately to the intestinal load of Cr. In any

Even in the nonoccupational environment the concentration of

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Thus, increased ambient concentrations of Cr have been reported in

the vicinity of industrial sites (U.S. EPA, 1978). In the proximity

of water cooling towers, for instance, where Cr was employed as

a corrosion inhibitor, air levels of Cr as high as 0.05 ug/m’ have

been repor ted. However, even such a relatively high level is not

likely to greatly alter total Cr uptake. The possibil-ity that

smoking might contribute to the pulmonary load of Cr has not been

fully evaluated.

Of course, if the lungs represent a target organ for Cr, additional

pulmonary loads may assume significance even though total

body Cr may not have been materially increased by the inhalation

exposure. Although such exposure can lead to a significant increase

in urinary excretion of Cr, it is not clear to what extent

the Cr added to systemic pools originated in the lungs or was

alternatively absorbed from the intestines following pulmonary

clearance of the Cr-containing particles. In any case, pulmonary

Cr does not appear to be in full equilibrium with other Cr pools in

the body. This conclusion is based on the fact that the Cr content

of the lungs, unlike that of the rest of the body, may actually

increase with age (Mertz, 1969). Prolonged pulmonary retention of

inhaled Cr is also reflected by the fact that the Pulmonary concentration

of the element usually exceeds that of other organs. The

relatively slow clearance of Cr from the lungs was also noted by

Baetjer, et al. (1959a), who found that 60 days after intratracheal

instillation into guinea pigs, 20 percent of a dose of CrC13 remained

in this tissue.

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Dermal

Compounds of Cr permeate the skin fairly readily when applied

in the hexavalent form: trivalent Cr compounds react directly with

epithelial and dermal tissue. Cutaneous exposure is primarily a

problem of the workplace; many lesions have been described under

these conditions, including ulceration and sensitization. There is

little evidence, however, to suggest that cutaneous absorption significantly

contributes to the total body load of Cr in the normal

environment.

Evaluation of Relative Contribution of Different Exposure ?outes

to Body Burden

The three previous sections review briefly the uptake of Cr by

ingestion, inhalation, and cutaneous absorption. Yone of the three

routes of entry will lead to harmful levels of Cr in the body when

exposure involves only the low levels of the element normally found

in food, water, and air. Indeed, it may be recalled (see Ingestion

section) that the average American may actually suffer from mild Cr

deficiency. The major fraction of body Cr originating in the qenera1

environment is contributed by ingestion. In industrial surroundings,

by contrast, other routes of exposure may become more

significant. Uptake of Cr by inhalation may pose special. risks

here. This conclusion follows from the fact that the lungs tend to

retain Cr more than do other tissues (see Inhalation section). The

Carcinogenicity section deals further with pulmonary effects of

exposure to Cr in air.

Under normal conditions of exnosure, considerable variabilitv

has been observed in the Cr concentrations of different tissues.

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It is difficult to assess, however, to what extent the wide range

of values reported reflects analytical problems rather than true

individual variations. As a first approximation, an average level

of around 2 ug Cr/g ash may be derived from the work of Tipton and

Cook (1963) and of Imbus, et al. (1963) for most soft tissues and

be ten times higher: there is no evidence to suggest that Cr is a

bone-seeking element. If we further assume that the average ash

content of soft tissues approximates 1 percent of fresh weight, a

total body burden in the adult of the order of 2 mg may be calculated.

Results of Schroeder, et al. (1962) showed values of Cr in

human tissues of the order of 0.05 ug/g fresh weight, which would

correspond to a total adult body burden of around 3 to 4 mg; Schroeder

(1965) suggested an upper limit of 6 mg Cr in a 70 kg man.

These values are presented here to indicate the net result of Cr

uptake by ingestion, inhalation, and cutaneous absorption under

represent a marginally deficient state.

PHARMACOYINETICS

Absorption, Distribution, Metabolism, and Excretion

Analysis of the movement of Cr through various body pools, and

determination of the size and turnover rates of these pools, are

complicated by several facts. In the first place it is likely that

different Cr compounds will exhibit different kinetic characteristics

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chemical methods emoloyed for the estimation of biological Cr concentrations

do not adequately distinguish between different forms

of Cr present in the original sample. For instance, the results of

Schroeder, et al. (1962) suggest that both hexavalent and trivalent

Cr may occur in the ash of biological materials. However, precise

conclusions on this point are difficult because the chemical forms

of Cr may be changed during the ashing. Third, difficulties of

interpretation arise from the fact that one chemical species of Cr

may be transformed into another in the body, for instance as bv

reduction of Cr (VI) to Cr (III).

The complexity of the pharmacokinetics of Cr to be predicted

from such considerations is observed both in man and in experimental

animals. This situation may be illustrated by reference to the

urinary excretion of Cr under normal conditions. In man, the kidneys

account for 80 Percent or more of Cr excretion by nonexposed

individuals (NAS, 1974) ; urinary excretion amounts on the average

to 5 to 10 pg/day or less (see Ingestion from Water and Food section).

Such a value corresponds to less than 1 percent of the total

body burden as estimated in the Evaluation of Relative Contribution

of Different Exposure Routes to Body Burden section: it also ap-

Proximately equals the average daily dietary retention of Cr (see

Ingestion from Water and Food section). The body thus apsears

roughly to be in steady state with regard to Cr. It would not be

correct to infer, however, that the turnover rates of the various

true only if Cr taken in by one of the routes of entry discussed in

the Exnosure section always equilibrated evenly with different body

pools.

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Although little information is available on changes in specific

radioactivities of Cr in different body compartments following

administration of "Cr, there is strong evidence to show that different

compartments exhibit distinctly different turnover kinetics.

Lim (1978) reports the kinetics of radiochromium (III) distribution

in humans. Three major accumulation and clearance components

were found for liver, spleen, and thigh; liver and spleen

contained the higher concentrations. Normally in man, the highest

concentration of Cr is found in the lungs, and oulmonarv levels

tend to rise with age while the Cr content of other tissues falls.

Apparently the lung obtains most of its Cr from the air, not from

oral loads, and pulmonary Cr does not come into equilibrium with

other body pools of Cr (see Inhalation section).

Similar conclusions on nonequilibration of body pools can be

drawn from measurements on the excretion kinetics of 51 Cr (ISI) injected

into rats. At least three kinetic compartments were observed

in this case (Flertz, et al. 1965), with half-lives respectively

of 0.5, 5.9, and 83.4 days. The Cr in a slowly equilibrating

compartment in man was estimated to oossess a half-life of 616

days (U.S. EPA, 1978). Injection of 1 mg of unlabeled Cr into

rats, a very large dose compared to the oresumptive body burden as

calculated in the Evaluation of Relative Contributions of Different

Exposure !?outes to Body Burdens section, exerted little effect on

the rate of tracer excretion from the slow compartment. The finding

that even a very large excess of Cr does not affect this compartment

further indicates that ingested or injected Cr does not

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necessarily pass through every body compartment on its way to

excretion. Finally, this conclusion is supported by the observation

that the pool from which Cr (at least in some systems) enters

plasma following administration of glucose is not readily labeled

by injected 51 Cr (administered as CrC13) (Mertz, 1969).

As is the case with other metals, chromium normally circulates

in plasma primarily in a bound, nondiffusible form (Mertz, 1969).

At low levels of Cr (III) the iron-binding protein siderophilin

complexes most of the Cr present, but at higher levels of Cr other

plasma proteins also become involved. The high affinity of Cr

(III) for siderophilin presumably reflects the fact that this protein

provides the normal mechanism of transport for Cr to the tissues.

A small fraction of plasma Cr is also Dresent in a more diffusible

form, complexed to various small organic molecules which

are filtered at the glomerulus and partially reabsorbed in the

renal tubule. The suggestion that this reabsorption may involve an

active transport process (Davidson, et al. 1974) is not suDported

by the evidence presented. Chromium very tightly bound in lowmolecular

weight complexes such as Cr-EDTA may serve as a glomerular

indicator, being freely filtered but not reabsorbed (Stacy and

Thorburn, 1966).

The half-life of plasma Cr is relatively short, and cells tend

to accumulate the element to levels higher than that present in

plasma. Presumably this accumulation results from intracellular

trapping of Cr compounds which penetrate cells in the hexavalent

form and then react with cell constituents, such as hemoglobin in

the case of the erythrocyte. Within the cells, Cr (VI) will be re-

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duced to Cr (III) and remain trapped in this form. In any case, the

lack of equilibration of Cr between plasma and cells renders invalid

the use of plasma levels as indicators of total exposure.

Another reason for the limited usefulness of plasma Clr levels

as a measure of body burden is the likelihood that plasma Cr can be

identified with one of the rapidly excreted Cr compartments discussed

rise in plasma Cr reported by some authors to occur after administration

of a glucose load is not derived from a rapidly labeled

poolr it is followed by increased urinary excretion of Cr (Mertz,

1969). In summary, little can be concluded at this time about the</