# TOXICOLOGICAL REVIEW
OF 

# TRIVALENT CHROMIUM (CA S N o . 16065-83-1) 

## In Suppor tof Summar y Infor m ati o n on the Inte gr ate d Ri sk Infor m ati o n Sy ste m (IRIS)

August 1998

U.S. Environmental Protection Ag ency W a shing t on, DCDISCLAIM ER

Thi s docum enthas been revi ewed i n accordance wi th U.S

. Envi ronm ent a l P r ot ect i o n Ag ency policy

. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. This document may underg o revisions in the future. The most upto-dat e ve rsion will be a v a ilable e l e c tronic a lly via the I R I S Home Pa g e at http://www.epa.g ov/iris.

iiCONTENTS —TOXICOLOG ICAL REVIEW F O R TRIVALENT CHROMIUM (CAS No. 16065-83-1)

F O REWOR D ................................................................v AUTHORS , CONTR I BUTORS , AND REV IEW ER S

............................... . v i LI S T O F A B B R E V IA T I O N S

................................................. . v i i 1. IN TRODUCT I O N ...........................................................1 2. CHEM I C A L AND P HYS I C A L IN FORMAT I ON RE LE VANT TO AS S E S S M ENT S .....2 3. TOX I COK INET I CS RE LE VANT TO AS S E S S M ENT S ............................3 3.1. AB SORPT I ON FACTORS IN HUMANS AND EXPER IMENTA L AN IMA L S

. . 3 3.1.1. Ora l .......................................................3 3.1.2. Inhalatio n ..................................................4 3.1.3. Distributio n .................................................5 3.1.4. Metabolis m .................................................7 3.1.5. The Essentialit y of Chromiu m ..................................7 4

. H A Z A R D ID E N T IF I C A T I O N .................................................8 4.1. STUD IES IN HUMAN S ..............................................8 4.1.1. Ora l .......................................................8 4.1.2. Inhalatio n ..................................................8 4.2. PRECHRON I C AND CHRON I C STUD IES AND CANCER B I OASSAYS IN AN IMA L S —ORA L AND INHA LAT I O N

............................. 1 2 4.2.1. Chronic Oral Studie s ......................................... 1 2 4.2.2. Subchronic Oral Studie s ...................................... 1 3 4.2.3. Chronic Inhalation Studie s .................................... 1 4 4.2.4. Subchronic Inhalation Studie s ................................. 1 5 4.3. REPRODUCT IVE/DEVE L OPMENTA L STUD IES—ORA L AND INHA LAT I O N

............................................................... 1 7 4.3.1. Oral Studie s ...................................................... 1 7 4.3.2. Inhalation Studie s ........................................... 1 8 4.4. OTHER STUD IE S

................................................ 1 9 4.4.1. Contact Dermatiti s .......................................... 1 9 4.4.2. To x i cant In teraction s......................................... 1 9 4.4.3. Genotox icit y ...... ......................................... 1 9 4.5. SYNTHES I S AND EVA LUAT I ON OF MA J O R NONCANCER EFFECTS AND MODE OF ACT I ON ( IF KNOW N)—ORA L AND INHA LAT I O N

......... 2 0 4.5.1. Oral Studie s ................................................ 2 0 4.5.1.1. Human Studie s ...................................... 2 0 4.5.1.2. Animal Studie s ...................................... 2 0 iiiCONTENTS ( c ont i nue d)
4.5.2. Inhalation Studies ...........................................2 1 4.5.2.1. Human Studies ......................................2 1 4.5.2.2. Animal Studies ......................................2 1 4.6. W E I GHT-OF-EVID ENCE EVALUATI ON AND CANCER CHARACTERIZ ATI ON

...............................................................2 2 4.7. OTHER HAZ ARD ID ENTIF I CATI ON I SSUES ..........................2 2 4.7.1. Possible Childhood Susceptibility ..............................2 2 4.7.2. Possible Sex Differences ......................................2 2 5

. D O S E

- R E S P O N S E A S S E S S M E N T S ..........................................2 3 5.1. ORAL REF E RENCE DOSE (RfD) .....................................2 3 5.1.1. Choice of Principal Study and Critical Effect .........................................................2 3 5.1.2. Methods of Analy s is .........................................2 3 5.1.3. RfD Derivation .............................................2 4 5.2. INHALATI ON REFERENCE CONCENTRATI ON (RfC) ..................2 5 5.3. CANCER ASSESSMENT ............................................2 6 6. MAJ O R CONCLU S I ONS IN THE CHARACTERIZ ATI ON OF HAZ ARD AND DOS E RES P ONS E .....................................2 6 6.1. HUMAN HAZ ARD POTENTIAL .....................................2 6 6.2. DOSE RESPONSE .................................................2 7 7

. R E F E R E N C E S ............................................................2 8 AP P E NDIX A. EXTERNAL P EER REVIEW

— S U MMARY OF COMMENTS AND DI S P O S I TI ON ..........................3 9

ivF O REWORD The purpose of this Tox i colog i cal Review is to provide scientific support and rationale for the haz ard and dose-response assessment in I R I S pertaining to chronic ex posure to triva l e nt c hromium. Itis not inte nde d to be a c ompre he nsive tre atise on the c he mic a l or t ox i c ol og i c a lnatur e of tri va l e nt c hr om i um ( III)

. In Se c tion 6, EPA ha s c har a c t e rize dits ove ra ll c onfide nc e in the qua ntitative a nd qualitative aspects of hazard and dose response. Matters considered in this characterization include knowledg e g aps, uncertainties, quality of data, and scientific controversies. This c har a c t e rization is pre s e n te d in a n e ffort to make appare nt the limitations of the a sse ssme n t a nd to aid and g u ide the risk assessor in the ensuing steps of the risk assessment process. F or other g e neral information about this assessment or other questions relating to I R I S , the reader is referred to EPA’s Risk In formation Hotline at 202 -56 6

- 1676

.

vAUTHORS , CONTRIBUTORS , AND REVIEWERS

Ch em i c al Man ager/ Au th or Peter C. Grevatt, Ph.D., EPA Reg i on 2 Revi ew ers Thi s docum entand sum m ary i n form at i on on I R I S have recei ved peer revi ew both by EP A scientists and by independent scientists ex ternal to EPA. Subsequent to ex ternal review and incorporation of comments, this assessment has underg one an Ag ency wide review process whereby the I R I S Prog ram Manag e r has achieved a consensus approval among the Office of Research and Development; Office of Air and Radiation; Office of Prevention, Pesticides, and Tox i c Substances; Office of Solid W a ste and Emerg e ncy Response; Office of W a ter; Office of Policy , Planning , and Evaluation; and the Reg i onal Offices. In tern al E PA Revi ew ers Robert B e nson, Ph.D., D.A.B

. T., Reg i on 8 Charles Hiremath, Ph.D., National Center for Environmental Assessment Annie J arabek, National Center for Environmental Assessment W i nona Victery , Ph.D., D.A.B

. T., Reg i on 9 E x tern al P eer Revi ew ers Richard Anderson, Ph.D., U.S. Department of Ag riculture Robe rt Chap in, Ph.D., Na tiona l In stitute of Environme n ta l He a lth Sc ie nc e s Robert Drew, Ph.D., Consultant in Tox i colog y Gunter Obersorster, D.V.M., Ph.D., University of Rochester Eliz abeth T. Snow, Ph.D., New York University Medical Center Summaries of the ex ternal peer reviewers’ comments and the disposition of their recommendations are in Appendix A.

viLIST OF ABBREVIATIONS

B A L b ronchoalveolar lavag e B M D b enchmark dose B W body weig ht C A S R N C hem i cal Abstract s S e rvi ce R e g i stry Numb er ESADDI estimated safe and adequate daily dietary intake GTF g l u cose t o l e rance fact or IR IS In t e g r at e d R i s k In f o rm at i o n S y s t e m MTD m a x imum tole rate d dose NOAEL no-observed-adverse-effect level NOEL no-observed-effect level ppb parts pe r billion ppm parts pe r million RfC i nhalation reference concentration R f D o ral reference dose

vii1. INTRODUCTION This document presents backg r ound and justification for the haz ard and dose-response assessment summaries in EPA’s In teg r ated Risk In formation Sy stem (I RI S). I R I S Summaries may include an oral reference dose (RfD), inhalation reference concentration (RfC) and a carci nog eni c i t y assessm ent
. The RfD and RfC provide quantitative information for noncancer dose-response a sse ssme n ts. The RfD is ba se d on the a ssumption thatthre sholds e x ist for c e rta in tox i c e ffe c t s such as cel l u l ar necrosi s but m a y notex i s tfor other t o x i c effect s such as som e carci nog eni c responses. Itis ex pressed in units of mg /kg

- day

. In g e neral, the RfD is an estimate (with uncertainty spanning perhaps an order of mag n itude) of a daily ex posure to the human population (including sensitive subg roups) that is likely to be without an appreciable risk of deleterious e ffe c t s during a life time

. The inha lation RfC is a n a l og ous to the ora l RfD. The inha lation RfC considers tox i c effects for both the respiratory sy stem (portal-of-entry ) and for effects peripheral to the respiratory sy stem (ex trarespiratory or sy stemic effects). Itis g e nerally ex pressed in units of mg /m 3

. The carcinog enicity assessment provides information on the carcinog enic haz ard potential of the substa nc e in que stion a nd qua ntitative e s timate s of risk from ora l e x posure a nd inha lation ex posure. The information includes a weig ht-of-evidence judg ment of the likelihood that the ag ent is a human carcinog en and the conditions under which the carcinog enic effects may be e x pre sse d. Qua n titative risk e s timate s ar e pre s e n te d in thre e wa y s . The slope factor is the re sult of application of a low-dose ex trapolation procedure and is presented as the risk per mg /kg

- day

. The unit risk is the qua ntitative e s timate in te rms of e ithe r risk pe r μ g /L drinking wa te r or risk per μ g /m 3 air breathed. Another form in which risk is presented is a drinking water or air concentration providing cancer risks of 1 in 10,000; 1 in 100,000; or 1 in 1,000,000. Development of these haz ard identifications and dose-response assessments for trivalent c h romium ha s followe d the g e ne ra l g u ide line s for risk a sse ssme n t a s se t forth by the Nationa l Research Council (1983). EPA g u idelines that were used in the development of this assessment ma y inc l ude the following : the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1986a), Guide line s for the He alth Risk Asse ssme n t of Che m ic al Mix t ure s(U.S. EPA, 1986b), Guide line s for Mutagenicity Risk Assessment (U.S. EPA, 1986c), Gui del i n es f o r Devel opmenta l T oxi ci t y Risk Assessment (U.S. EPA, 1991), Proposed Guidelines for Neurotoxicity Risk Assessment (U.S. EPA, 1995a), Proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1996a), Guidelines for Reproductive Toxicity Risk Assessment (U.S. EPA, 1996b), and Guide line s for Neurotoxicity Risk Assessment (U.S. EPA, 1998a); Recommendations for and Documentation of Biological Values for Use in Risk Assessment (U.S. EPA, 1988); (proposed) Inte rim Polic y for Particle Size and Limit Concentration Issues in Inhalation Toxicity (U.S. EPA, 1994a); Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry (U.S. EPA, 1994b); Peer Review and Peer Involvement at the U.S. Environmental Protection Agency (U.S. EPA, 1994c); Use of the Benchmark Dose Approach in Health Risk Assessment (U.S. EPA, 1995b); Science Policy Council Handbook: Peer Review (U.S. EPA, 1998b); and 1memorandum from EPA Administrator, Carol B r owner, dated March 21, 1995, Subject: Gui d ance on R i sk C h aract eri z at i on. Literature search strateg i es employ ed for this compound were based on the CASRN and atle a s t one c o mmon na me . At a minimum, the following databa se s we re se ar c h e d : RTECS, HSDB , TSCATS, CCRI S, GENETOX, EMI C , EMI C B A CK, DART, ETI CB ACK, TOXLIN E, CANCERLINE, MEDLIN E AND MEDLIN E backfiles. Any pertinent scientific information submitted by the public to the I R I S Submission Desk was also considered in the development of this document.

2. CHEMICAL AND P H YSICAL INF O RMATION RELEVANT TO ASSESSMENTS Chromium (Cr) is a me ta llic e l e m e n t be long ing to the first tra n sitiona l se rie s of the periodic table. Elemental chromium has a CAS Reg i stry Number of 7440-47-3. The three most st abl e form s i n whi c h chrom i u moccurs i n th e envi ronm entare th e 0 (m et al and al l o y s ), +3 (tri val e ntchrom i u m ) , and +6 (hex avel entchrom i u m ) val e nce st at es. In th e +3 val e nce st at e, th e c h e mistry of c h romium is dominat e dby the formation of stab le c o mple x e s with both org a nic a n d inorg a nic lig ands (Hartford, 1979). In the +6 valence state, chromium ex ists as ox o species such as C r O 3 and CrO 4 2- that are strong ly ox idiz ing (Cotton and W ilkinson, 1980). Chromium in the ambient air occurs from natural sources, industrial and product uses, and burning of fossil fuels and wood. The most important industrial sources of chromium in the atmosphere orig inate from ferrochrome production. Ore refining , chemical and refractory processing , cement-producing plants, automobile brake lining and catalytic converters for automobiles, leather tanneries, and chrome pig m ents also contribute to the atmospheric burden of chromium (F ishbein, 1981). Chromate chemicals used as mist inhibitors in cooling towers and the mist forme dduring c h rome plating ar e probably the primary sourc e s of Cr(VI ) e mitte d a s mists in the atmosphere (Towill et al., 1978). Sc ar c e information e x ists in the lite rature re g arding the nature of the c h e mic a l spe c i e s p r e s e n t i n th e at m o s p h e r e . U n d e r n o rm a lc o n d i t i o n s , C r ( III) a n d C r ( 0 ) i n th e a i r d on o t underg o any reaction (Towill et al., 1978). Cr(VI ) in the air eventually reacts with dust particles or other p o l l u t a n t s t of o rm C r ( III) ( N A S , 1974); however, the ex act nature of such atmospheric reactions has not been studied ex tensively

. Chromium is removed from air by atmospheric fallout and precipitation (F ishbein, 1981). The atmospheric half-life for the phy sical removal mechanism depends on the particle siz e and particle density of atmospheric chromium. Chromium particles of small aerodynamic diameter (< 10 μ m ) may remain airborne for long periods and may be transported g r eat distances by wind currents and diffusion forces. Surface runoff, deposition from air, and release of municipal and industrial waste waters are th e sources of chrom i u mi n surface wat e rs. The m o stsi g n i f i cantrem oval m echani s mfor C r ( III) f r o m th e a q u at i ce n v i r o n m e n t i s p r e c i p i t at i o n a s C r 2 O 3 · × H 2 O followed by sedimentation. Cr(VI ) , however, can ex ist in aquatic media as a water-soluble complex anion and may persist in water for long periods. Cr(VI ) is a moderately strong ox idiz ing ag ent and will react with org a nic

2m at t e r o r o th e r r e d u c i n g a g e n t s t of o rm C r ( III)

. T h e r e f o r e , i n s u r f ace wat e r ri ch i n org a ni c content, Cr(VI ) will ex hibit a much shorter lifetime (Callahan et al., 1979). Chromium probably occurs as insoluble Cr 2 O 3 · × H 2 O in soil, g i ve n thatorg a nic matte r in soil converts soluble chromate to insoluble Cr 2 O 3 (U.S. EPA, 1983). There is no known chemical process that can cause chromium to be lost from soil. The primary processes by which c h romium is lost from soil ar e phy sic a l

. F o r e x a mple , c h romium in soil c a n be tra n sporte d to the atmosphere by way of dust or aerosol formation (U.S. EPA, 1983). Chromium is also transported from soil throug h runoff. Runoff can remove both chromium ions and bulk precipitates of chromium. In addition, flooding of soils and the subsequent anaerobic decomposition of plant matter may increase dissolution of Cr 2 O 3 in soil throug h c o mple x ation (U.S . EP A, 1983). The water-soluble complex e s may cause leaching of chromium from soil. Pag e (1981) reported the detection of a small concentration (l μ g /L mean concentration) of chromium at a frequency of approx imately 100% in g r ound water collected from New J e rsey . The bioconcentration factor (B CF ) for Cr(VI ) in fish muscle appears to be < l.0, but values of 125 and 192 were obtained for oy ster and blue mussel, respectively (U.S. EPA, 1980). F o r C r ( III) , B C F v a l u e s o f 116, 153, and 86 were obtained with the American oy ster, soft shell clam, and blue mussel, respectively (U.S. EPA, 1983).

3. TOXICOK I NETICS RELEVANT TO AS S E S S M ENTS 3.1. ABSORP TION F ACTORS IN HUMANS AND EXP E RIMENTAL ANIMALS 3.1.1. Oral Based on fecal ex cret i on of 51 Cr following oral administration of 51 Cr Cl 3 to human patients, Donaldson and B arreras (1966) estimated absorption to be approx imately 0.4%. When 51 Cr Cl 3 was administered intraduodenally , absorption was not appreciably chang e d. In rats, approx imately 2% of the intrag astric dose of CrCl 3 appeared t o be absorbed based on fecal e x c r e tion of c h romium. J e juna l a d ministra tion only slig htly inc r e a s e dthe appare nt ab sorption of Cr Cl 3. Anderson et al. (1983) confirmed the low absorption of trivalent chromium in humans following the administration of 200 μ g of Cr( III) tri c h l o ri d e , a n d th e y s u g g e s t e d th at th e absorption efficiency of trivalent chromium is dependent on dietary intake. Anderson et al. (1986) reported that at low levels of dietary intake (10 μ g ) about 2% of trivalent chromium was absorbed. W h en intake increases to > 40 μ g , the absorption efficiency dropped to approx imately 0.5%. B unker et al. (1984) determined that elderly subjects absorbed less than 3% of trivalent c h romium ing e ste din the die t
. A number of animal studies confirm that trivalent chromium is poorly absorbed in the g a strointestinal tract. Visek et al. (1953) estimated that less than 0.5% of ing e sted CrCl 3 was absorbed throug h the g a strointestinal tract of the rat. Mertz et al. (1965) estimated that rats absorbed less than 3% of a sing le dose of CrCl 3 by g a vag e . MacKenzie et al. (1959) estimated that less than 3% of a sing le dose of CrCl 3 by stomach tube was absorbed in rats. Og awa (1976) 3found g a strointestinal absorption of CrCl 3 to be less than 3% in rats. Henderson et al. (1979) determined that hamsters absorbed less than 1.5% of an administered oral dose of trivalent chromium. F u rthermore, Mertz et al. (1965) reported that absorption in rats was independent of the administered dose and dietary chromium status (deficient or supplemented in chromium) of th e a n i m a l s . C r ( III) w a s f ound to be better absorbed in fasted than in fed rats (MacKenz i e et al., 1959). 3.1.2. Inhalation A number of factors can influence the absorption of chromium following inhalation, inc l uding the size , ox idation sta t e a nd solubility of the c h romium partic le s, the a c tivity of alveolar macrophag e s, and the interaction of chromium with biomolecules following deposition in the lung (ATSDR, 1993). Absorption of inhaled chromium compounds following occupational ex posure has been demonstrated by the measurement of chromium in the serum and urine and hair of workers in the chromium industry (Minoia and Cavalleri, 1988; Randall and Gibson, 1987; Tossavainen et al., 1980). Cr( III) i s l e s s w e l l ab s o r b e d th a n C r ( V I) d u e t oth e re lative inab ility of Cr( III) t oc r o s s c e l lm e mb r a n e s . H o w e v e r , w o rk e r s e x p o s e d t oC r ( III) lig nosulfonate dust at 0.005-0.23 mg Cr( III) /m 3 had detectable concentrations of chromium in the urine at the end of the workday (Kiilunen et al., 1983). Animal studies have shown that trivalent chromium is absorbed very slowly by inhalation. B aetjer et al. (1959a) administered CrCl 3 to g u ine a pig s intratra c h e a lly

. Te n minute s post-treatment, 69% of the administered dose remained in the lung s, while 4% was found in the blood and tissues. Percentag e s of administered chromium found in the lung s 24 hours, 30 day s , and 60 day s post-treatment were 45%, 30%, and 12%, respectively

. These investig ators hypothe size d thatthe slow ab sorption of triva l e n t c h romium is due to the fa c tthatit forms i n sol ubl e comp l e x e s wi thm acrom ol ecul e s. Furtherm ore, cl earance fromth e respi r at ory tr act t o the g a strointestinal tract may be a factor when chromium compounds are administered by inhalation. Visek et al. (1953) found similar results when 51 Cr Cl 3 wa s instille d intratra c h e a lly in g u ine a pig s . In this study , ab sorption from the lung s wa s e s timate d to be approx imate ly 5%. The au thors sug g e ste dthatthe ma jority of the CrCl 3 wa s c l e ar e dfrom the lung s by muc o c iliary a c tion and passed th roug h th e g a stroi n t e st i n al tr actbecause 55% and 7% of th e adm i n i s t e red 51 Cr had been recovered fromth e feces and uri n e, respect i v el y , wi th i n 7 day s . W a da et al. (1983) ex posed male Sprag u e-Dawley strain rats to CrCl 3 at an atmospheric concentration of 14.1 mg /m 3 (Cr) and observed that the chromium was associated with both hig h

a nd low-mole c u lar-we i g h t prote i ns. The c h romium thatre ma ine din the lung s wa s a ssoc i at e d with the hig h -molecular-weig h t fraction, and this fraction slowly decreased with time following e x posure . The le ve l of c h romium a ssoc i at e dwith the low-mole c u lar-we i g h t fra c tion re ma ine d constant for the 5 day s of observation following treatment; however, chromium associated with this fraction accumulated with time in the liver. The authors sug g e sted that the low-molecularweig ht protein may be involved in the absorption and transport of chromium following inhalation.

4Suz uki et al. (1984) ex posed rats to potassium dichromate(VI ) or Cr( III) tri c h l o ri d e b y inhalation and determined that while lung clearance of both valence states was dependent on p art i c l e s i z e , C r ( V I) w a s ab s o r b e d w i th th r e e f o l d g r e at e r e f f i c i e n c y th a n C r ( III)

. 3.1.3. Distribution M u c h w o rk h a s b e e n p e r f o rm e d o n i n v i v or e d u c t i o n o f C r ( V I) t oC r ( III) , a n d s o m e characteriz ations can be made. In g e sted hex a valent chromium is efficiently reduced to the trivalent form in the g a strointestinal tract (DeF lora et al., 1987). In the lung s, hex a valent chromium can be reduced to the trivalent form by ascorbate and g l utathione. The reduction by a s c o rbat e is more rapid tha n thatby g l utathione a nd re sults in a shorte r re side nc e time in the lung s (Suz uki and F ukuda, 1990). There is no evidence that trivalent chromium is converted to hex a valent chromium in biolog ical sy stems (Amdur et al., 1993). O n c e ab s o r b e d , C r ( III) c o mpounds are cleared rapidly from the blood and more slowly from the tissues. Hopkins (1965) injected 0.1 μ g 51 Cr (as chromium chloride)/100g intravenously in male rats. The blood chromium content as a percentag e of the blood concentration decreased from 94% at 30 minutes to 17% in 24 hours and to 5% at 96 hours. Li m et al. (1983) followed distribution of 51 Cr Cl 3 after intravenous administration in six adults. W ithin several hours of dosing , > 50% of the chromium in plasma was distributed to the liver, spleen, and other org a ns. After 3 months, the liver contained > 50% of the total body burden of 51 Cr

. Visek et al. (1953) reported org a n distribution of several chromium salts following intravenous injection in rats. CrCl 3 concentrated in the liver, spleen, and bone marrow; once deposited, it cleared slowly

. The liver in the CrCl 3 -ex posed rats was the only org a n to clear sig n ificant amounts of chromium over the study period (45 day s ). In rats receiving i n tr ap e ri t o n e a l a d m i n i s tr at i o n o f C r ( III) n i tr at e f

o r

3 0o r 6 0d a y s , th e h i g h e s t l e v e l s o f c h r o m i u m were observed in the liver, followed by the kidney s , testes, and brain. Tissue concentration i n creased nonl i n earl y wi th dose, and concentr at i ons i n th e ki dney i n creased si g n i f i cant l y wi th duration (Tandon et al., 1979). Trivalent chromium was detected only in the livers of mice following administration of 4.8, 6.1, or 12.3 mg Cr( III) /k g - d a y a s c h r o m i u m ( III) tri c h l o ri d e i n drinking water for 1 y ear (Maruy ama, 1982). Tissue concentrations were 40-90 times below those reported following administration of hex a valent chromium in this study

. MacKenz i e et al. (1958) reported that tissue concentrations of rats g i ven Cr( III) tri c h l o ri d e w e r e n i n e f o l d l o w e r than those g i ven potassium dichromate in drinking water. Sullivan et al. (1984) treated adult and n e o n at a lr at s w i th a n a c u t e o r a ld o s e o f r a d i o l ab e l e d C r ( III) tri c h l o ri d e . S e v e n d a y s f o l l o w i n g th e dose, neonates and adults retained approx imately 35% and 0.2% of the dose in the g u t, respectively

. Neonates accumulated 0.12%, 0.05%, and 0.0088% in the kidney , liver, and lung , while adults accumulated 0.003%, 0.002% and 0.0003% in the kidney , liver and lung , respectively

. Red blood cells were found to accumulate sig n ificantly more chromium than white blood cells following intravenous administration of CrCl 3 in the rat (Coog an et al., 1991). M i c e g i v e n a

s i n g l e i n tr ap e ri t o n e a l i n j e c t i o n o f C r ( III) tri c h l o ri d e w e r e f

ound to have retained 87%, 73%, and 45% of the dose on day 3, 7, and 21 post-treatment. The retention of 5c h romium wa s attribute dto the formation of triva l e n t c h romium c o mple x e s with prote i ns a n d amino acids (B ry son and Goodall, 1983). Mertz (1969) studied placental transfer of a variety of chemical forms of trivalent c h romium in rats. Ma le a nd fe ma le rats fe d c o mme rc ia l or c h romium-de ple t e dy e a s t die t s a n d drinking water with or without 2 ppb chromium were mated. Neonates whose dams were fed the c o mme rc ia l die tc onta i ne d ne ar ly twic e the c h romium a s ne onate s of da ms fe d the c h romiumdeficient diet. Ex posure of dams to trivalent chromium in drinking water did not increase the chromium content of the neonates. Neonatal concentrations of chromium were not increased following a d ministration of CrCl 3 intravenously or by g a vag e before, during , or after mating

. However, administration of chromium in the form of g l ucose tolerance factor (GTF ) by g a vag e during g e station resulted in levels in neonates that were 20%-50% of those in the dams. Danielsson et al. (1982) studied placental transfer of trivalent chromium in mice following intravenous injection of CrCl 3 . The hig h est maternal chromium concentrations were found in the renal cortex , skeleton, liver, and ovaries. The fetal concentration of chromium was 0.4% and 0.8% of the maternal serum concentration when dams were injected in mid- and late-g estation, respectively

. Chromium accumulated in the fetal skeleton and y o lk sac placenta. Iijima et al. (1983) also reported that trivalent chromium crossed the placenta of mice injected intrap e ritone a lly with CrCl 3 . Visek et al. (1953) reported that an insig n ificant amount of 51 Cr crossed the placenta of rats in the 24 hours following intravenous injection reg ardless of the c h e mic a l form inje c t e d, the va le nc e stat e , the g e stationa l sta g e , or the size of the litte r. In no instance was the radioactivity measured in the fetuses g r eater than 0.13% of the dose. Casey and Hembridg e (1984) demonstrated that chromium can be transferred to infants throug h breast milk. The breast milk of 45 lactating women was found to have a chromium content averag ing 0.3 μ g /L

. These concentrations were taken to represent backg r ound levels in women whose chromium ex posure occurs primarily throug h the diet. Hex a valent chromium readily enters cells throug h the phosphate and sulfate anionex chang e carrier pathway , althoug h a portion may remain in plasma for an ex tended period (W ieg a nd et al., 1985). W h ile Cr( III) c o mpounds are unable to cross the cell membrane by this pathway (Gray and Sterling , 1950), they may enter cells, but only with very low efficiency (L ewalter et al., 1985; O’F l aherty , 1996). Hex a valent chromium is reduced to the trivalent form intracellularly by the action of g l utathione (Debetto and Lu ciani, 1988; Petrilli and De F l ora, 1978b). F o llowing reduction to the trivalent form, chromium may interact with cellular macromolecules, including DNA (W ieg a nd et al., 1985), or may be slowly released from the cell (B ishop and Surg enor, 1964). A phy si ol og i cal l y based m odel for chrom i u mhas recent l y been devel oped, whi c h i n c o rp o r at e s ab s o rp t i o n a n d d i s p o s i t i o n s c h e m e s f o r

C r ( V I) a n d C r ( III) th r o u g hout the body (O’F laherty , 1996). The model was calibrated on the basis of published oral and intratracheal ki n e t i cs tu d i e s u s i n g s o l u b l e C r ( III) a n d C r ( V I) i n th e r a t , a n d i t accounts for most of the major f

e atu r e s o f c h r o m i u m ki n e t i c s i n th e r at , i n c l u d i n g r e d u c t i o n o f C r ( V I) t oC r ( III)

. T h e m o d e l s u g g e s t s th e f

o l l o w i n g i n v i v od i s p o s i t i o n f

o r

c h r o m i u m . B o th C r ( III) a n d C r ( V I) ar e poorly absorbed from the lung and the g a strointestinal tract. F o llowing inhalation ex posure, chromium may be absorbed into the sy stemic circulation, transferred to the g a strointestinal tract by 6mucociliary action, or remain in the lung

. Cr(VI ) is reduced to Cr( III) i n a l l t i s s u e s , i n c l u d i n g th e l u n g a n d th e g a s tr o i n t e s t i n a ltr a c t
. B o th C r ( III) a n d C r ( V I) ar e b e t t e r ab s o r b e d f

r o m th e g a s tr o i n t e s t i n a l tr a c t i n th e f

a s t e d th a n i n th e f

e d s t at e , a n d th e ab s o rp t i o n e f f i c i e n c y o f C r ( III) salts is larg ely dependent on the nutritional status of the animal as well as the nature of the anion m aki n g u pth e C r ( III) s a l t
. T h e m o d e l a s s u m e s th at r e d u c t i o n o f C r ( V I) d o e s n o t o c c u r i n th e plasma. Cr(VI ) enters cells by the phosphate and sulfate anion-ex chang e carrier pathway

. Cr( III) travels in the bloodstream larg ely bound to amino acids, other org a nic acids, and plasma proteins s u c h a s g l o b u l i n s . T h e c o mp l e x e s o f C r ( III) w h i c h ar e bound to lower molecular weig ht lig ands are most likely to be able to traverse cell membranes (Mertz , 1969). A sig n ificant amount of absorbed chromium is taken up in the bone (Witmer and Harris, 1991; Weber, 1983). Chromium is also concentrated in tissues of the liver, kidney , and spleen. Once in the cell, Cr(VI ) may be r e d u c e d t oC r ( III) , w h i c h m a y s u b s e q u e n t l y i n t e r a c t w i th c e l l u l ar m a c r o m o l e c u l e s , i n c l u d i n g DNA (W ieg a nd et al., 1985), or may be slowly released from the cell (B ishop and Surg enor, 1964). The model sug g e sts that the bioaccessibility of chromium to absorption processes may be the sing le most importa nt fa c t or de te rmining the tox i c ity of a spe c i fic c h romium sourc e (O’F laherty , 1996). G i v e n th e r ap i d r e d u c t i o n o f C r ( V I) t oC r ( III) i n v i vo, it is relevant to consider whether environmental ex posures to Cr(VI ) or administration of Cr(VI ) in controlled animal ex periments i s e s s e n t i a l l y i d e n t i c a l t oe n v i r o n m e n t a l e x p o s u r e s t oC r ( III) o r a d m i n i s tr a t i o n o f C r ( III) i n c o n tr o l l e d e x p e ri m e n t s . W h i l e c o n s i d e r ab l y m o r e d at a ar e a v a i l ab l e f

o r

C r ( V I) th a n f

o r

C r ( III) , i t appears at present that ex posures to Cr(VI ) have considerably different outcomes than ex posures t oC r ( III)

. C r ( V I) h a s b e e n s h o w n t ob e m o r e t o x i c o l o g i c a l l y a c t i v e th a n C r ( III) a s i t m o r e r e a d i l y crosses cel l m e mb ranes. The Ag ency has prepared th e Tox i col o g i cal R e vi ews and I R I S S u m m ari e s f o r

C r ( V I) a n d C r ( III) f r o m th i s p e r s p e c t i v e . 3.1.4. Metabolism Triva l e n t c h romium pote n tiate s the a c tivity of insulin in vitro a nd in vitro. In the biolog ic a lly a c tive form, c h romium oc c u rs in a c o mple x re fe rre d to a s GTF , te ntative l y ide n tifie d as a chromium-nicotinic acid complex

. GTFhas been sug g e sted to operate throug h activation of membrane phosphoty r osine phosphatase in mammals, althoug h the complete structure of the complex has not been identified (Mertz , 1993; Davis et al., 1996). 3.1.5. The Essentiality of Chrom i um C r ( III) p o t e n t i at e s i n s u l i n a c t i o n i n p e ri p h e r a lt i s s u e a n d i s e s s e n t i a lf o r

l i p i d , p r o t e i n , a n d fat me tabolism in a n ima ls a nd huma n s. Chromium de fic i e n c y c au se s c h a n g e s in the me tabolism of g l ucose and lipids and may be associated with maturity -onset diabetes, cardiovascular diseases, and nervous sy stem disorders (Anderson, 1993, 1995). The National Research Council (NRC) has identified an estimated safe and adequate daily dietary intake (ESADDI ) for chromium of 50-200 μ g /day (NRC, 1989), corresponding to 0.71-2.9 μ g /kg

- day for a 70 kg adult.

7The F ood and Drug Administration (F DA) has selected a Reference Daily In take for chromium of 120 μ g /d (U.S. DHHS, 1995).

4. HAZARD IDENTIF I CATION He x a va le nt c h romium is wide ly c onside r e dto ha ve sig n ific a n tly g r e at e r tox i c ity tha n the trivalent form. This results in part from the recog n ition of hex a valent chromium as a known human carcinog en by the inhalation route of ex posure, from the caustic properties of many of the hex a valent compounds, the g r eater absorption of the hex a valent species following ex posure by ing e stion and inhalation, and the ability of hex a valent chromium to efficiently traverse cell me mbra ne s. Howe ve r, re lative l y fe w studie s ar e a v a ilable in the lite rature thatdire c tly a ddre s s the tox i city of trivalent chromium, particularly by the inhalation route of ex posure. This lack of data re sults in c onside r ab le unc e rta inty re g arding the ha zard a ssoc i a t e dwith e x posure s to triva l e n t c h romium.

4.1. STUDIES IN HUMANS 4.1.1. Oral The e sse ntia l role of triva l e n t c h romium in g l uc ose a nd lipid me tabolism ha s be e n wide ly studied; however, only one study was located that addressed the oral tox i city of trivalent chromium in humans. Kusiak et al. (1993) reported increased mortality due to stomach cancer in g o ld miners in Ontario, Canada. Ex posures to arsenic, chromium, mineral fiber, diesel emissions, and aluminum powder were considered as possible ex planations for the ex cess stomach cancer. The authors found that the ex cess incidence of stomach cancer was best associated with the time-weig h ted index of ex posure to chromium in miners under the ag e of 60. Howe ve r, a similar a ssoc i ation be twe e n the inde x of e x posure to c h romium a nd e x c e ss stoma c h cancer was not seen in older g o ld miners in this study

. Althoug h diet is an important risk factor in the onset of stomach cancer, the study was unable to consider the role of dietary habits in the onset of stomach cancer in the study population. W h ile the authors sug g e st that chromium or a subst a nce cl osel y associ at ed wi th chrom i u mm a y be th e causat i v e ag entfor st om ach cancer, th e inability to consider important confounding factors and the absence of a clear pattern of disease incidence with increasing ex posure make this association hig h ly uncertain. The substantial uncert a i n t i e s rel at e d t o th e associ at i on bet w een chrom i u mex posure and di sease i n ci dence and the sig n ificant confounding factors make this study unusable for risk assessment purposes. 4.1.2. Inhalation Occupational ex posure to chromium by inhalation has been studied in the chromate manufacturing and ferrochromium industries; however, ex posures all include mix ed ex posures to b o th C r ( III) a n d C r ( V I)

. T h e C r ( V I) s p e c i e s i s w i d e l y c o n s i d e r e d t ob e th e e t i o l o g i ca g e n t i n reports of ex cess cancer risk in chromium workers. However, studies are inadequate to rule out a

8c o n tri b u t i o n b y C r ( III) , a n d C r ( V I) c a nnot be unequivocally demonstrated to be the etiolog i c ag ent for noncarcinog enic effects following inhalation. S tu d i e s a d d r e s s i n g e x p o s u r e s t oC r ( III) a l o n e ar e n o t a v a i l ab l e , a n d th e r o l e o f C r ( III) i n d i s e a s e f

o l l o w i n g e x p o s u r e s t om i x tu r e s o f C r ( III) a n d C r ( V I) c a nnot be determined. Sig n ificant r e d u c t i o n o f C r ( V I) t oC r ( III) o c c u r s i n th e l u n g s , a n d ab s o rp t i o n o f C r ( III) f r o m l u n g t i s s u e i s known to occur (O’F laherty , 1996). In order to be comprehensive, a summary of the results of studies involving mix ed ex posures to Cr( III) a n d C r ( V I) i s p r e s e n t e d b e l o w . A number of epidemiolog i c studies have considered the association between inhalation of chromium and noncarcinog enic endpoints, including upper respiratory irritation and atrophy , l o wer respi r at ory effect s, and sy st em i c effect s. B l oomfield and B l um (l928) ex amined 23 men from six chromium plating plants in the United States. F ourteen of these workers ty pically spent 2-7 hours/day over vats of chromic acid, which g e nerated airborne hex a valent chromium rang ing from 0.12-5.6 mg /m 3

. These m e n ex perienced nasal tissue damag e , including perforated septum (2), ulcerated septum (3), chrome holes (6), nosebleed (9), and inflamed mucosa (9). In g e neral, the nine remaining workers ex amined, who were not directly ex posed to chromium vapors, had only inflamed mucosae. The authors concluded that chromic acid at concentrations g r eater than 0.1 mg /m 3 is like l y to c au se nasal tissue injury

. However, while no concentrations lower than 0.12 mg /m 3 were observed, injury to nasal tissue caused by lower concentrations could not be ruled out. Machle and Greg orius (1948) reported an incidence of nasal septal perforation of 43.5% in 354 employ ees who worked in a chromate-producing plant that manufactured sodium c h romate a nd bic h romate
. At the time of the study , a i rborne c h romate c onc e n trations ra ng e d from 0.1 to 2.8 mg /m 3

. The plant had been in operation for at least 17 y ears, and some empl oy ees probabl y worked i n th e pl antwhen reverberat ory furnaces, a prom i n entsource of hi g h chromate ex posure, were used. Mancuso (1951) reported on phy sical ex aminations of a random sample of 97 workers from a chromate-chemical plant. The results indicated that 61 of the 97 workers (63%) had septal perforation. The data sug g e sted to the author that Cr( III) m a y b e p art l y r e s ponsible for the perforations; however, there were insufficient data to make an unequivocal conclusion. The U.S. Public Health Service conducted a study of workers in seven chromate-producing plants in the early 1950s. Of 897 chromate industry workers in the study , 57% were found to have a nasal septum perforation. Perforated septum was observed even in workers employ ed fewer than 6 months. The study indicated that ex posure to chromate results in severe nasal tissue destruction, but ex posure levels were not measured; hence, the data are of limited usefulness for risk assessment purposes (F ederal Security Ag ency , 1953). Vig liani and Z u rlo (1955) reported nasal septal perforation in workers ex posed to chromic acid and chromates in concentrations of 0.11-0.15 mg /m 3

. The leng ths of ex posure were not known. Hanslian et al. (1967) reported on otolaryn g o log i c ex aminations of 77 persons 9ex posed to chromic acid aerosol during chrome plating

. Of those, 19% were observed to have septal perforation and 48% to have nasal mucosal irritation. The workers averag ed 6.6 y ears of ex posure to an airborne chromium concentration of 0.4 mg /m 3

. In 14 pe rsons, papilloma s of the oral cavity and larynx were found. The diag nosis of papilloma was confirmed by histolog ic ex amination. There were no sig n s of atyp ical g r owth or malig nant deg e neration. Kleinfeld and Russo (1965) reported some deg r ee of nasal septal ulceration in seven of nine workers in a chrome-plating plant, with four of seven demonstrating frank perforations. Analy s es of air samples showed chromium concentrations of 0.18-1.4 mg /m 3

. Data re g arding the leng th of ex posure and ex posure concentration for individual workers were not available. Gomes (1972) ex amined 303 employ ees who worked in 81 electroplating operations in Sao Paulo, B r az il. Over two-thirds of the workers had mucous membrane or cutaneous lesions, with many of them having ulcerated or perforated nasal septa. The duration of ex posure was not stated, but the author mentioned that the harmful effects were noted in under 1 y ear. A direct correlation between workers ex posed to a g i ven airborne concentration of Cr(VI ) and the development of harmful effects could not be made. Cohen and Kramkowski (1973) and Cohen et al. (1974) ex amined 37 workers (7 male and 30 female) employ ed in the nickel-chrome department of an electroplating plant in comparison with 21 workers (15 male and 6 female) in other areas of the plant not sig n ificantly ex posed to chromic acid. Smoking demog r aphic data was not provided. Environmental air samples were collected from breathing z ones of several workers in the ex posed and control g r oups to determine concentrations of total chrome and Cr(VI )

. B rief medical histories were confined to the ear, nose, throat, and cutaneous structures. W ithin 1 y ear of employment, 12 workers ex perienced nasal ulceration or perforation. Nasal ulcers and perforations were associated with total chromium concentrations of 1.4 to 49.3 μ g /m3 , averag ing 7.1 μ g /m 3 , and Cr(VI ) concentrations of 0.09 to 9.1 μ g /m3 , averag ing 2.9 μ g /m 3

. Ninety -five percent of the 37 workers studied ex hibited patholog ic chang e s in nasal mucosa in a concentration-duration response. More than half of the workers employ ed less than 1 y ear had nasal patholog y that was more severe than simple redness of the nasal mucosa. Almost all the workers (35 of 37) employ ed long er than 1 y ear had nasal tissue damag e . The authors noted the lack of g ood industrial hy g i ene practices, implicating direct contact, such as touching of the nose with chromium-contaminated hands, as a potentially important route of ex posure. Lu cas and Kramkowski (1975) conducted a health haz ard evaluation of 11 employ ees in the “hard” chrome area of an industrial plating facility

. The averag e ag e of the employ ees was 39 y ears, and the averag e duration of employment in the hard chrome area was 7.5 y ears. Medical ex aminations were conducted to evaluate the presence of dermatitis, chrome holes, old chrome hole scars, ulcerated nasal septum, infection of the mucosa, nasal redness, perforated nasal se ptum, re dde ne d throat , c onjunc tivitis, a nd whe e z ing

. Environme n ta l a i r sa mple s we re col l ect ed fromth e breathi ng z one on al l workers i n th e hard chrom e area t o det e rm i n e th e concentrations of hex a valent chromium. Cr(VI ) concentrations rang ed from 1 to 20 μ g /m 3 , averag i n g 4 μ g /m 3

. However, the authors attributed the nasal patholog y primarily to direct contact. Clinical observations included injection of the nasal mucosa in five workers, ulcerated 10nasal septum in two workers, atrophic scarring indicative of the presence of past ulceration in two workers, and complete perforation of the nasal septum in four workers. Poor hy g i ene practices, including touching the nose with the hand, were noted at the plant and represented a confounding factor in the etiolog y of the nasal lesions. Markel and Lu cas (1973) conducted a health haz ard evaluation of 32 workers at a “cold dip” chrome plating plant who were employ ed in the chrome department or who reg u larly spent a portion of their workday in that area. Twenty of the employ ees worked in the chrome area of the plant for more than 5 y ears. A total of 16 personal and 7 g e neral air samples were taken to determine the concentrations of Cr(VI )

. Max imum airborne Cr(VI ) concentration was 3 μ g /m 3

. No workers were found to have ulcerated nasal mucosa or perforated nasal septa. Half of the 32 employ ees had varying deg r ees of mucosal irritation. The authors did not consider this to be sig n ificant, because the survey was carried out at the peak of the 1972-1973 influenz a epidemic. Li ndberg and Hedenstierna (1983) compared lung function, the condition of the nasal septum, and subjective symptoms related to respiratory health (data obtained by questionnaire) in unex posed controls (119) and workers (43) ex posed to chromic acid in chrome plating operations. W o rkers were further divided into low (< 2 μ g Cr[ V I ] /m 3 ) and hig h (> 2 μ g Cr [VI ] /m 3 ) ex posure g r oups. Complaints of diffuse nasal symptoms (“constantly running nose,” “stuffy nose,” or “a lot to blow out”) were reg i stered by 4/19 workers in the low g r oup and half of the 24 workers in the hig h g r oup. The authors reported reddening of the nasal mucosa at 1 to 2 μ g /m 3 and nasal irritation (chronic and nasal septal ulceration and perforation) in two-thirds of the subjects at concentrations from 2 to 20 μ g /m3

. All workers with nasal ulceration had been ex posed to chrome acid mist, which contained Cr(VI ) at 20 μ g /m 3 , or g r eater near the baths. F o r pulmonary function measurements, chang e s in vital capacity and forced ex piratory volume at 1 second (F EV l ) were seen fromC r(VI ) ex posures g r eat er th an 2 μ g /m 3

. Ex amination of the nasal septum revealed that damag e was sig n ificantly g r eater in ex posed workers than in unex posed controls and appeared to be somewhat more severe in the hig h g r oup than in the low g r oup. There was a tendency for lung function parameters to return to normal over a 2-day weekend. In the United States, 97 workers in chromate-producing plants had a hig h er incidence of severely red throats and pneumonia, but they did not show any increase in the incidence of other respiratory diseases when compared with control g r oups. Althoug h bilateral hilar enlarg ement was observed, there was no evidence of ex cessive pulmonary fibrosis in these workers (F ederal Security Ag ency , 1953). The various lung chang e s described in these workers may represent a nonspecific reaction to irritating material or a specific reaction to chromium compounds. Many of the conditions mentioned occur widely in the g e neral population (NAS, 1974). Li ndberg and Vesterberg (1983b) studied urinary ex cretion of proteins in 24 currently employ ed chrome platers and 27 former chrome platers. Results were compared with those for a g r oup of 37 referents. Ex posures for current workers were determined using personal samplers and were found to rang e from 2 to 20 μ g /m 3 , with an averag e level of 6 μ g /m 3

. Ex posures of former platers were thoug ht to be hig h er than those for the current workers. The duration of ex posure rang ed from < 1 to 26 y ears. Cr(VI ) ex posure was found to result in renal effects in a dose-dependent fashion (based on elevated ex cretion of � -2-microg l obulin as an indicator of 11nephrotox icity ) in current workers ex posed to 4 to 20 μ g /m 3 Cr(VI ) over 8-hour shifts. The effect may be reversible since former chrome platers did not have an elevated concentration of either B

- 2-microg l obulin or albumin in their urine. Most of the currently ex posed workers were also observed to have irritation symptoms of the airway s, including ulcerated nasal septum and complete perforations. Severe objective and subjective levels for the airway effects occurred at no-observed-adverse-effect levels (NOAEL s ) for renal tox i city

. In another study , Saner et al. (1984) did not find increased urinary � -2-mic rog l obulin levels in tannery workers in comparison with referent control workers. However, comparison of urinary chromium concentrations of the tannery workers in this study versus the chrome platers in the Li ndberg and Vesterberg (1983a,b) study sug g e sts that the latter had distinctly hig h er chrom i u mex posures. Ex posure to vapors of chromium salts has been suspected as a cause of asthma, coug hing , wheez ing , and other respiratory distress in ferrochromium workers (L ang ard, 1980). Novey et al. (1983) identified chromium-specific antibodies in a 32-y ear-old white male worker who ex perienced a productive coug h, wheez ing , and dy spnea within 2 weeks of beg i nning a new job el ectropl at i n g wi th chrom i u m . L aborat ory t e st i n g of th i s i ndi vi dual was perform ed wi th pl acebo and nickel and chromium solutions vaporiz ed by heat. The nickel and chromium solutions precipitated asthmatic symptoms identical to those ex perienced on the job. The authors c onc lude d thatthe a ffe c t e dindividua l de ve lope d a n a c quire d se nsitivity to c h romium a nd nic k e l vapors. A c tu a lC r ( III) a n d C r ( V I) e x p o s u r e l e v e l s i n m a n y o f th e s tu d i e s at tri b u t i n g r e s p i r at o ry effects to chromium were unknown. In addition, data on other confounding factors such as smoking were frequently unavailable. These caveats sig n ificantly complicate determination of th e pot ent i a l heal th effect s associ at ed wi th ex posure t o chrom i u m . Various other disease states have been attributed to chromium, but in most cases, the etiolog i c relation to chromium is doubtful because of the presence of other chemicals (NAS , 1974). These studies, reviewed by the U.S. EPA (1984), will not be reviewed here.

4.2. P R ECHRONIC AND CHRONIC STUDIES AND CANCER BIOASSAYS IN ANIMALS —ORAL AND INHALATION 4.2.1. Chronic Oral Studies T w oo r a lc h r o n i cr o d e n t b i o a s s a y s o f C r ( III) w e r e l o c a t e d i n th e literature. I v ankovic and Preussman (1975) fed 60 male and female rats (per dose g r oup) 0%, l%, 2%, or 5% Cr 2 O 3 , baked in bread, 5 day s /week for 600 feeding day s (120 weeks). The primary purpose of this study was t o assess th e carci nog eni c pot ent i a l of C r2 O 3 . The au thors e s timate d, ba se d on me a s ure s of food consumption and body weig ht (bw), that rats consumed 360 g /kg bw, 720 g /kg bw, and 1,800 g /kg bw of total Cr 2 O 3 over the duration of the study in the l%, 2%, and 5% Cr 2 O 3 feedi n g g r oups, respectively

. The animals were maintained on control diets following termination of the 12ex posure until they became moribund or died. No adverse effects were noted at any feeding le ve l. The hig h e s t dose le ve l (5%), whic h re pre s e n te d a tota l Cr 2 O 3 consumption for 600 day s of feeding of 1,800 g /kg bw, corresponds to a total Cr( III) i n t ak e o f 1,232 g /kg or 1,467 mg /kg

- day , ex panding ex posure over 840 day s (600 day s at 5 day s /week = 120 weeks or 840 day s ). The lack of tox i city g i ven the hig h concentrations of trivalent chromium used in the dose g r oups may reflect the poor absorption of trivalent chromium by the oral route of ex posure (Visek et al., 1953; Mertz et al., 1965; MacKenz i e et al., 1959; Og awa, 1976; Henderson et al., 1979). Cr( III) has been found to be better absorbed in fasted than in fed rats (MacKenz i e et al., 1959). The use of baked bread as a vehicle for dosing may have further reduced the absorption of chromium in the I v ankovic and Preussman (1975) study

. Schroeder et al. (1965) ex posed 54 male and 54 female Swiss mice to drinking water that contained 5 ppm chromium (as chromium acetate) for life (0.46 mg Cr( III) /k g / d a y )

. N oi n c r e a s e in the inc i de nc e of tumors wa s se e n in the tre at e da n ima ls with re spe c tto c ontrols. Similar results were obtained by Schroeder et al. (1965) for L ong -Evans rats. The dose of trivalent chromium used in this study was 2,000- to 10,000-fold lower than the dose in the I v ankovic and Preussman (1975) study , and most likely did not approach the max imum tolerated dose (MTD). The Schroeder et al. (1965) study is considered to be an inadequate test of carcinog enicity

. 4.2.2. Subc hr onicOr al Studie s Several subchronic studies reg arding oral ex posure to trivalent chromium were located in the literature. Akatsuka and F a irhall (1934) fed cats 50-100 mg of Cr( III) / d a y f

o r

1

- 3 m o n th s . No effects on weig hts or g r oss or microscopic patholog y of major org a ns were noted. This study cannot be used for quantitative risk assessment since the dose and duration of ex posure were not defined precisely

. MacKenz i e et al. (1958) provided rats with 25 ppm Cr( III) i n d ri n ki n g w at e r f

o r

1 2 months and noted no chang e in body weig ht, macroscopic or microscopic patholog y , or clinical chemistry variables. The MacKenz i e et al. (1958) study sug g e sts a no-observed-effect level (NOEL ) at 25 ppm CrCl 3 , equivalent to 8.2 ppm trivalent chromium. Assuming that an averag e rat weig hs 0.35 kg and consumes 0.035 L water/day , 8.2 ppm is adjusted to 0.82 mg trivalent c h romium/kg bw/da y . I v ankovic and Preussman (1975) fed rats baked bread containing up to 5% chromic ox ide (C r 2 O 3 ) for 90 day s . The only effects observed were reductions in the absolute weig hts of the livers and spleens of animals in the hig h -dose g r oup, which does not necessarily represent an adverse effect. This study sug g e sts a NOAEL of 5% Cr 2 O 3 (50,000 ppm), althoug h no clear adverse effects were observed at any dose used in the study

. The authors calculated, based on measured food consumption and body weig ht, that male rats in the 5% feeding g r oup consumed 180 g /kg Cr 2 O 3 total over the 88-day ex perimental period. This corresponds to 1,399 mg /kg

- day C r ( III)

. Anderson et al. (1997) fed Sprag u e-Dawley rats 0-100 mg /kg Cr( III) c h l o ri d e o r C r ( III) tripicolinate (trivalent chromium coordinated with 2-carbox y p y ridine) in the diet for 24 weeks. 13No statistical differences in body weig ht or blood variables were noted among the g r oups ex amined at 11, 17, or 24 weeks. Histolog ical ex amination of the animals in the hig h -dose g r oups did not reveal any detectable differences. Animals fed chromium picolinate were found to have liver and kidney chromium concentrations two- to threefold g r eater than those fed c h romium c h loride , de monstrating the hig h e r ab sorption of c h romium tripic olinat e . No tox i c ity was observed in any of the dose g r oups in this study

. 4.2.3. Chronic Inhalation Studies S e v e r a la n i m a ls tu d i e s h a v e b e e n p e r f o rm e d t oa s s e s s th e c ar c i n o g e n i cp o t e n t i a l o f C r ( III) in the re spirat ory tra c t
. Only one study wa s loc at e dthatutilize da n e x posure route similar to that ex pected for humans (inhalation of chromium dusts) (B aetjer et al., 1959b). Three strains of mice (strain A, Swiss, and C57B L ) were ex posed to chromiumcontaining dust (B aetjer et al., 1959b). These strains have, respectively , hig h, medium, and low spontaneous lung tumor incidences. The dust was similar to that found in the chromium chemical manufacturing industry , containing 13.7% Cr(VI ) ox ide (CrO 3 ) and 6.9% Cr( III) o x i d e (C r 2 O 3 ), along with other metal ox ides. In addition, potassium dichromate (K 2 Cr 2 O 7 ) was added at a level of 1%. The animals were ex posed to the dust-laden atmosphere containing between 0.5 and 1 mg total chromium 4 hours/day , 5 day s /week for an averag e of 39.7 weeks (rang e of 16 to 58 weeks). At death or termination of ex posure, the lung s were ex amined bymeans of a lowpower microscope, and abnormal tissues were submitted for histolog ic confirmation of tumors. The incidence of lung tumors was not different in ex posed mice of any strain as compared with approx imately equal numbers of the appropriate controls of unex posed mice of the same ag e. There was also no difference in those strains having hig h spontaneous tumor incidence with re g ard to the a v e r a g e numbe r of tumors pe r mouse or the pe rc e n t of mic e with multiple tumors. The lung tumors present in both control and treated animals were adenomas, which appeared to be histolog ic a lly similar; howe v e r , in e x pose da n ima ls, the a d e noma s de ve lope d slig htly e ar lie r in the strain A mice. Three additional small g r oups of mice (two g r oups of 10 Swiss female mice and one g r oup of 9 female strain A mice) were ex posed to hig h concentrations of chromium dust (7.8 to 13 mg Cr/m 3 ) in a nose-only chamber 0.5 hours/day , 5 day s /week for 43, 52, and 20 weeks, respectively

. No increase in the incidence of lung tumors was observed. Itis unclear from the report whether the MTD was achieved by the dosing reg imen used in these studies. Data on lung chromium content presented in the report indicated levels that were considerably lower than those observed in humans ex posed occupationally

. Ambig u ity reg arding the MTD and the variation in ex posure periods used complicates the interpretation of the results. S e v e r a ls tu d i e s a s s e s s e d th e c ar c i n o g e n i cp o t e n t i a l o f C r ( III) i n th e r e s p i r at o ry tr a c t following ex posure by intratracheal introduction, intrapleural injection, or intrabronchial implantation (B aetjer et al., 1959b; Hueper and Payn e, 1962; L e vy and Venitt, 1975; L e vy and Martin, 1983). These studies did not report an increased incidence of tumors following ex posure to triva l e n t c h romium.

14B aetjer et al. (1959b) suspended a chromium dust, similar in composition to that used in the inhalation studies, in olive oil, and z i nc chromate and barium chromate in saline prior to intratracheal introduction into strain A, Swiss, and C57B L mice and mix ed-breed rats (W istar and McCollum stocks). The mice each received five to six installations of 0.01 to 0.05 mg chromium at 4- to 6-week intervals, while the rats received 15 introductions at the same dose at 2-week intervals. The total duration of the studies was between 32 and 52 weeks. The mice tre at e dwith c h romium ha d a tumor inc i de nc e similar to a g e - matc he d c ontrols, a nd the rats in both the treated and control g r oups had no benig n or malig nant tumors. Hueper and Payn e (1962) noted that no implantation site tumors were observed in 42 rats during a 24-month period following eig h t intrapleural implantations of 25 mg trivalent chromium acet at e i n g e l at i n over a 13-m onth peri od. The National In stitute for Occupational Safety and Health (NI O SH, 1975) criteria document on hex a valent chromium described a written communication (L evy and Venitt, 1975) reporting the results of a study performed at the Chester B eatty Research In stitute in L ondon. Random-bred P arton W i star rats of both sex e s received a pellet in the left inferior bronchiolus via tracheotomy under anesthesia. The rats were kept for 2 y ears. One hundred rats were used in the test g r oup. The pellets that were implanted contained 2 mg g r ound chromite ore suspended 50/50 (weig h t/weig h t) in cholesterol. Neg ative control g r oups received either blank metal pellets or pellets and vehicle. Positive control g r oups received 3-methy l cholanthrene. The lung s of all rats e ithe r dying during the study or kille d a tits te rmination we re e x a mine dboth ma c r osc opic a lly a nd mic rosc opic a lly

. No bronc hia l c ar c i noma s of the le ft lung we re obse r ve d in the c h romite ore test g r oup. L e vy and Martin (1983) conducted an ex tensive investig ation of 21 chromium-containing test materials in W i star rats by intrabronchial implantation of a stainless steel wire mesh pellet containing 2 mg test material suspended in 2 mg cholesterol. The rats were allowed to live for 2 y ears, after which the study was terminated. No bronchial carcinomas were observed in the g r oup receiving hig h silica chrome ore ( III)

. 4.2.4. Subc hr onicInhalation Studie s Data from subc hronic a n ima l studie s ide n tify the re spirat ory tra c ta s the primary targ e tof chromium tox i city following inhalation. J ohansson et al. (1986) ex posed rabbits to aerosols of hex a valent (0.9 mg /m 3 Na 2 Cr O 4 ) or trivalent (0.6 mg /m 3 C r(NO 3 ) 3 ) chromium for 5 day s /week, 6 hours/day for 4 to 6 weeks. The number of macrophag e s obtained from the lung s of the rabbits ex posed to Cr(VI ) was sig n ificantly increased. W h ile the numbers of macrophag e s from rabbits e x p o s e d t oC r ( III) w e r e n o t i n c r e a s e d , s tri ki n g m o rpholog ic chang e s were observed, including round dark chromium-rich inclusions in the cytoplasm, an increased number of cells with a sm ooth i n act i v e cel l surface, enl arg ed Gol g i apparatu s, and a t e ndency t o ward el ong at ed cel l shape. The macrophag e s from rabbits ex posed to Cr(VI ) showed less marked morpholog ic c h a n g e s th a n th o s e e x p o s e d t oC r ( III)

.

15J ohansson et al. (1980) ex posed g r oups of four rabbits to chromium dust at concentrations of 3.1 mg /m 3 and 0.6 mg /m 3 for 5 day s /week, 6 hours/day for 4 weeks. Macrophag e s collected from rabbits ex posed to the hig h er concentration of chromium phag o cytiz ed sig n ificantly more chromium particles than the controls, althoug h the number of nonviable macrophag e s was less than 3%. Akatsuka and F a irhall (1934) ex posed two cats to chromium carbonate dust at a level that varied from 3.3-83 mg /m 3 (averag e = 58.3 mg /m 3 ) for 86 sessions. Each session varied from 10-60 minutes, averag ing 28 minutes for one cat and 57 minutes for the other. No effects in terms of g r oss or microscopic patholog y were observed upon termination of the ex periment. Ex amination of control animals, if there were any , was not reported. Glaser et al. (1985) ex posed 5-week-old male W i star rats to aerosols of sodium dichromate at concentrations rang ing from 0.025 to 0.2 mg Cr(VI ) /m 3 22 hour/day in subacute (28 day s ) or subchronic (90 day s ) protocols. Subacute and subchronic ex posures to Cr(VI ) a e r osol c onc e n trations re sulte d in a positive c o rre lation be twe e n e x posure dose a nd sig n ific a n t effects on alveolar macrophag e s and immunolog ic function. Inhaled chromium was found to preferent i a l l y accum u l at e i n th e l ung fol l o wi ng ex posure t o chrom at e aerosol s. Lung and spl een weig hts were sig n ificantly increased after both subacute and subchronic inhalation of chromate aerosols at concentrations g r eater than 0.025 mg /m 3

. Se rum c onte n ts of trig ly c e ride s a n d phospholipids differed sig n ificantly from controls ( p < 0.05) in rats ex posed subchronically to 0.2 mg /m 3 c h romate
. Inha lation of Cr(VI ) a e r osols stimula te d the humora l immune sy ste m . Differences in the mean total serum immunog lobulin were sig n ificant at ex posures above 0.025 mg /m 3 , while ex posures to aerosol concentrations g r eater than 0.1 mg /m 3 resulted in depression of the immune sy stem stimulation. The primary antibody response to the B

- cell-dependent antig en sheep red blood cell was elevated in a chromium-time and dose-dependent manner. The immune-stimulating effect of subchronic ex posure to an aerosol with 0.05 mg /m 3 c h romium wa s not reversed after 2 months of fresh air reg e neration. The spleen T-lymphocyt e subpopulation was also stimulated by subchronic ex posure to 0.2 mg /m 3 c h romium. B r onc hoa lve o lar la va g e (B AL ) cell counts were sig n ificantly decreased following subchronic ex posure to levels above 0.025 mg /m 3 chromium. The number of lymphocyt es and g r anulocyt es showed a slig ht but sig n ificant increase in the lavag e fluids of the subacute and subchronically ex posed g r oups. At subacute ex posure concentrations up to 0.05 mg /m 3 , the phag o cytic activity of the alveolar macrophag e s increased; however, subchronic ex posure at 0.2 mg /m 3 decreased th i s funct i o n sig n ificantly

. F o llowing subacute ex posure to 0.2 mg /m 3 chromium, reductions in macrophag e cell counts and phag o cytic activities correlate with an observed lower clearance of inhaled iron ox ide. Glaser et al. (1990) ex posed 8-week-old male W i star rats to sodium dichromate at 0.05, 0.1, 0.2, and 0.4 mg Cr(VI ) /m 3 22 hours/day , 7 day s /week for 30-90 day s . Chromium-induced effects were observed to occur in a strong dose-dependent manner. The authors observed obstructive respiratory dy spnea and reduced body weig ht following subacute ex posure at the hig h er dose levels. The mean white blood cell count was increased at all doses ( p < 0.05) and was related to sig n ificant dose-dependent leukocyt osis following subacute ex posures. Mean lung weig hts were sig n ificantly increased at ex posure levels of 0.1 mg /m 3 following both the subacute 16and subchronic ex posures. Accumulation of macrophag e s was seen in all of the ex posure g r oups and was postulated to be a chromium-specific irritation effect that accounted for the observed increases in lung weig hts. F o cal inflammation was observed in the upper airway s following the subchronic ex posure. B A L analy s es provided more detailed information on the nature of the dichromateinduced irritation effect. B A L albumin was increased following the subacute ex posure and was taken to indicate ex udation into the alveolar reg i on as an early irritation effect. The mean protein content of the cell-free lavag e fluid was sig n ificantly increased in a dose-dependent fashion after the subacute and subchronic ex posures. However, protein levels returned to control levels following a recovery period. Cytosolic lactate dehy drog enase and the number of mononuclear macrophag e s were also elevated following the subacute and subchronic ex posures, particularly at the hig h est dose levels. The enz yme activity and number of macrophag e s returned to the control level following the recovery period. The authors concluded that chromium inhalation induced pneumocyt e tox i city and sug g e sted that inflammation is essential for the induction of most chromium inhalation effects and may influence the carcinog enicity of Cr(VI ) compounds (Glaser et al., 1990). L ee et al. (1988) ex posed g r oups of 30 male and 30 female rats to 0.5 mg /m 3 or 25 mg /m 3 Cr O 2 (IV) for 6 hours/day , 5 day s /week for 2 y ears. Dust-laden alveolar macrophag e s with slig ht ty

pe I I pneumocyt e hyperplasia were noted following ex posure at 0.5 mg /m 3

. Inhaled particles were deposi t e d m a i n l y i n th e al veol i adj acent t o th e al veol ar duct s , and th e dustpart i c l e s appeared as dense particles and were phag o cytiz ed by intra-alveolar macrophag e s. Ex posure at 25 mg /m 3 overwhel m e d th e l ung cl earance m echani s m s and resul t e d i n si g n i f i cant i n creases i n dust-laden macrophag e s, bronchioloalveolar cell hy perplasia with foamy macrophag e response, and cholesterol g r anuloma in females in comparison with males. Two female rats developed we ll-diffe re ntiate d c y stic ke ratinizing squa mous c e ll c ar c i noma s with no tumor me ta sta s is. The tumors were not characteriz ed as neoplastic lesions.

4.3. REP R ODUCTIVE/DEVELOP M ENTAL STUDIES—ORAL AND INHALATION 4.3.1. Oral Studies No studies were located on reproductive or developmental effects in humans following e x p o s u r e t oC r ( III) c o mpounds. Male and female rats treated with 1,806 mg Cr( III) k g / d a y a s C r ( III) o x i d e 5 d a y s / w e e k f

o r

6 0d a y s b e f o r e g e s t a t i o n a n d th r o u g hout the g e station period had normal fertility , g e stational leng th, and litter size (I vankovic and Preussman, 1975). Z ahid et al. (1990) fed B A LB /c albino Swiss mice trivalent (chromium sulfate) and hex a valent (potassium dichromate) chromium at concentrations of 100, 200, and 400 ppm for 35 day s in the diet. The authors stated that the ex posure g r oups included seven animals per g r oup, and an additional seven animals were used as controls, althoug h the report presents conflicting summaries of the actual g r oup siz e s throug hout the report. F o llowing the treatment, the authors e x a mine dthe te ste s a nd e p ididymis of the a n ima ls. The e p ididymis wa s we ig he d a nd minc e d 17suspended in buffered formalin. Sperm counts were then subsequently determined and sperm were ex amined for morpholog ical abnormalities. Testes were fix e d with B ouin’s fluid for 1 week and were subsequently sectioned to 0.6 micron thickness and stained with haematox y lin and eosin for histolog ic ex amination. Ten sections were chosen randomly from the anterior, middle, and posterior parts of each testis and studied. One seminiferous tubule was chosen and ex amined to determine the cellular stag es of spermatog e nesis and the number of deg e nerated tubules. Statistical analy s es of the data were conducted using the t -t estbet w een m eans and th e 2 × 2 conting e ncy Chi-square test between percentag e s. The authors reported deleterious effects on the male mouse testes, including ambig uous levels of deg e neration in the outermost cellular lay e rs of the seminiferous tubules, reduced (or absence of) spermatog onia per tubule, accumulation of g e rm cells in the resting spermatocytes stag e, reduced sperm count in the epididymis, and increased percentag e of morpholog ically abnormal sperm at all chromium sulfate dose levels. The authors concluded that the small but sig n ificant increase of hex a valent c h romium in the te ste s of fe d a n ima ls induc e dsig n ific a n t de g e ne ration. Serious questions have been raised reg arding the desig n and conduct of this study (F inley et al., 1993; NTP, 1996a,b, 1997). The methods utilized by Z ahid et al. (1990) are considered to be insufficient to identify spermatog onia, likely g e nerated nonreproducible counts of epididym al sperm, and resulted in the biolog ically implausible conclusion of reduction in spermatog onia numbers concurrent with unchang ed spermatocyte and spermatid numbers. Additional questions have been raised with reg ard to uncertainties reg arding the actual g r ouping s of animals used and the statistical analy s is of the data (F inley et al., 1993). Elbetieha and Al-Hamood (1997) ex amined fertility following chromium chloride ex posures in mice. Sex u ally mature male and female mice were ex posed to 1,000, 2,000, or 5,000 mg /L chromium chloride in drinking water for 12 weeks. The effects of the ex posures on fertility were ex amined at 140 day s . No mortality or clinical sig n s of tox i city were reported in any g r oup of male or female mice ex posed at any concentration in the ex periment. The authors reported a number of effects, althoug h in many cases the results were not strong lydosedependent. The authors reported ex posure of male mice to 5,000 ppm trivalent chromium compounds for 12 weeks had adverse impacts on male fertility

. Testes weig hts were increased in the males ex posed in the 2,000 and 5,000 mg /L dose g r oups, while seminal vesicle and preputial g l and weig hts were reduced in the 5,000 mg /L ex posed males. The number of implantation sites and viable fetuses were sig n ificantly reduced in females ex posed to 2,000 and 5,000 mg /L chromium chloride. The authors did not report the amount of water ing e sted by the animals, othe r tha n to note thatwate r ing e stion wa s re duc e din a n ima ls e x pose dto c h romium. While the results of this study sug g e st the potential presence of reproductive effects, the lack of dose dependence in reported effects and the absence of data indicating actual ex posures to the animals preclude the use of these data in risk assessment. 4.3.2. Inhalation Studies No studies were located on reproductive or developmental effects in humans following e x p o s u r e t oC r ( III) c o mpounds. No histopatholog ic abnormalities were observed in the testes of rats ex posed to 0.1 mg total chromium (as a 3:2 mix ture of Cr(VI ) triox i de and Cr( III) o x i d e ) f o r 1818 months (Glaser et al., 1986, 1988). No additional data reg arding the teratog e nicity of inhaled triva l e n t c h romium c ould not be loc at e din the a v a ilable lite rature
.
4.4. OTHER STUDIES 4.4.1. Contact Derm atitis Dermal ex posure to chromium has been demonstrated to produce irritant and allerg ic contact dermatitis (B ruyn zeel et al., 1988; Polak, 1983; Cronin, 1980; Hunter, 1974). Primary irrita nt de rmatitis is re late d to the dire c tc ytotox i c prope rtie s of c h romium, while a lle rg ic c onta c t dermatitis is an inflammatory response mediated by the immune sy stem. Allerg ic contact dermatitis is a cell-mediated immune response that occurs in a two-step process. In the first step (induction), chromium is absorbed into the skin and trig g e rs an immune response (sensitization). Sensitized individuals will illicit an allerg ic dermatitis response when ex posed to chromium above a threshold level (Polak, 1983). Induction is g e nerally considered to be irreversible. Chromium a lle rg ic de rmatitis is c h ar a c t e rize dby symptoms of e rythe ma , swe lling , papule s , sma l l vesicles, dryn ess, scaling , and fissuring (Adams, 1990; MacKie, 1981). Chromium is one of the most common contact sensitizers in males in industrialized countries (F owler, 1990; Cronin, 1980) and is associated with occupational ex posures to numerous materials and processes, including chrome plating baths, chrome colors and dy es, cement, tanning ag ents, wood preservatives, anticorrosive ag ents, welding fumes, lubricating oils and g r eases, cleaning materials, and tex tiles and furs (B urrows and Adams, 1990; Polak et al., 1973). Solubility and pH appear to be the primary determinants of the capacity of individual chromium compounds to elicit an allerg ic response (Freg e rt, 1981; Polak et al., 1973). The low solubility Cr( III) c o mpounds are much less efficient contact allerg ens than Cr(VI ) (Spruit and van Neer, 1966). W h ile chromium compounds have been found to elicit an allerg ic response in occupational setting s , this endpoint is not considered suitable for the development of a noncancer dose-response assessment. 4.4.2. Toxicant Interactions Asc o rbic , pic o linic , a nd nic o tinic a c i ds ha ve a ll be e n de monstrat e dto fa c ilitate the ab s o rp t i o n o f C r ( III) th r o u g h th e i n t e s t i n a l w a l l ( A n d e r s on, 1997; ATSDR, 1993). 4.4.3. G e notoxicity Trivalent chromium has been demonstrated to decrease the fidelity of DNA synthesis (Snow and Xu, 1991; Snow, 1994). Trivalent chromium chloride has been shown to produce g e notox ic DNA adducts that inhibit DNA replication and are mutag e nic (Snow, 1994). In g e neral, trivalent chromium was not mutag e nic in bacterial assay s when tested with or without a mammalian activation sy stem (Venitt and L e vy , 1974; Petrilli and DeF l ora, 1977, 1978a,b). In one study , triva l e n t c h romium wa s muta g e nic in Bac c illus subtilis , but this a c tivity wa s low compared with compounds of hex a valent chromium (Nakamuro et al., 1978). 19The r e is c onflic ting information with re g ard to the ab ility of triva l e n t c h romium to interact with DNA. Compounds of trivalent chromium were found to be clastog e nic in B A LB /c cel l s as C r C l 3 (Raffetto, 1977); CHO cells as CrCl 3 , C r(NO 3 ) 3 , KC r(S O 4 ) 2 , or Cr(CH 3 COO) 3 (L evis and Majone, 1979); Don Chinese hamster cells as hy drated CrCl 3 (Ohno et al., 1982); and cultured human leukocyt es as Cr(CH 3 COO) 3 (Nakamuro et al., 1978). However, compounds of C r ( III) w e r e n o t c l a s t o g e n i ci n m o u s e F M 3 A c e l l s a s C r 2 (S O 4 ) 3 (Umeda and Nishimura, 1979), cultured human leukocyt es as CrCl 3 or Cr(NO 3 ) 3 (Nakamuro et al., 1978), or Don Chinese ha mste r c e lls a s Cr 2 (S O 4 ) 3 (Ohno et al., 1982). C r ( III) p i c o l i n at e w a s s h o w n t op r oduce chromosome damag e 3- to 18-fold above the control levels following soluble doses of 0.05, 0.1, 0.5, and 1.0 mM over a 24-hour treatment. The c h romosome da ma g e wa s infe rre d to re sult from the pic o linat e lig a nd following the d e m o n s tr at i o n o f c l a s t o g e n i c i t y i n th e ab s e n c e o f C r ( III) ( S t e arn s e t a l

. , 1995).

4.5. SYNTHESIS AND EVALUATION OF MAJOR NONCANCER EF F E CTS AND MODE OF ACTION (IF K N OWN)—ORAL AND INHALATION 4.5.1. Oral Studies 4.5.1.1. Hum a n Studie s No hum an studi es addressi ng noncarci nog eni c effect s of tri v al entchrom i u mwere l o cat ed in the a v a ilable lite rature
. 4.5.1.2. Anim al Studie s T w oo r a lc h r o n i cr o d e n t b i o a s s a y s o f C r ( III) w e r e l o c a t e d i n th e literature. I v ankovic and Preussman (1975) fed male and female rats up to 5% Cr 2 O 3 baked in bread 5 day s /week for 120 weeks. No adverse effects were noted at any feeding level. Schroeder et al. (1965) ex posed mice a n d r at s t od ri n ki n g w at e r c o n t a i n i n g 5 p p m C r ( III) f o r

l i f e . N oi n c r e a s e i n th e i n c i d e n c e o f tumors wa s se e n in the tre at e da n ima ls with re spe c tto c ontrols. Anderson et al. (1997) evaluated the subchronic tox i city of Sprag u e-Dawley rats fed 0- 100 mg /kg Cr( III) c h l o ri d e o r C r ( III) tri p i c o l i n a t e i n th e d i e t f

o r

2 4w e e k s . N os t at i s t i c a l differences in body weig ht or blood variables were noted among the g r oups ex amined at 11, 17, or 24 weeks. Histolog ic ex amination of the animals in the hig h -dose g r oups did not reveal any detectable differences. No tox i city was observed in any of the dose g r oups in this study

.

204.5.2. Inhalation Studies 4.5.2.1. Hum a n Studie s All of the available studies of occupational ex posures include mix ed ex posures to both C r ( III) a n d C r ( V I)

. T h e C r ( V I) s p e c i e s h a s b e e n s u g g e s t e d a s th e l i k e l y e t i o l o g i ca g e n t i n r e p o rt s of ex cess cancer risk in chromium workers; however, Cr(VI ) cannot be unequivocally demonstrated to be the etiolog i c ag ent for noncarcinog enic effects following inhalation. W h ile d at a a d d r e s s i n g e x p o s u r e s t oC r ( III) a l o n e ar e n o t a v a i l ab l e , s i g n i f i c a n t r e d u c t i o n o f C r ( V I) t o C r ( III) o c c u r s i n th e l u n g s , a n d ab s o r p t i o n o f C r ( III) f r o m l u n g t i s s u e i s known to occur (ATSDR, 1993; O’F l aherty , 1996). The following discussion presents results of studies involving mix ed e x p o s u r e s t oC r ( III) a n d C r ( V I)

. 4.5.2.1.1. Respiratory tract effects . Three studies on chrome platers seem to provide some quantitative information on upper respiratory irritation after ex posure to Cr(VI ) as chromic acid. Cohen et al. (1974) reported that nasal ulcers and perforations were associated with total chromium concentrations of 1.4 to 43.9 μ g /m 3 , averag ing 7.1 μ g /m 3 , and Cr(VI ) concentrations of 0.09 to 9.1 μ g /m 3 , averag ing 2.9 μ g /m 3

. The authors i mp l i cat ed di rectcont act , such as touching of the nose with chromium-contaminated hands, as a potentially important route of ex posure. Lu cas and Kramkowski (1975) reported similar results following worker ex posure to Cr(VI ) concentrations rang ing from 1 to 20 μ g /m 3 , averag i n g 4 μ g /m 3

. Li ndberg and Hedenstierna (1983) also found similar effects on nasal patholog y and subjective symptoms. They reported reddening of the nasal mucosa at 1 to 2 μ g /m 3 , and nasal irritation (chronic and nasal septal ulceration and perforation) in two-thirds of the subjects at concentrations from 2 to 20 μ g /m 3

. Chang e s in vital capacity and forced ex piratory volume were reported following C r(VI ) ex posures g r eat er th an 2 μ g /m 3

. 4.5.2.1.2. R e n a l effect s . Cr(VI ) ex posure as low as 4 to 6 μ g /m 3 has been reported to result in el evat ed ex cret i on of � -2-microg l obulin (Lindberg and Vesterberg , 1983b). The effect may be reversible since former chrome platers did not have an elevated concentration of either � -2-mic rog l obulin or a l bumin in the i r urine

. In conclusion, effects on the airway s and kidney have been observed in chrome platers ex posed subchronically to chromic acid mist containing chromium in air at concentrations g r eat er th an 1 μ g /m 3

. Such effects include reddening of nasal mucosa, nasal irritation (ulceration, perforation), chang e s in pulmonary function, and renal proteinuria. F e w of the available studies, however, provide quantitative concentration-response data on chromium health effect s. 4.5.2.2. Anim al Studie s In

th e o n l y s tu d y s p e c i f i c a l l y a d d r e s s i n g n o n c ar c i n o g e n i ce f f

e c t s b y i n h a l at i o n o f C r ( III) , J ohansson et al. (1986) ex posed rabbits to aerosols of trivalent chromium (Cr(NO 3 ) 3 ) at concentrations of 0.6 and 0.9 mg /m 3 for 6 hours/day , 5 day s /week for 4-6 weeks. Striking morpholog ic chang e s were observed, including round dark chromium-rich inclusions in the 21cyt opl asm , an i n creased number of cel l s wi th a sm ooth i n act i v e cel l surface, enl arg ed Gol g i apparatus, and a tendency toward elong ated cell shape. J ohansson et al. (1980) ex posed rabbits to chromium dust at 3.1 mg /m 3 and 0.6 mg /m 3 for 5 day s /week, 6 hours/day for 4 weeks. Alveolar macrophag e s harvested from the ex posed a n ima ls pha g o c ytize dsig n ific a n tly more c h romium partic le s tha n those harve s te d from c ontrols, althoug h the number of nonviable macrophag e s was within the normal rang e (less than 3%) (J ohansson et al., 1980).

4.6. WEIG HT-OF - EVIDENCE EVALUATION AND CANCER CHARACTERIZ ATION Appl yi ng th e cri t e ri a for eval uat i n g th e overal l wei g htof evi d ence for carci nog eni c i t y t o huma n s outline din EPA’s Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1986a), trivalent chromium is most appropriately desig n ated a Group D–Not classified as to its human c artinog e n ic ity

. Using the Proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1996a), there are inadequate data to determine the potential carcinog enicity of trivalent chromium. The classification of hex a valent chromium as a known human carcinog en raises a c onc e rn for the c ar c i nog e n ic pote n tia l of triva l e n t c h romium. The inab ility to e l uc idat e the c ontribution of triva l e n t c h romium to c a n c e r inc i de nc e following e x posure s to tota l c h romium mix ture s in the s e studie s pre c l ude s a se parate de te rmination of whe the r triva l e n t c h romium alone has carcinog enic potential. Data from oral and inhalation ex posures of animals to trivalent c h romium ar e ina d e quate to de te rmine the c ar c i nog e n ic ity of triva l e n t c h romium. The In ternational Ag ency for Research on Cancer (IARC, 1990) concluded that animal data are i n a d e q u at e f

o r

th e e v a l u at i o n o f th e c ar c i n o g e n i c i t y o f C r ( III) c o m pounds. F u rthermore, althoug h there is sufficient evidence of respiratory carcinog enicity associated with ex posure to c h r o m i u m , th e r e l at i v e c o n tri b u t i o n s o f C r ( III) , C r ( V I) , m e t a llic c h romium, or soluble ve rsus insoluble chromium to carcinog enicity cannot be elucidated.

4.7. OTHER HAZ ARD IDENTIF I CATION ISSUES 4.7.1. P o ssible Childhood Susceptibility A number of factors may differentially affect the response of children to tox i cants such as C r ( III)

. T h e s e f

a c t o r s i n c l u d e d i e t , p h y s i c a le n v i r o n m e n t , a s w e l la s m atu r a t i o n o f p h y s i o l o g i c a l a nd bioc he mic a l proc e sse s. At pre s e n t, the r e is too little information to make a n y stat e m e n ts about how these factors may specifically affect the tox i colog i cal responses of Cr( III) i n c h i l d r e n , be th ey cancer or noncancer. 4.7.2. P o ssib l e S e x Dif f

eren ces At present, there is too little information to make any statements about the ex tent to whic h me n diffe r from wome n in susc e p tibility to Cr( III) t o x i c i t y .
225. D O SE- R ESP O N S E A SSESSM EN TS 5.1. ORAL REF E RENCE DOSE (Rf D ) The RfD is ba se d on the a ssumption thatthre sholds e x ist for c e rta in tox i c e ffe c t s suc h a s cellular necrosis, but may not ex ist for other tox i c effects such as carcinog enicity

. In g e neral, the RfD is a n e s timate (with unc e rta inty spa nning pe rhap s a n orde r of ma g n itude ) of a da ily e x posure to the human population (including sensitive subg roups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Please refer to the Oral RfD B ackg r ound Document (on I R I S ) for an elaboration of these concepts. 5.1.1. Choice of P r incipal Study and Critical Ef f

ect Re lative l y fe w studie s we re loc at e din the lite rature thata ddre sse d the ora l tox i c ity of C r ( III)

. Iv a nkovic and Preussman (1975) fed rats baked bread containing up to 5% chromic ox ide (Cr 2 O 3 ) for 840 day s . No effects due to Cr 2 O 3 treatment were observed at any dose level. I v ankovic and Preussman (1975) also fed rats baked bread containing up to 5% Cr 2 O 3 for 90 day s . The only effects observed were reductions in the absolute weig hts of the livers and spleens of animals in the hig h -dose g r oup. The absence of tox i city of trivalent chromium following these e x tra o rdinarily hig h dose s like l y re fle c tthe low ora l bioa va ilability of die t ary Cr 2 O 3 . In a subchronic study , Anderson et al. (1997) evaluated the tox i city of 0-100 mg /kg C r ( III) c h l o ri d e a n d C r ( III) tri p i c o l i n at e f

e d t oS p r a g u e - D a w l e y r a t s i n th e d i e t
. B o th o f th e s e forms of c h romium ha ve c onside r ab ly hig h e r bioa va ilability tha n thatof Cr 2 O 3 . Histolog ic ex amination of the animals in the hig h -dose g r oups did not reveal any detectable differences with controls, and no tox i city was observed in any of the dose g r oups in this study

. Dose levels in this study were considerably lower than those used by I v ankovic and Preussman (1975). Elbetieha and Al-Hamood (1997) ex amined fertility following chromium chloride ex posures in sex u ally mature mice at concentrations of 1,000, 2,000, or 5,000 mg /L chromium c h loride in drinking wate r for 12 we e k s. No morta lity or c linic a l sig n s of tox i c ity we re re porte d in any g r oup of male or female mice ex posed at any concentration in the ex periment. The authors reported a number of effects on male fertility , althoug h in many cases the results were not strong ly dose dependent. The authors also reported a reduced number of implantation sites and viable fetuses in ex posed females. The authors did not report the amount of water ing e sted by the a n ima ls, othe r tha n to note thatwate r ing e stion wa s re duc e din a n ima ls e x pose dto c h romium. W h ile this study sug g e sts the potential presence of reproductive effects, the lack of dose dependence in reported effects and the absence of data indicating actual ex posures to the animals preclude the use of these data in risk assessment. The I v ankovic and Preussman (1975) studies are considered to be most appropriate for development of the RfD. 5.1.2. Methods of Analysis

23I v ankovic and Preussman (1975) fed g r oups of 60 male and 60 female rats chromic ox ide (C r 2 O 3 ) baked in bread at dietary levels of 0%, 1%, 2%, or 5%, 5 day s /week for 600 feeding s (840 total day s ). B ody weig ht and food consumption were monitored. The averag e total amounts of ing e sted Cr 2 O 3 were g i ven as 360, 720, and 1,800 g /kg bw for the 1%, 2%, and 5% treatment g r oups, respectively

. The animals were maintained on control diets following termination of ex posure until they became moribund or died. All major org a ns were ex amined histolog ic a lly

. Othe r tox i c o log i c para me te rs we re not me ntione d e x plic itly but ma y ha ve i n cl uded som e or al l of those descri bed for th e accomp anyi ng subchroni c study (see bel o w). No effects due to Cr 2 O 3 treatment were observed at any dose level. I v ankovic and Preussman (1975) also treated rats (both sex e s, 12-19 rats/g roup) at dietary levels of 0%, 2%, or 5% Cr 2 O 3 in bread, 5 day s /week for 90 day s . F ood consumption and body we ig ht we re monitore d. Tox i c o log i c para me te rs inc l ude d se rum prote i n, bilirubin, he matolog y , urinaly s is, org a n weig hts, and histopatholog y . W ith the ex ception of reductions (12%-37%) in the absolute weig hts of the livers and spleens of animals in the hig h -dose g r oup, no effects could be detected that could be attributed to the Cr 2 O 3 tre atme nt. 5.1.3. Rf D Derivation No effects were reported at any dose level in I v ankovic and Preussman (1975) chronic study

. The hig h est dose g r oup (receiving 5% Cr 2 O 3 in the diet for 600 feeding s ) can be considered a NOAEL for the study and was selected for derivation of the reference dose. The 5% dose g r oup received an equivalent of 1,800 g /kg body weig ht. Adjustment of this dose level based on the amount of ing e sted Cr( III) ( 0.6849 Cr/g Cr 2 O 3 ) and the feeding schedule (600 feeding day s × 5 day s /7 day s ) yi elds an adjusted NOAEL of 1,468 mg /kg

- d. The lack of tox i city g i ven the hig h concentrations of trivalent chromium used in the dose g r oups may reflect the poor absorption of trivalent chromium by the oral route of ex posure (Visek et al., 1953; Mertz et al.,1965; MacKenz i e et al., 1959; Og awa, 1976; Henderson et al., 1979). Cr( III) h a s b e e n f

ound to be better absorbed in fasted than in fed rats (MacKenz i e et al., 1959). The use of baked bread as a vehicle for dosing may have further reduced the absorption of chromium in the I v ankovic and Preussman (1975) study

. The adjusted NOAEL is further modified by two 10-fold uncertainty factors to account for the e x pe c t e dinte rspe c i e s a nd inte rhuma n variab ility in lie u of spe c i fic data
. An a dditiona l 10-fold modifying factor is applied to reflect database deficiencies, including the lack of a study in a nonrodent mammal, lack of unequivocal data evaluating reproductive impacts, and the concern reg arding potential reproductive effects raised by the study of Elbetieha and Al-Hamood (1997). The following additional uncertainties relate to the NOAEL derived from the I v ankovic and Preussman (1975) study : (1) the effects observed in the 90-day study were not ex plicitly addressed in the 2-y ear study ; (2) the effect of the vehicle (baked bread) on absorption of chromium is uncertain, and the relevance of this dosing reg imen to ex posures in the environment is unclear; and (3) animals were allowed to die naturally after ex posure stopped (2 y ears) and only then was histolog y performed. Application of the 100-fold uncertainty factor and 10-fold modifying factor to the adjusted NOAEL of 1,468 mg /kg

- d g i ves the reference dose of 1.5 mg /kg

- d. 245.2. INHALATION REF E RENCE CONCENTRATION (RfC ) The inha lation RfC is ba se d on the a ssumption tha tthre sholds e x ist for c e rta in tox i c effect s such as cel l u l ar necrosi s but m a y notex i s tfor other t o x i c effect s such as carci nog eni c i t y . In g e ne ra l, the RfC is a n e s timate (with unc e rta inty spa nning pe rhap s a n orde r of ma g n itude ) of a daily ex posure to the human population (including sensitive subg roups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Studies of occupational ex posure to chromium by inhalation all involve mix ed ex posures t ob o th C r ( III) a n d C r ( V I)

. W h i l e d at a a d d r e s s i n g e x p o s u r e s t oC r ( III) a l o n e ar e n o t a v a i l ab l e , s i g n i f i c a n t r e d u c t i o n o f C r ( V I) t oC r ( III) o c c u r s i n th e l u n g s , a n d ab s o rp t i o n o f C r ( III) f r o m l u n g tissue is known to occur (O’F laherty , 1996). Cr(VI ) cannot be unequivocally demonstrated to be the sole e tiolog i c a g e n t for nonc ar c i nog e n ic e ffe c t s following inha lation. Three studies on chrome platers reported upper respiratory irritation after ex posure to Cr(VI ) as chromic acid. In the study of Cohen et al. (1974), nasal ulcers and perforations were associated with total chromium concentrations of 1.4 to 43.9 μ g /m3 , averag ing 7.1 μ g /m 3

. Ninety -five percent of the 37 workers studied ex hibited patholog ic chang e s in nasal mucosa in a concentration-duration response. More than half of the workers employ ed less than 1 y ear had nasal patholog y that was more severe than simple redness of the nasal mucosa. Almost all workers (35 of 37) employ ed long er than 1 y ear had nasal tissue damag e . The authors implicated direct contact, such as touching of the nose with chromium-contaminated hands, as a potentially important route of ex posure. Lu cas and Kramkowski (1975) revealed similar results. Li ndberg and Hedenstierna (1983) also found similar effects on nasal patholog y and subjective symptoms. All workers with nasal ulceration had been ex posed to chrome acid mist, which contained Cr(VI ) at 20 μ g /m 3 , or g r eater near the baths. Chang e s in vital capacity and forced ex piratory volume were seen following Cr(VI ) ex posures g r eater than 2 μ g /m 3

. O n l y o n e a n i m a ls tu d y a d d r e s s e d e x p o s u r e t oC r ( III) b y i n h a l a t i on. J ohansson et al. (1986) reported the results of a subchronic study in which rabbits were ex posed to aerosols of triva l e n t c h romium (Cr(NO 3 ) 3 ) at concentrations of 0.6 and 0.9 mg /m 3 for 6 hours/day , 5 day s /week for 4-6 weeks. Striking morpholog ic chang e s were observed, including round dark chromium-rich inclusions in the cytoplasm, an increased number of cells with a smooth inactive cel l surface, enl arg ed Gol g i apparatu s, and a t e ndency t o ward el ong at ed cel l shape. Thi s study utilized small g r oups and focused on endpoints that are not considered to be appropriate for d e v e l o p m e n t o f a n R f C f o r

C r ( III)

. Data are considered to be inadequate for development of an RfC due to the lack of a r e l e v a n t t o x i c i t y s tu d y a d d r e s s i n g r e s p i r at o ry e f f

e c t s o f C r ( III)

. T h e c u r r e n t l y a v a i l ab l e d a t a ar e ina d e quate to e l uc idat e the c ontribution of triva l e n t c h romium to re spirat ory e ffe c t s obse r ve d following occupational ex posures to mix tures of trivalent and hex a valent chromium. The one a n ima l study thate v a l uate d the tox i c ity of triva l e n t c h romium by the inha lation route of e x posure (J ohansson et al., 1986) utilized only one ex posure concentration and did not identifya lowestobserved-adverse-effect level. As a result, this study is considered inadequate to support the 25development of an RfC for trivalent chromium, and an RfC for trivalent chromium cannot be de ve lope d atthis time

.
5.3. CANCER ASSESSMENT Occupational ex posure to airborne chromium has been studied in the chromate manufacturing and ferrochromium industries; in all cases ex posures all include mix ed ex posures t ob o th C r ( III) a n d C r ( V I)

. D at a a d d r e s s i n g e x p o s u r e s t oC r ( III) a l o n e ar e n o t a v a i l ab l e . C r ( V I) has been classified as a known human carcinog en, and the contribution of Cr( III) t oth e o b s e r v e d lung cancer in these populations cannot be elucidated from these studies. Animal data are i n a d e q u at e f

o r

th e e v a l u at i o n o f th e c ar c i n o g e n i c i t y o f C r ( III) c o m pounds. The two oral studies located in the available literature (Schroeder et al., 1965; I v ankovic and Preussman, 1975) reported neg ative results for rats and mice. Several animal studies have been performed to assess th e c ar c i n o g e n i cp o t e n t i a lo f C r ( III) b y i n h a l at i on. These studies have not found an increased incidence of lung tumors following ex posure either by natural routes, intrapleural injection or intrabronchial implantation (B aetjer et al., 1959b; Hueper and Payn e, 1962; L e vy and Venitt, 1975; L e vy and Martin, 1983). F o r the reasons stated above, a quantitative dose-response a s s e s s m e n t h a s n o t b e e n g e n e r at e d f

o r

C r ( III)

.
6. MAJOR CONCLUS IONS IN THE CHARACTERIZATION OF HAZARD AND DOS E RES P ONS E 6.1. HUMAN HAZ ARD P O TENTIAL Chromium is a natura lly oc c u rring e l e m e n t thatma y e x ist in se ve ra l c h e mic a l forms a n d val e nce st at es i n th e envi ronm ent
. The m o stcom m onl y occurri ng val e nce st at es are chrom i u m m e t a l( 0 ) , tri v a l e n t c h r o m i u m ( III) , a n d h e x a v a l e n t c h r o m i u m ( V I)

. C r ( III) p o t e n t i a t e s th e a c t i o n of insulin in pe riphe ra l tissue a nd is e sse ntia l for a n ima ls a nd huma n s. Adults in the Unite d States are estimated to ing e st approx imately 60 μ g /day of chromium from food (ATSDR, 1993). NRC has identified an ESADDI for chromium of 50-200 μ g /d (NRC, 1989), corresponding to 0.71-2.9 μ g /kg / day for a 70 kg adult. F DA has selected a Reference Daily In take for chromium of 120 μ g /d (U.S. DHHS, 1995). The bioa va ilability of c h romium ma y be the sing le most importa nt fa c t or de te rmining the tox i city of a specific chromium source (O’F laherty , 1996). In g e sted hex a valent chromium is e ffic i e n tly re duc e dto the triva l e n t form in the g a strointe stina l tra c t
. Ga strointe stina l ab sorption o f

C r ( V I) o c c u r s w i th g r e at e r e f f i c i e n c y th a n ab s o rp t i o n o f C r ( III) , a n d ab s o rp t i o n o f i n g e s t e d triva l e n t c h romium is e s timate d to be le ss tha n 3%. Triva l e n t c h romium is ab sorbe dve ry slowly by inhalation. F o llowing inhalation ex posure, chromium may be absorbed into the sy stemic circulation, transferred to the g a strointestinal tract by mucociliary action, or remain in the lung

.

26A sig n ificant amount of absorbed chromium is taken up in the bone, liver, kidney , and spleen. Hex a valent chromium readily crosses cell membranes throug h the phosphate and sulfate a n i o n - e x c h a n g e c ar ri e r p ath w a y . C r ( III) c o mpounds may cross cell membranes, but only with ve ry low e ffic i e n c y . The r e is c onflic ting information re g arding the ab ility of triva l e n t c h romium to interact with DNA. In g e neral, trivalent chromium was not mutag e nic in bacterial assay s when tested with or without a mammalian activation sy stem. Occupational ex posure to trivalent chromium and other chromium compounds by inhalation has been studied in the chromate manufacturing and ferrochromium industries; h o w e v e r , a l l s tu d i e s i n c l u d e m i x e d e x p o s u r e s t ob o th C r ( III) a n d C r ( V I)

. W h i l e th e C r ( V I) speci es i s th e l i k el y et i o l o g i c ag ent i n report s of ex cess cancer ri sk i n chrom i u mworkers, studi es ar e i n a d e q u at e t oru l e o u t a

c o n tri b u t i o n o f C r ( III) t oc h r o m i u m c ar c i n o g e n i c i t y , a n d d at a a d d r e s s i n g e x p o s u r e s t oC r ( III) a l o n e ar e n o t a v a i l ab l e . Re lative l y fe w studie s we re loc at e din the lite rature thata ddre sse d the ora l or inha lation t o x i c i t y o f C r ( III)

. N oe f f

e c t s o th e r th a n r e d u c t i o n s o f th e ab s o l u t e w e i g h t s o f l i v e r s a n d s p l e e n s o f

r at s h a v e b e e n o b s e r v e d f

o l l o w i n g o r a l e x p o s u r e t oC r ( III)

. W h i l e s tri ki n g m o rpholog ic chang e s occurred in the macrophag e s of rabbits ex posed to Cr( III) a e r o s o l s i n th e o n e i n h a l at i o n s tu d y o f C r ( III) i n a n i m a l s , th e d at ab a s e i s i n a d e q u at e t os upport development of an RfC for C r ( III)

. Chromium is one of the most common contact sensitizers in industrialized countries, and a lle rg ic c onta c tde rmatitis is a ssoc i at e dwith oc c upationa l e x posure s to nume r ous mate ria l s a n d processes, including chrome plating baths, chrome colors and dy es, cement, leather tanning ag ents, and wood preservatives.

6.2. DOSE RESP ONSE Studies of inhalation of mix tures of trivalent and hex a valent chromium in occupational populations support the classification of Cr(VI ) as a known human carcinog en but provide i n a d e q u at e d at a f

o r

e v a l u at i o n o f c ar c i n o g e n i c i t y o f C r ( III) c o m pounds. T h e d at ab a s e o n n o n c ar c i n o g e n i ce f f

e c t s o f C r ( III) i s a l s ol a c ki n g . R e l at i v e l y f

e ws tu d i e s we re loc at e din the lite rature thata ddre sse d the ora l tox i c ity of Cr( III)

. O f th e s e , th e Iv a nkovic and Preussman (1975) study was judg ed to be the only study suitable for development of an RfD f

o r

C r ( III)

. T h e c o n f i d e n c e i n th e R f D d e v e l o p e d u s i n g th e Iv a nkovic and Preussman (1975) study is low. The primary purpose of the I v ankovic and Preussman (1975) study was to assess th e carci nog eni c pot ent i a l of C r 2 O 3 . The confidence in the principal study is considered low because of th e l ack of ex pl i c i tdet a i l on study prot ocol and resul t s . No effect s due t o C r 2 O 3 treatment were observed at any dose level in this study

. No macroscopic or histolog ic sig n s of tox i city were noted in the 2-y ear study , althoug h the effects observed in the 90-day study were not e x plic itly a ddre sse d. Anima ls in this study we re a llowe d to die natura lly a f te r e x posure stopped (2 y ears) and only then was histolog y performed. Data on potential reproductive and d e v e l o p m e n t a le f f

e c t s o f C r ( III) ar e l a c ki n g . A m o d i f yi n g f

a c t o r o f 1 0w a s ap p l i e d t oth e 27adjusted NOAEL to account for the potential reproductive tox i city identified by the study of Elbetieha and Al-Hamood (1997) and the absence of a credible study addressing reproductive endpoints. The adjusted NOAEL is further modified by two 10-fold uncertainty factors to account for the ex pected interspecies and interhuman variability in lieu of specific data. Only o n e s tu d y w a s l o c at e d th at s p e c i f i c a l l y a d d r e s s e d n o n c ar c i n o g e n i ce f f

e c t s o f C r ( III) b y th e inhalation route of ex posure (J ohansson, 1986). W h ile this study reported striking morpholog ic chang e s in the macrophag e s of rabbits ex posed to Cr( III) a e r o s o l s , th e d at ab a s e i s i n a d e q u at e t o support development of an RfC for Cr( III)

. N a s a ls e p tu m i rri t at i on, atrophy , and perforations have been widely reported following mix ed ex posures to hex a valent and trivalent chromium in the oc c upationa l se tting

. The a v a ilable studie s ar e ina d e quate to de te rmine whe the r triva l e n t chromium contributed to the observed effects.

7. REF E RENCES Adachi, S. (1987) Effect of chromium compounds on the respiratory sy stem. Part 5. L ong term i nhal at i on of chrom i c aci d m i s t i n el ectropl at i n g by C 57BL fem a l e m i ce and recapi tu l at i on on our ex perimental studies. J pn J Ind Health 29:17-33. Adachi, S; Yoshimura, H; Katy ama, H; et al. (1986) Effects of chromium compounds on the respiratory sy stem. Part 4. L ong term inhalation of chromic acid mist in electroplating to I C R female mice. J pn J Ind Health 28:283-287. Adams, RM. (1990) In : Occupational skin disease, 2nd ed. Adams, RM, ed. Philadelphia: W

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. Saunders, pp. 26-31. Ag ency for Tox i c S ubst a nces and Di sease R e g i stry (ATS DR ) P ubl i c Heal thS e rvi ce, U.S

. Department of Health and Human Services. (1993) Tox i colog i cal profile for chromium. TP92/08. Atlanta, GA. Akatsuka, K; F a irhall, J

. (1934) The tox i colog y of chromium. J Ind Hy g 16:1-24. Amdur, MO; Doull, J ; Klaassen, CD. (1993) Casarett and Doull’s Tox i colog y . New York: Mc Gra w Hill. Anderson, RA; Polansky , MM; B ry d en, NA; et al. (1983) Effects of chromium supplementation on urinary Cr ex cretion of human subjects and correlation of Cr ex cretion with selected clinical parameters. J Nutr 113:276-281. Anderson, RA. (1986) Chromium metabolism and its role in disease processes in man. Clin Phy s iol B i ochem 4:31-41. Anderson, RA. (1993) Recent advances in the clinical and biochemical effects of chromium deficiency . Prog Clin B i ol Res 380:221-234.

28Anderson, RA. (1995) Chromium and parenteral nutrition. Nutrition 11(1 suppl.):83-86. Anderson, RA; B ry d en, NA; Polansky , MM. (1997) L ack of tox i city of chromium chloride and chromium picolinate in rats. J Am Coll Nutr 16(3):273-279. B aetjer, AM; Damron, C; B udacz , V. (1959a) The distribution and retention of chromium in men and animals. Arch Ind Health 20:136-150. B aetjer, AM; L o wney , J F ; Steffee, H; et al. (1959b) Effect of chromium on incidence of lung tumors in mice and rats. Arch Ind Health 20:124-135. B i shop, C; Surg enor, M, eds. (1964) The red blood cell: a comprehensive treatise. New York: Academ i c P r ess. B l oomfield, J J ; B l um, W

. (1928) Health haz ards in chromium plating

. Public Health Rep 43: 2330-2351. B ruynzeel, DP; Hennipman, G; van Ketel, WG. (1988) Irritant contact dermatitis and chromiumpassivated metal. Contact Derm 19:175-179. B ry s on, W G ; Goodall, CM. (1983) Differential tox i city and clearance kinetics of chromium ( III) or (VI ) in mice. Carcinog enesis 4:1535-1539. B unker, VW ; L a wson, MS; Delves, HT. (1984) The uptake and ex cretion of chromium by the elderly

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38AP P E NDIX A. EXTERNAL P EER REVIEW— S U MMARY OF COMMENTS AND DIS P OS ITION The support document and I R I S summary for trivalent chromium have underg one both internal peer review performed by scientists within EPA and a more formal ex ternal peer review perform ed by sci e nt i s t s i n accordance wi th EP A g u i d ance on peer revi ew. C o m m e nt s m a de by the inte rna l re vie w e r s we re a ddre sse d prior to submitting the doc ume n ts for e x te rna l pe e r re vie w a nd ar e not part of this appe ndix

. The e x te rna l pe e r re vie w e r s we re ta ske dwith providing writte n answers to g e neral questions on the overall assessment and on chemical-specific questions in areas of scientific controversy or uncertainty

. A summary of sig n ificant comments made by the ex ternal reviewers and EPA’s response to these comments follows. Com m e nts on G e ne ral Q u e s tions 1. Are you aware of any other data/studies that are relevant ( i .e., useful for the hazard identification or dose-response assessment) for the assessment of the adverse health effects, both cancer and noncancer, of this chemical? A. Com m e n t : A new report has been found showing sig n ificant embry o tox i c and fetotox i c d a m a g e d u e t oe x p o s u r e o f r at s a n d m i c e t oh i g h d o s e s o f C r ( V I) o r C r ( III) i n d ri n ki n g w at e r . I don’t feel confident rederiving an RfD based on these data, and the doses are clearly very hig h. However, derivation of an RfD based on an observed tox i colog i cal effect appears to be preferable to an RfD based on a NOAEL

. Response to Com m e nt: The report has been added to the reproductive/developmental studies section of the tox i colog i cal review document. The study reports on a variety of embry o tox i c and fetotox i c endpoints; however, many of the observed effects did not occur in a clear dose-dependent fashion. F u rther, the authors did not indicate the amount of water ing e sted by the animals and only stated that water ing e stion was reduced in the treatment g r oups relative to the controls. This omission precludes determination of the actual doses ex perienced by the treated animals. This study is not considered to be sufficient for development of the RfD for C r ( III)

. B . C o mme n t : The study by B aetjer et al. (1959b) needs some more discussion reg arding the question as to whether the MTD has been achieved in this particular study

. Fr om the published paper there is no indication that, indeed, the animals had been sufficiently dosed, and it is therefore questionable whether this study should be labeled an adequate carcinog enicity study

. Response to Com m e nt: The discussion has been added to the tex t
. C. Com m e n t : T h e d o c u m e n t s c o rr e c t l y s t at e th at C r ( V I) g e t s tr a n s f o rm e d t oC r ( III) i n v i vo, but they skirt the issue of whether or not a Cr(VI ) study is really a study of in vivo ex posure to C r ( III)

.

39Response to Com m e nt: G i v e n th e r ap i d r e d u c t i o n o f C r ( V I) t oC r ( III) i n v i tr o , i t i s relevant to consider whether environmental ex posures to Cr(VI ) or administration of Cr(VI ) in c o n tr o l l e d a n i m a l e x p e ri m e n t s i s e s s e n t i a l l y i d e n t i c a l t oe n v i r o n m e n t a le x p o s u r e s t oC r ( III) o r a d m i n i s tr at i o n o f C r ( III) i n c o n tr o l l e d e x p e ri m e n t s . W h i l e c o n s i d e r ab l y m o r e d at a ar e a v a i l ab l e f

o r

C r ( V I) th a n f

o r

C r ( III) , i t ap p e ar s at p r e s e n t th at e x p o s u r e s t oC r ( V I) h a v e c o n s i d e r ab l y d i f f

e r e n t o u t c o m e s th a n e x p o s u r e s t oC r ( III)

. T h e A g e n c y h a s p r e p ar e d th e T o x i c o l o g i c a l R e v i e w s a n dIR IS f i l e s f o r

C r ( V I) a n d C r ( III) f r o m th i s p e r s p e c t i v e .
2. For the RfD and RfC, has the most appropriate critical effect been chosen ( i .e., that adverse effect appearing first in a dose-response continuum) ? For the cancer assessment, are the tumors obse r v e d biologic a lly signific ant? Re le v ant to human he alth? Points re le v ant to this determination include whether or not the choice follows from the dose-response assessment, whether the effect is considered adverse, and if the effect ( i ncluding tumors observed in the cancer assessment) and the species in which it is observed is a valid model for humans. A. Com m e n t : I bel i e ve th e Ag ency i s a bi tconservat i v e reg ardi n g th e confi d ence of th e R f D. The I v ankovic and P r eussman (1975) study appears to be done according to acceptable practices atthe time

. I a l so take issue with the modifying fa c t ors. The Ag e n c y use da modifying fa c t or of 10 to reflect uncertainty in the database. I disag r ee with the speculation that the NOAEL could be a L OAEL

. The fact that uptake is low and variable does not justify such a hig h uncertainty factor, and the fact that the animals died naturally if anything would tend to increase disease incidence rates. I believe a threefold modifying factor is sufficient. I would also note that the authors arbitrarily dropped the RfD by an additional 1/3 by rounding down from 1.468 to 1. A more realistic estimate mig ht be 1,468/300 = 5 mg /kg

- day

. Response to Com m e nt: In orde r to be c onse r vative re g arding the limite d databa se on C r ( III) , th e A g e n c y s upports the use of a 10-fold modifying factor to reflect uncertainty in the databa se , inc l uding unc e rta inty re sulting from the de fic i e n c i e s in the databa se a ddre ssing potential reproductive and developmental effects. The speculation that the NOAEL could be a L OAEL has been removed from the document. The RfD has been rounded to 1.5. B . C o mme n t : In consideration of uncertainties surrounding the critical study for the RfD, such as the appropriateness of the method of administration (in baked bread, which mig ht be ex pected to ha ve a le sse r bioa va ilability tha n if a d ministe re d in fe e dor wate r), the use/ applic ation of a modifying factor of 3 (reducing the RfD to about 0.3 mg /kg

- day ) seems appropriate. Response to Com m e nt: The derivation of the RfD using the data of I v ankovic and P r eussman (1975) incorporated a 10-fold uncertainty factor to account for uncertainties in the study , including the likely low absorption of chromium from the baked bread. The Ag ency considers the current uncertainty factors to be sufficient for development of the RfD.

3. Have the noncancer and cancer assessments been based on the most appropriate studies? These studies should present the critical effect/cancer ( t umors or appropriate precursor) in 40the clearest dose-response relationship. If not, what other study ( o r studies) should be chosen and why? A. Com m e n t: The RfC should be for total chromium since it is not clear that soluble chromium species make up all of the hex a valent chromium species in the mix ture, nor that insoluble c h romium spe c i e s c onsist sole ly of triva l e n t spe c i e s . F u rthe rmore , the data sug g e st thatthe r e mig ht be a positive inte ra c tion be twe e n the two forms of c h romium a nd tha tthe risk for e x posure t o a m i x tu re i s not th e sum(or averag e) of th e ri sks fromei th er speci es. However, th e avai l abl e data do not provide any evidence that trivalent chromium alone is tox i c by inhalation. The data ar e inc onc lusive with re g ard to inha lation e x posure to triva l e n t c h romium. Response to Com m e nt: C onsi d erabl e dat a are avai l abl e reg ardi n g th e effect s of inhalation of hex a valent chromium in the form of chromic acid mists and hex a valent chromium particulates. The limited data available for trivalent chromium sug g e st that this compound may behave essentially as a nuisance dust upon inhalation. The Ag ency considers the data to be insufficient to support the application of the RfCs derived for hex a valent chromium to the tri v al entspeci es.
4. Studies included in the RfD and RfC under the heading “Supporting/Additional Studies” are meant to lend scientific justification for the designation of critical effect by including any relevant pathogenesis in humans, any applicable mechanistic information, any evidence corroborative of the critical effect, or to establish the comprehensiveness of the database with respect to various endpoints ( s uch as reproductive/developmental toxicity studies)

. Should other studies be included under the “Supporting/Additional” category? Should some studies be removed? A. Com m e n t : Some of the stat e m e n ts re late d to the g e notox ic e ffe c t s of triva l e n t c h romium ar e ei th er i n accurat e or m i s l eadi n g . Response to Com m e nt: The recommended modifications to this section have been made. B . C o mme n t : The new data on reproductive tox i city of chromium in the drinking water needs to be carefully compared to the NTP study in which rats and mice were fed potassium chromate in the diet. The form of chromium and route of ex posure are clearly of paramount importance. Response to Com m e nt: A discussion comparing and contrasting the results of the NTP studies and the new report has been added to the reproductive/developmental studies section of the Tox i colog i cal Review document. The report of Elbetieha and Al-Hamood (1997) raises the possibility of reproductive effects at very hig h doses, but the observed endpoints do not show a clear dose response, and the authors did not provide the data on drinking water ing e stion required to determine the doses ex perienced by the treatment g r oups. This study is not considered sufficient for development of the RfD.

415. For the noncancer assessments, are there other data that should be considered in developing the uncertainty factors or the modifying factor? Do you consider that the data support the use of different ( default) values than those proposed? A. Com m e n t : The appropriate data have been considered in developing the uncertainty factors and the modifying factor.

6. Do the confidence statements and weight-of-evidence statements present a clear rationale and accurately reflect the utility of the studies chosen, the relevancy of the effects ( c ancer and noncancer) to humans, and the comprehensiveness of the database? Do these statements make sufficiently apparent all the underlying assumptions and limitations of these assessments? If not, what needs to be added? A. Com m e n t : The evi d ence for th e rol e or l ack of rol e of tri v al entchrom i u mi n hum an cancer is not convincing l y presented. In particular the lack of effect of feeding rats chromium-laden bread is not balanced by any demonstration of chromium uptake in the animals. Response to Com m e nt: The Tox i col o g i cal R e vi ew docum entconcl udes th at th ere are inadequate data to determine the potential carcinog enicity of trivalent chromium. This should not be construed as a conclusion that trivalent chromium is not carcinog enic.

C

o m m e n t s on C h em i c al -S

peci fi c Qu esti o n s 1. Are the conclusions of Z ahid et al. ( 1990) regarding potential reproductive toxicity of Cr( III) in any way countered by the results of the NTP study? A. Com m e n t : I f NTP was not able to reproduce Z ahid’s results, I do not believe Z ahid’s results should be considered. B . C o mme n t : The Z ahid et al. studies are supported, but in a more realistic fashion by the studies of J uniad and Kanojia. Response to Com m e nts: The studies of Z ahid et al. (1990) and J uniad et al. and Kanojia et al. (1996) did not involve common endpoints. The NTP study was unable to repeat the finding s of Z ahid et al. The results of J uniad and Kanojia provide evidence of reproductive and fetotox i c effects of Cr(VI ) at hig h doses but do not support the finding s of Z ahid et al. reg arding t o x i c i t y o f C r ( III)

. C. Com m e n t : Additional description should be provided reg arding the report of Z ahid et al. in re lation to the NTP study

. Response to Com m e nt: Additional description has been added.

422. Are th ere any st udi es avai l abl e w h i c h coul d be used to devel op an Rf C

f

o r t r i v al ent chromium? A. Com m e n t : I a g r e e w i th th e d o c u m e n t th at th e r e ar e n oa d e q u at e d at a f

o r

C r ( III)

. B . C o mme n t : I ag ree wi th EP A’s assessm ent th at th ere are no sui t abl e dat a set s t o use i n c a l c u l at i n g a n R f C f o r

a i r b o rn e C r ( III)

. Response to Com m e nts: A n R f C f o r

a i r b o rn e C r ( III) h a s n o t b e e n d e v e l o p e d

.
3. The principal study ( M ancuso, 1975) and the follow-up study ( M ancuso, 1997) show the best dose-response relationship for total chromium, but animal data only support a conclusion of carcinogenicity of hexavalent chromium. Should the potency estimate address total chromium or hexavalent chromium? A. Com m e n t : Mancuso alleg e s that his data support a conclusion that both Cr( III) a n d C r ( V I) are carcinog ens. His data set is very small, and in my view, it lacks the power to disting u ish between Cr(VI ) and total chromium. The animal data present a convincing story that Cr( III) i s not carcinog enic. Hence, I believe the potency estimates should address only hex a valent chromium. EPA should be more ex plicit as to why they discount Mancuso’s alleg ation. Response to Com m e nt: Additional commentary has been added to the section addressing the conclusion that only Cr(VI ) is known to be carcinog enic by the inhalation route of ex posure. B . C o mme n t : The potency estimate should be based on total chromium but should note that the ex posure is mix ed (and g i ve the relative proportions of Cr( III) a n d C r ( V I) t ow h i c h th e w o rk e r s were ex posed). Althoug h it is probably true that the carcinog enicity is due to the hex a valent chromium, the finding that trivalent chromium can be taken up by the aveolar macrophag e s could imply that the carcinog enic process may be modulated by the presence of trivalent chromium. Response to Com m e nt: The Ag ency acknowledg es that the cohort was occupationally ex posed to mix tures of trivalent and hex a valent chromium, and ag rees that it is probably true that the carcinog enicity is due to the hex a valent chromium. The ratio of trivalent and hex a valent chromium in the mix ture have been provided. However, the Ag ency considers the data on carcinog enicity of trivalent chromium to be insufficient to support a conclusion that trivalent chromium contributed to the cancer observed in the cohort. The Ag ency concluded that Cr(VI ) is known to be carcinog enic in humans and that data are insufficient to form a conclusion reg arding the pote n tia l c ar c i nog e n ic ity of triva l e n t c h romium. C. Com m e n t : Itis obvious that based on the human data hex a valent chromium is a Group A carci nog en. However, because of th e i n suffi ci entdat a , a contri but i on of th e tri v al entchrom i u m cannot be ruled out since the workers are alway s ex posed to a mix ture of both chromium ty pes.

43Response to Com m e nt: The Tox i col o g i cal R e vi ew docum entconcl udes th at th ere are insuffic i e n t data to de te rmine whe the r triva l e n t c h romium is a c ar c i nog e n. This c onc lusion should not be misconstrued as ruling out a role for trivalent chromium in carcinog enicity

.
4. There is a Canadian study that relates stomach cancer to gold mining following exposures to chromium. Does this study justify/support determination of an oral factor for chromium? A. Com m e n t : No. Response to Com m e nt: The Canadian study has not been used to develop an oral slope factor for chromium. REF E RENCES Ju n a i d , M ; M u rth y , R C ; S a xe n a , D K

. ( 1996) Embry o t o xi c i t yo f o r a l l ya d m i n i s t e r e d c h r o m i u m i n mice: Ex posure during the period of org a nog enesis. Tox i col L e tt 84:143-148. Kanojia, R K ; J u n a i d , M; Murthy , RC. (1996) Chromium induced teratog e nicity in female rat. Tox i col L e tt 89:207-213. Mancuso, TF . (1975) In ternational Conference on Heavy Metals in the Environment, Toronto, CN, Oct. 27-31. Mancuso, TF . (1997) Chromium as an industrial carcinog en: Part 1. Am J Ind Med 31:129-139. Z ahid, Z R ; Al-Hakkak, Z S ; Kadhim, AHH; et al. (1990) Comparative effects of trivalent and hex a valent chromium on spermatog e nesis of the mouse. Tox i col Environ Chem 25:131-136.

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