# TOXICOLOGICAL REVIEW
OF 

# HEXAVALENT CHROMIUM (CA S N o . 18540-29-9)


## 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)

A ugust 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 and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. This document may underg o re visions in the future

. The most up-to-dat e ve rsion will be a v a ilable e l e c tronic a lly via the I R I S Home P a g e at http://www.epa.g ov/iris.

iiCONTENTS —TOXICOLOG ICAL REVIEW F O R HEXAVALENT CHROMIUM (CAS No. 18540-29-9)

F O R E W O R D .................................................................v AUTHORS , CONTRI BUTORS , AND REVIEW ERS

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

.................................................. v i i 1. IN TRODUCTI ON ...........................................................1 2. CHEMI C AL AND P HYS I C AL IN FORMATI ON RELE VANT TO AS S E S S M ENTS .....2 3. TOXI COKINETI CS RELE VANT TO AS S E S S M ENTS ............................4 3.1. AB SORPTI ON FACTORS IN HUMANS AND EXPERIMENTAL ANIMAL S

. . 4 3.1.1. Oral .......................................................4 3.1.2. Inhalation ..................................................4 3.1.3. Metabolism .................................................5 3.1.4. The Essentiality of Chromium ..................................6 4

. H A Z A R D ID E N T IF I C A T I O N .................................................7 4.1. STUDIES IN HUMANS ..............................................7 4.1.1. Oral .......................................................7 4.1.2. Inhalation ..................................................7 4.2. SUB C HRONI C, CHRONI C STUDIES AND CANCER B I OASSAYS IN A N IM A L S ............................................................1 7 4.2.1. Chronic Oral Studies .........................................1 7 4.2.2. Subchronic Oral Studies ......................................1 7 4.2.3. Chronic Inhalation Studies ....................................1 8 4.2.4. Subchronic Inhalation Studies .................................2 0 4.3. REPRODUCTIVE/DEVEL OPMENTAL STUDIES .......................2 3 4.3.1. Oral Studies ................................................2 3 4.3.2. Inhalation Studies ...........................................2 6 4.4. OTHER STUDIES ..................................................2 6 4.4.1. Contact Dermatitis ..........................................2 6 4.4.2. Tox i cant In teraction s.........................................2 7 4.4.3. Genotox icity ...............................................2 7 4.5. SYNTHESI S AND EVALUATI ON OF MAJ O R NONCANCER EFFECTS ....2 8 4.5.1. Oral Studies ................................................2 8 4.5.1.1. Human Studies ......................................2 8 4.5.1.2. Animal Studies ......................................2 8 4.5.2. Inhalation Studies ............................................2 9 4.5.2.1. Human Studies ......................................2 9 iiiCONTENTS ( c ont i nue d)

4.5.2.2. Animal Studies ......................................3 0 4.6. W E I GHT-OF-EVID ENCE EVALUATI ON AND CANCER C H A R A C T E R IZ A T I O N ...........................................3 1 4.7. OTHER HAZ ARD ID ENTIF I CATI ON I SSUES ..........................3 2 4.7.1. Possible Childhood Susceptibility ..............................3 2 4.7.2. Possible Sex Differences ......................................3 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 ..........................................3 2 5.1. ORAL REF E RENCE DOSE (RfD) .....................................3 2 5.1.1. Choice of Principal Study and Critical Effect ......................3 2 5.1.2. Method of Analy s is ..........................................3 4 5.1.3. RfD Derivation .............................................3 5 5.2. INHALATI ON REFERENCE CONCENTRATI ON (RfC) ..................3 5 5.2.1. Choice of Principal Study and Critical Effect ......................3 5 5.2.2. RfC Derivation .............................................3 8 5.2.2.1. Chromic Acid Mists and Dissolved Hexavalent Chromium Aerosols ............................................3 8 5.2.2.2. Hexavalent Chromium Dusts ...........................3 9 5.3. CANCER ASSESSMENT ............................................4 1 5.3.1. Summary ..................................................4 1 5.3.2. Dose-Response Data .........................................4 1 5.3.3. Dose Conversion ............................................4 2 5.3.4. Ex trapolation Method ........................................4 3 6. MAJ O R CONCLU S I ONS IN THE CHARACTERIZ ATI ON OF HAZ ARD AND DOS E RES P ONS E ........................................4 6 6.1. HUMAN HAZ ARD POTENTIAL .....................................4 6 6.2. DOSE RESPONSE .................................................4 9 7

. R E F E R E N C E S ............................................................5 1 AP P E NDIX A. EXTERNAL P EER REVIEW

— S U MMARY OF COMMENTS AND DI S P O S I TI ON ..........................6 5

ivF O REWORD
The purpose of this Tox o log i cal Review is to provide scientific support and rationale for the haz ard identification and dose-response assessment in I R I S pertaining to chronic ex posure to Cr(VI )

. Itis not intended to be a comprehensive treatise on the chemical or tox i colog i cal nature of Cr(VI )

. In Se c tion 6, EPA ha s c h ar a c t e rize dits ove ra ll c onfide n c e in the qua ntitative a n d 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 h ar 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 n d to aid and g u ide the risk assessor in the ensuing steps of the risk assessment process. F o r 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 513-569-7254.

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 Director 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 ater; Office of Planning and Evaluation; and Reg i onal Offices. In tern al E PA Revi ew ers Robert B e nson, Ph.D., D.A.B

. T., EPA Reg i on 8 Herman Gibb, Ph.D., EPA NCEA, W a shing t on, DC Annie J arabek, EPA NCEA, RTP, NC Charles Hiremath, Ph.D., EPA NCEA, W a shing t on, DC W i nona Victery , Ph.D., EPA Reg i on 9

E x tern al P eer Revi ew ers Richard Anderson, Ph.D. US DA Robert Chapin, Ph.D. NIEHS Robert Drew, Ph.D. Consultant in Tox i colog y Gunter Obersorster, D.V.M., Ph.D. Unive r sity of Roc h e s te r 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 A LF B r onchoalveolar lavag e fluid BC F B i o concentr at i on fact or BMC B enchm ark concentr at i o n B M D B enchmark dose C A S R N C hem i cal Abstract s S e rvi ce R e g i stry Numb er CS Composite score ESADDI Estimated safe and adequate dietary intake 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 LD H L act at e dehy drog enase L OAEL L owest-observed-adverse-effect level L O EL L o west-observed-effect level MCH M ean corpuscular hemog l obin MCV M ean corpuscular volume MED M inimum e ffe c tive dose NOAEL N o-observed-adverse-effect level NOEL N o-observed-effect level PCMR Proportionate cancer mortality ratio ppm Parts pe r million RfC Inhalation reference concentration R f D O ral reference dose Rvd D ose -rating va lue R v e E ffect-rating value SI R S tandard incidence ratio SMR S ta ndard morta lity ratio TW A T i m e -wei g h t e d averag e

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 assessments. 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 c e llular necrosis but may not ex ist for other tox i c effects such as some carcinog enic responses. Itis e x pre sse d in units of mg /kg

- da y . In g e ne ra l, the RfD is a n e s timate (with unc e rta inty spa nning 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 effects during a lifetime. The inhalation RfC is analog ous to the oral RfD. The inhalation 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 hex a valent 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 memorandum 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. 1Literature search strateg i es employ ed for this compound were based on the CASRN and at le 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 In th e hex a val e ntst at e, chrom i u mex i s t s as ox o speci es such as C r O 3 and CrO 4 2- ) th atare strong ly ox idiz ing (Cotton and W ilkinson, 1980). The CAS Reg i stry numbers and the solubilities of a few important hex a valent chromium compounds are g i ven in Table 1. In solution, hex a valent chromium ex ists as hy drochromate (HCrO 4 - ), chromate (C rO 4 2- ), and dichromate (Cr 2 O 7 2- ) ionic species. The proportion of each ion in solution is pH dependent. In basic and neutral pH, the chromate form predominates. As the pH is lowered (6.0 to 6.2), the hy drochromate concentration increases. At very low pH, the dichromate species predominate (U.S. EPA, 1984). The primary sources of hex a valent chromium in the atmosphere are chromate chemicals use da s rust inhibitors in c ooling towe rs a nd e mitte d a s mists, partic ulat e matte r e mitte d during manufacture and use of metal chromates, and chromic acid mist from the plating industry (ATS DR, 1993). Hex a valent chromium in air eventually reacts with dust particles or other pollutants to form trivalent chromium (NAS, 1974); however, the ex act nature of such atmospheric reactions has not been studied ex tensively

. B o th hex a valent and trivalent chromium are removed from air by atmospheric fallout and precipitation (F ishbein, 1981). The atmospheric half-life for the phy sical removal mechanism is dependent on the particle siz e and particle de nsity

. Chromium partic le s of sma ll a e r odyna mic dia m e t e r (< 10 μ m ) will re ma in a i rborne for a long period (U.S. EPA, 1984). He x a va le nt c h romium ma y e x ist in a quatic me dia a s wa te r-soluble c o mple x a n ions a n d m a y persi s t i n wat e r. Hex a val e ntchrom i u mi s a strong ox i d i z i n g ag entand m a y reactwi th org a nic matte r or othe r re duc ing a g e n ts to form triva l e n t c h romium. The triva l e n t c h romium will e v e n tua lly be pre c i pitate d a s Cr 2 O 3 ·x H 2 O. Therefore, i n surface wat e r ri ch i n org a ni c cont ent , hex a valent chromium will ex hibit a much shorter lifetime (Callahan et al., 1979). Any he x a va le nt c h romium in soil is e x pe c t e dto be re duc e dto triva l e n t c h romium by org a nic matter. The primary processes by which the converted trivalent chromium is lost from soil are aerial transport throug h aerosol formation and surface water transport throug h runoff (U.S. EPA, 1984). Very little chromium is leached from soil because it is present as insoluble Cr 2 O 3 ·x H 2 O (F ishbein, 1981).

2The bioconcentration factor (B CF ) for hex a valent chromium in fish muscle appears to be < 1.0 (U.S. EPA, 1980), but values of 125 and 192 were obtained for oy ster and blue mussel, respectively (U.S. EPA, 1980).

Table 1. CAS num bers and aqueous solubilities of selected hexavalent chrom i um c o m p ounds Com p ound CAS No. Wate rsolubility Ammonium chromate 7788-98-9 40.5 g / 100 mL at 30 � C (NH 4 ) 2 Cr O 4 Calcium chromate 13765-19-0 2.23 g / 100 mL at 20 � C Ca Cr O 4 Chromic acid 1333-82-0 61.7 g / 100 mL at 0 � C Cr O 3 Potassium chromate 7789-50-6 62.9 g / 100 mL at 20 � C K 2 Cr O 4 Potassium dichromate 7789-50-9 4.9 g / 100 mL at 0 � C K 2 Cr 2O 7 Sodium chromate 7775-11-3 87.3 g / 100 mL at 30 � C Na 2 Cr O 4 Sodium dichromate dihy drate 7789-12-0 230 g / 100 mL at 0 � C

Sources: W east, 1980; Hartford, 1979.

33. 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 Gastroi n t e st i n al absorpt i on of C r(VI ) occurs wi thg r eat er effi ci ency th an absorpt i on of C r ( III) , thoug h absorption of ing e sted hex a valent chromium is estimated to be less than 5%. Donaldson and B arreras (1966) fed Na 51 Cr O 4 to rats and humans. B a sed on mean urinary ex cretion, 51 Cr

, absorption was estimated to be 2.1% in humans. In rats, approx imately 2% of the adm i n i s t e red dose was absorbed based on fecal ex cret i on of 51 Cr when Na 51 Cr O 4 was a d ministe re d intra g a s tric a lly

. In te stina l ab sorption of he x a va le nt c h romium appe ar s to be si g n i f i cant l y affect ed by cont actwi thg a stri c j u i ces. W h en Na 51 Cr O 4 was introduced to humans intraduodenally (avoiding contact with g a stric juices), approx imately half of the chromium was absorbed based on fecal ex cretion. Similar results were observed following intrajejunal a d ministration in ra ts. In c ubation of he x a va le nt c h romium with g a stric juic e s prior to intraduodenal or intrajejunal administration in humans and rats, respectively , virtually eliminated ab sorption of c h romium. Absorption of triva l e n t c h romium ( 51 Cr Cl 3 ) was not i n creased by intraduodenal or intrajejunal administration. The authors demonstrated that hex a valent c h romium is re duc e dto the triva l e n t form by inc ubation with g a stric juic e s a nd c onc lude d that re duc tion of he x a va le nt c h romium to the triva l e n t form in the stoma c h sig n ific a n tly re duc e s absorption by the oral route of ex posure. Gastric juices have peak reductive capacity 2 to 4 hours after a meal and are at a minimum between meals and at nig h t (DeF lora et al., 1987). Anderson et al. (1983) confirmed the low absorption of trivalent chromium in humans following oral administration of 200 μ g of CrCl 3 . MacKenz i e et al. (1959) administered Na 51 Cr O 4 to rats by g a vag e . B a sed on urinary ex cretion, absorption was estimated to be 6% in fasted rats and 3% in nonfasted rats. The rate of absorption was twofold g r eater than that observed following administration of 51 Cr Cl 3 by g a vag e . Absorption of hex a valent chromium was found to be increased by three- to fivefold following inte stina l a d ministra tion of Na 51 Cr O 4 , consistent with reduction of hex a valent chromium during passag e throug h the stomach. Absorption of hex a valent and trivalent chromium was found to be less than 1.4% in the hamster (Henderson et al., 1979), while Visek (1953) estimated that less than 0.5% of ing e sted CrCl 3 wa s ab sorbe dthroug h the g a strointe stina l tra c tof the rat. 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 following occupational ex posure has been demonstrated by measurement of chromium in the serum, urine, and hair of workers in the chromium industry (Minoia and Cavalleri, 1988; Randall and Gibson, 1987; Tossavainen et al., 1980).

4L a ng ard et al. (1978) demonstrated that water-soluble hex a valent chromium, such as chromic acid, is absorbed rapidly following inhalation by rats. However, insoluble hex a valent c h romium, suc h a s zinc c h romate , is le ss we ll ab sorbe d. Anima ls we re e x pose dto zinc c h romate dust at a level of 7.35 mg /m 3

. After 0, 100, 250, and 350 min of ex posure, the concentrations of chromium in the blood (μ g /ml) were 0.007, 0.024, 0.22, and 0.31, respectively

. In the second part of this study , rats were ex posed to the same level for 6 hours on 4 consecutive day s . B l ood concentrations appeared to peak at the end of the second ex posure and then beg a n to decline slowly

. Mean blood chromium values measured at the end of each ex posure period averag ed 0.03, 0.56, 0.46, and 0.34 μ g /ml for ex posures l-4, respectively

. No sig n ificant differences in absorption as reflected by blood chromium levels were noted between the sex e s or between day and nig h t ex posures. Suz 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. Metabolism In vivo r e d u c t i o n o f C r ( V I) t oC r ( III) h a s b e e n w i d e l y s tu d i e d , a n d s o m e c h ar a c t e ri z at i o n s can be made. In g e sted hex a valent chromium is efficiently reduced to the trivalent form by the g a stric juices (DeF lora et al., 1987). Hex a valent chromium can also be reduced to the trivalent form in the epithelial lining fluid of the lung s by ascorbate and g l utathione. The reduction by a s c o rbat e is more rapid tha n by g l utathione , a nd re sults in a shorte r re side nc e time for c h romium in the lung s (Suz uki and F ukuda, 1990). Once absorbed into the bloodstream, hex a valent chromium readily enters red blood cells throug h the phosphate and sulfate anion-ex chang e carrier pathway , thoug 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 red cell membrane by this pathway (Gray and Sterling , 1950), they may enter red blood cells, but only with very low efficiency (Mertz , 1969; O’F l aherty , 1996). Hex a valent chromium is reduced to the trivalent form in the red blood cell by the action of g l utathione (Debetto and Lu ciani, 1988; Petrilli and De F l ora, 1978a). During 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).

Visek et al. (1953) reported that an insig n ificant amount of 51 C r crossed th e pl acent a of rats in the 24 hours following intravenous injection reg ardless of the chemical form injected, the va le nc e stat e , the g e stationa l sta g e , or the size of the litte r. In no insta n c e wa s the ra dioa c tivity measured in the fetuses g r eater than 0.13% of the dose. Danielsson et al. (1982) reported that sodi umdi chrom at e crossed th e pl acent a m o re readi l y th an C r( III) tri c h l o ri d e f

o l l o w i n g intravenous injection of mouse dams. Casey and Hembridg e (1984) demonstrated that chromium c a n be tra n sfe rre d to infa nts throug h bre a s t milk. The bre a s t milk of 45 la c t a ting wome n wa s 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. 5A 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 r p 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 at , a n d 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 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 ls 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 a nd the g a strointe stina l tra c t
. F o llowing inha lation e x posure , c h romium ma y be absorbed into the sy stemic circulation, transferred to the g a strointestinal tract by mucociliary action, or remain in the lung

. Cr(VI ) is reduced to Cr( III) i n a l lt 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) s a l t s i s l ar g e l y dependent on the nutritional status of the animal as well as the nature of the anion making up the C r ( III) s a l t
. T h e m o d e la 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 p l a s m a . C r ( V I) enters cells by the phosphate and sulfate anion-ex chang e carrier pathway

. Cr( III) tr a v e l s i n th e bloodstream larg ely bound to amino acids, other org a nic acids, and plasma proteins such as 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) th at 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 reduced 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 D N A (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 lahe rty , 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 controlled ex periments. Althoug h considerably more data are available for Cr(VI ) than for 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 s u m m ari e 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 . 3.1.4. The Essentiality of Chrom i um C r ( III) i n i t s b i o l o g i c a l l y a c t i v e f

o rm ( g l u c o s e t o l e r a n c e f

a c t o r , o r G T F , a d i n i c o t i n at o c h r o m i u m [ III] g l u t ath i o n e - l i k e c o mp l e x ) , f a c ilitates interaction of insulin with its receptor site, i n f l u e n c i n g g l u c o s e , p r o t e i n , a n d l i p i d m e t ab o l i s m . T h u s , C r ( III) i s e s s e n t i a lf o r

a n i m a l s a n d human being s . Inorg a nic chromium compounds do not appear to have insulin-potentiating a c tivity

. Chromium de fic i e n c y ma y c au se c h a n g e s in the me tabolism of g l uc ose a nd lipids. In some studies, dietary supplementation with chromium reversed chang e s in g l ucose tolerance and serum lipids. The National Research Council has identified an estimated safe and adequate daily dietary intake (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 (DHHS, 1995). 64. HAZARD IDENTIF I CATION 4.1. STUDIES IN HUMANS 4.1.1. Oral C r ( V I) i s c o n s i d e r ab l y m o r e t o x i cth a n C r ( III)

. A c r o s s - s e c t i o n a l s tu d y o f 155 villag e rs report e d th e effect s of envi ronm ent a l cont am i n at i on of wel l wat e r adj acent t o a chrom i u mal l o y plant. Cr(VI ) concentrations were reported as 20 mg /L , with an estimated dose rate of 0.57 mg /kg

- day (Z hang and Li , 1987). Reported effects at this dose included oral ulcers, diarrhea, abdominal pain, indig e stion, vomiting , leukocyt osis, and presence of immature neutrophils. Effects data for lower ex posure doses were not available. Other reports of tox i c effects in humans are limited to case reports from accidental poisoning s. Some Cr(VI ) compounds (such as potassium tetrachromate and chromic acid) are potent ox idiz ing ag ents, and are thus strong irritants of mucosal tissue. Effects included metabolic acidosis, acute tubular necrosis, kidney failure, and death (Sary a n and Reedy , 1988). 4.1.2. Inhalation Occupational ex posure to chromium compounds has been studied in the chromateproduction, chrome-plating and chrome pig m ent, ferrochromium production, g o ld mining , leather tanning , and chrome alloy production industries. W o rkers in the chromate industry are ex posed to both trivalent and hex a valent compounds of chromium. Epidemiolog i cal studies of chromate production plants in J apan, Great B ritain, W e st Germany , and the United States have revealed a correlation between occupational ex posure to chromium and lung cancer, but the specific form of chromium responsible for the induction of cancer was not identified (Machle and Greg orius, 1948; B aejter, 1950a,b; B i dstrup, 1951; Mancuso and Hueper, 1951; B rinton et al., 1952; B i dstrup and Case, 1956; Todd, 1962; Tay l or, 1966; Enterline, 1974; Mancuso, 1975; Ohsaki et al., 1978; Sano and Mitohara, 1978; Hay e s et al., 1979; Hill and F e rg uson, 1979; Alderson et al., 1981; Hag u enor et al., 1981; Satoh et al., 1981; Korallus et al., 1982; Fr entz el-B eyme, 1983; L a ng ard and Vig a nder, 1983; W atanabe and F ukuchi, 1984; Davies, 1984; Mancuso, 1997). Mancuso and Hueper (1951) conducted a proportional mortality study of a cohort of chromate workers (employ e d for > l y ear from 1931 to 1949 in a Painesville, OH, chromate plant) in order to investig ate lung cancer associated with chromate production. Of the 2,931 deaths of males in the county where the plant is located, 34 (1.2%) were due to respiratory cancer. Of the 33 deaths among the chromate workers, however, 6 (18.2%) were due to re spirat ory c a n c e r . Within the limitations of the study de sig n, this re port strong ly sug g e ste da n increased incidence of respiratory cancer in the chromate-production plant. In an update of the Mancuso and Hueper (1951) study , Mancuso (1975) followed 332 of the workers employ ed from 1931-1951 until 1974. B y 1974, > 50% of this cohort had died. Of 7these men, 63.6%, 62.5%, and 58.3% of the cancer deaths for men employ ed in 1931-1932, 1933-1934 and 1935-1937, respectively , were due to lung cancer. Lung cancer death rates inc r e a s e dwith inc r e a s e s in e x posure to tota l c h romium, a nd sig n ific a n t de position of c h romium was found in the lung s of workers long after the ex posure ceased. The ag e-specific lung cancer rate s from a nd g r a d ie nt e x posure s to tota l c h romium from this study ar e pre s e n te d in Table 2. Mancuso (1975) reported that these lung cancer deaths were related to insoluble (trivalent), soluble (hex avalent), and total chromium ex posure, but the small numbers involved make identification of the specific form of chromium responsible for the lung cancer uncertain. Mancuso (1997) recently updated this study , following the combined cohort of 332 workers until 1993. Of 283 deaths (85% of the cohort identified), 66 lung cancers were found (23.3% of all deaths and 64.7% of all cancers). Lung cancer rates clearly increased by g r adient level of ex posure to total chromium. The relationship between g r adient level of ex posure and lung cancer rates is less clear for trivalent and hex a valent chromium. The rates of lung cancer within the cohort are consistent with those reported in Mancuso (1975) and provide further support for the cancer risk assessment based on those data. Hay e s et al. (1979) conducted a study of 2,101 male workers in a chromium chemicals production plant in B a ltimore, MD, to determine whether employment in a modernized facility resulted in a reduction in the risk of lung cancer in comparison with that seen in workers employ ed in older production facilities. Mortality data for the workers were compared with c au se -spe c i fic morta lity rate s for B a ltimore c ity ma le s, a nd c o rre lations we re ma de be twe e n a history of having worked in specific job positions and cancer of the lung

. W o rkers with lung cancer as an underlyi ng or contributory cause of death were individually matched to controls sel ect ed frompl antworkers who di ed of causes other th an cancer. Many of th e speci fi c causes of death, including several sites of malig nancy , showed results well below the ex pected number. While the ne we r fa c ility ha d be e n c onstruc te d to re duc e e x posure to c ar c i nog e n s, worke r s in the new facility were still found to have an increased risk of lung cancer. B o th short-term and long

term workers were found to have ex cess risk for lung cancer, but the effect was more pronounced in the long -term workers. A dose-response relationship with respect to leng th of employment was observed, and long -term laborers were found to have a max imum risk (standard mortality ratio [ S MR] = 3.9) between 15 and 19 y ears after the initial ex posure. A history of having worked with hig h ly soluble hex a valent chromium compounds in the “wet end” of the production process was part i c ul arl y associ at ed wi th an i n creased ri sk of l ung cancer. Am ong th e workers i n the low- ex posure g r oup (n = 699), no ex cess risk was demonstrated. The authors were unable to obtain suitable data to account for cig arette smoking in the study population, and assumed that the smoking habits of workers were similar to those of the in the g e neral population. Pastides et al. (1994) conducted a retrospective cohort study in the United States’ larg est c h romate c h e mic a l s ma nufa c turing fa c ility in Ca stle Ha yn e , NC. This pla n t wa s de sig n e dto reduce the hig h level of chromium ex posure found at most of the older chromate production facilities. The study utilized more than 5,000 personal breathing zone samples collected over a 15-y ear period. Occupational, medical, and smoking data from current and former employ ees were collected using a questionnaire. A healthy

- worker effect was observed in the population. The r e wa s no inc r e a s e drisk of morta lity or c a n c e r a m ong e mploy e e s who worke donly atthis 8Table 2.Age-specific lungcancer deathrates andgradientexposures to totalchromiumMg/m3- Yrs. total insoluble chromiumAge<1.001.0-1.992.0-3.994.0-5.996.0-6.997.0-7.998+a45-5455-6465-74DeathsPerson-yearsDeathsPerson-yearsDeathsPerson-years1886170712352459335611662583146221824348425018031592113142314039804102621203381aData in the last column are not used in EPA’s risk assessment because the range of exposure in this class is not known,and it does not appear reasonable to assume that all three age groups had an identical exposure distribution.

9Source: Mancuso, 1975.facility , thoug h a subg roup of workers who transferred from older facilities was found to have hig h e r risks of morta lity a nd c a n c e r . Rosenman and S t anbury (1996) recently reported on a study of lung cancer risk in a population of former workers from four facilities that produced chromium compounds from chromite ore. Workers at these facilities between 1937 and 1971 were found to have proportionate cancer mortality ratios (PCMR) of 1.51 for white men and 1.34 for black men. The PCMRs were found to increase with duration of employment and time since first employment. The authors also reported a PCMR for nasal/sinus cancer of 5.18. The lung cancer risk remained elevated for more than 20 y ears following the cessation of ex posure. W h ile the study was unable to account for smoking habits of the workers, the lack of increase in other smoking -related diseases sug g e sted that the lung cancer was not related to smoking

. The authors were unable to disting u ish risk from trivalent and hex a valent chromium, and were also unable to ex amine risk by e x posure e s timate s. Alex ander et al. (1996) reported on a study of lung cancer in chromate-ex posed aerospace workers with a minimum of 6 mo ex posure to hex a valent chromium. Standard incidence ratios (SI R s) for lung cancer were determined on the basis of the duration of employment in chromateex posure jobs and cumulative ex posure. The authors reported an inverse relationship between lung c a n c e r risk a nd e s timate s of c u mulative c h romate e x posure in spra y pa inte rs. Ele v at e dlung cancer risks were found for subjects who worked as chrome platers or surface processor tank tenders, sanders/maskers, and polishers, but the numbers are too low to establish a clear associ at i on bet w een chrom at e ex posure and l ung cancer ri sk i n th ese workers. The authors sug g e st ed th at th e l ack of i n creased l ung cancer ri sk am ong spray pai n t e rs m a y refl ect th e e x posure to c h romate in pa int mists, whic h the y sug g e ste dma y re nde r the he x a va le nt c h romium le ss biolog ic a lly a c tive

. Studies of workers in chromate pig m ent production plants have demonstrated an association with increased risk of lung cancer. Hay e s et al. (1989) studied workers employ ed between 1940 and 1969 in a lead and z i nc chromate pig m ent production plant in New J e rsey . The SMR for lung cancer was 160, based on comparison with U.S. lung cancer rates for white males. W o rkers in the hig h -ex posure g r oup were continuously ex posed to g r eater than 2 mg /m 3 chromate dust; workers in the moderate-ex posure g r oup were occasionally ex posed to concentrations between 0.5 and 2 mg /m 3 ; and workers in the low-ex posure g r oup were infrequently ex posed at concentrations below 0.1 mg /m 3

. Sig n ificant SMRs were also found for lung cancer in nonwhite males and stomach cancer in white males. Air monitoring revealed that ex posures were l ead chrom at e . Davies (1978, 1979) studied three chromate pig m ent plants in Eng l and, two of which produced both z i nc and lead chromate, and one which produced only lead chromate. The cohort of ex posed workers consisted of employ ees with � 1 y ear of service and for whom vital statistics were available as of 1977. Using these g u idelines, 396 and 136 subjects were obtained from the plants producing both z i nc and lead chromate, and 114 subjects were obtained from the plant that produc e donly le a dc h romate
. The obse r ve d morta lity from lung c a n c e r in the diffe re nt pla n ts wa s c o mpar e dto the e x pe c t e dmorta lity ba se d on nationa l lung c a n c e r morta lity rate s for a l l 10males in Eng l and and W a les. An elevated risk of lung cancer was present only in the plants producing both z i nc and lead chromate. The authors sug g e sted that these data indicated that z i nc chrom at e was associ at ed wi thth e et i o l o g y of l ung cancer, whereas l ead chrom at e was not
. Davies (1984) conducted a follow-up study on workers in the same three chromate pig m ent production plants. W o rkroom chromium concentrations and smoking statistics for the workers were notavai l abl e i n any of th e fact ori e s. El evat ed S M R s for l ung cancer were observed, particularly for workers employ ed prior to improvements in industrial hy g i ene. W o rkers in the hig h - and medium-ex posure g r oups in a plant producing lead and z i nc chromates had an SMR for lung cancer of 232. W o rkers in hig h - and medium-ex posure g r oups in a second lead and z i nc chromate production plant had a SMR for lung cancer of 373. The SMR for workers in hig h and medium g r oups ex posed to lead, z i nc, and strontium chromate was 562. In the third plant, only lead chromate pig m ents were produced, and no ex cess lung cancer deaths were reported. L a ng ard and Norseth (1975) reported on three pig m ent plants in Norway that were in operation between 1948 and 1972 (one of the plants was broug ht on line in the y ear the study ended). A total of 133 workers were identified as employ ees at the three plants during this time period. Of the 133, 24 had been employ ed > 3 y ears, and of this cohort, 3 cases of lung cancer were identified throug h the Cancer Reg i stry of Norway

. All of the lung cancer cases had been employ ed for 5 y ears or long er. Data from the cancer reg i stry indicated an ex pected number of lung cancer cases among those employ ed of 0.079; thus, the observed number of cases was 38 times g r eater than ex pected, based on the g e neral population. Ex posure levels determined by personal monitoring were reported for the plants for the y ear 1972, with chromium levels in the two older plants rang ing between 0.04 and 1.35 mg /m 3 and levels in the new plant between 0.01 and 0.08 mg /m 3

. Althoug h an increased risk of lung cancer was indicated, two of the individuals with lung cancer were moderate to heavy smokers. Nevertheless, a relative risk of lung cancer of 38 could not be ex plained by differences in smoking between the study cohort and the Norweg ian population. L a ng ard and Vig a nder (1983) conducted a follow-up study on workers employ ed for at least 3 y ears in the same chromate pig m ent producing factories. W o rkroom monitoring revealed sig n ificantly elevated concentrations of hex a valent chromium (0.01 - 1.35 mg /m 3 ), and an SMR for lung cancer of 4,444 was reported. W o rkers in this g r oup were ex posed over a period of 6-9 y ears. Frentz el-Beyme (1983) reported that the observed number of lung cancer deaths ex ceeded those ex pected among workers in five chromate pig m ent plants in the Netherlands and W e st Germany

. In only one factory , however, was this ex cess statistically sig n ificant. The authors did not find a lung cancer mortality dose-response by intensity or duration of ex posure. The analy s is was limited by the numbers of deaths in each categ ory . Several studies of the chrome-plating industry have demonstrated a positive relationship between cancer and ex posure to chromium compounds (Roy le, 1975; Fr anchini et al., 1983; Sorahan et al., 1987). Roy l e (1975) studied mortality in the chromium plating industry in Eng l and in a retrospective study between 1969 and 1972. W o rkers in this industry are ex posed to hex a valent chromium in the form of chromic acid mist and some sodium dichromate dust. 11The study traced 1,238 chrome plating workers employ ed for > 3 months along with 1,284 ma nua l labore r s use da s c ontrols. The r e wa s little diffe re nc e in smoking habits be twe e n the g r oups. There was a sig n ificant ( p < 0.05) difference in the death rate for cancer at all sites, 3.15% in chrome platers as compared to 1.63% in controls. Deaths from malig nancy of the lung and g a strointestinal tract were each increased, thoug h not sig n ificantly

. Fr anchini et al. (1983) conducted a retrospective cohort study of 178 workers in nine It a lia n c h rome plating pla n ts to de te rmine the morta lity of worke r s e mploy e dfor atle a s t 1 y e ar between J a nuary 1951 and December 1981. The mortality ex perience of workers was compared to that for the It alian male population of the same ag e during the follow-up period. Direct ex posure measures from the plants were not available, but the ex posures were related to airborne chromium concentrations taken from It alian electroplating plants in 1980, after industrial hy g i ene practices had improved considerably

. A sig n ificant ex cess of all malig nancies and lung cancer specifically was found for the workers in “hard” chromeplating plants, who were ex pected to have the g r eatest chromium ex posures. While the small size of the cohort limited the statistical power of the study and confounding factors were not assessed, this study is taken to provide sug g e st i v e evi d ence of a causal rel at i onshi p bet w een ex posure t o chrom i c aci d and cancer. Sorahan et al. (1987) conducted a mortality study of nickel/chromium platers in Eng l and who were employ ed between 1946 and 1983. Ex posure in these the plants was to soluble hex a valent chromic acid mist (CrO 3 ). The cohort in the study included a population of 2,689 workers (1,288 men, 1,401 women). Workers’ ex posure to chromium was estimated based on participation in any of eig h t chromeplating job categ ories and on cumulative duration of employment in chrome bath jobs. The mortality ex perience of the cohort was evaluated throug h comparison with that ex pected for the g e neral population of Eng l and and W a les, as well as throug h c o mparison of the e s timate d c h rome e x posure s of worke r s who die din a g i ve n y e ar with those of matc hing survivors in the sa me follow-up y e ar , c ontrolling for se x , y e ar of starting chrome employment, and ag e starting in chrome employment. Overall, compared with the g e neral population, sig n ificant differences were found for all cancers, cancers of the lung and bronc hus, c a n c e r of the nose a nd na sa l c a v itie s, c a n c e r of the stoma c h, a nd primary c a n c e r of the liver. The results were particularly striking for chrome bath workers, who were likely the most heavily ex posed to chromium. Sig n ificant positive associations were found between cancers of the lung and bronchus and duration of chrome bath work. Some studies of the chromeplating industry have reported inconclusive results (Silverstein et al., 1981; Okubo and Tsuchiy a , 1979; Takahashi and Okubo, 1990; It oh et al., 1996). Okubo and Tsuchiy a (1979) conducted a cohort study of 889 Toky o chrome platers, with an unspecified number of controls selected from the same factories. The study included a 6-y ear follow-up period. The investig ation was conducted by a questionnaire sent to the manag e r of each fact ory , and vi t a l st at i s t i c s were ascert a i n ed usi n g th e records of th e Toky o Heal thIn surance Society of the Plating Industry

. The recovery rate of the questionnaire was 70.5%. Among the 889 male chromium platers, 19 deaths were observed, or about 50% of those ex pected (healthy

worker effect). In contrast, the authors reported a slig htly hig h er percentag e of deaths in the control g r oup. The authors reported neg ative results for the relationship between chromeplating

12and lung cancer; however, the results were not related to well-defined ex posure data and the study utilize da ve ry short follow-up pe riod. Takahashi and Okubo (1990) reported on an epidemiolog i cal study of metal platers in 415 small chromeplating plants in J apan. Members of the cohort were all male workers employ ed as platers for at least 6 mo between April 1970 and September 1976. The follow-up period ex tended until 1987 and no members of the cohort were lost to follow-up. The members of the cohort were classified into two subg roups based on their work histories: 52% of the cohort had more than 6 mo ex perience in chrome plating and 48% of the cohort had more than 6 mo plating ex perience using metals other than chromium. The mean duration of ex posure before the followup period was 12.3 y ears. The study lacked direct ex posure measures, and smoking histories for the workers were not available. All-cause mortality in the cohort was slig htly below the ex pected number (healthy

- worker effect). The study demonstrated that ex posure to metal plating is associated with a statistically sig n ificant increase in lung cancer, thoug h the elevated SMR was not statistically sig n ificant in either of the two plater subg roups. W h ile chromium platers with initial ex posure prior to 1960 had a 2.5-fold (thoug h statistically insig n ificant) ex cess incidence of lung cancer, there was no increase in numbers of deaths due to lung cancer relative to the le ng th of time e x pose dto c h rome pla ting

. The re sults of this study ar e c onside r e de quivoc a l reg arding the relationship between chromeplating and lung cancer. It oh et al. (1996) subsequently reported on a prospective cohort study of the same cohort of 1,193 workers at small J apa ne se plating fa c ilitie s. While a tre nd toward statistic a l sig n ific a n c e for risk of lung c a n c e r was seen in the chromium plating subg roup, the study lacked sufficient statistical power to form a cl ear concl u si on. Silverstein et al. (1981) found a statistically sig n ificant increase ( p < 0.001) in the lung cancer proportionate mortality ratios for both male and female white employ ees in a die-casting and electroplating plant. In this plant, workers were ex posed to chromium during electroplating , but nickel and copper were also used in electroplating

. Other operations of the plant included z i nc alloy die-casting , buffing and polishing , and cleaning of z i nc and steel parts. No conclusion can be made from this study reg arding the association of chromium electroplating and lung cancer mortality , because of the employ ees’ ex posure to other potential carcinog ens. A number of epidemiolog i cal studies have considered the association between inhalation of Cr(VI ) 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 (1928) ex amined 23 men from 6 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 to 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, 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 na sa l tissue injury

. However, no concentrations lower than 0.12 mg /m 3 were observed, and injury to nasal tissue caused by lower concentrations could not be ruled out. 13Machle 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 10 to 2,800 μ g /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 and Hueper (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 are 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 less than 6 mo 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 ex posed to chromic acid aerosol during chrome plating

. Among this g r oup, 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 persons, papillomas 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 7 of 9 workers in a chromeplating plant, with 4 of 7 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 le ng 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. More than 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 < l 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 were not provided. Environmental air samples were collected from breathing z ones of several workers in the ex posed and control 14g 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 l 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 nasal 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” chromeplating 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 chromeplating operations. Ex posed workers were divided into low- (< 2) and hig h - (> 2 μ g Cr[ V I ] /m 3 ) ex posure g r oups based on th e ex posures th ey were l i k el y t o have ex peri enced i n th e workpl ace. C o mp l a i n t s 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-ex posure g r oup and half of the 24 workers in the hig h ex posure 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 15concentrations from 2 to 20 μ g /m 3

. 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 than 20 μ g /m 3 near the baths. Chang e s in pulmonary function measurements, as determined by chang e s in vital capacity and forced ex pi at ory vol um e at1 sec (FEV l ), were seen i n workers who ex peri enced C 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 -ex posure g r oup than the low-ex posure 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 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 (1983a) 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 posure levels 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 nephrotox icity ) in current workers ex posed to 4 to 20 μ g /m 3 Cr(VI ) over 8-hour shifts. The effect m a y be reversi b l e because form er chrom e pl at ers di d nothave an el evat ed concentr at i on of e ithe r � -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 NOAEL levels 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 to referent control workers. However, comparison of urinary chromium concentrations of the tannery workers in this study versus the chromeplaters in the Li ndberg and Vesterberg (1983a,b) study sug g e sts that the latter had distinctly hig h er chromium ex posures. 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 EPA (1984) and ATSDR (1993), will not be reviewed here.

164.2. SUBCHRONIC, CHRONIC STUDIES AND CANCER BIOASSAYS IN ANIMALS 4.2.1. Chronic Oral Studies Only one chronic study pertaining to the oral tox i city of hex a valent chromium was located in the available literature. Anwar et al. (1961) ex posed dog s orally to potassium chromate in drinking water for 4 y ears. Treatment levels were 0, 0.45, 2.25, 4.5, 6.75, and 11.2 ppm potassium chromate; there were two dog s/g r oup. No effects were observed with reg ard to g r oss and microscopic analy s is of all major org a ns, urinaly s is, and weig hts of spleen, liver, and kidney

. 4.2.2. Subc hr onicOr al Studie s The National Tox i colog y P r og ram recently conducted a three-part reproductive tox i city study to investig ate oral ing e stion of hex a valent chromium in ex perimental animals (NTP, 1996a,b, 1997). Rats and mice were ex posed to 0 - 400 ppm potassium dichromate daily in the diet for 9 weeks. Animals were ex amined for body weig hts; feed and water consumption; org a n weig hts; microscopic evaluation of the liver, kidney , and ovaries; hematolog y ; histolog y of the testis and epididym us for Sertoli nuclei and preleptotene spermatocyte counts in Stag e X or XI tubules; and chromatin analy s is. No treatment-related hematolog y finding s were reported ex cept for slig ht decreases in mean corpuscular volume (MCV) and mean corpuscular hemog l obin (MCH) values in the male and female treatment g r oups receiving 400 ppm potassium dichromate (24 mg /kg

- day )

. The finding s were characteriz ed by the authors as sug g e stive of a potential bone marrow/erythroid response. The authors considered the 100 ppm (6 mg /kg

- day ) dose g r oup to be representative of the NOAEL for the study

. The studies are described in g r eater detail in the reproductive/developmental section of this document. MacKenz i e et al. (1958) ex posed g r oups of eig h t male and eig h t female Sprag u e-Dawley rats to 0-11 ppm (0-11 mg /L ) hex a valent chromium (as K 2 Cr O 4 ) for 1 y ear in drinking water. The control g r oup (10/sex ) received distilled water. A second ex periment involved three g r oups of 12 male and 9 female rats. One g r oup was g i ven 25 ppm (25 mg /L ) chromium (as K 2 Cr O 4 ), a second g r oup received 25 ppm chromium in the form of chromic chloride, and the controls ag ain received distilled water. The results of the MacKenz i e et al. study are presented in Table 3. No sig n ificant adverse effects were seen on appearance, weig ht g a in, or food consumption, and there were no patholog ic chang e s in the blood or other tissues in any treatment g r oup. The rats recei vi ng 25 ppmof chrom i u m(as K2 Cr O 4 ) showed an approx imate 20% reduction in water consumption. This dose corresponds to 2.5 mg Cr(VI ) /kg / day based on actual body weig ht and water consumption data. B l ood was ex amined monthly , and tissues (livers, kidney s , and femurs) were ex amined at 6 mo and 1 y ear. Spleens were also ex amined at 1 y ear. The 25 ppm g r oups (and corresponding controls) were ex amined similarly , ex cept that no animals were killed at 6 mo. An abrupt rise in tissue chromium concentrations was noted in rats treated with g r eater than 5 ppm. The authors stated that “apparently , tissues can accumulate considerable quantities of chromium before patholog ical chang e s result.” In the 25 ppm treatment g r oups, tissue c onc e n trations of c h romium we re approx imate ly nine time s hig h e r for those tre a t e dwith he x a va le nt c h romium tha n for the a n ima ls e x pose dto triva l e n t c h romium. 17Table 3. Subc hr onicor al toxic i ty of he xavale n t c h r o m i umin r a ts Nu m b er of anim als D o se and c o m p ound P eriod of exp o su re Endpoint s m o nit o r e d an d ef f

ect 9 females, 12 males at 25 ppm 10 males, 19 females at 9 ppm 8 ma le s, 8 fe ma le s at other treatment levels 0, 0.45, 2.2, 4.5, 7.7, 11, 25 ppm as potassium dichromate in drinking water 1 y ear No effect based on body weig ht, g r oss ex ternal condition, histopatholog ical analy s is, and blood c h e mistry

.

Source: MacKenz i e et al., 1958.
Gross and Heller (1946) reported that 0.125% K 2 Cr O 4 in the fe e dof rats wa s tole rate d without observable effects. A dose of 0.25% in the diet resulted in “subnormal condition,” including roug h coat and “subnormal” y oung born to treated animals. Doses of 0.5% and 1% in fe e dre sulte d in diarrhe a , roug h dirty c o a t s, a nd ste rility

. Z n CrO 4 a d ministe re d in the fe e dat levels of 0.125%, 0.25%, 0.5%, and 1.0% resulted in subnormal appearance, roug h and dirty coats, and sterility at all dose levels. Group sizes, duration of treatment, and criteria for de te rmining ste rility we re not re porte d. 4.2.3. Chronic Inhalation Studies Two studies have provided sug g e stive evidence of carcinog enicity in mice and rats following inhalation of hex a valent chromium (Nettesheim et al., 1971; Glaser et al., 1986). Nettesheim et al. (1971) ex posed C57B 1 mice to 13 mg calcium chromate/m 3 (4.33 mg Cr [VI ] /m 3 as calcium chromate dust), 5 hours/day , 5 day s /week for life. Chromium ex posure resulted in a cessation of body weig ht g a in at 6 mo followed by a decrease in body weig ht thereafter. B r onchial epithelial effects rang ed from marked hy perplasia and atrophy to necrosis, sug g e st i n g th atth e m a x i m u mt o l e rat e d dose m a y have been ex ceeded i n th i s study

. In fla mmatory infiltration into the sube pithe lium inc l uding prolife r ation of bronc hia l e p ithe lia l cells was noted. Distension of terminal bronchioli and alveoli resembling emphy sema was associated with alveolar proteinosis. A 2.8% increase in the number of lung tumors was reported with respect to controls. However, statistical analy s is was not performed, and the sig n ificance of these results is unclear. In a review of this study , IA RC (1990) concluded that a sig n ificant ex cess of treatment-related tumors was not observed. Nettesheim identified 4.33 mg of calcium c h romate dust/m 3 as a L OAEL for th e occurrence of epi th el i a l necrosi s , m arked hyperpl a si a and atrophy of the pulmonary bronchi, emphy sema-like chang e s, and atrophy of the spleen and liver. The sing le dose used in this study raises the question whether 4.33 mg Cr(VI ) /m 3 actual l y represent s a L OAEL

.

18Glaser et al. (1986) ex posed male W i star rats (20/g r oup) to aerosols of sodium chromate at measured concentrations of 0.025, 0.05, and 0.1 mg Cr(VI ) /m 3 , 22 hr/day , 7 day s /week for 18 mo. An additional g r oup was ex posed to a py roliz ed Cr(VI ) /Cr( III) ( 3 : 2 ) o x i d e m i x tu r e at 0.063 C r(VI ) /m 3

. The animals were held under conventional conditions for 12 mo following the ex posure. B ody weig hts and mortality were similar among all ex posure g r oups and controls. Primary lung tumors (1 adenocarcinoma and 2 adenomas) and 1 squamous cell carcinoma of the pharynx were evident in the hig h -chromate ex posure g r oup. Itis not clear whether the adenocarcinoma and adenomas occurred in the same animal or in different animals. One primary lung adenoma was observed in the ox ide-ex posed g r oup. Primary lung tumors were not observed in the controls or low-chromate ex posure g r oups. Dose-dependent retention of chromium was seen in the chromate- and ox ide-ex posed g r oups relative to the controls. At the conclusion of the study , lung chromium retention was 10-fold g r eater in the ox ide-ex posed g r oup than in the hig h

chromate-ex posed g r oup. Sig n ificantly increased lung weig hts were determined for the ox ideex posed g r oup and g r eater liver weig hts in the hig h -ex posure g r oup of the chromate. Pig m entloaded macrophag e s were found in a dose-dependent manner in rats ex posed to chromate and to the ox ide. Ox ide-ex posed rats developed focal thickened septa, partially combined with interstitial fibrosis and accumulation of eosinophilic substance in the alveolar lumens. Ox ideex posed g r oups also demonstrated elevated white- and red-blood cell counts, elevated serum cholesterol, and decreased total serum immunog lobulin levels. The results of this study may provide evidence of a weak carcinog enic potency of aerosols of both sodium dichromate and C r ( V I/III) o x i d e ( G l a s e r e t a l

. , 1986; Glaser et al., 1988). Steinhoff et al. (1983) investig ated the carcinog enicity of soluble sodium dichromate and c a l c i um c h romate in Spra g u e - Da wle y rats via intratra c h e a l a d ministration a nd re porte d positive carcinog enic effects. The study consisted of 10 treatment g r oups, one neg ative control g r oup, and two positive control g r oups. Each test g r oup contained 40 male and 40 female rats (10 weeks ol d atth e out set )

. The desi g n of th e dose l e vel s sel ect ed was such as t o assess th e i mp act s of the chemicals delivered in sing le hig h doses or in the same dose distributed over a 5-day period. The duration of the study was 2 y ears and 8 months. Doses rang ed from 0.5 to 1.25 mg /kg

. Rats a d ministe re d sodium dic h romate or c a l c i um c h roma te one or five time s pe r we e k had no sig n ificant reduction in survival periods as compared to controls, ex cept in the case of females treated with calcium chromate 5 × 0.25 mg /kg / week. An increased incidence of lung tumors as compared to controls was observed in the treated g r oup in which sodium dichromate was administered in a sing le dose of 1.25 mg

. No lung tumors were observed in the other sodium dichromate treatment g r oups. In rats administered calcium chromate, statistically sig n ificant increases in lung tumors were found in g r oups treated with a sing le dose of 1.25 mg /kg as well as in the g r oup treated with 5 × 0.25 mg /kg / week distributed over a period of 5 day s . There i s som e evi d ence th athex a val e ntchrom i u mm a y be carci nog eni c fol l o wi ng intrapleural implantation of calcium chromate (Hueper and Payn e, 1962) or intrabronchial implantation of strontium chromate, calcium chromate, or z i nc chromate (L evy and Martin, 1983). These tumors, however, were observed only at the site of implantation. Steffee and B aetjer (1965) observed statistically sig n ificant increases in lung tumors following intratracheal

19instillation of 0.01 to 0.03 mg zinc chromate in strain A mice. The instillations were performed at2-we e k inte rva l s a nd the a n ima ls we re obse r ve d until de ath. In contrast, intratracheal and intrapleural implantation studies of other chromium compounds have not demonstrated increases in tumor incidences. Mix e d hex a valent and trivalent chromium-containing dust was not carcinog enic in strain A Swiss and C57B L mice and mix ed-breed rats following intratracheal implantation (B aetjer et al., 1959). Steffee and B aetjer (1965) did not observe increases in lung adenomas following instillation of chromium dust, zinc chromate, and lead chromate into the tracheas of g u inea pig s and rabbits. Hueper and Payn e (1962) reported similar neg ative results after instillation of strontium chromate or calcium c h romate suspe nde d in g e latin; howe v e r , the e x pe rime nta l de ta il in the re port wa s insuffic i e n t for adequate evaluation. Hueper and Payn e (Hueper, 1955, 1958; Payn e, 1960; Hueper and Payn e, 1962) described a series of studies in rats treated by intrapleural injection of a number of hex a valent or trivalent compounds. Hueper (1955) injected powdered metallic chromium into the pleural cavity of rats, g u inea pig s , and mice and observed no sig n ificant increase in tumor incidence, either at the injection site or in other org a ns. Payn e (1960) implanted chromite roast, from which the soluble sodium chromate was ex tracted, into the pleural cavity of 35 rats. None of the 35 control animals developed tumors, and three of the treated animals developed tumors at the implantation site. In an earlier study , Hueper (1958) using chromite roast not leached of sodium chromate, none of the 25 treated male B e thesda rats developed implantation site tumors during 24 mo; however, the early deaths of nine of the treated animals decreased the number of animals at risk. Hueper and Payn e (1962) noted that no implantation site tumors were observed in 42 rats during a 24-mo period following eig h t implantations of 25 mg of trivalent chromium acet at e i n g e l at i n over a 13-m o peri od. B aetjer et al. (1959) chronically ex posed three strains of mice (Strain A, Swiss, and C57B l) a nd mix e d -bre e drats to approx imate ly l mg c h romium dust/m 3 , 4 hours/day , 5 day s /week over a rang e of 16-58 weeks, and reported no increase in the incidence of lung tumors with respect to untreated controls. Similar results were obtained by Steffee and B aetjer (1965) for W i star rats, rabbits, and g u inea pig s ex posed to chromium dust. L a skin (1972) ex posed rats and hamsters to calcium chromate aerosol at a level of 2 mg /m 3 (0.67 mg Cr(VI ) /m 3 ) for 589 day s out of an 891-day study

. Althoug h some laryng eal hyperplasias and metaplasias were observed in both species tested, details pertaining to controls were not g i ven in the available review. 4.2.4. Subc hr onicInhalation Studie s Data from a n ima l studie s ide n tify the re spirat ory tra c ta s the primary targ e tof c h romium tox i city following inhalation. 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 hr/day in subacute (28 day ) or subchronic (90 day ) protocols. Subacute and subchronic e x posure s 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 and sig n ificant effects on alveolar macrophag e s and immunolog ical function. Inhalation of Cr(VI ) a e r osols stimulate d the humora l immune sy ste m . Diffe re nc e s in the me a n tota l se rum 20immunog 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 � -cell-dependent antig en sheep red blood cell was elevated in a c h romium time - a nd dose

- de pe nde nt ma nne r. The immune stimulating e ffe c tof subc hronic ex posure to an aerosol with 0.05 mg /m 3 chromium was not reversed after 2 months of fresh air reg e neration. Subchronic ex posure to 0.2 mg /m 3 chromium resulted in depression of the immune-stimulating effect relative to the response at 0.05 mg /m 3

. The spleen T-lymphocyt e subpopulation was also stimulated by subchronic ex posure to 0.2 mg /m 3 c h romium. B r onchoalveolar lavag e (B AL ) cell counts were sig n ificantly decreased following subchronic ex posure to levels above 0.025 mg /m 3 chromium, thoug h it was not clear whether the e ffe c tive n e ss of the la va g ability of the c e lls wa s a lte re d atthe hig h e r dose le ve ls. The numbe r of lymphocyt es and g r anulocyt es showed a slig ht but sig n ificant increase in the lavag e fluids of the 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 de c r e a s e dthis func tion sig n ific a n tly , c o mplic ating the inte rpre tation of this result. 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. Inhaled chromium was found to preferentially accumulate in the lung following ex posure to chromate aerosols. Lung and spleen weig hts were sig n ificantly increased ( p < 0.005) after both subacute and subchronic inhalation of chromate aerosols at concentrations g r eater than 0.025 mg /m 3

. Serum contents of trig ly cerides and phospholipids differed sig n ificantly from controls ( p < 0.05) in rats ex posed subchronically to 0.2 mg /m 3 c h romate
. Glaser et al. (1990) presented a paper at the Second European Meeting of Environmental Hy g i ene that reported ex posure of 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 hr/day , 7 day s /week for 30-90 day s . Chromium-induced effects occurred 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 and 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 21pneumocyt 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). J 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, thoug h the number of nonviable macrophag e s was less than 3%. J ohansson et al. (1986) ex posed g r oups of rabbits to aerosols of hex a valent (0.9 mg Cr [VI ] /m 3 as Na 2 Cr O 4 ) or trivalent (0.6 mg Cr[ III] /m 3 as Cr[ N O 3 ] 3 ) chromium 5 day s /week, 6 hours/day for four to six 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 r ab b i t s 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 ical chang e s were observed, including round dark chromium-rich inclusions in the cytoplasm, an increased number of cells wi th 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 cell shape. The macrophag e s from rabbits ex posed to Cr(VI ) showed less marked morpholog ical 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)

. 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) 6 hr/day , 5 day s /week for 2 y ears. There were no compound-related differences in weig ht g a in between ex posed and control g r oups and no ex posure-related mortality in any ex posed g r oup. There were no compound-related lesions in the vital org a ns and tissues other than in the lung s of ex posed rats. 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 intraalveolar macrophag e s. Ex posure at 25 mg /m 3 was sug g e sted to have overwhelmed the lung clearance mechanisms and resulted in sig n ificant increases in dust-laden macrophag e s, bronchoalveolar cell hy perplasia with foamy macrophag e response, and cholesterol g r anuloma. The mechanism of action was not confirmed in the study , and the observation of dust particles in the alveolar macrophag e s is not necessarily indicative of overloading of the lung clearance mechanism. At 24 mo, the dust deposition and effects were increased sig n ificantly , with severe dust-laden macrophag e s, dust deposition in peribronchial lymphoid tissue, hyperplasia of Type I I pneumocyt es, and collag e niz e d fibrosis occurring in 100% of all lung tissues ex amined in either g e nder. Two female rats developed welldiffe 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. Mice ex posed to 1.81 or 3.63 mg /m 3 Cr(VI ) as CrO 3 for 1 y ear developed nasal septal perforation, loss of cilia, and metaplasia of the lung , trachea, and bronchus (Adachi, 1987; Adachi et al., 1986)

224.3. REP R ODUCTIVE/DEVELOP M ENTAL STUDIES 4.3.1. Oral Studies Hig h doses of Cr(VI ) compounds have been reported to cause developmental tox i city in mice. Trivedi et al. (1989) ex posed mice to 250, 500, and 1,000 ppm potassium dichromate daily throug h drinking water during the entire g e stational period. The authors reported decreased fetal weig ht, increased resorptions, and increased abnormalities (tail kinking , delay e d ossification of the cranium) in ex posed mice. The medium- and hig h -dose g r oups reg i stered sig n ificant reductions in body weig ht g a in when compared to controls. The most sig n ificant finding of the study was the complete absence of uterine implantation in the hig h -dose g r oup. The 250 and 500 ppm dose g r oups also showed sig n ificant incidences of resorption as compared to controls. The au thors obse r ve d sig n ific a n t inc r e a s e s in pre impla ntation a nd postimpla ntation losse s a nd dose

dependent reductions in total weig ht and crown-rump leng th in the lower dose g r oups. Additional effects included treatment-related increases in abnormalities in the tail, wrist forelimbs and subdermal hemorrhag ic patches in the offspring

. Z ahid et al. (1990) fed B A LB /C albino Swiss mice trivalent (chromium disulfate) 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, thoug h conflicting summaries of the actual g r oup siz e s are presented 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 suspended in buffered formalin. Sperm counts were then subsequently determined and sperms 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 ical 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 absent) 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 sperms at all dose levels. The authors concluded that the small but sig n ificant increase of hex a valent chromium in the testes of fed a n ima ls induc e dsig n ific a n t de g e ne ra tion. 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 in the Z ahid et al. study 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 a n ima ls use da nd the statistic a l a n a l y s is of the data
. 23The National Tox i colog y P r og ram recently conducted a three-part study to investig ate oral ing e stion of hex a valent chromium in ex perimental animals (NTP, 1996a,b, 1997). The study included a determination of the potential reproductive tox i city of potassium dichromate in Sprag u e-Dawley rats, a repeat of the study of Z ahid et al. (1990) using B A LB /C mice, and a Reproductive Assessment by Continuous B r eeding study in B A LB /C mice. The study in the Sprag u e-Dawley rat (NTP, 1996a) was conducted in order to g e nerate data in a species commonly used for reg u latory studies. Groups of 24 males and 48 females were ex posed to 0, 15, 50, 100, or 400 ppm potassium dichromate daily in the diet for 9 weeks followed by a recovery period of 8 weeks. Six male and 12 female rats were sacrificed after 3, 6, or 9 full weeks of treatment or after the full recovery period. Animals were ex amined for body weig hts; feed and water consumption; org a n weig hts; microscopic evaluation of the liver, kidney , and ovaries; hematolog y ; histolog y of the testis and epididym us for Sertoli nuclei and preleptotene spermatocyte counts in Stag e X or XI tubules; and chromatin analy s is. No treatment-related hematolog y finding s were reported ex cept for slig ht decreases in MCV and MCH values in the male and female treatment g r oups receiving 400 ppm potassium dichromate (24 mg /kg

- day )

. W h ile the trends in MCV and MCH were not larg e and were within the reference rang es (Charles River L aboratories, 1993), they are consistent with the finding s of the comp ani on studi es i n BALB / C m i ce (see bel o w) and were charact eri z ed by th e authors as sug g e stive of a potential bone marrow/erythroid response. The authors considered the 100 ppm (6 mg /kg

- day ) dose g r oup to be representative of the NOAEL for the study

. The reproductive study in B A LB /C mice (NTP, 1996b) was conducted to reproduce the conditions utilized by Z ahid et al. (1990) in their ex amination of comparative effects of trivalent and hex a valent chromium on spermatog e nesis of the mouse. Groups of 24 male and 48 female B A LB /C mice were ex posed to 0, 15, 50, 100, or 400 ppm potassium dichromate in the diet for 9 weeks followed by a recovery period of 8 weeks. Six male and 12 female mice were sacrificed after 3, 6, or 9 full weeks of treatment or after the full recovery period. Animals were ex amined for body weig hts; feed and water consumption; org a n weig hts; microscopic evaluation of the liver, kidney , and ovaries; hematolog y ; histolog y of the testis and epididym us for Sertoli nuclei and preleptotene spermatocyte counts in Stag e X or XI tubules; and chromatin analy s is. Treatment-related effects included a slig ht reduction in the mean body weig hts in the 400 ppm males and the 100 ppm females, a slig ht increase in food consumption at all dose levels, a slig ht decrease in MCV and MCH at 400 ppm, and cytoplasmic vacuoliz ation of the hepatocyte at 50, 100 and 400 ppm. None of the effects on spermatog e nesis reported by Z ahid et al. (1990) were observed in this study

. On the basis of the cytoplasmic vacuoliz ation of the hepatocyte in the 50, 100, and 400 ppm dose g r oups, the authors selected 15 ppm (4 mg /kg

- day ) as the NOAEL

. The potential reproductive tox i city of potassium dichromate was further evaluated in B A LB /C mice using the Reproductive Assessment by Continuous B r eeding protocol (NTP, 1997). In the continuous breeding phase of the study , g r oups of 20 male and female pairs of a n ima ls (F 0 ) were ex posed to dose levels of 0, 100, 200, and 400 ppm potassium dichromate, based on the previous study of reproductive effects in B A LB /C mice. Litters born after the continuous breeding phase (F 1 ) recei ved th e sam e concentr at i ons of pot assi umdi chrom at e as the i r F 0 parents. F 1 animals were used for assessment of second-g e neration reproductive tox i city

. 24Atsex u al m atu ri t y , 20 control ani m a l s of each sex and 20 tr eat ed ani m a l s of each sex i n each dose g r oup were selected as breeding pairs (avoiding sibling mating s ), cohabitated for 7 day s , and then separated. Offspring were counted and ex amined for terminal body and org a n weig hts and recei ved spermand t i ssue anal y s i s . The NTP studi es were desi g n ed t o repeat th e fi ndi ng s of Z ahid using methods of g r eater rig o r and definition, but were unable to do so. The reproductive assessment indicated that potassium dichromate administered at 100, 200, or 400 ppm in the diet to male and female B A LB /C mice is not a reproductive tox i cant in either sex

. F e rtility and the preg nancy index (number delivering /number cohabitated) were not affected by continued ex posure to potassium dichromate. No treatment-related differences were observed in the mean averag e litters per pair, number of live pups per litter, proportion of pups born alive, sex ratio, absolute live pup weig ht, or adjusted live pup weig ht. Mean body weig hts of the hig h -dose F 0 and F 1 animals were slig htly decreased relative to controls, and mean food consumption in the F 1 a n ima ls wa s inc r e a s e dre lative to c ontrols. Me a n ab solute live r we ig hts in the hig h -dose g r oup F 0 animals were decreased relative to controls. Treatment-related chang e s were observed in the he matolog y data for the F 1 a n ima ls. The MCV wa s slig htly de c r e a s e din the hig h -dose ma le s, and the MCH was slig htly decreased in the female animals in all dose g r oups. The authors sug g e sted that the NOAEL was not established in this study because of the slig ht decrease in MCH in the females of the 100 ppm (22.4 mg /kg

- day ) dose g r oup. J unaid et al. (1996) ex posed female Swiss albino mice to 250, 500, or 750 ppm potassium dic h romate in drinking wate r to de te rmine the pote n tia l e mbry o tox i c ity of he x a va le nt c h romium during day s 6-14 of g e station. No notable chang e s in behavior or clinical sig n s were observed in the control or treated dams. Chromium levels in blood, placenta, and fetus increased in a dosedependent fashion over the course of the study

. The authors reported retarded fetal development and embry o - and fetotox i c effects including reduced fetal weig ht, reduced number of fetuses (live and dead) per dam, and hig h er incidences of stillbirths and postimplantation loss in the 500 and 750 ppm dosed mothers. Sig n ificantly reduced ossification in nasal, frontal, parietal, interparietal, caudal, and tarsal bones was observed in the hig h -dose g r oup, while reduced ossification in only the caudal bones was observed in the 500 ppm dose g r oup. B a sed on the body weig ht of the animals (30 +/- 5 g ) and the drinking water ing e sted by the animals in the 250 ppm dose g r oup (8.0 ml/mouse/day ) , the dose level in the 250 ppm g r oup can be identified as 67 mg /kg

- da y . Kanojia et al. (1996) ex posed female Swiss albino rats to 250, 500, or 750 ppm potassium dic h romate in drinking wate r to de te rmine the pote n tia l te ra tog e nic ity of he x a va le nt c h romium preg estationally for 20 day s . No notable chang e s in behavior or clinical sig n s were observed in the control or treated dams. Chromium levels in blood, placenta, and fetus were sig n ificantly increased in the dams of the 500 and 750 ppm dose g r oups. The authors reported a reduced number of corpora lutea and implantations, retarded fetal development, and embry o - and fetotox i c effects including reduced number of fetuses (live and dead) per dam and hig h er incidences of stillbirths and postimplantation loss in the 500 and 750 ppm dosed mothers. Sig n ificantly reduced parietal and interparietal ossification was observed in the hig h -dose g r oup. B a sed on the body weig ht of the animals (175 +/- 25 g ) and the drinking water ing e sted by the animals in the 250 ppm dose g r oup (26 ml/mouse/day ) the dose level in the 250 ppm g r oup can be ide n tifie d a s 37 mg /kg

- da y . 25Elbetieha and Al-Hamood (1997) ex amined fertility following potassium dichromate ex posures in mice at concentrations considerably g r eater than those used by NTP. Sex u ally mature male and female mice were ex posed to 1,000, 2,000, 4,000, or 5,000 mg /L potassium dic h romate in drinking wate r for 12 we e k s. The e ffe c t s of the e x posure s on fe rtility wa s 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. Ex posure of male mice to hex a valent chromium compounds for 12 weeks had adverse impacts on the male reproductive sy stem and fertility , thoug h the mating capability of the mice was not affected. F e rtility was sig n ificantly reduced in males ex posed to 5,000 mg /L potassium dichromate. Testes weig hts were sig n ificantly 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 sig n ificantly reduced in the 5,000 mg /L ex posed males. The numbers of implantation sites and viable fetuses were sig n ificantly reduced in females impreg n ated by males ex posed to 2,000 and 4,000 mg /L

. The numbers of implantations and viable fetuses were sig n ificantly reduced in preg nant females ex posed to 2,000, 4,000, and 5,000 mg /L of the hex a valent chromium compound. The finding s of J unaid et al. (1996) and Kanojia et al. (1996) are consistent with those of Trivedi et al. (1989), and studies sug g e st the presence of embry o tox i c and fetotox i c effects of pota ssium dic h romate following ora l e x posure s in mic e a nd rats. The studie s utilize dsimilar dose le ve ls provide d in the drinking wate r of fe ma le mic e a nd rats. The dose le ve ls ar e similar to those used by the NTP study , which demonstrated no reproductive effects following administration of potassium dichromate in the diet. Itcannot be determined whether the lack of reproductive tox i city demonstrated in the NTP studies are reflective of the reduced bioa va ilability of he x a va le nt c h romium provide d in the die tin c o mparison to tha tprovide d in drinking water, or whether the NTP studies identified a NOAEL for reproductive effects. 4.3.2. Inhalation Studies No developmental effects were reported in rats ex posed to 0.2 mg /m 3 Cr(VI ) as sodium dichromate for three g e nerations (Glaser et al., 1984). No histopatholog ical effects of the testes were reported following ex posure of rats to 0.2 mg /m 3 Cr(VI ) as sodium dichromate for 28 or 90 day s (Glaser et al., 1985) or 0.1 mg /m 3 Cr(VI ) as sodium dichromate for 18 mo (Glaser et al., 1986, 1988).

4.4. OTHER STUDIES 4.4.1. Contact Derm atitis 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 chromeplating 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 26chromium 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). 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 ex hibit 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). 4.4.2. Toxicant Interactions Potassium dichromate has been reported to potentiate the effects of the nephrotox ins, mercuric chloride, citrinin, hex achlorobutadiene, and maleic acid (ATSDR, 1993). The g e notox icity of hex a valent chromium has also been shown to be altered in the presence of other compounds, including ascorbic acid and vitamin E and thiol compounds (Susa et al., 1994). Vita min B 2 has been reported to enhance the cytotox i city of sodium chromate (ATSDR, 1993). 4.4.3. G e notoxicity Hex a valent chromium is rapidly taken up by cells throug h the sulfate transport sy stem (Sug iy ama, 1992). Once inside the cell, Cr(VI ) is quickly reduced to the trivalent form by cellular reductants, including ascorbic acid, g l utathione, and flavoenz ym es, such as cytochrome P

- 450 g l utathione reductase, and riboflavin. The intracellular reduction of Cr(VI ) g e nerates re a c tive c h romium V a nd c h romium IV inte rme d iate s a s we ll a s hy drox y l fre e ra dic a l s ( � OH) and sing let ox y g en ( 1 O 2 ). A variety of DNA lesions are g e nerated during the reduction of Cr(VI ) to C r ( III) , i n c l u d i n g DNA strand breaks, alkali-labile sites, DNA-protein and DNA-DNA crosslinks, and ox idative DNA damag e , such as 8-ox o-deox y g uanosine. The relative importance of the different chromium complex e s and ox idative DNA damag e in the tox i city of Cr(VI ) is unknown. Hex a valent chromium has been shown to be g e notox ic only in the presence of appropriate reducing ag ents in vitro or in viable cell sy stems in vitro or in vivo. Hex a valent chromium has be e n shown to be muta g e nic in ba c t e ria l sy ste m s in the ab se nc e of a ma mma lia n a c tivating sy stem (Venitt and L e vy , 1974; Nishioka, 1975; Nakamuro et al., 1978; Green et al., 1976; Kanematsu et al., 1980; L o froth and Ames, 1978; Newbold et al., 1979; B onatti et al., 1976; F ukanag a et al., 1982), and not mutag e nic when a mammalian activating sy stem is present (L ofroth, 1978; Petrilli and DeF l ora, 1977, 1978a,b). Hex a valent chromium is also mutag e nic in eukary otic test sy stems (B onatti et al., 1976; Newbold et al., 1979; F ukanag a et al., 1982) and clastog e nic in cultured mammalian cells (Raffetto, 1977; L e vis and Majone, 1979; Umeda and 27Nishimura, 1979; Tsuda and Kato, 1977; Newbold et al., 1979; Nakamuro et al., 1978; Stella et al., 1982; Ohno et al., 1982; Gomez

- Arroy o et al., 1981; W ild, 1978; Sarto et al., 1982). Hex a valent chromium in the presence of g l utathione has been demonstrated to produce g e notox ic DNA adducts that inhibit DNA replication and are mutag e nic (Snow, 1994).

4.5. SYNTHESIS AND EVALUATION OF MAJOR NONCANCER EF F E CTS 4.5.1. Oral Studies 4.5.1.1. Hum a n Studie s C r ( V I) i s c o n s i d e r ab l y m o r e t o x i cth a n C r ( III)

. A c r o s s - s e c t i o n a l s tu d y r e p o rt e d th e effect s of envi ronm ent a l cont am i n at i on of wel l wat e r adj acent t o a chrom i u mal l o y pl ant
. C r(VI ) concentrations were reported as 20 mg /L , with an estimated ex posure dose of 0.57 mg /kg

- day (Z hang and Li , 1987) No lower dose levels were reported in this study

. Reported effects included oral ulcers, diarrhea, abdominal pain, indig e stion, vomiting , leukocyt osis, and presence of immature neutrophils. The sing le hig h dose level reported in the study limits its usefulness for qua ntitative risk a sse ssme n t purpose s . Other reports of tox i c effects in humans are limited to case reports from accidental poisoning s. Some Cr(VI ) compounds are potent ox idiz ing ag ents (such as potassium te tra c h romate a nd c h romium triox i de ) a nd ar e thus strong irrita nts of muc o sa l tissue

. Effe c t s included metabolic acidosis, acute tubular necrosis, kidney failure, and death (Sary a n and Reedy , 1988). 4.5.1.2. Anim al Studie s Only one chronic study pertaining to the oral tox i city of hex a valent chromium was located in the available literature. Anwar et al. (1961) ex posed dog s orally (2 dog s/g r oup) to potassium chromate in drinking water for 4 y ears. No effects were observed with reg ard to g r oss and microscopic analy s is of all major org a ns, urinaly s is, and weig hts of spleen, liver, and kidney

. A NOEL of 0.31 mg potassium chromate/kg / day can be established from this study

. The small g r oup size in this study limits its usefulness for quantitative risk assessment purposes. Mackenz i e et al. (1958) ex posed g r oups of male and female rats to potassium dichromate (0-25 ppm of hex a valent chromium) in drinking water for 1 y ear. No effects were observed at any level of treatment, and a NOEL of 2.5 mg /kg

- day can be established based on body weig ht, g r oss ex ternal condition, histopatholog ical analy s is, and blood chemistry

. J unaid et al. (1996) ex posed female Swiss albino mice to 250, 500, or 750 ppm potassium dic h romate in drinking wate r to de te rmine the pote n tia l e mbry o tox i c ity of he x a va le nt c h romium during day s 6-14 of g e station. The authors reported retarded fetal development and embry o - and fetotox i c effects including reduced fetal weig ht, reduced number of fetuses (live and dead) per dam, and hig h er incidences of stillbirths and postimplantation loss in the 500 and 750 ppm dosed 28mothers. Sig n ificantly reduced ossification in bones was also observed in the medium- and hig h

dose g r oups. B a sed on the body weig ht of the animals (30 +/- 5 g ) and the drinking water ing e sted by the animals in the 250 ppm dose g r oup (8.0 ml/mouse/day ) , the dose level in the 250 ppm g r oup can be identified as 67 mg /kg

- day

. Kanojia et al. (1996) ex posed female Swiss albino rats to 250, 500, or 750 ppm potassium dic h romate in drinking wate r to de te rmine the pote n tia l te ratog e nic ity of he x a va le nt c h romium preg estationally for 20 day s . The authors reported a reduced number of corpora lutea and implantations, retarded fetal development, and embry o - and fetotox i c effects including reduced numbe r of fe tuse s (live a nd de a d ) pe r da m a nd hig h e r inc i de nc e s of stillbirths a n d postimplantation loss in the 500 and 750 ppm dosed mothers. Sig n ificantly reduced parietal and interparietal ossification was observed in the hig h -dose g r oup. B a sed on the body weig ht of the animals (175 +/- 25 g ) and the drinking water ing e sted by the animals in the 250 ppm dose g r oup (26 ml/mouse/day ) , the dose level in the 250 ppm g r oup can be identified as 37 mg /kg

- day

. Elbetieha and Al-Hamood (1997) ex posed sex u ally mature male and female mice to 1,000, 2,000, 4,000, or 5,000 mg /L potassium dichromate in drinking water for 12 weeks. The effects of the ex posures on fertility was ex amined at 140 day s . The authors reported adverse impacts on the male reproductive sy stem and fertility , thoug h the mating capability of the mice was not affected. Testes weig hts were sig n ificantly 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 sig n ificantly reduced in the 5,000 mg /L ex posed males. The number of implantation sites and viable fetuses was sig n ificantly reduced in females impreg n ated by males ex posed to 2,000 and 4,000 mg /L , and the numbers of implantations and viable fetuses was sig n ificantly reduced in preg nant females ex posed to 2,000, 4,000, and 5,000 mg /L of the hex a valent chromium compound. In formation reg arding the amount of water consumed by the animals was not provided in this study

. 4.5.2. Inhalation Studies 4.5.2.1. Hum a n Studie s 4.5.2.1.1. Respiratory tract effects . Thre e studie s on c h rome plat e r s provide some qua ntitative information on 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 /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

. 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. A subsequent study by Lu cas and Kramkowski (1975) revealed similar re sults. Cr(VI ) c onc e n trations ra ng e dfrom 1 to 20 μ g /m 3 , averag i n g 4 μ g /m 3 . The authors attributed the nasal patholog y primarily to direct contact. Li ndberg and Hedenstierna 29(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 ex posed to concentrations of 2 to 20 μg /m 3

. 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 than 20 μ g /m 3 near the baths. Chang e s in pulmonary function (vital capacity and forced ex piatory volume) were seen at Cr(VI ) ex posures g r eater than 2 μ g /m 3

. 4.5.2.1.2. R e n a l effect s . Ex posure to Cr(VI ) at concentrations as low as 4 to 6 μ g /m 3 has been reported to result in elevated ex cretion of ß-2-microg l obulin (Lindberg and Vesterberg , 1983b). The effect m a y be reversi b l e because form er chrom e pl at ers di d nothave an el evat ed concentration of either ß-2-microg l obulin or albumin in their urine. Saner et al. (1984) did not find increased urinary ß-2-microg l obulin levels in tannery workers in comparison to referent control workers. However, urinary chromium concentrations in the Saner et al. study were likely distinctly lower than those in the study of Li ndberg and Vesterberg

. In summary , effects on the airway s and kidney have been observed in chromeplaters ex posed subchronically to chromic acid mist containing Cr(VI ) in air at concentrations g r eater tha n 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. Many of the available studies lack quantitative concentration-response data on chromium health effects suitable for quantitative risk assessment. 4.5.2.2. Anim al Studie s Data from studie s in rats, mic e , a nd rabbits ide n tify the re spirat ory tra c ta s the primary targ et of chromium tox i city following inhalation. Glaser et al. (1985) ex posed rats to 0-0.2 mg C r(VI ) /m 3 22 hr/day , 7 day s /week for 90 day s . The authors reported increased lung and spleen weig ht, and increased macrophag e activity and percent lymphocyt es in B A L fluid. Glaser et al. (1990) ex posed rats to 0-0.4 mg Cr(VI ) /m 3 , 22 hr/day , 7 day s /week for 30-90 day s and reported hyperplasia, increased lung weig ht, macrophag e infiltration, and LDH in bronchoalveolar lavag e fluid (B ALF )

. The authors 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. Rats ex posed to 0.5 mg /m 3 Cr O 2 (IV) 6 hr/day , 5 day s /week for 2 y ears produced dustladen alveolar macrophag e s with slig ht Type I I pneumocyt e hy perplasia. Ex posure at 25 mg /m 3 ove rwhe lme d the lung c l e ar a n c e me c h a n isms a nd re sulte d in sig n ific a n t inc r e a s e s in dust-la de n macrophag e s, bronchoalveolar cell hy perplasia with foamy macrophag e response, and cholesterol g r anuloma (L ee et al., 1988). Mice ex posed to 1.81 or 3.63 mg /m 3 Cr(VI ) as CrO 3 for 1 y ear developed nasal septal perforation, loss of cilia, and metaplasia of the lung , trachea, and bronchus (Adachi, 1987; Adachi et al., 1986). Epithelial chang e s of the bronchial tree rang ing from necrosis and atrophy to hyperplasia were observed in mice ex posed to 4.3 Cr/m 3 a s Ca Cr O 4 dust for 18 months (Nettesheim et al., 1971). 30Rabbits ex posed 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 phag o cytiz ed sig n ificantly more chromium particles than the controls, thoug h the number of nonviable macrophag e s was less than 3% (J ohansson et al., 1980). In a subsequent study , rabbits were ex posed to aerosols of hex a valent (0.9 mg /m 3 Na 2 Cr O 4 ) or trivalent (0.6 mg /m 3 Cr [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, while striking morpholog ical chang e s were observed in macrophag e s of r ab b i t s e x p o s e d t oC r ( III) ( J o h a n s s o n e t a l

. , 1986).

4.6. WEIG HT-OF - EVIDENCE EVALUATION AND CANCER CHARACTERIZ ATION Applyi ng the c rite ria outline din the Guide line s for Carc inog e n Risk Asse ssme n t (U.S. EPA, 1986) for evaluating the overall weig ht of evidence for carcinog enicity to humans, hex a valent chromium is most appropriately desig n ated a Group A - Known Human Carcinog en. Using the proposed Guidelines for Carcinog en Risk Assessment (U.S. EPA, 1996), hex a valent chromium is most appropriately desig n ated a known human carcinog en by the inhalation route of ex posure on the following basis. The potential carcinog enicity of chromium by the oral route of ex posure cannot be determined at this time. Results of occupational epidemiolog i c studies of chromium-ex posed workers are consistent across investig ators and study populations. Dose-response relationships have been established for chromium ex posure and lung cancer. W o rkers in the chromium industry are e x p o s e d t ob o th C r ( III) a n d C r ( V I) c o mpounds. Because only Cr(VI ) has been found to be carcinog enic in animal studies, however, data support only the classification of Cr(VI ) as a hum an carci nog en. Animal data provide sug g e stive evidence of the carcinog enicity of hex a valent chromium. Hex a valent chromium compounds have produced the following tumor ty pes in animal assay s : l u n g tu m o r s f o l l o w i n g i n h a l at i o n o f a e r o s o l s o f s o d i u m c h r o m at e a n d p y r o l i z e d C r ( V I) / C r ( III) ox ide mix ture s in rats, lung tumors following intratra c h e a l a d ministration of sodium dic h romate in rats, intrapleural implant site tumors for various Cr(VI ) compounds in rats, intrabronchial implantation site tumors for various Cr(VI ) compounds in rats, intramuscular injection site tumors in rats and mice, and subcutaneous injection site sarcomas in rats. In flammation is considered to be essential for the induction of most chromium inhalation effects and may influence the carcinog enicity of Cr(VI ) compounds (Glaser et al., 1985). In vitro data are sug g e stive of a potential mode of action for hex a valent chromium carcinog enesis. Cr(VI ) readily passes throug h cell membranes and is rapidly reduced intra c e llularly to g e ne rate re a c tive Cr(V) a nd Cr(IV) inte rme d iate s a nd re a c tive ox y g e n spe c i e s . The reactive ox y g en species may interact with DNA to form premutag enic lesions. Hex a valent chromium has been shown to be mutag e nic in bacterial assay s , y easts, and V79 cells, and Cr(VI ) compounds decrease the fidelity of DNA synthesis in vitro and produce unscheduled DNA synthesis as a consequence of DNA damag e . Chromate has been shown to transform both primary c e lls a nd c e ll line s . 31IA RC (1990) concluded that there is sufficient evidence of respiratory carcinog enicity in humans occupationally ex posed during chromate production. Animal data were considered supportive of the epidemiolog i cal data; however, the relative contributions to carcinog enic risk of me ta llic c h romium, triva l e n t c h romium, he x a va le nt c h romium, or soluble ve rsus insoluble chromium compounds could not be elucidated. IA RC (1982) classified chromium and chromium compounds as Group I chemicals. At present, the carcinog enicity of hex a valent chromium by the oral route of ex posure cannot be determined. One study of miners in Ontario sug g e sted that ex posure to chromium may have been associated with stomach cancer, but other human and animal studies have not reported similar e ffe c t s.

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 Cr(VI )

. These factors include diet and phy sical environment as well as maturation of phy siolog ic 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 statements about how these factors may specifically affect the tox i colog i cal responses of Cr(VI ) i n chi l d ren, be th ey cancer or noncancer. 4.7.2. P o ssib l e S e x Dif f

eren ces The e x te nt to whic h me n diffe r from wome n in susc e p tibility to c h romium tox i c ity ha s not been reported. The most sig n ificant health effects associated with ex posure to Cr(VI ) involve the respiratory sy stem and kidney

. W h ile effects on the respiratory sy stem are unlikely to differ sig n ificantly with g e nder, the effect of g e nder on kidney tox i city is unknown.

5. D O SE- R ESP O N S E A SSESSM EN TS 5.1. ORAL REF E RENCE DOSE (Rf D ) 5.1.1. Choice of P r incipal Study and Critical Ef f

ect Relatively few studies were located that addressed the oral tox i city of Cr(VI )

. One human study located in the literature, Z h ang and Li (1987), reported on health effects in Chinese villa g e rs who c onsume ddrinking wate r from a we ll c onta minat e dwith he x a va le nt c h romium from an alloy plant in J i nz hou. The J i nz hou area is heavily industrializ ed. In 1965, the well water in a nearby suburban area was found to be stained y e llow, presumably because of chromium contamination from a mining operation which had beg un operating in 1959. The mining operation was initially conducted in pilot scale, with a poor recovery rate for chromium (24.5%). F u ll-scale operation beg a n in 1965. At this time, waste water was g e nerated at a rate of 32125 pounds/hour and contained concentrations of up to 105 mg /L hex a valent chromium. W a ste water was deposited directly into a surface channel. Following sedimentation, the surface water concentration was still in ex cess of 20 mg /L

. In addition to the surface water discharg e, the mining operation g e nerated hex a valent chromium-containing steam and a considerable amount of c h romium-c onta i ning mine ta iling s . The ta iling s we re store din a n ope n wa ste pile , c onta i ning approx imately 300,000 pounds of waste, covering an area of 50 hectares. The waste pile constituted an additional source of g r ound water contamination throug h leaching and surface water runoff. In 1965, more than 28% of the area g r ound water samples were observed to be contaminated with chromium, with 54% of the samples contaminated at a concentration of 20 mg /L or g r eater. Ground water samples were found to be contaminated over an area of 10 square kilometers. In 1965, the material in the waste pile was found to contain an averag e of 1.55% hex a valent chromium. The soil in the vicinity of the waste pile was found to contain an averag e concentration of hex a valent chromium of 4,700 mg /kg , and 0.3 pounds/day of hex a valent chromium was estimated to leach into the g r ound water from the waste pile. In addition, irrig ation water for the considerable ag ricultural operation in the vicinity of J i nz hou was contaminated with chromium at concentrations of 0.006-0.739 mg /L

. However, concentrations in soil and produce in the ag ricultural areas were only slig htly elevated above the controls. In 1965, a study of 155 subjects ex posed to drinking water at concentrations of approx imately 20 mg /L of hex a valent chromium was conducted outside J i nz hou. Subjects were observed to have sores in the mouth, diarrhea, stomach ache, indig e stion, and vomiting

. Subjects were observed to have elevated white blood cell counts with respect to controls, as well as a hig h er per capita rate of cancers, including lung cancer and stomach cancer. Precise ex posure concentrations, ex posure durations, and confounding factors were not discussed, and this study does not provide a NOAEL for the observed effects. However, the study sug g e sts that g a strointestinal effects may occur in humans following ex posures to hex a valent chromium at levels of 20 ppm in drinking water (Z hang and Li , 1987). Several animal studies addressing oral tox i city of hex a valent chromium were located in the literature. Anwar et al. (1961) ex posed g r oups of female dog s (2/g roup) to up to 11.2 ppm Cr(VI ) in drinking water for 4 y ears with no effect. MacKenz i e et al. (1958) ex posed g r oups of Sprag u e-Dawley rats (16-21/g r oup) to up to 25 ppm Cr(VI ) in drinking water for 1 y ear. No sig n ificant adverse effects were seen in any treatment g r oup. B o th the Mackenz i e et al. (1958) and Anwar et al. (1961) studies are limited by the small number of animals/g roup and the lack of an observed effect at any dose level. W h ile the MacKenz i e et al. study has the additional limitation of being conducted for only 1 y ear, this study is considered to be more useful for risk assessment because of the identification of a NOAEL value and the larg er number of animals per dose g r oup that those available from Anwar et al. (1961). Elbetieha and Al-Hamood (1997) reported adverse impacts on the male reproductive sy ste ma nd fe rtility , a nd re duc e dnumbe rs of impla ntations a nd viab le fe tuse s in pre g na nt fe ma le s following ex posures to hex a valent chromium. In formation reg arding the amount of water consumed by the animals was not provided, and this study is not considered useful for this risk assessment.

33The National Tox i colog y Prog ram (NTP 1996a,b, 1997) did not observe reproductive effects in either sex of B A LB /C mice or Sprag u e-Dawley rats following oral ex posures to 15 - 400 ppm Cr(VI ) in the diet. J unaid et al. (1996) and Kanojia et al. (1996) ex posed female Swiss albino mice and female Swiss albino rats, respectively , to 250, 500, or 750 ppm potassium dichromate in drinking water to determine the potential embry o tox i city of hex a valent chromium during day s 6-14 of g e station. The authors reported retarded fetal development and embry o - and fetotox i c effects including reduced fetal weig ht, reduced number of fetuses (live and dead) per dam, and hig h er incidences of stillbirths and postimplantation loss in the 500 and 750 ppm dosed mothers. Sig n ificantly reduced ossification in bones was also observed in the medium- and hig h -dose g r oups. B a sed on the body weig ht and the drinking water ing e sted by the animals in the 250 ppm dose g r oup, the ex posure levels in the 250 ppm g r oups can be identified as 67 mg /kg

- day and 37 mg /kg

- da y in mic e a nd rats, re spe c tive l y . The J unaid et al. (1996) and Kanojia et al. (1996) studies utilized doses approx imately 10-fold hig h er than those used in Mackenz i e et al (1958), but neither of the reproductive studies identified a clear NOAEL for the embry o tox i c effects of hex a valent chromium. Based on the body weig ht and the drinking water ing e sted by the animals in the low-dose g r oups (250 ppm), the L OAEL s of 67 mg /kg

- day and 37 mg /kg

- day can be identified from J unaid et al. (1996) and Kanojia et al. (1996) in mice and rats, respectively

. Application of 10-fold uncertainty factor to ex trapolate from L OAEL s to NOAEL s in these studies would g e nerate NOAEL s of 6.7 mg /kg

day and 3.7 mg /kg

- day , respectively

. These ex trapolated NOAEL values are similar to, and support the use of, the NOAEL of 2.5 mg /kg

- day identified from the study of MacKenz i e et al. (1958) for development of the reference dose. 5.1.2. Method of Analysis MacKenz i e et al. ex posed g r oups of eig h t male and eig h t female Sprag u e-Dawley rats to 0.45-11.2 ppm (0.45-11.2 mg /L ) hex a valent chromium (as K 2 Cr O 4 ) for 1 y ear in drinking water. The control g r oup (10/sex ) received distilled water. A second ex periment involved three g r oups of 12 male and 9 female rats. One g r oup was g i ven 25 ppm (25 mg /L ) chromium (as K 2 Cr O 4 ), a second received 25 ppm chromium in the form of chromic chloride, and the controls ag ain received distilled water. No sig n ificant adverse effects were seen in appearance, weig ht g a in, or food consumption, and there were no patholog ic chang e s in the blood or other tissues in any treatment g r oup. The rats receiving 25 ppm of chromium (as K 2 Cr O 4 ) showed an approx imate 20% reduction in water consumption. This dose corresponds to 2.5 mg Cr(VI ) /kg / day based on actual body weig ht and water consumption data. F o r rats treated with 0-11 ppm (in the diet), blood was ex amined monthly and tissues (livers, kidney s and femurs) were ex amined at 6 mo and 1 y ear. Spleens were also ex amined at 1 y ear. The 25 ppm g r oups (and corresponding controls) were ex amined similarly , ex cept that no a n ima ls we re kille d at6 mo. An ab rupt rise in tissue c h romium c onc e n trations wa s note din rats tr eat ed wi thg r eat er th an 5 ppm

. The authors st at ed th at“apparent l y , t i ssues can accum u l at e c onside r ab le qua ntitie s of c h romium be fore patholog ic a l c h a n g e s re sult.” In the 25 ppm 34treatment g r oups, tissue concentrations of chromium were approx imately 9 times hig h er for those treated with hex a valent chromium than for the trivalent g r oup. Similar no-effect levels have been observed in dog s. Anwar et al. (1961) observed no sig n ificant effects in female dog s (2/dose g r oup) g i ven up to 11.2 ppm Cr(VI ) (as K 2 Cr O 4 ) in drinking water for 4 y ears. The calculated doses were 0.012-0.31 mg /kg of Cr(VI )

. 5.1.3. Rf D Derivation No effect s were report e d atany dose l e vel i n th e MacKenz i e etal . study

. The hi g h est dose g r oup (25 mg /L ) was selected for derivation of the reference dose. B a sed on the body weig ht of the rat (0.35 kg ) and the averag e daily drinking water consumption for the rat (0.035 l/day ), this dose can be converted to g i ve an adjusted NOAEL of 2.5 mg /kg

- day

. 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 threefold uncertainty factor is applied to the adjusted NOAELto compensate for the less-thanlife time e x posure duration in the Ma c K e n zie e ta l . study

. A thre e f old modifying fa c t or is applie d to address concerns raised by the study of Z h ang and Li (1987). The total uncertainty factor applied to the adjusted NOAEL is 900. Application of the uncertainty factor to the adjusted NOAEL of 2.5 mg /kg

- day g i ves the reference dose of 3 × 10 -3 mg /kg

- da y .
5.2. INHALATION REF E RENCE CONCENTRATION (RfC ) The inhalation reference concentration (RfC) is based on the assumption that thresholds ex i s tfor cert a i n t o x 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 suc h a s c ar c i nog e n ic ity

. 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 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 effects during a lifetime. 5.2.1. Choice of P r incipal Study and Critical Ef f

ect Numerous studies have reported upper respiratory , lower respiratory , and kidney effects in humans and animals following ex posures to hex a valent chromium. Of these endpoints, upper a nd lowe r re spirat ory e ffe c t s appe ar to be the most se nsitive a nd ar e disc usse d in g r e a t e r de ta il below. Three studies have focussed on nasal mucosal irritation, atrophy , and perforation following occupational ex posures to chromic acid mists (Cohen et al., 1974; Lu cas and Kramkowski, 1975; Li ndberg and Hedenstierna, 1983). Of these, the study of Li ndberg and Hedenstierna provides the most information on ex posure levels and symptoms reported by ex posed workers. Respiratory symptoms, lung function, and chang e s in nasal septum were studied in 104 workers (85 males, 19 females) ex posed in chromeplating plants. W o rkers were interviewed using a standard questionnaire for the assessment of nose, throat, and chest

35symptoms. Nasal inspections and pulmonary function testing were performed as part of the study

. The median ex posure time for the entire g r oup of ex posed subjects (104) in the study was 4.5 y ears (0.1-36 y ears). F o rty

- three subjects ex posed almost ex clusively to chromic acid ex perienced a mean ex posure time of 2.5 y ears (0.2-23.6 y ears). The subjects ex posed almost ex clusively to chromic acid were divided into a low-ex posure g r oup (8 hr TW A below 0.002 mg /m 3 , N = 19) and hig h ex posure g r oup (8 hr TW A above 0.002 mg /m 3 , N = 24). Ex posure measurements using personal air samplers were performed for 84 subjects in the study on 13 diffe re nt da y s . Ex posure for the re ma ining 20 worke r s wa s a ssume d to be similar to that m easured for workers i n th e sam e area. Ni net een offi ce empl oy ees were used as control s for nose and throat symptoms. A g r oup of 119 auto mechanics whose lung function had been e v a l uate d by similar te c hnique s wa s se le c t e da s c ontrols for lung func tion me a s ure m e n ts. Smoking habits of workers were evaluated as part of the study

. At mean ex posures below 0.002 mg /m 3 , 4/19 workers from the low-ex posure g r oup complained of subjective nasal symptoms. Atrophied nasal mucosa were reported in 4/19 subjects from this g r oup and 11/19 had smeary and crusty septal mucosa, which was statistically hig h er than controls. No one ex posed to levels below 0.001 mg /m 3 c o mpla ine dof subje c tive symptoms. At mean concentrations of 0.002 mg /m 3 or above, approx imately one-third of the subjects had reddened, smeary , or crusty nasal mucosa. Atrophy was seen in 8/24 workers, which was sig n ificantly different from controls. Eig h t subjects had ulcerations in the nasal mucosa and five had perforations of the nasal septum. Atrophied nasal mucosa was not observed in any of the 19 controls, but smeary and crusty septal mucosa occurred in 5/19 controls. Short-term effects on pulmonary function were evaluated by comparing results of tests taken on Monday and Thursday among ex posed g r oups and controls. No sig n ificant chang e s were seen in the low-ex posure g r oup or control g r oup. Nonsmokers in the hig h -ex posure g r oup ex perienced sig n ificant differences in pulmonary function measurements from the controls, but the re sults we re within norma l limits. The authors concluded that 8-hour mean ex posures to chromic acid above 0.002 mg /m 3 may cause a transient decrease in lung function, and that short-term ex posures to g r eater than 0.02 mg /m 3 may cause septal ulceration and perforation. B a sed on the results of this study , a L OAEL of 0.002 mg /m 3 can be identified for incidence of nasal septum atrophy following ex posure to chromic acid mists in chromeplating facilities. Itshould be noted that there are sig n ific a n t unc e rta intie s re late d to the use of this L OAEL for de ve lopme n t of a n RfC for he x a va le nt c h romium in the e nvironme n t. The r e is c onside r ab le unc e rta inty with re g ard to the relevance of the nasal septum atrophy endpoint observed in the chromeplating industry to ex posure to hex a valent chromium in the environment. The effects were observed in chromeplaters ex posed to chromic acid mists near the plating baths. Environmental ex posures would most likely occur throug h contact with hex a valent chromium dusts. An additional uncertainty is related to the determination of dose in the Li ndberg and Hedenstierna study

. Nasal septum atrophy in this study was related to time-weig h ted averag e (TWA) ex posures to chromic acid. The most sig n ificant effects (nasal septum perforation) were observed in workers who 36ex peri enced peak ex cursi ons t o l e vel s consi d erabl y g r eat er th an th e TW A. It i s uncert a i n whether the peak ex cursion data or the TW A are more appropriate for the determination of dose in this study

. An alternative approach to development of the RfC is to focus on respiratory effects following inha lation of he x a va le nt c h romium partic ulat e s . Two studie s provide hig h qua lity data on lower respiratory effects following ex posures to chromium particulates (Glaser et al., 1990; Glaser et al., 1985). Glaser et al. (1990) ex posed 8-week-old male W i star rats to sodium dichromate at 0.05 - 0.4 mg Cr(VI ) /m 3 22 hr/day , 7day s /week for 30-90 day s . Chromiuminduced effects occurred 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 and 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, and albumin and LDH in B A LFwere increased following the ex posure. 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. (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 hr/day in subacute (28 day ) or subchronic (90 day ) protocols. Chromium-induced effects occurred in a dose-dependent manner. Lung and spleen weig hts were sig n ificantly increased ( p < 0.005) after both subacute and subchronic ex posures at concentrations g r eater than 0.025 mg /m 3

. Di fferences i n th e m ean total serum immunog lobulin were also 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 immune-stimulating effect of subchronic ex posure was not reversed after 2 mo of fresh air reg e neration. B A L 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 this function sig n ificantly

. The spleen T-lymphocyt e subpopulation was stimulated by subchronic ex posure to 0.2 mg /m 3 c h romium, a nd se rum c onte n ts of trig ly c e ride s and phospholipids differed sig n ificantly from controls ( p < 0.05) at this concentration. Tog e ther, these studies provide useful information on chromium ex posure-related impacts including lung and spleen weig ht, lactate dehy drog enase (LDH) in B A LF , protein in B A LF , and a l bumin in B A LF

. The c e llular c onte n t of B A LFis c onside r e dre pre s e n tative of initia l pulmonary injury and chronic lung inflammation, which may lead to the onset of pulmonary fibrosis (Henderson, 1988). While these studies present dose-dependent results on sensitive indicators of lower respiratory tox i city , potential upper respiratory impacts resulting from the 37ex posures were not addressed. Glaser et al. (1990) states that the upper respiratory tract was ex amined, but these data are not reported. In lig ht of the numerous reports of severe upper re spirat ory impa c t s following e x posure to c h romic a c i d in the oc c upationa l se tting , the studie s of Glaser et al. alone are not considered sufficient to support derivation of an RfC for chromium. W h ile the studies of Li ndberg and Hedenstierna (1983) and Glaser et al. (1985, 1990) are independently considered insufficient for development of an RfC for hex a valent chromium, taken tog e ther these offer an approach for development of an RfC. 5.2.2. Rf C Derivation Li ndberg and Hedenstierna (1983) will be used to support development of an RfC for upper respiratory effects of chromic acid mists and dissolved hex a valent chromium aerosols, and Glaser et al. (1985, 1990) will be used to support development of an RfC for lower respiratory e ffe c t s from c h romium partic ulat e s . 5.2.2.1. Chrom i c Acid Mists and Dissolved Hexavalent Chrom i um Aerosols A L OAEL for nasal septum atrophy of 2 μ g /m 3 chromic acid can be identified based on the results of Li ndberg and Hedenstierna (1983). At TW A ex posures g r eater than 2 μ g /m 3 , nasal septum ulceration and perforations occurred in addition to the atrophy reported at lower concentrations. The L OAEL is based on an 8-hour TW A occupational ex posure. The L OAEL is adjusted to account for continuous ex posure according to the following equation: L OAEL c = 2 μ g /m 3 × (MVho/MVh) × 5 day s /7 day s where: L OAEL c is the L OAEL for continuous ex posure MVho is the breathing volume for an 8-hour occupational ex posure (10 m 3 ) MVh i s the breathing volume for a 24-hour continuous ex posure (20 m 3 ) The L OAEL of 2 μ g /m 3 based on a TW A ex posure to chromic acid is converted to a L OAEL for continuous ex posure of 0.714 μ g /m 3

. An uncertainty factor of 3 is applied to the L OAEL to ex trapolate from a subchronic to a chronic ex posure, an uncertainty factor of 3 is applied to account for ex trapolation from a L OAEL to a NOAEL , and an uncertainty factor of 10 is applied to the L OAEL to account for interhuman variation. The total uncertainty factor applied to the L OAEL is 90. Application of the uncertainty factor of 90 to the L OAEL of 0.714 μg /m 3 g e nerates an RfC for upper respiratory effect of chromic acid mists and dissolved hex a valent chromium aerosols of 0.008 μ g /m3

.

385.2.2.2. Hexavalent Chrom i um Dusts Glaser et al. (1990) ex posed male W i star rats to 0.05-0.4 mg /m 3 sodium dichromate 22 hr/day , 7 day s /week for 30 or 60 day s , or 90 day s with a 30-day recovery period. In Glaser et al. (1985), male W i star rats were ex posed to 0.025 - 0.2 mg /m 3 sodium dichromate 22 hr/day , 7 day s /week for 28 or 90 day s . Data were reported on numerous endpoints indicative of lung tox i city

. One approach for development of an RfC using these data was offered by Malsch et al. (1994), who g e nerated an inhalation RfC for chromium dusts using a benchmark concentration (B MC) approach. The Ag ency based its RfC derivation on this approach. After ex cluding ex posures for periods of less than 90 day s from the B M C analy s is, Malsch et al. (1994) developed B M Cs for lung weig ht, lactate dehy drog enase (LDH) in B A LF , protein in B A LF , albumin in B A LF , and spleen weig ht. The Malsch et al. (1994) analy s is defined the benchmark concentration as the 95% lower confidence limit on the dose corresponding to a 10% relative chang e in the endpoint compared to the control. Dose-effect data were adjusted to account for discontinuous ex posure (22 hr/day ) and the max imum likelihood model was used to fit continuous data to a polynomial mean response reg r ession, yi elding max imum likelihood e s timate s of 36 -78 μ g /m 3 and B M Cs of 16 - 67 μ g /m 3

. Malsch et al. (1994) applied dosimetric a d justme nts a nd unc e rta inty fa c t ors to the B M Cs to de te rmine a RfC ba se d on the following equation: Rf C = B M C × RDDR UF A × UF F × UF H where: RfC is the inha la tion re fe re nc e c onc e n tration B M C i s the be nc hmark c onc e n tration (lowe r 95% c onfide n c e limit on the dose corresponding to a 10% relative chang e in the endpoint compared to the control) RDDR is the reg i onal deposited dose ratio to account for pharmacokinetic differences between speci es UF A is a threefold uncertainty factor to account for pharmacodynamic differences not addressed by the RDDR UF F is a threefold uncertainty factor to account for ex trapolating from subchronic to chroni c ex posures; and UF H is a 10-fold uncertainty factor to account for the variation in sensitivity among members of the human population The RDDR factor is incorporated to account for differences in the deposition pattern of inhaled hex a valent chromium dusts in the respiratory tract of humans and the W i star rat test animals (J arabek et al., 1990). The RDDR of 2.1355 was taken from U.S. EPA (1990), based on the mass median aerodynamic diameter (0.28 μ mfor dose levels of 50-100 μ g /m 3 and 0.39 for dose levels of 100-400 μ g /m 3 ) and the g e ometric standard deviation (1.63 for dose levels of 50- 100 μ g /m 3 and 1.72 for dose levels of 100-400 μ g /m 3 ) of the particulates reported in Glaser et al. (1990). A 3.16-fold uncertainty factor (midpoint between 1 and 10 on a log scale) was incorporated to account for the pharmacodynamic differences not accounted for by the RDDR. An additional 3.16-fold uncertainty factor was incorporated to account for the less-than-lifetime
39ex posure in Glaser et al. (1990), and a 10-fold uncertainty factor was applied to account for variation in the human population. A total uncertainty factor of 100 was applied to the B M C in addition to the RDDR. Glaser et al. (1990) reported that LDH in B A LFincreased in a dose-dependent fashion from 50 to 400 μ g /m 3 sodium dichromate, and this endpoint g e nerated the lowest B M C (16 μg /m 3 ) and RfC (0.34 μ g /m 3 ). LDH in B A LFis c onside r e dthe a m ong the most se nsitive indicators of potential lung tox i city (Henderson, 1984, 1985, 1988; B eck et al., 1982; Venet et al., 1985), as LDH is found ex tracellularly after cell damag e and BALFis the closest site to the orig inal lung injury

. LDH in B A LFmay also reflect chronic lung inflammation, which may lead to pulmonary fibrosis throug h prevention of the normal repair of lung tissue (Henderson, 1988). Several uncertainties must be addressed with reg ard to the B M C and RfC developed by Malsch et al. (1994). Potentially important endpoints including upper airway effects and potential renal or immunolog ical tox i city were not addressed in the Glaser et al. (1985, 1990) studies and could not be included in the B M C analy s is. W h ile LDH in B A LFresulted in the lowest B M C and RfC, several of the effects noted in Glaser et al. (1985, 1990) can be considered indicative of an inflammatory response, and mig ht be equally suited to development of the RfC. In addition, the threefold uncertainty factor accounting for the use of a subchronic study may not be sufficiently protective for long -term effects. W h ile the analy s is acknowledg ed the importance of particle siz e and airway deposition in the development of the RDDR, the potential impact of different particle siz e s in respiratory tox i city by hex a valent chromium particulates was not addressed. Several of these uncertainties have been conservatively addressed in the analy s is of Malsch et al. (1994). LDH in B A LFg e nerated the lowest estimate of the B M C from the effects noted by Glaser et al. (1985, 1990). This effect can be considered to be indicative of cell damag e that occurs prior to fibrosis, as LDH appears in B A LFfollowing cell ly sis. W h ile other endpoints considered in the Malsch et al. (1994) analy s is demonstrated a relatively better curve fit tha n LDH in B A LF , the mode l g e ne rate d a c onse r vative fit in the data thatis unlike l y to overestimate the B M C, and the curve fit for LDH in B A LFis considered to be acceptable. LD H in BALFas reported in Glaser et al. (1990) is considered to be an acceptable endpoint for development of an RfC for inhalation of hex a valent chromium particulates, and Malsch et al. (1994) used a reasonable approach for development of a B M C based on this endpoint. The threefold uncertainty factor used to account for the subchronic study is insufficient for development of the RfC for inhalation of chromium particulates. Glaser et al. (1985) demonstrated that at the end of the 90-day ex posure period, chromium was still accumulating in the lung tissue of the te st a n ima ls, sug g e sting thatlowe r long -te rm e x posure s mig ht le a dto accumulation of a critical concentration in the lung

. Subchronic studies also may not adequately predi c t th e presence of i n fl am m at o ry effect s froml o wer l ong -t ermex posures. The Ag ency has therefore determined that a 10-fold uncertainty factor accounting for the use of a subchronic study is more appropriate in this case for the development of the RfC for inhalation of chromium particulates.

40Selection of a threefold uncertainty factor to account for the pharmacodynamic differences not accounted for by the RDDR, an additional 10-fold uncertainty factor to account for the less-than lifetime ex posure in Glaser et al. (1990), and a 10-fold uncertainty factor to account for variation in the human population g e nerates a total uncertainty factor of 300. Application of the total uncertainty factor of 300 and the RDDR of 2.1576 to the B M C g e nerated by Malsch et al. (1994) based on LDH in B A LF(Glaser et al., 1990) results in an RfC of 0.1 μg /m 3 for inhalation of hex a valent chromium particulates. The selected RfCs are 0.008 μ g /m 3 for chromic acid mists and dissolved hex a valent chromium aerosols and 0.1 μ g /m 3 for hex a valent c h romium partic ulat e s .
5.3. CANCER ASSESSMENT 5.3.1. Sum m a ry The r e ar e ma ny e p ide miolog i c studie s de monstrating thathe x a va le nt c h romium (CrVI ) is a potential human carcinog en, but few provide adequate ex posure data for use in risk estimation. Mancuso (1975) provides limited but adequate information for this purpose, and Mancuso' s data ar e use da s the ma in databa se for e s timating the c ar c i nog e n ic pote n c y of he x a va le nt c h romium. Three foreig n studies on ferrochromium plants were also considered for use in the potency c a l c u lations. Fr om the qua ntitative risk a sse ssme n t vie w point, the s e studie s ar e le ss a d e qua te than the Mancuso study

. F o r the Norweg ian study (L ang ard et al., 1980), the ex posure measurements were taken in 1975, while some workers could have been ex posed to chromium as early as 1928, when the ambient dust levels were much hig h er than in later y ears. F o r the Swedish study (Ax e lsson et al., 1980), the chromium-ex posed workers did not show a sig n ificant increase of lung cancer, and thus only the statistical upper bound of the response can be used in potency estimation. Itis ex pected that the use of data from the Norweg ian and Swe d ish studie s would re sult in a n ove re stimation of the true c ar c i nog e n ic pote n c y of he x a va le nt chromium. W h ile a Russian study (Pokrovskay a and Shabyn ina, 1973) does not have the deficiencies of the other two foreig n studies, the cohort in this study is not well defined and is not suitable for use in risk assessment. Anima l data from intratra c h e a l studie s we re not use dto e s timate the c ar c i nog e n ic pote n c y of chromium by inhalation because there is limited pharmacokinetic information relating the distribution of chromium to lung tissues by inhalation and by intratracheal administration. This information is needed to reconcile the differences in dose distribution between these two ex posure patterns. F u rthermore, the phy siolog ical mechanism of dose distribution by intratracheal administration may depend (in a nonlinear fashion) on the dose levels used in the ex periment, as evidenced by the observation that a sing le administration of sodium dichromate induced a carcinog enic response in Sprag u e-Dawley rats but failed to induce a response when the same weekly dose was g i ven over 5 day s (Steinhoff et al., 1983). 5.3.2. Dose-Response Data

41The Mancuso (1975) study was based on a cohort of 332 white male workers who were employ ed in a chromate plant between 1931 (when the plant beg a n to operate) and 1937, and who were followed to 1974. Mancuso reported lung cancer death rates by levels of ex posure to soluble, insoluble, and total chromium concentrations. B ecause only lung cancer mortality for total chromium ex posure was reported by ag e g r oup, only the dose-response data for total c h romium we re use dto e s timate the c ar c i nog e n ic pote n c y of he x a va le nt c h romium. The use of dose-response data for total chromium would result in an underestimation of the potency of he x a va le nt c h romium. An a dditiona l unc e rta inty of the study wa s the a ssumption tha tthe smoking habits of chromate workers were similar to those of the g e neral white male population. This a ssumption ma y le a dto a n ove re stimation of the role of he x a va le nt c h romium in lung cancer seen in the cohort. Ex posure information in the Mancuso study was derived from an industrial hy g i ene study of the plant conducted in 1949 (B ourne and Yee, 1950). In this study , TW As of ex posure to i n sol ubl e, sol ubl e, and t o t a l chrom i u mper cubi c m e t e r were cal cul at e d for each occupat i on and for each worker in every department. Using these data and company personnel records, Mancuso wa s ab le to c a l c u late a n e s timate of e x posure to soluble , insoluble , a nd tota l c h romium by duration of ex posure (in mg /m 3 /y ears) for each member of the 1931-37 cohort. In 1949, after the industrial hy g i ene study had been conducted, the company initiated a comprehensive prog ram de sig n e dto re duc e e mploy e e s ' e x posure s a nd improve ma nufa c turing e ffic i e n c y . Until thattime , however, the company had not undertaken any prog rams for the purpose of reducing employ ee ex posure. Itshould be noted that B ourne and Yee (1950), who conducted the industrial hy g i ene survey in 1949, reported that “in order to meet price and quality competition, improvements in equipment and processes have been made periodically during the past 18 y ears, and it is the universal ex perience of industrial hy g i ene personnel that g r eater process efficiency is almost invariab ly a ssoc i at e dwith a more he a lthful working e nvironme n t. The r e f ore , the r e se e m s little doubt that atmospheric contamination in the past was g r eater than in 1949.” Nonetheless, no concerted effort was made to reduce employ ee ex posure until late in 1949, and because this partic ular pla n t wa s a re lative l y mode rn one atthe time of the surve y , it is unlike l y that improvements in efficiency over the period 1931 to 1949 would have reduced employ ee e x posure to a g r e ate x te nt. Thus, Ma nc uso is c onside r e dto ha ve utilize da re a s onable approx imation of what workers in the study cohort were ex posed to during their entire working history

. Ex posure in the cohort may be slig htly underestimated because of the likelihood that a g r eater proportion of the “total ex posure” was contributed prior to 1949 than after 1949. The effects of underestimating the ex posure concentration, as well as the effects of other uncertainties on the e s timation of pote n c y , ar e a ddre sse d in Se c tion 6. 5.3.3. Dose Conversion Table 3, which is taken from Mancuso (1975), presents ag e-specific lung cancer deaths, corresponding person-y ears, and rang e of ex posures to total chromium. To estimate the lifetime cancer risk due to ex posure to chromium, it is assumed that an ex posure, D (mg /m 3 /y ears), as presented in Table 3, is equivalent to the continuous ex posure d (μ g /m 3 ) cal cul at e d by

42d = D × 8 × 240 × 10 3 μg /m 3 fLe 24 365 where L e is the midrang e in each ag e categ ory , f is the fraction of time in ag e ex posed, and 8/24 and 240/365 are the fractions of a day and y ear, respectively , that a worker spent at the plant. F o r insta n c e , if D = 8 mg /m 3 /y ears, L e = 60, and f = 0.65, then d = 44.96 μ g /m 3

. The assumption of f = 0.65 implies that the cohort ex posure to chromium beg a n at approx imately ag e 20. The assumption is that the particular ex posure pattern (unknown) leading to the cancer mortality rates as observed is equivalent to the continuous constant ex posure starting from the ag e when ex posure beg a n. This assumption may or may not be realistic. However, it would be less realistic to make a different assumption concerning the ex posure pattern when the ex posure estimates provided in Mancuso (1975) were determined using the weig hted averag e of the durat i on of ex posure for each respect i v e j ob th e worker had. S i nce th e person-y ear i n each cat eg ory present e d i n Tabl e 2 i s very sm al l , th e ex posure c at e g orie s ar e c o mbine da s shown in Table 4 to inc r e a s e statistic a l stab ility

. The la st c o lumn of Table 4 is g i ven for the purpose of identifyi ng which ex posure categ ories in Table 2 are combined. The midrang e of ag e and ex posure concentration is used in Table 4. Data in this table ar e use dto e s timate the life time c a n c e r risk due to c h romium e x posure . 5.3.4. Extrapolation Method Ithas been widely recog n iz ed (e.g ., Doll, 1971) that the ag e-specific incidence curve tends to be linear on doubly log arithmic g r aphs, or equivalently , the ag e-specific incidence follows the mathe m atic a l form: I ( T) = bT k- l where b and k are parameters that may be related to other factors such as dose, and T may be one of th e fol l o wi ng th ree cases: 1. T i s ag e when cancer i s observed, 2. T is the time from the first e x posure to obse r ve d c a n c e r , or 3. T is the time from e x posure to c a n c e r minus the minimum time for a c a n c e r to be c linic a lly recog n i z ed.

43T a b l e 4. Com b i n ed age-sp eci f i c l u n g can cer d e ath rates an d total ch rom i u m exp o su re (i n μg /m 3 ) Age C oncentration (μ g/m 3 ) Death s P erson -years B a ck grou n d rate b Exposur e ran g e 50 50 50 60 60 60 70 70 5.66 25.27 46.83 4.68 20.79 39.08 4.41 21.29 3 6 6 4 5 5 2 4 1,345 931 299 1,063 712 211 401 345 6.05 × 10 -4 6.05 × 10 -4 6.05 × 10 -4 1.44 × 10 -3 1.44 × 10 -3 1.44 × 10 -3 1.57 × 10 -3 1.57 × 10 -3 � 1.99 2.0-5.99 6.0-7.99

� 1.99 2.0-5.99 6.0-7.99

� 1.99 2.0-7.99

a The m i drang e of each expos ure categ oryin Table 2 is f i rs t conv erted to μ g /m 3 byusing f = 0.65 in the f orm ula des c ribed in the s ection “ d ata av ailable f or potencycalculations .” The concentrations pres e nted in this table are the av erag es of s e v e ral expos ure categ ories w eig hted bycorres ponding pers on- y ears .
b Backg round rate is es tim ated f rom 1964 U

. S

. V ital S tatis tics

. The y ear 1964 is s elected becaus e it is es tim ated that a larg e proportion of lung cancer deaths occurred during that y ear. This model has been shown to arise from the somatic mutation hy pothesis of carcinog enesis (Armitag e and Doll, 1954; Whittemore, 1978; Whittemore and Keller, 1978). It has al so been shown t o ari s e fromth e epi g enet i c hypothesi s when th e reversi b l e cel l u l ar chang e is prog rammed to occur randomly (W atson, 1977). These authors and many others have used this mode l to inte rpre t a nd/or e s timate pote n c y from huma n data
. Sinc e the data thatc ould be use dfor risk e s timation ar e limite d, a simple mode l tha tfits the data should be used. Therefore, the observed ag e-specific incidence is assumed to follow the model I ( t,d) = B ( t) + h(t,d) where B ( t) is the backg r ound rate at ag e t and h(t,d) = Q(d) t k- l with Q(d) = q of dose d. l d + q 2 d 2 , a function

Onc e the para me te rs q l , q 2 , a nd k ar e e s timate d, the life time c a n c e r risk a ssoc i at e dwith a n ex posure d by ag e t, taking into account the competing risk, can be calculated by

t s 44P(t,d) = o � h(s,d)ex p {-[ o � h(y ,d)dy + A(s)] }ds whe r e e x p[-A(s)] is the probability of surviving to a g e s a nd h(t,d) = I ( t,d) - B ( t) is the ag e-specific incidence after adjusting the backg r ound rate. To estimate the parameters in h(t,d) we assume, as is usually done, that the number of lung cancer deaths, X, at ag e t, follows the Poisson distribution with the ex pected value E(X) = N × [ B + Q(d) t k- 1 ] where N is the person-y ear associated with X, B is the backg r ound rate at ag e t, and Q(d) = q l d + q 2 d 2

. Using the B M DP computer prog ram P3R and the theory relating the max imum likelihood and nonlinear least square estimation by J e nnrich and Moore (1975), the parameters q l , q 2 , and k are estimated by the method of max imum likelihood as q l = 1.11 × 10 -7 , q 2 = 1.84 × 10 -9 , and k = 2.915; the corresponding standard deviations are respectively 7.8 × 10 -7 , 1.2 × 10 -8 , and 1.7. Thus, th e ag e-speci fi c cancer death i n ci dence atag e tdue t o chrom i u mex posure d μ g /m 3 is g i ven by h(t,d) = Q(d) t l.915 where Q(d) = 1.11 × 10 -7 d + 1.84 × 10 -9 d 2 The model fits the data well, as can be seen from the g oodness-of-fit statistic

x 2 = � (0-E) 2/E = 1.60 which has, asymptotically , a chi-square distribution with 5 deg r ees of freedom under the model specified. The observed and predicted values used in calculating x 2 are (3, 2.5), (6, 7.2), (6, 5.1), (4, 3.1), (5, 6.7), (5, 4.1), (2, 1.4), and (4, 4.3). Taking into account the competing risk, the lifetime probability of lung cancer death due to e x posure to c h romium d μ g /m 3 is g i ven by L P(L ,d) = o � h(t,d)ex p {-[ ( Q(d)/2.915) t 2.915 + A(t)] }dt whe r e L is the ma x imum huma n life time a nd is mathe m atic a lly e quiva le nt to infinity , sinc e the probability of surviving bey ond L is 0. At low doses approx imately , P(L ,d) = d × P(L , l) 45whe r e P(L , l) is the life time c a n c e r risk due to e x posure to 1 μ g /m 3 of chromium. The unit risk, P(L , l), has been adopted by the EPA as an indicator of the carcinog enic potency of a chemical compound. 5.3.5. Inhalation Unit Risk To calculate the unit risk, P(L ,1) it is necessary to know ex p[ -A(t)] , the probability of surviving to a g e t. Sinc e this probability c a n only be e s timate d, it is a ssume d thatthe surviva l probability is c onsta nt ove r a 5-y e ar inte rva l , a s provide d in the U.S. Vita l Statistic s. Using this approx imation and by integ r ating the formula P(L ,1) we have P(L ,1) = � [ e x p (-3.87 × 10 -8 t i- 1 2.9l5 ) - ex p(-3.87 × 10 -8 t i 2.9l5 )] × P i

= 1.16 × 10 -2/μ g /m 3 where (t i- l , t i ) is a 5-y ear interval and P i is the probability of surviva l up to the a g e t i- l . P i is assumed to be a constant over the interval and is estimated from the 1975 U.S. Vital Statistics. As a crude approx imation, the carcinog enic potency of chromium can be also be cal cul at e d by B = (R -1) × P o/ d, where P o = 0.036 is the estimated lung cancer mortality rate for the U.S. population, R is the relative risk of the lung cancer deaths in the cohort, and d is the

“ s ta ndardize d ” life time dose c onc e n tration to whic h the worke r s we re a ssume d to be e x pose d

. Thi s approach i s used by EP A t o cal cul at e carci nog eni c pot ency when th e onl y dat a avai l abl e are the re lative risk e s timate a nd a n a v e r a g e e x posure c onc e n tration. F o r the Mancuso (1975) data, the relative risk R and the “standardiz ed” dose d are estimated respectively to be R = 7.2 and d = 15.5 μ g /m 3

. They are cal cul at e d by comb i n i n g th e rel at i v e ri sks and dose concentr at i ons i n each of th e ag e-ex posure cat eg ori e s, wei g ht ed by th e relative mag n itude of person-y ears, as shown in Table 4. The r e f ore , the c ar c i nog e n ic pote n c y of he x a va le nt c h romium (CrVI ) is e s timate d to be B = (7.2-1) × 0.036/15.5 = 1.4 × 10 -2/μ g /m 3 This crude estimate is only slig htly hig h er than the previous estimate, 1.2 × 10 -2/μ g /m 3

.
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 pre s e n t in roc k s, soils, pla n ts, a n ima ls, a n d volc a n ic e missions. Chromium ma y e x ist in se ve ra l c h e mic a l forms a nd va le nc e stat e s in the 46envi ronm ent
. The m o stcom m onl y occurri ng val e nce st at es are chrom i u mm e t a l (0), tri v al ent C r ( III) , a n d h e x a v a l e n t C r ( V I)

. T h e p ri m ary s o u r c e s o f h e x a v a l e n t c h r o m i u m i n th e e n v i r o n m e n t ar e most like l y c h romate c h e mic a l s use da s rust inhibitors in c ooling towe rs a nd e mitte d a s mists, partic ulat e matte r e mitte d during ma nufa c ture a nd use of me ta l c h romate s, a nd c h romic a c i d mist from the chromeplating industry

. Hex a valent chromium in the atmosphere may react with dust particles or other pollutants to form trivalent chromium, or may be removed from air by atmospheric fallout and precipitation. Hex a valent chromium may ex ist in aquatic media as wate rsoluble c o mple x a n ions a nd ma y pe rsist in wa te r. He x a va le nt c h romium ma y a l so ma y reactwi th org a ni c m at t e r or other reduci n g ag ent s t o formtri v al entchrom i u m . Hex a val e nt c h romium in soil te nds to be re duc e dto triva l e n t c h romium by org a nic matte r. C r ( III) p o t e n t i at e s th e a c t i o n o f i n s u l i n i n p e ri p h e r a l t i s s u e a n d i s e s s e n t i a lf o r

a n i m a l s a n d huma n be ing s . Adults in the Unite d Stat e s ar e e s timate d to ing e st approx imate ly 60 μ g /da y of chromium from food (ATSDR, 1993). The national Research Council has identified an estimated safe and adequate daily dietary intake (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 (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) , t houg h absorption of ing e sted he x a va le nt c h romium is e s timate d to be le ss tha n 5%. F o llowing inha lation e x posure , c h romium may be absorbed into the sy stemic circulation, transferred to the g a strointestinal tract by mucociliary action, or remain in the lung

. A number of factors can influence the absorption of chromium following inhalation, including the size, ox idation state, and solubility of the chromium particles; the activity of alveolar macrophag e s; and the interaction of chromium with biomolecules following deposition in the lung

. Inhaled hex a valent chromium can be reduced to the trivalent form by ascorbate and g l utathione. Absorption of inhaled chromium 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

. W ater-soluble hex a valent chromium has been shown to be absorbed rapidly by inhalation in rats. A 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 very low efficiency

. Cr(VI ) readily passes throug h cell membranes and produces a number of potentially mutag e nic DNA lesions upon intracellular reduction to Cr( III)

. H e x a v a l e n t c h r o m i u m is mutag e nic in bacterial assay s , y easts, and V79 cells, and transforms both primary cells and cell line s . Results of occupational epidemiolog i c studies of chromium-ex posed workers across investig ators and study populations consistently demonstrate that chromium is carcinog enic by the inhalation route of ex posure. W h ile data from these studies could be used to sug g e st that total chromium is carcinog enic by inhalation, animal data support the human carcinog enicity data 47only on hex a valent chromium. Hex a valent chromium compounds have been shown to produce the following tumor type s in a n ima l a ssa y s : intra m usc u lar inje c tion site tumors in ra ts a nd mic e , intrap le ura l impla nt site tumors in ra ts, intrab ronc hia l impla ntation site tumors in ra ts, a n d s u b c u t a n e o u s i n j e c t i o n s i t e s ar c o m a s i n r at s . W o rk e r s ar e e x p o s e d t ob o th C r ( III) a n d C r ( V I) compounds. Because only Cr(VI ) has been found to be carcinog enic in animal studies, however, it was concluded that only Cr(VI ) should be classified as a human carcinog en. At present, the carcinog enicity of hex a valent chromium by the oral route of ex posure cannot be determined because of a lack of sufficient epidemiolog i cal or tox i colog i cal data. One study of miners in Ontario sug g e sted that ex posure to chromium may have been associated with stoma c h c a n c e r , but othe r huma n a nd a n ima l studie s ha ve not re porte d similar e ffe c t s. A number of epidemiolog i cal studies of workers in chromium production facilities have demonstrated an association between inhalation of Cr(VI ) and upper respiratory irritation and atrophy , lower respiratory effects, and renal effects. There is sig n ificant uncertainty reg arding the relevance of occupational ex posures to chromic acid mists to environmental ex posures to hex a valent chromium particulates, as well as the role of direct contact between chromiumcontaminated hands and nasal passag e s in the studies reporting nasal irritation, atrophy , and nasal se ptum pe rforation in the oc c upationa l se tting

. Anima l studie s ha ve re porte d a varie t y of e ffe c t s including perforation of the nasal septum, necrosis, atrophy and hyperplasia of the bronchial epithelium, bronchioliz ation of the alveoli, alveolar proteinosis, chang e s in lung weig ht, lactate dehy drog enase in B A LF , albumin in B A LF , chang e s in tracheal and submandibular lymph nodes, atrophy of the spleen and liver, and ulcerations in the stomach and intestinal mucosa following ex posures to Cr(VI ) compounds by inhalation (Steffee and B aetjer, 1965; Nettesheim et al., 1971; Glaser et al., 1985; Glaser et al., 1990). Little data e x ist re g arding he a lth e ffe c t s re sulting from ing e stion of he x a va le nt c h romium. A sing le c r oss-se c tiona l study wa s loc at e dthatre porte d e ffe c t s in huma n s re sulting from ing e stion of c h romium-c onta minat e dwe ll wa te r. Re side nts of a villa g e in China we re re porte d to have ex perienced oral ulcers, diarrhea, abdominal pain, indig e stion, vomiting , leukocyt osis, and presence of immature neutrophils. Other reports of tox i c effects of Cr(VI ) in humans are limited to case reports from accidental poisoning s. W ith the ex ception of increased body burden of chromium, no sig n ificant adverse effects have been observed in animal studies following ing e stion of c h romium. Hig h oral doses of hex a valent chromium compounds have been reported to cause reproductive and developmental tox i city in mice, including decreased fetal weig ht, increased resorptions, and increased abnormalities. A recent study in mice and rats determined that hex a valent chromium is not a reproductive tox i cant in either sex

. 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 chromeplating baths, chrome colors and dy es, cement, tanning ag ents, and wood preservatives.

486.2. DOSE RESP ONSE The data of Mancuso (1975) were used to g e nerate the unit risk for inhalation of hex a valent chromium of 1.2 × 10 -2/μ g /m 3

. A recent follow-up study (Mancuso, 1997) is supportive of the conclusions of Mancuso (1975); however, several important uncertainties in the potency estimate result from the use of the Mancuso data for the dose-response estimation. The risk of he x a va le nt c h romium is e s timate d on the ba sis of the tota l c h romium obta i ne d fromal l th e sol ubl e and i n sol ubl e chrom i u mt o whi c h workers were ex posed. S i nce th ere are likely differences between the chromium compounds to which workers were ex posed, the potency of hex a valent chromium compounds may be underestimated. B ourne and Yee (1950) r e p o rt e d th at th e r at i o s o f C r ( III) t oC r ( V I) c o n c e n tr at i o n s i n th e a i r b o rn e d u s t i n n i n e m a j o r departments in the plant in which the Mancuso cohort worked rang ed from 1 to 3, ex cept for two de partme nts whe r e the ratios we re 6 for the lime a nd a s h ope ra tion a nd 52 for the ore preparation. Ex cluding the ore operation, the max imum ratio of trivalent chromium to hex a valent chromium is 6, and thus the underestimation of the risk for hex a valent chromium is unlikely to be g r eater than sevenfold. Use of the hy g i ene data collected in 1949 may result in a slig ht underestimation of the levels of ex posure workers ex perienced between 1931 and 1937. However, because the plant was relatively modern in the 1930s, the underestimation is unlikely to be larg e. I f an underestimation of 2 times were assumed, then the unit risk would be reduced from 1.2 × 10 -2/μ g /m 3 to 6 × 10 -3 /μ g /m 3

. The risk pre s e n te d in this re port ma y be some wha tove re stimate d a s a re sult of the a ssumption thatsmoking habits of c h romate worke r s we re similar to those of the g e ne ra l white male population. Itis g e nerally accepted that the proportion of smokers is hig h er for industrial workers (thus the hig h er backg r ound incidence rates) than for the g e neral population. F o r ex ample, the backg r ound ag e-specific rate of lung cancer at ag es 50, 60, and 70 could be 40% g r eater than that presented in Table 4 should it be assumed that 80% of the chromate workers in the Mancuso study were ever-smokers (individuals who smoke at least 100 cig arettes during their lifetimes) and only 50% of the g e neral white male population were ever-smokers. F o r ex ample, if the backg r ound rate of lung cancer mortality (due to smoking ) for the cohort in Table 4 is increased by 40%, then the corresponding unit risk would be reduced by about 25%, or from 1.2 × 10 -2/μ g /m 3 to 8.7 × 10 -3 /μ g /m 3

. Re lative l y fe w studie s in the lite rature a ddre ss the ora l tox i c ity of Cr(VI )

. The Z h a n g a n d Li (1987) human study reported on health effects in 155 Chinese villag e rs who consumed drinking water contaminated with hex a valent chromium at 20 ppm. Only one ex posure level was included and the study did not indicate whether the drinking water was contaminated with other materials in addition to hex a valent chromium. The study also did not address whether potential airborne ex posures to hex a valent chromium from the plant or other confounding factors may have contributed to observed effects. The ex posure period was unknown, and the study could not provide a NOAEL for the observed effects. However, the study of Z h ang and Li sug g e sts that

49g a strointestinal effects in humans may occur at an ex posure level of 20 ppm of hex a valent c h romium in drinking wate r. Two studies have reported fetotox i c and developmental effects of Cr(VI ) in mice and rats at ex posure levels of 250 - 700 ppm in drinking water (J unaid et al., 1996; Kanojia et al., 1996). W h ile neither of these studies provide clear NOAEL values, L OAEL s for fetotox i city can be used to ex trapolate to NOAEL s of 6.7 mg /kg

- day and 3.7 mg /kg

- day in mice and rats, respect i v el y . B o th the MacKenzie et al. (1958) and Anwar et al. (1961) animal studies are limited by a small number of animals/g roup and a lack of an observed effect at any dose level. The MacKenzie et al. study has the additional limitation of being conducted for less than a lifetime. However, the MacKenz i e study was considered to be most suitable for the dose-response assessment for ing e sted chromium and g e nerated an adjusted NOAEL of 2.5 mg /kg

- day

. The adjusted NOAEL from the MacKenz i e study was modified by two 10-fold uncertainty factors to account for the ex pected interspecies and interhuman variability in lieu of specific data. An additional threefold uncertainty factor is applied to the adjusted NOAEL to c o mpe n sate for the le ss-tha n -life time e x posure duration in the Ma c k e n zie study

. A modifying factor of 3 is applied to account for uncertainties resulting from study of Z h ang and Li

. The total uncertainty factor applied to the adjusted NOAEL is 900, yi elding an RfD of 3 × 10 -3 mg /kg

- da y . C onfi d ence i n th e oral reference dose i s l o w. C onfi d ence i n th e chosen study i s l o w because of the small number of animals tested, the small number of parameters measured, and the lack of tox i c effect at the hig h est dose tested. Confidence in the database is low because the supporting studies are of equally low quality , because of concerns raised by the study of Z h ang and Li , and because of the lack of information on teratog e nic endpoints. L o w confidence in the RfD follows. Two RfCs have been g e nerated for hex a valent chromium. The RfC for chromic acid mists and dissolved hex a valent chromium aerosols is based on a study of workers in a chromium plating facility (Lindberg and Hedenstierna, 1983). The occurrence of nasal mucosal atrophy in the Li ndberg and Hedenstierna study is consistent with previous reports that ex posure to chromium acid mists is associated with ulceration of the mucous membranes and perforation of the cartilag i nous portions of the nasal septum (Hamilton and Hardy , 1974). Several uncertainties result from the ex posure characteriz ation in the Li ndberg and Hedenstierna (1983) study

. W h ile nasal mucosal atrophy has been consistently reported following occupational ex posure to chromic acid mists, it is uncertain whether these ex posures are relevant to ex posures to hex a valent chromium particulates in the environment. The L OAEL for this study is based on an 8-hour TW A concentration. However, it is possible that the ex posure response may be better ex plained by the peak ex posure rather than the TW A dose. The authors acknowledg e that nasal septum ulcerations and perforations did not correlate with mean ex posure concentrations in the 2-20 μ g /m 3 g r oup and observed that damag e to the nasal septum correlated better with short-term peak ex posure than with 8-hour mean ex posures. The report does not provide sufficient detail on peak ex posures to resolve this issue unequivocally , and in the absence of additional data, the RfC was g e nerated based on the TW A ex posure. The RfC 50based on Li ndberg and Hedenstierna (1983) is applicable only to chromic acid mists and dissolved hex a valent chromium aerosols. Confidence in the RfC for chromic acid mists and dissolved hex a valent chromium aerosol s i s l o w. C onfi d ence i n th e chosen study i s l o w because uncert a i n t i e s reg ardi n g th e ex posure charact eri z at i on and th e rol e of di rectcont actfor th e cri t i cal effect

. C onfi d ence i n th e database is low because the supporting studies are equally uncertain with reg ard to the ex posure characteriz ation. L o w confidence in the RfC follows. The RfC for hex a valent chromium particulates was developed based on Glaser et al. (1985, 1990). Several uncertainties are associated with the use of these studies for development of the RfC. Glaser et al. (1985, 1990) did not provide details of upper respiratory , reproductive, or re na l e ffe c t s re sulting from the e x posure s , a nd did not inc l ude c h romic a c i d mists or dissolve d he x a va le nt c h romium a e r osols in the i r study

. This unc e rta inty ha s be e n a ddre sse d by limiting the RfC developed on the basis of Glaser et al. (1985, 1990) to lower respiratory effects from inhalation of hex a valent chromium dusts. Uncertainty results from the use of a subchronic study for development of the chronic RfC. This uncertainty was addressed by the use of a 10-fold uncertainty factor to account for potential chronic effects. Itis uncertain which of the endpoints reported in Glaser et al. (1985, 1990) is most appropriate for development of the B M C. LDH in B A LFwas used for development of the RfC, as this endpoint is considered to be a sensitive indic at or of tox i c ity a nd provide s the most c onse r vative e s timate of the B M C ba se d on the Gla s e r et al. (1985, 1990) data. Uncertainty in the dose-response curve for LDH in B A LFwas addressed throug h the use of a conservative model fit of the data. Confidence in the RfC for hex a valent chromium particulates is medium. Confidence in the chosen study is medium because of uncertainties reg arding upper respiratory , reproductive, a nd re na l e ffe c t s re sulting from the e x posure s . Me dium c onfide n c e in the RfC follows.

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58Malsch, PA; Proctor, DM; F i nley , B L . (1994) Estimation of a chromium reference concentration using the benchmark dose method: a case study . Reg l Tox i col Pharmacol 20:58-82.

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60Raffetto, G. (1977) Direct interaction with cellular targ ets as the mechanism for chromium carcinog enesis. Tumorig e nesis 63:503-512. Rosenman, KD; Stanbury , MS. (1996) Risk of lung cancer among former chromium smelter workers. Am J Ind Med 29:491-500. Roy l e, H. (1975) Tox i city of chromic acid in the chromium plating industry (2). Environ Res 10:141-163. Saner, G; Yuz b asiy an, V; Cig d em, S. (1984) Hair chromium concentration and chromium ex cretion in tannery workers. B r J Ind Med 41:263-266. Sano, T; Mitohara, I

. (1978) Occupational cancer among chromium workers. J pn J Chest Disorders 37:90-101. Sarto, F ; Ceminato, I ; B i anihi, V; et al. (1982) In creased incidence of chromosomal aberrations and si st er chrom at i dex chang e s i n workers ex posed t o chrom i c aci d (C rO 3 ) i n el ectropl at i n g factories. Carcinog enesis (L ondon) 3:1011-1016. Sary an, LA ; Reedy , M. (1988) Chromium determinations in a case of chromic acid ing e stion. J Anal Tox i col 12:162-164. Satoh, H; F ukuda, Y; Terii, K; et al. (1981) Epidemiolog i c study of workers eng a g e d in the manufacturing of chromium compounds. J Occup Med 23(12):835-838. Silverstein, M; Mirer, F ; Kotelchuck, D; et al. (1981) Mortality among workers in a die-casting and electroplating plant. Scand J W o rk Environ Health 7(4):156-165. Snow, ET. (1994) Effects of chromium on DNA replication in vitro. Environ Health Perspect 102(Suppl. 3):41-44. Sorahan, T; B u rg ess, DC; Waterhouse, J A . (1987) A mortality study of nickel/chromium platers. B r J Ind Med 44:250-258. Spruit, D; van Neer, F C J

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61Steinhoff, S; Gad, SC; Hatfield, GK; et al. (1986) Carcinog enecity study with sodium dichromate in rats. Ex p Pathol 30:129-141. Stella, M; Mentaldi, A; Rossi, R; et al. (1982) Clastog e nic effects of chromium on human lymphocyt es in vitro and in vivo . Mutat Res 101:151-164. Sug i y a ma, M. (1992) Role of phy siolog ical antiox i dants in chromium (VI )-induced cellular injury . Fr ee Rad B i ol Med 12:397-407. Susa, N; Ueno, S; F u rukawa, Y. (1994) Protective effects of thiol compounds on chromateinduced tox i city in vitro and in vivo. Environmental Health perspectives 102(suppl. 3):247-250. Suz uki, Y; F ukuda, K. (1990) Reduction of hex a valent chromium by ascorbic acid and g l utathione with special reference to the rat lung . Arch Tox i col 64:169-176. Suz uki, Y; Homma, K; Minami, M; et al. (1984) Simultaneous determination of chromium in rats ex posed to hex a valent chromium and trivalent chromium aerosols. Ind Health 22:261-267. Takahashi, K; Okubu, T. (1990) A prospective cohort study of chromium plating workers in J apan. Arch Environ Health 45:107-111. Tay l or, F H . (1966) The relationship and duration of employment as reflected by a cohort of chromate workers. Am J Public Health 56:218-229. Todd, GE. (1962) Tobacco manufacturers’ standing committee research papers. No. 1. Statistics of smoking in the United King dom, 3rd ed. L ondon: Tobacco Research Council. Tossavainen A; Nurminen, P; Mutanen, P; et al. (1980) Application of mathematical modeling for a sse ssing the biolog ic a l ha lf-time s of c h romium a nd nic k e l in fie l d studie s . B r J Ind Me d 37:285-291. Trivedi, B ; Saz e na, RC; Murthy , RC; et al. (1989) Embry o tox i city and fetotox i city of orally administered hex a valent chromium in mice. Reprod Tox i col 3:275-278. Tsuda, H; Kato, K. (1977) Chromosomal aberrations and morpholog ical transformation in hamster embry onic cells treated with potassium dichromate. Mutat Res 46:87-94. Umeda, M; Nishimura, M. (1979) Inducibility of chromosomal aberrations by metal compounds in cultured mammalian cells. Mutat Res 67:221-229. U.S. EPA. (1980) Ambient water quality criteria for chromium. Environmental Criteria and Assessment Office, Cincinnati, OH. EPA 440/5-80-035. NTI S PB 81-117467. Available from National Technical In formation Service, Spring field, VA.

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64AP 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 hex a valent 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 perform ed accordance wi th EP A g u i d ance on peer revi ew (U.S . EP A, 1992). Comments made by the internal reviewers were addressed prior to submitting the documents for ex ternal peer review and are not part of this appendix

. The ex ternal peer re vie w e r s we re ta ske dwith providing writte n a n swe r s to g e ne ra l que stions on the ove ra ll 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 c o mme nts follows. C

o m m e n t s on Gen e ral Qu esti o n s for IR IS Peer R evi ew ers 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 : S i nce Mancuso has recently updated his cohort and since the information is al ready referenced i n th e I R I S and th e Tox i col o g i cal R e vi ew docum ent , I bel i e ve th e cancer sl ope factors should be recalculated from the total chromium data and the Cr(VI ) data. Response to Com m e nt: The Ag ency ag rees that the cancer slope factor should be recalculated from the updated cohort. The Ag ency is unable to do so in a time frame consistent with the I R I S Pilot proc e ss, a nd will take up re vision of the slope fa c t or whe n possible

. B . C o mme n t : In calculating the oral reference dose the authors used data from a rodent study by MacKenz i e et al. (1958) and discounted data from a human study by Z h ang et al. I am concerned that the NOAEL in the animal study ex ceeded the level reported in the C h inese study (20 ppm) thatc au se d se rious illne ss in huma n s. Response to Com m e nt: The study of Z h ang and Li (1987) raises concerns for human g a strointestinal effects at hig h dose levels in drinking water; however, the ex posure data in this study are limited, the duration of ex posure is unknown, the presence of confounding factors is not addressed, and a NOAEL could not be identified from the study

. W h ile these uncertainties preclude the use of this study for risk assessment, a threefold modifying factor has been applied to the NOAEL derived from the study of MacKenz i e et al. (1958) to address the concerns raised by the study of Z h ang and Li (1987). C. Com m e n t : Several new reports have been found showing sig n ificant embry o tox i c and f

e t o t o x i cd 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 water. I don’t feel confident rederiving an RfD based on this 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

. 65Response to Com m e nt: The reports have been added to the reproductive/developmental studies section of the tox i colog i cal review document and have been considered in the development of the RfD for Cr(VI )

. The new reports do not provide a clear NOAEL for the fetotox i c and embry o tox i c effects. Ex trapolated L OAEL s derived from the studies of J unaid et al. (1996) and Kanojia et al. (1996) are similar to and support the use of the NOAEL identified in the study of MacKenz i e et al. (1958) for development of the RfD. D. Com m e n t : T h e d o c u m e n t s c o r r e c t l y s t a t 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)

. Response 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 vo, it is 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 l e 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 s u m m ari e 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 : The descriptions of the study used to develop the RfC for chromic acid mist were confusing

. W h ile I ag ree that the L OAEL is 0.002 mg /m 3 , I question the uncertainty factor of 3 to ex trapolate from subchronic to chronic ex posure. Virtually all the workers in the hig h dose level in the Li ndberg cohort had sig n ificant effects even thoug h the duration of ex posure for workers with nasal ulcerations rang ed from 5 mo to more than 10 y ears. Response to Com m e nt: The descriptions of the study of Li ndberg and Hedenstierna (1983) have been improved. The ex perience of workers at the hig h dose level with sig n ificant e ffe c t s ove r a subc hronic e x posure pe riod doe s not e liminat e the possibility tha tsimilar e ffe c t s could occur at considerably lower doses over a chronic ex posure period. In order to account for this uncertainty , the Ag ency favors use of a threefold factor to ex trapolate from the subchronic to chronic ex posures. B . C o mme n t : The authors arg u e th at th e th reefol d uncert a i n t y fact or used by Mal s ch etal . i s insufficient. I disag r ee. In the Glasser paper the concentration in the lung appears to be approachi n g a m a x i m u mat90 day s . The authors al so sug g e st th at i n fl am m at o ry effect s from lowe r long -te rm e x posure s ma y oc c u r. In my e x pe rie n c e infla mmation is a n e ar ly symptom a n d

66in some cases even reg r esses in the presence of continuing ex posure. Thus, I would use Malsch’s calculations as published yi elding a RfC of 0.34 mg /m 3

. Response to Com m e nt: In formation from Glaser (1985) shows that chromium is still accum u l at i n g i n th e l ung and ki dney at th e end of th e 90-day ex posure peri od and th ere i s insufficient information to determine how well subchronic studies predict chronic inflammation. The Ag ency supports the use of a 10-fold uncertainty factor to ex trapolate from a subchronic to a chronic study

. C. Com m e n t : The a dditiona l unc e rta inty fa c t or of 3 (for the RfD) to c o mpe n sate for le ss tha n life time e x posure duration in the Ma c K e n zie e ta l . study c a n be que stione d. Why not apply a

10- fold uncertainty factor for this purpose, based also on the relatively low number of animals used in the study ? Response to Com m e nt: The use of the MacKenz i e et al. study for development of the RfD is considered to be conservative, g i ven the lack of an observed effect in the animals. Even in lig ht of the re lative l y low numbe r of a n ima ls in the study , the thre e f old unc e rta inty fa c t or is considered by the Ag ency 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 the clearest dose-response relationship. If not, what other study ( o r studies) should be chosen and why? A. Com m e n t : A level of 0.002 mg /m 3 in the Li ndberg and Hedenstierna study was chosen as the L OAEL for the RfC. This level caused sig n ificant symptoms, including atrophied nasal mucosa, in workers ex posed, whereas no symptoms were seen at a level of 0.001 mg /m 3

. Therefore, why not use this lower level as a NOAEL ? Response to Com m e nt: Althoug h no subjective irritation occurred in the subg roup ex posed at 0.001 mg /m 3 , the distribution of the four cases of atrophy in this g r oup was not provided, which precluded desig n ation of a NOAEL at 0.001 mg /m 3

. B . C o mme n t : The RDDR is based on aerodynamic diameters of particles used in the animal studies; however, it would be helpful to also know something about ambient particle siz e s containing chromium such that a more appropriate dosimetric adjustment across species using differences in particle deposition between rodents and humans can be applied. Response to Com m e nt: Data on ambient particle siz e s containing chromium are ne c e ssarily site spe c i fic , a nd will vary de pe nding on the nature of the c onta minat e dme dia a n d e x posure se tting

. While it mig ht be of inte re st to de te rmine the a mbie n t partic le size distribution in order to develop a site-specific RDDR, these data cannot be practically incorporated into the RDDR in order to account for all of the possible ambient ex posures. The assessment has utilized the data in the Ag ency ’s g u idance for development of RfCs for this purpose. 67C. Com m e n t : Itappears that the endpoint albumin in bronchoalveolar lavag e fluid showed even g r eater effects than LDH, and I wonder why this endpoint was not selected for the benchmark approach. Response to Com m e nt: LDH in B A LFprovided a B M D approx imately one-half that of albumin in B A LF(Malsch et al., 1994). In order to be conservative and focus on the critical effect, LDH in B A LFwas chosen as the endpoint for development of the RfC. D. Com m e n t : The fact that chromium was still accumulating in lung tissue at the end of a 90- day ex posure does not sug g e st that lower long -term ex posures will lead to accumulation of a critical concentration in the lung

. This depends very much on the clearance kinetics, and at low concentrations lung levels will reach an equilibrium that is lower than that achieved at hig h er concentrations. Response to Com m e nt: The Ag ency acknowledg es the possibility that at low concentrations lung levels will reach an equilibrium which is lower than that achieved at hig h er concentrations. However, in the absence of data, it cannot be demonstrated that chronic ex posures will not lead to accumulation of a critical concentration in the lung

. In order to c onse r vative l y re fle c tthe unc e rta inty on this issue , the Ag e n c y ha s utilize da 10-fold unc e rta inty factor to account for less-than lifetime ex posure.

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 : 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 reports has been added to the reproductive/developmental studies section of th e t o x i col o g i cal revi ew docum ent
. B . C o mme n t : Some of the statements related to the g e notox ic effects of hex a valent chromium are 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.

685. For the noncancer assessments, are there other data that should be considered in developing the uncertainty factors of 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 : No com m e ntrecei ved.

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 non-cancer) 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: Yes.

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. regarding potential reproductive toxicity of Cr( III) in any way countered by the results of the NTP study? A. Com m e n t : The Cr(VI ) document does a superficial job of communicating the deficiencies of the Z ahid study

. Response to Com m e nt: Additional information has been provided in the reproductive/developmental effects section to address this concern.

2. Should separate RfCs be generated for chromic acid mists and particulates of hexavalent chromium? A. Com m e n t : Yes. B . C o mme n t : Ye s, the bioa va ilability a nd phy siolog ic a l e ffe c t s of the s e two forms of c h romium appe ar to diffe r substa ntia lly

. Response to Com m e nts: Separate RfCs have been g e nerated for chromic acid mists and particulates of hex a valent chromium. 3. Should the RfCs apply to both Cr( V I) and Cr( III) or only to Cr( V I) ? A. Com m e n t : The RfCs based on data from Li ndberg and Hedenstierna and Glaser are appropriate only for Cr(VI )

.

694. Are th ere any st udi es avai l abl e that coul d be used to devel op an Rf C

f

o r t r i v al ent chromi um? A. Com m e n t : T h e A g e n c y h a s d e t e rm i n e d th at a n R f C f o r

C r ( III) c a nnot be developed and I ag ree.

5. 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 support a conclusion of carcinogenicity only for hexavalent chromium. Should the potency estimate address total chromium or hexavalent chromium? A. Com m e n t: The potency estimate should be based on total chromium, but should note that th e ex posure i s m i x ed. Response to Com m e nts: EPA will re e v a l ua te the pote n c y e s timate for c h romium ba se d on the recent Mancuso update in the future. B . C o mme n t : The potency estimates should be based on hex a valent chromium. Response to Com m e nt: EPA will re -e va luat e the pote n c y e s timate for c h romium ba se d on the recent Mancuso update in the future.

6. 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 : I believe the Canadian study should not be used to determine an oral slope factor. Response to Com m e nt: The Canadian study has not been used to determine an oral slope factor.

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