efsa-opinion-chromium-food-drinking-water

Chromium in food and drinking water
Mammalian cells
Cr(VI) compounds are also mutagenic in mammalian cell lines. Potassium dichromate was reported to
significantly increase mutation frequency at the HPRT locus in Chinese hamster cells AT3-2 and V79
(Paschin et al., 1983), and calcium chromate at the TK locus in mouse lymphoma cells L5178Y
(McGregor et al., 1987). Clastogenic activity (micronuclei, chromosomal aberrations and sister
chromatid exchanges) of Cr(VI) compounds (i.e. calcium chromate, chromic acid, potassium
chromate, potassium dichromate, sodium chromate and sodium dichromate) was reported by several
groups in cultured CHO cells (Levis and Majone, 1979; Bianchi et al., 1980; Koshi and Iwasaki, 1983;
Seoane and Dulout, 1999), mouse mammary FM3A carcinoma cells (Umeda and Nishimura, 1979),
human fibroblasts (MacRae et al., 1979; Seoane and Dulout, 2001; Wise et al., 2002, 2004; Holmes et
al., 2006), human epithelial cells (Wise et al., 2006) and human lymphocytes (Nakamuro et al., 1978;
Sarto et al., 1980; Gomez-Arroyo et al., 1981; Imreh and Radulescu, 1982; Stella et al., 1982). In
general, metabolic activation is not required to detect the mutagenic/clastogenic effects observed in
mammalian cells in culture indicating that Cr(VI) is a direct-acting mutagen.
Repair processes have been shown to modulate Cr(VI)-induced mutagenicity. Reynolds et al. (2004)
showed that human cells efficiently repair chromium−DNA adducts by nucleotide excision repair
(NER) whereas NER-deficient XP-A, XP-C and XP-F cells were severely compromised in their
ability to repair chromium-DNA lesions. Intracellular replication of Cr-modified plasmids
demonstrated increased mutagenicity in cells with inactive NER (see also Mode of action). Brooks et
al. (2008) showed that CHO cells deficient either in NER or base excision repair, grown under the
standard ascorbate-deficient conditions, presented a lower HPRT mutation frequency than wild-type
cells (Brooks et al., 2008). The CONTAM Panel noted that the results of the study may be opposite to
what would be expected, and that the authors postulated that, in the absence of excision repair
processes, DNA damage is channeled into an error-free system of DNA repair or damage tolerance.
Morphological cell transformation has also been reported in BALB/3T3, Syrian hamster embryo, and
the Rauscher leukemia virus-infected Fischer rat embryo cell lines and rat liver epithelial cells
(DiPaolo and Casto, 1979; Dunkel et al., 1981; Briggs and Briggs, 1988).
In vivo assays
Cr(VI) compounds have tested positive for mutations in Drosophila melanogaster in several studies
(Graf and Wurgler, 1996; Amrani et al., 1999; Spano et al., 2001; Kaya et al., 2002) where larvae
were fed the test substance at the lowest effective concentration of 0.1 mM (Amrani et al., 1999).
Positive genotoxicity was observed for Cr(VI) in numerous studies in rats and mice following
administration of Cr(VI) compounds via the parenteral, intratracheal or inhalation route (Table H8,
Appendix H). Contrasting data have been reported when Cr(VI) was admistered orally (summarised in
Table 18 and described in details in Table H7, Appendix H).
The three drinking water exposure positive studies include induction of mutations in a DNA deletion
assay using C57BL/6Jpun/pun mice (Kirpnick-Sobol et al., 2006) and induction of chromosomal
damage in two mouse strains (NTP, 2007). In the study by Kirpnick-Sobol et al. (2006) chromosome
deletions were detected in the offspring of exposed pregnant females (lowest effective dose: 62.5 mg
Cr(VI)/L). Statistically significant increases in micronuclei formation with a dose-response were
observed in peripheral erythrocytes of am3-C57BL/6 mice (lowest effective dose: 43.6 mg Cr(VI)/L),
equivocal results (nearly significant positive trend) in the B6C3F1 strain and no effects in BALB/c
mice (NTP, 2007).
Other studies have reported negative results in bone marrow or peripheral blood cells following oral
exposure to Cr(VI) compounds (Mirsalis et al., 1996; Shindo et al., 1989; De Flora et al., 2006).
Two studies compared the effects of the parenteral versus oral admistration route within the same
experimental setting (Shindo et al., 1989; De Flora et al., 2006). In both cases genotoxicity was
detected when the test item was administered i.p. and negative results were observed when
administered orally in the drinking water or by gavage. In particular, in the study by Shindo et al
(1989) potassium chromate administered to MS/Ae and CD-1 mice by i.p. injection induced the
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