Daily Archives: July 19, 2015

Chromium 6 Not Mutagenic in its Mode of Action

Thompson CM, Young RR, Suh M, Dinesdurage HR, Elbekai RH, Harris MA, Rohr AC, Proctor DM. Assessment of the mutagenic potential of cr(VI) in the oral mucosa of big blue® transgenic f344 rats. Environ Mol Mutagen. 2015 May 22. doi: 10.1002/em.21952.

Exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water was associated with an increased incidence of oral tumors in F344 rats in a 2-year cancer bioassay conducted by the National Toxicology Program. These tumors primarily occurred at 180 ppm Cr(VI) and appeared to originate from the gingival mucosa surrounding the upper molar teeth. To investigate whether these tumors could have resulted from a mutagenic mode of action (MOA), a transgenic mutation assay based on OECD Test Guideline 488 was conducted in Big Blue® TgF344 rats. The mutagenic oral carcinogen 4-nitroquinoline-1-oxide (4-NQO) served as a positive control. Mutant frequency was measured in the inner gingiva with adjacent palate, and outer gingiva with adjacent buccal tissue. Exposure to 10 ppm 4-NQO in drinking water for 28 days increased mutant frequency in the cII transgene significantly, from 39.1 ± 7.5 × 10-6 to 688 ± 250 × 10-6 in the gingival/buccal region, and from 49.8 ± 17.8 × 10-6 to 1818 ± 362 × 10-6 in the gingival/palate region. Exposure to 180 ppm Cr(VI) in drinking water for 28 days did not significantly increase the mutant frequency in the gingival/buccal (44.4 ± 25.4 × 10-6 ) or the gingival/palate (57.8 ± 9.1 × 10-6 ) regions relative to controls. These data indicate that high (∼180,000 times expected human exposure), tumorigenic concentrations of Cr(VI) did not significantly increase mutations in the gingival epithelium, and suggest that Cr(VI) does not act by a mutagenic MOA in the rat oral cavity.

Water Quality Criteria for Bisphenol A; China

Lei Guo, Zhengyan Li, Pei Gao, Hong Hu, Mark Gibson. Ecological risk assessment of bisphenol A in surface waters of China based on both traditional and reproductive endpoints. Chemosphere. Volume 139, November 2015, Pages 133–137

Bisphenol A (BPA) occurs widely in natural waters with both traditional and reproductive toxicity to various aquatic species. The water quality criteria (WQC), however, have not been established in China, which hinders the ecological risk assessment for the pollutant. This study therefore aims to derive the water quality criteria for BPA based on both acute and chronic toxicity endpoints and to assess the ecological risk in surface waters of China. A total of 15 acute toxicity values tested with aquatic species resident in China were found in published literature, which were simulated with the species sensitivity distribution (SSD) model for the derivation of criterion maximum concentration (CMC). 18 chronic toxicity values with traditional endpoints were simulated for the derivation of traditional criterion continuous concentration (CCC) and 12 chronic toxicity values with reproductive endpoints were for reproductive CCC. Based on the derived WQC, the ecological risk of BPA in surface waters of China was assessed with risk quotient (RQ) method. The results showed that the CMC, traditional CCC and reproductive CCC were 1518 μg L−1, 2.19 μg L−1 and 0.86 μg L−1, respectively. The acute risk of BPA was negligible with RQ values much lower than 0.1. The chronic risk was however much higher with RQ values of between 0.01–3.76 and 0.03–9.57 based on traditional and reproductive CCC, respectively. The chronic RQ values on reproductive endpoints were about threefold as high as those on traditional endpoints, indicating that ecological risk assessment based on traditional effects may not guarantee the safety of aquatic biota.