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Toxicities of methylmercury chloride (CH3HgCl) and methylmercury hydroxide (CH3HgOH) to cultured neuroblastoma cell line SH-SY5Y in vitro are evaluated. This is the comparative study between two methylmercury compounds to find out the extent of toxicity of these compounds are toxic to SH-SY5Y cell line. Both cytotoxicity and genotoxicity experiments were carried out to find out the more toxic compound. For cytotoxicity study, four staining assay methods independently with trypan blue (TB), acridine orange/ethidium bromide (AO/EB), 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT), and neutral red (NR) were used and the comet assay method was done for genotoxicity study. The obtained toxicity data were used for probit analysis. In cytotoxicity, CH3HgCl had minimum inhibitory concentration (MIC) value in each assay method as 3 mg/L invariably; LC25 values were in the range 7.41 to 10.23 mg/L, and LC50 values were 14.79 to 15.48 mg/L; while LC75 values were 20.89 to 26.91 mg/L. Moreover, LC100 value was 30 mg/L, known from comet assay experiments for CH3HgCl. Similarly for CH3HgOH, the MIC value in each assay method was invariably 3 mg/L, the LC25 values were in the range 12.58 to 16.59 mg/L, and LC50 values were 19.49 to 23.44 mg/L; LC75 values were 27.54 to 30.90 mg/L and LC100 value was 42 mg/L in each assay done for cytotoxicity and genotoxicity studies. Computed DNA fragmentation indices in comet assays were 98.6 ± 0.57 30 mg/L with CH3HgCl and 76 ± 5.29 30 mg/L with CH3HgOH. This study clearly indicated that methylmercury chloride is more toxic than methylmercury hydroxide to SH-SY5Y cell line. Toxicity of Hg had been quantified with in vitro cultured human neuroblastoma cell line; since it has neurotoxic effects, its neural evaluation has implications in environmental health issues.

The present study examines the toxicity of HgCl2, using in vitro grown lymphocytes from human umbilical cord blood. Lymphocytes were diluted with Dulbecco’s modified Eagle’s medium, and were grown in the presence of grading doses of HgCl2. The cell-toxicity on grown lymphocytes was assessed using three staining procedures, trypan blue (TB) assay, acridine orange/ethidium bromide (AO/EB) staining and propidium iodide (PI) staining cytologically; and 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay. The standard procedure was carried out for monitoring the live cell density. Additionally, the comet assay was done to ascertain levels of HgCl2 in inducing the nuclear disruption of lymphocytes. Mean results of three independent experiments are presented. Probit-computed lethal concentration (LC) values obtained were in ranges, 5.00–16.22 mg/l as LC25, 13.18–24.54 mg/l as LC50, and 25.12–34.67 mg/l HgCl2 as LC75, respectively at 24 h with incubation with HgCl2, using TB, AO/EB, PI staining procedures and the MTT assay. Experimentally, the minimum inhibitory concentration (MIC), the highest permissive concentration (HPC) and the LC100 values were in ranges, 5, 35–40 and 40–45 mg/l, respectively, for cytotoxicity. With comet assay data, the MIC value was 5 mg/l, whereas the HPC and LC100 values were 35 and 40 mg/l, respectively; and LC25, LC50 and LC75 values were 15.48, 20.41 and 28.84 mg/l HgCl2, respectively. Thus, HgCl2 levels higher than 5 mg/l and below 40–45 mg/l were toxic to in vitro cultured human lymphocytes.