Cytogenetic damage related to low levels of methyl mercury contamination in the Brazilian Amazon

The mercury rejected in the water system, from mining operations and lixiviation of soils after deforestation, is considered to be the main contributors to the contamination of the ecosystem in the Amazon Basin. The objectives of the present study were to examine cytogenetic functions in peripheral lymphocytes within a population living on the banks of the Tapajós River with respect to methylmercury (MeHg) contamination, using hair mercury as a biological indicator of exposure. Our investigation shows a clear relation between methylmercury contamination and cytogenetic damage in lymphocytes at levels well below 50 micrograms/gram, the level at which initial clinical signs and symptoms of mercury poisoning occur. The first apparent biological effect with increasing MeHg hair level was the impairment of lymphocyte proliferation measured as mitotic index (MI). The relation between mercury concentration in hair and MI suggests that this parameter, an indicator of changes in lymphocytes and their ability to respond to culture conditions, may be an early marker of cytotoxicity and genotoxicity in humans and should be taken into account in the preliminary evaluation of the risks to populations exposed in vivo. This is the first report showing clear cytotoxic effects of long-term exposure to MeHg. Although the results strongly suggest that, under the conditions examined here, MeHg is both a spindle poison and a clastogen, the biological significance of these observations are as yet unknown. A long-term follow-up of these subjects should be undertaken.

Genotoxic effects of mercury on in vitro cultures of human cells

Mercury is a highly deleterious environmental pollutant, with recognized mutagenic and teratogenic efects. Given this, we evaluated the changes induced in vitro by two mercury compounds (mercury chloride - MC - and methyl mercuric chloride - MMC) on the genetic) material of a human lymphoblastoid cell line (TK6) on the basis of both the frequency of mutations at the hprt locus, and the number of chromosomic anomalies. The frequencies of HPRT mutants in the TK6 cell line following exposure to the mercury compounds are inconclusive with regard to a mutagenic effect. However, both mercury compounds exhibit a clear cytotoxic effect, which increases with dosage. There was also no statiscally significant increase in the frequency of chromosomic bleakage or gaps, nor in the number of cells with chromosomic alterations in the lymphoblastoid line. Nevertheless, MMC did provoke a marked reduction in the frequency of mitosis, both on its own and in combination with MC.