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.

Biomarkers of DNA damage in marine mammals.

Certain environmental contaminants found in marine mammals have been shown to cause DNA damage and cancer. The micronuclei (MN), sister chromatid exchange (SCE) and/or chromosome aberration (CA) assays were used to assess baseline (spontaneous) levels of DNA damage in blood lymphocytes of individuals of the relatively healthy and lightly contaminated Arctic beluga whale (Delphinapterus leucas), Sarasota Bay, FL, bottlenose dolphin (Tursiops truncatus) and Northwestern Atlantic grey (Halichoerus grypus) and harp (Phoca groenlandicus) seal populations. MN cell (MNC) frequencies ranged between 2 and 14/1000 binucleated (BN) cells and were statistically similar between species. In bottlenose dolphins, MNC frequency was correlated with age and was significantly higher in females than in males. No intraspecific variation in MNC frequency was found in beluga whales. Intraspecific variation was not tested in seals due to the small sample size. Frequencies of SCEs and total CAs, excluding gaps, ranged, respectively, between 1 and 15 SCE(s)/per cell and 4-6 CAs/100 cells in beluga whales. SCE and CA frequencies did not vary with age or sex in beluga whales. The MN, SCE and CA assays were found to be practical tools for the detection of DNA damage in marine mammals and could be used in the future to compare DNA damage between relatively lightly and highly contaminated populations.

Genotoxic effects of mercury on in vitro cultures of human cells.

Mercury is a highly deleterious environmental pollutant, with recognized mutagenic and teratogenic effects. 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 statistically 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.

Induction of micronuclei in vitro by organochlorine compounds in beluga whale skin fibroblasts.

Beluga whales (Delphinapterus leucas) inhabiting the St. Lawrence estuary are highly contaminated with environmental pollutants and have a high incidence of cancer. Environmental contaminants may be partly responsible for the high cancer incidence observed in this population. DNA damage plays an important role in the development of cancer. The micronuclei (MN) assay was used to test the genotoxic potential of organochlorine (OC) pesticides with and without external metabolic factor in skin fibroblasts of an Arctic beluga whale. Toxaphene, chlordane and p,p'-DDT induced significant (p<0. 05) concentration-response increases of micronucleated cells (MNCs). Statistically significant increases in MNCs, ranging from 1.7- to 5-folds when compared to control cultures, were observed for 0.05, 0. 5, 5 and 10 microg/ml toxaphene, 2, 5 and 10 microg/ml chlordane and 10 and 15 microg/ml p,p'-DDT. Presence of exogeneous metabolic factor (S9) completely abolished the MN induction potency of chlordane and p,p'-DDT, and toxaphene induced MN formation at higher concentrations (0.5 microg/ml) than without S9 mix. The ecotoxicological significance of MN induction by low concentrations of toxaphene is unknown and do not imply that toxaphene is involved in the etiology of cancer in St. Lawrence beluga whales. However, because of the known genotoxicity of toxaphene and the long lifespan of beluga whales, it cannot be excluded that toxaphene may pose a long-term genetic hazard to the more contaminated whales of this population.

Effects of lymphocyte subpopulations on the clonal assay of HPRT mutants: occupational exposure to cytostatic drugs.

The mutagenic effect of occupational exposure to antineoplastic agents was studied in chemotherapy nurses and pharmacists using the T-lymphocyte clonal assay. A significant increase in mutant frequency was observed compared to controls. However, in the present study, cloning efficiency without selection (CEU) was significantly reduced in exposed personnel raising the possibility of an overestimation of the calculated MF. Changes in lymphocyte populations and clonal potential of T-cells were also observed following exposure. CEU was related to % CD4 cells but CE with selection (CETG) was not. Differences in clonal ability of T-cells under selective and unselective conditions coupled with differential lethal effect of antineoplastic agents on lymphocyte subsets may result in inaccurate estimation of MF.

HPRT-mutant frequency and lymphocyte characteristics of workers exposed to ionizing radiation on a sporadic basis: a comparison of two exposure indicators, job title and dose.

Using the clonal HPRT-mutant frequency assay, mutant frequencies of humans have been shown to rise following exposure to large doses of mutagens during radiotherapy, chemotherapy or after an atom bomb explosion. Success in relating mutant frequencies to exposure to high levels of mutagens has encouraged researchers to examine the effects of lower doses, such as those found among workers exposed at their jobs. In order to relate low doses of mutagens to biological effects, accurate characterization of exposure is critical, but most occupational studies are forced to use gross measures of exposure derived from job title or professional judgments as to potential exposure. Mutant frequencies and other relevant lymphocyte characteristics of 58 industrial workers were related to exposure status in two ways. When workers were classed as "exposed" or "unexposed" to ionizing radiation, no difference in any biological variable was seen between the two groups. When dosimeter readings were used as the exposure indicator, significant relationships appeared between dose and mutant frequency and CD4/CD8 lymphocyte subpopulation ratios. Mutant frequency was also positively related to age and smoking status. The time course of exposure and of appearance of mutant cells is discussed and it is suggested that this relationship receive attention in occupational studies of genotoxic effects.

Effect of caffeine on ozone-sensitivity in Saccharomyces cerevisiae.

The addition of 0.1% caffeine to the plating medium markedly reduced the ozone-survival of the wild-type and the rad1 and rad6 mutants of Saccharomyces cerevisiae, whereas no effect was observed in the rad52 mutant. Since, in S. cerevisiae, caffeine has been reported to interfere with the recombinational repair pathway under the control of the RAD52 gene, these results support previous observations suggesting that this pathway is involved in the repair of ozone-induced DNA damage.

Genetic effects of ozone: induction of point mutation and genetic recombination in Saccharomyces cerevisiae.

The mutagenicity and recombinogenicity of the atmospheric pollutant, ozone, were investigated in several strains of Saccharomyces cerevisiae. It was observed that ozone induced a variety of genetic events, such as forward and reverse mutations as well as gene conversion and mitotic crossing-over. However, when compared to known mutagens like ultraviolet light, X-rays and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), ozone appeared to be a weak mutagen.

Ozone response in wild type and radiation-sensitive mutants of Saccharomyces cerevisiae.

The effect of ozone exposure on Saccharomyces cerevisiae was studied. Factors such as ozone concentration, treatment time, media, initial cell concentration and growth phase were shown to influence ozone response in this organism. Logarithmic phase cells were much more sensitive than stationary phase cells to the lethal effect of ozone. The radiation-sensitive mutants rad3, rad6, rad51 and rad52 of S. cerevisiae were exposed, in water, to 50 ppm of ozone for 30 min. On comparing their survival curves, the rad51 and the rad52 mutants showed a greater sensitivity to ozone exposure than the wild type.