To detect the incidence and persistence of potential chromosome damage induced by iodine-131 therapy, we applied the cytokinesis-block micronucleus assay to peripheral blood lymphocytes from hyperthyroidism and thyroid cancer patients treated with 131I. Two groups of patients were evaluated in a longitudinal study; one group was composed of 47 hyperthyroid patients and the other of 39 thyroid cancer patients. In the hyperthyroidism group, the micronuclei frequency was determined before 131I therapy and 1 week, 1 month and 3 months after it. Furthermore, an additional sample was taken from a subgroup of 17 hyperthyroidism patients 6 months after treatment. In the thyroid cancer group, the analysis was also conducted over time, and four samples were studied: before treatment and 1 week, 6 months and 1 year later. Simultaneously, a cross-sectional study was performed with 70 control subjects and 54 thyroid cancer patients who had received the last therapeutic dose 1-6 years before the present study. In the hyperthyroidism group a significant increase in the micronuclei average was found over time. In the sample obtained 6 months after therapy, the micronuclei mean frequency was practically the same as in the sample taken 3 months before. In the thyroid cancer group a twofold increase in the frequency of micronuclei was seen 1 week after therapy. Although this value decreased across time, the micronuclei frequency obtained 1 year after 131I therapy remained higher than the value found before it. Concerning the data from the cross-sectional study, a significant increase in the frequency of micronuclei was detected in the subgroup of thyroid cancer patients treated between 1 and 3 years before the current study. These results indicate that exposure to 131I therapy induces chromosome damage in peripheral lymphocytes and that the cytokinesis-block micronucleus assay is sensitive enough to detect the genetic damage by exposure to sufficiently high levels of radiation from internal radioactive sources.

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Sister chromatid exchanges (SCE) and chromosome aberrations (CA) were studied in the lymphocytes of 70 male agricultural workers occupationally exposed to several pesticides and 69 matched controls, without indication of exposure to pesticides, from 'El Maresme' (Barcelona, Spain), Comparison between both groups revealed that the individuals exposed to pesticides show substantial clastogenic effects in their lymphocytes without indication of increases in the basal frequency of SCE; moreover, these effects seem to be additive, increasing with the duration of exposure measured in years. When two confounding factors such as age and smoking habits are considered, we found that these factors increase significantly the expression of SCE although no effect was detected in the expression of CA.

The herbicides alachlor and maleic hydrazide were evaluated for genotoxicity in peripheral blood human lymphocyte cultures. Sister-chromatid exchanges (SCE), chromosome aberrations (CA) and micronuclei (MN) were scored as genetic endpoints. To detect possible metabolic modifications in the genotoxicity of both herbicides, the cultures for SCE and MN demonstration were also treated with S9 fraction. From our results we conclude that, in the absence of metabolic activation, the two herbicides induce significant increases in the frequency of SCE, although the concentrations needed to be effective are very different. Thus, alachlor gave positive results at concentrations ranging from 1 microg/ml, and maleic hydrazide at concentrations ranging from 100 microg/ml. In addition, alachlor appears to be clastogenic in both the CA and MN assays, but only at the highest concentration tested (20 microg/ml). The co-treatment with the S9 fraction produced a slight decrease in the induction of SCE with both herbicides: nevertheless, it does not seem to affect the response in the MN assay.

Two pyrethroid insecticides, cypermethrin and fenvalerate, were tested for their ability to induce chromosome structural aberrations and sister chromatid exchanges in cultured human peripheral blood lymphocytes. Fenvalerate, but not cypermethrin, increased the frequencies of chromosome-type aberrations and sister chromatid exchanges. In addition, both pyrethroids affected the cell cycle causing a decrease in the proliferative rate index at concentrations greater than 10 micrograms/ml.