212 vivo and in vitro before and following primary short-term exposure to Pirimor was undertaken. The frequency of cells with chromosome aberrations in all the occupational groups examined was significantly increased in comparison with the matched controls. In spite of the interindividual variation each substance was characterized by its own 'limit of saturation' of the maximum level of aberrant metaphases. This did not depend on the length of working time under constant conditions. The value of chromosome aberrations showed no obvious differences in repeated (with 1-year interval) observations on workers exposed to zineb. In the case of Pirimor the clastogenic effect was observed already 4 days after the initial exposure. The similarity of these data and results obtained when the maximum effective concentration of Pirimor was used in vitro (5.0-4.8% aberrant metaphases respectively) permits one to suggest that the frequency of chromosome aberrations in occupational groups even after short-term contact with chemical is close to maximum level. These results confirming the mutagenic hazards of ziram, zineb and Pirimor to somatic human cells were sufficient to work out the hygienic recommendations for a restricted exposure level of workers to these pesticides and to regulate their use in agriculture.
91 Platonova, V.I., Institute of Medical Genetics, Moscow (U.S.S.R.)
Dynamics of sister-chromatid exchanges (SCE) induced by thiophosphamide The regularity of SCE arising in dependence on thiophosphamide concentration and time of culture fixation was investigated. Human lymphocyte cultures were treated by thiophosphamide in concentrations of 0-25 m g / m l at 60 and 96 h before fixation. At 36 h before fixation the cultures were treated by BrdU. Metaphases in the second mitosis were analysed for SCEs. It was found that the number- of SCEs per cell is increasing in direct proportion to the substance concentration and is decreasing exponentially with time of culture fixation under constant exposition to BrdU.
92 Plooy, A.C.M., M. Van Dijk, S. Bonatti and P.H.M. Lohman, Medical Biological Laboratory TNO, 2280 AA Rijswijk (The Netherlands)
Platinum compounds with anti-tumour activity 10 platinum compounds, comprising both Pt(II) and Pt(IV) complexes, with different ligands, were studied. The cis compounds tested were known to possess (some) anti-tumour activity, the trans isomers were inactive. Tested were: cytotoxicity, mutagenicity, induction of chromosomal damage, of DNA damage and of DNA repair, and binding of Pt to the DNA, in cultured Chinese hamster ovary cells.