Effects of SO2 or NOx on toxic and genotoxic properties of chemical carcinogens. I. In vitro studies.

This paper describes in vitro studies on the effects of environmental pollutants (SO2/NOx) in biological systems. Basic physical, chemical and biochemical parameters were analyzed to establish the rate of SO2/NOx absorption by the culture medium. It was shown that the pH remains constant for 24 h of exposure to gas concentrations up to 50 p.p.m. The concentration of ions resulting from absorption of each pollutant in the liquid phase is dependent on their concentration in the gas phase and on exposure time. Short exposure times and high gas dosages resulted in similar doses in the medium as long exposure periods and low gas dosages. The activities of a human serum standard (alkaline phosphatase, ALP; aspartate amino transferase, AST; alanine amino transferase, ALT; gamma-glutamyltransferase, gamma-GT; lactate dehydrogenase, LDH) were determined after gaseous exposure to SO2 and NOx. The results revealed a distinct decrease in the activity of LDH after 1, 3 and 5 h exposure to 200 p.p.m. SO2. The effects of the pollutants were assayed in vitro using fetal hamster lung cells (FHLC), rat hepatocytes and the cell line CO60. For the determination of toxic effects, it was shown that the plating efficiency was a more sensitive parameter than the assay for trypan blue exclusion. Toxicity indicated as an increase of LDH leakage was not observed from FHLC in culture. Instead, a decrease of LDH was found following SO2 exposition. This decrease was similar to that observed for the human serum standard. The induction of DNA single-strand breaks was determined as a measure of genotoxic effects. SO2 application decreased the rate of DNA single-strand breaks induced by N-nitroso-acetoxymethyl-methylamine in both FHLC and in rat hepatocytes. SO2 or NOx treatment of CO60 cells for 1 h did not result in the induction of DNA amplification. HSO3- added directly to the medium as the sodium salt, however, distinctly induced the amplification of SV40 DNA. The amplification rates induced by benzo[a]pyrene or dimethylbenzanthracene were neither influenced by SO2, NOx nor HSO3-. An additive effect of HSO3- with either benzo[a]pyrene or dimethylbenzanthracene for this biological parameter was therefore not observed.