Connor, TH; Barrie, MD; Theiss, JC; Matney, TS; Ward, JB
Formalin (50000) mutagenicity in Salmonella-typhimurium was studied. Formalin, diluted in distilled water and used immediately, was tested for mutagenicity in Salmonella-typhimurium strains TA-100, TA-98, UTH-8414, and UTH-8413 via plate incorporation assays. In order to facilitate the investigation of S9 requirements, all component concentrations were held constant while S9 was used in volumes of 50, 100, or 150 microliters per plate. All other tests were performed using S9 obtained from Aroclor induced male Sprague-Dawley-rats in a volume of 150 microliters per plate. When formalin was tested up to toxic concentrations, the TA-100 strain and, to a slight extent, the TA-98 strain exhibited mutagenic responses. Strains UTH-8414 and UTH-8413, which are identical to the TA-100 and TA-98 strains except that they are capable of excision repair, were not mutated by formalin. A formaldehyde content of 60 to 70 micrograms (microg) usually produced the greatest number of revertants per plate in both the TA-100 and TA-98 strains. Above this dose, TA-98 strain revertant populations declined until toxicity was reached; however, a second peak was consistently observed near the 100microg per plate concentration in the TA-100 strain. The UTH-8414 and UTH-8313 strains were less susceptible to the toxic effects of formalin, implying that this substance induces repairable DNA damage, although increased mutagenicity was not noted at the higher doses. S9 reduced formalin toxicity in all strains tested, with concentrations of 100 and 150 microliters per plate producing similar mutagenic responses in the TA-100 strain, while a 50 microliter per plate concentration produced a lesser response. Without S9, a small reproducible revertant increase was noted in the TA-100 strain; however, the addition of S9 always produced greater increases. The authors conclude that mutagenicity in Salmonella-typhimurium decreases with an increase in the age of undiluted formalin, suggesting the formation of a less mutagenic species. Excision repair appears to be capable of repairing the genetic damage caused by formalin and, to some extent, the lethal effects of this substance.