Ames test was carried out as standard plate incorporation test11 with Salmonella typhimurium strains TA97a, TA100 and TA1535 with and without in vitro microsomal activation (by S9 rat liver homogenate). Strain specific genetic markers were verified prior to use. Mutagenic activities were expressed as induction factors, i.e. as multiples of the background levels. The results were considered positive if the tested sample produced a response which was at least twice as high as
the one found with the negative control.