3. Results
3.1. Salmonella typhimurium assay
The lacustrine source of mutagenic compounds was
identified as coming from the inlet of the Cosia river
[22]. Their mutagenic effects were evaluated by analysing
the water samples from this area. The results (Fig. 2)
showed a higher mutagenic activity of the water samples
if tested with the TA98 strain as opposed to the TA100
one and with the S9 addition as opposed to the
direct assay. The Cosia samples tested with the TA98
strain were all positive and the highest activity was
observed in the summer samples (May and July) to
which S9 had been added, starting froma dose of 0.05 L
equivalent per plate. The greatest activity reached a
Mutagenic Index of 25 by testing May 1998 sample
with the TA98 strain and S9 addition, while the lowest
mutagenic effect was observed in the Cosia sample
collected in November 1998 tested with the TA98
strain without S9 addition. In this last case, the toxic
effect on Salmonella was greater than the effect of the
mutagenicity. The results with the TA100 strain were all
negative, except for a Mutagenic Index of 2 that was
reached only for the May 1998 sample in one sample
concentration.