Mutagenic activity and presence of the strong mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2-(5H)-furanone (MX) in chlorinated raw and drinking waters in The Netherlands.

Chlorinated surface and drinking waters in The Netherlands were analysed for mutagenic activity (Ames test) and the strong mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Mutagenic activity and MX were formed during chlorine treatment of raw surface waters and purified surface water. Mutagenicity was also present in finished drinking waters which had been subjected to post-chlorination, but no MX could be detected. It is proposed that the mutagens responsible for most of the activity are acidic compounds as they were mainly extractable under acidic conditions. The precursors to the mutagenic compounds formed during post-chlorination of drinking water were efficiently removed by use of ozonation/activated carbon filtration. On the other hand, coagulation (Fe(III] in the presence of activated carbon powder seemed to have hardly any effect on the mutagen precursors. The calculated mutagenicity contribution from MX to the observed TA100 activity in the waters studied was less than 20%.