Mutagenicity and alkylating activity of the aqueous chlorination products of humic acid and their molecular weight fractions

Abstract

Fluka humic acid used as a model substrate in these studies was analysed for elemental and the oxygen-containing functional groups. It was chlorinated at C:Cl molar ratios of 1:1 and 1:0.3 and subsequently separated into molecular weight fractions by ultrafiltration. The freeze-dried, chlorinated humic acid and the respective molecular weight fractions were analyzed for TOC, TOX, alkylating activity using 4-( p-nitrobenzyl)pyridine and mutagenicity by the Ames/Salmonella/ microsome assay with strains TA-98 and TA-100. Results indicated that predominantly non-volatile, direct-acting mutagenic and/or alkylating agents were formed during humic acid chlorination and that these agents were unevenly distributed among the various molecular weight fractions. Formation of mutagenic and akylating agents were highly dependent upon level of chlorination and total organic carbon. Higher levels of mutagenic and alkylating activities were produced with increasing concentration of chlorine in the range of 0.4–1.2 chlorine equivalents per mole of carbon. However, both these activities in the freeze-dried, chlorinated humic acid solutions containing the non-volatiles or the fresh solutions decreased gradually with increasing pH and storage time, apparently due to degradation and hydrolysis of some of the components.