Transformation of 2,4-dichlorophenoxyacetic acid in four different marine and estuarine sediments: effects of sulfate, hydrogen and acetate on dehalogenation and side-chain cleavage

Enrichments initiated with marine and estuarine sediments from the Arthur Kill (NY/NJ estuary) and Paleta Creek (San Diego Bay, CA), transformed 2,4-dichlorophenoxyacetic acid to 4-chlorophenol in the presence of sulfate (25 mM). Transformation of 2,4-dichlorophenoxyacetic acid was not observed with two other marine sediments from Tuckerton, NJ and Flax Pond (Stony Brook, NY). The lag period prior to 2,4-dichlorophenoxyacetic acid loss or the time required for 50% removal of 2,4-dichlorophenoxyacetic acid (t(50)) in Arthur Kill and San Diego enrichments was not affected by the presence of sulfate, although the addition of hydrogen and acetate decreased the lag periods and t(50) values in these enrichments. The first step in the transformation or 2,4-dichlorophenoxyacetic acid was side-chain removal forming 2,4-dichlorophenol which was then dechlorinated to 4-chlorophenol. Second-generation Arthur Kill cultures dechlorinated 2,4-dichlorophenoxyacetic acid to 4-chlorophenoxyacetic acid. This dechlorination occurred both in the presence and absence of sulfate (25 mM); however, sulfate reduced the rate of dechlorination by approximately 50%. Second-generation cultures inoculated with the sulfate-amended enrichments consumed sulfate and dechlorinated 2,4-dichlorophenoxyacetic acid to 4-chlorophenoxyacetic acid concurrently when supplied with hydrogen and acetate; the rate of dechlorination was twice that of cultures that did not receive hydrogen and acetate. Sulfate consumption occurred only in cultures supplemented with hydrogen and acetate. These results indicate that dechlorination or an organochlorine pesticide in marine and estuarine sediments occurs in the presence of sulfate and the addition of readily utilizable carbon and electron donors can stimulate dechlorinating activity.