Abstract

In situ experiments using an injection/withdrawal system were done with five pesticides (atrazine, mecoprop, dinoseb, 1,3-dichloropropene and propachlor). Pesticides and a tracer (bromide) were injected 7 m below surface and withdrawn again 1.5 m downstreams. At the Bilthoven aquifer transformation of dichloropropene was found, the other pesticides (atrazine, dinoseb and propachlor) didn't interact with the aquifer material. At the Veendam aquifer dinoseb was completely retarded indicating degradation within two days. Dichloropropene was, as in Bilthoven, transformed and this is in agreement with laboratory research in which dichloropropene was hydrolysed. Atrazine was sorbed to the aquifer material and the partition coefficient was in the same order of magnitude as found in laboratory experiments. For propachlor retention was found. It was not clear, however, whether this retention was caused by sorption or by transformation or both. The Veendam aquifer is more reactive to pesticides than the Bilthoven aquifer and this is possibly caused by the difference in redox potential. The injection/withdrawal system is a good method to study the behaviour in aquifers.