Can a pollution event be detected using a single biological effects monitoring method?

The trends of malformation prevalence in embryos of dab, Limanda limanda, i n the southern North Sea after the year 1990 mirrored the drop in major pol lutants in the rivers draining into the German Eight. Despite this general decline, we detected a pollution event in the southern North Sea in winter 1995/1996 employing the prevalence of malformations in pelagic dab embryos as an indicator. An abrupt rise in malformation prevalence ill the embryos of dab, corresponded to a dramatic increase in DDT levels in parent fish fr om the same area, indicating a hitherto unnoticed introduction of considera ble quantities of DDT into the system. (C) 2001 Published by Elsevier Scien ce Ltd.