A cocktail of the s-triazines, simazine and atrazine, was introduced into three of four experimental tanks (volume=900 l) that contained a natural estuarine pelagic community from the Pomeranian Bight. Herbicide concentrations in the spiked tanks corresponded to about 10, 100 and 1000 times the background of the control with absolute values of each compound of 0.005 μg l−1 (control) and around 0.04, 0.6 and 6 μg l−1 (spiked tanks). Herbicide concentrations, as well as the response of phytoplankton and bacterial stock and turnover, were monitored over a period of 10 days. Both triazines remained at the initial levels in each system. In spite of high activity of both bacteria and microalgae, no herbicide-specific effect could be observed. This resistance is attributed to the inherent stability of a well established and balanced multi-species regenerating system. The low level of algae–herbicide interaction shows, however, that the coastal system under study has no degradative capacity with regard to those compounds. Riverine inputs will be transferred to the open Baltic with no major decontamination effects.
