ABSTRACT
The fate and biological effects of the herbicide metamitron (Goltix®) were studied using outdoor “microcosm” ponds (4.5 m3 stainless steel cylinders). The “microcosms” contained a bottom layer of natural lake sediment with benthic organisms plus all trophic levels of planktonic organisms and caged rainbow trout. Two successive applications of the exaggerated dose rates of 5 and 25 kg active ingredient / ha (corresponding to nominal concentrations of 0.4 and 2.0 mg/L water) of metamitron were applied to separate “microcosms” and one other “microcosm” was left untreated. Over a period of 5 months, the effects on the ecosystem (phytoplankton, zooplankton, macrobenthos and fish), and the distribution and fate of the herbicide were examined. Few biological effects were observed even at the higher application rate, despite laboratory results on green algae which indicated a potential hazard to these organisms at both dose rates. The lack of effects on phytoplankton in this study, in contrast to laboratory results, may be explained by the very short half life of metamitron in water under natural conditions.
