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3F - Coastal Zone Mgnt (WEP/183) Effects of organophosphates on estuarine benthic copepods during different seasons:Comparison of sediment toxicity tests and population response in the field. Bollmohr, Silke1, Gehlhar, Maren2, Schulz, Ralf2, 1 Department of Zoology, University of Cape Town, Cape Town, Western Cape, South Africa2 Zoological Institute, Technical University Braunschweig, Braunschweig, Lower Saxony, Germany ABSTRACT- Benthic copepod dynamics were examined in two estuaries in the False Bay, South Africa during different seasons. The one estuary receives organophosphate pollution from surrounding orchards since many years (Lourens estuary) whereas the control one is a natural estuary in the Western Cape without any agricultural impacts (Rooiels estuary). Both estuaries are temporarily open and are exposed to salinity and temperature increase during summer. During the sample period from June to November the natural control estuary showed normal seasonal dynamics with low abundances in winter (June to August) and a significant increase (p=0.043) during spring (Sept. to Nov.) with correlation to increased salinity and temperature. The estuary, receiving organophosphate pollution, showed very low benthic copepod abundances without an increase during spring but with high short-term peaks with no correlation to any abiotic factors. The acute effect of chlorpyrifos- and azinphos-methyl at different salinities (12 ppt and 33 ppt) were conducted using the epibenthic estuarine copepod (<Mesochra parva>), abundant in both estuaries. Under static conditions (96-h LC50) lethal concentrations of chlorpyrifos were lower than azinphos-methyl at both salinities. The toxicity of azinphos-methyl was increasing with higher salinity (LC50= 7.96 Key words: sediment toxicity test, estuary, benthic copepod, organophosphates |
g/kg (12ppt), LC50= 3.76