Hydrotheek

A study was made of the possible hazards of long-term exposure of freshwater ecosystems to low (< 1 mg m ^-3) concentrations of organophosphorus insecticides. Range-finding, acute and sub-acute (3 weeks) laboratory toxicity trials were carried out with parathion, azinphosmethyl, diazinon, malathion and parathion-methyl. The rates of dissipation of these compounds from the water phase of aquaria with and without plants and sediments were studied. The main test species were Daphnia magna, Asellus aquaticus, Chaoborus crystallinus and Cloeon dipterum. D. magna was the most sensitive species, 3-week no-effect concentrations ranged from 0.1 to 1.2 mg m ^-3) Parathion was the most toxic compound tested. Parathion and azinphosmethyl were tested in 3 x 1 x 1 m outdoor model ecosystems in concentrations < 1 mg m ^-3) over periods of more than 3 months. With a waterproof partition the model ecosystems were divided into two subsystems. Without insecticide treatment these subsystems developed similarly. Insecticide treatment of one subsystem resulted in developments dissimilar to those of the control. Parathion strongly reduced populations of Daphia spp (0.5 and 1 mg m ^-3) Simocephalus vetulus (1 mg m ^-3) Chydorus sphaericus (1 mg m ^-3) and Chaoborus crystallinus (1 mg m ^-3) No effects were observed at 0.2 mg m ^-3) Azinphosmethyl at 1 mg m ^-3) reduced populations of S. vetulus and Daphnia spp. No detrimental effects were observed on Cyclopoida and Ostracoda.