|Full text PDF:||http://rudar.ruc.dk/handle/1800/17566|
Acetylcholinesterase-inhibiting pesticides such as organophosphates and carbamates can cause adverse effects in non-target organisms. In the aquatic environment, the presence of pesticides can occur in pulses following e.g. surface run-off or spray drift after field application. The aim of this study was to investigate short-term and long-term effects of single pulse exposures of the organophosphate insecticide malathion and the carbamate insecticide pirimicarb. Acute toxicity tests were performed in order to evaluate effects of pirimicarb and malathion on daphnids, the endpoint being immobilization. The estimated EC50-48h of malathion and pirimicarb was used to determine the single pulse concentrations to be used in the single pulse exposure experiments which lasted for 21 days. The hypothesis for the pulse exposure experiments was that if the Area Under the Curve (the exposure time x concentration product) was the same for the treatments with either malathion or pirimicarb, the effects would be similar. The endpoints for the single pulse exposure experiments were growth, time to first offspring and the number of living offspring. D. magna (age < 24 h) were exposed to equal integrated pulses (the Area Under the Curve was kept constant) with malathion in nominal concentrations of 0.5, 1.0 and 8.0 µg/L for 48, 24 and 3 hours exposure, respectively. For pirimicarb exposure nominal concentrations were 7.5, 15 and 120 µg/L for 48, 24 and 3 hours exposures, respectively. Based on the pulse experiments with pirimicarb and malathion, it was found, that the chosen concentrations and exposure periods resulted in a significant effect on the average number of offspring pr. test animal compared to the controls. There were no differences in average number of offspring between long pulse exposure with high concentration and short pulse exposure with low concentration for both malathion and pirimicarb. The treatments with malathion, resulted in no significant change in the growth, whereas 2 of the three treatments with pirimicarb gave a significantly poorer growth of D. magna compared to the controls. D. magna exposed to pirimicarb and malathion had a delayed time to first offspring. The results from single pulse experiment did not support, that single pulse exposure experiments could provide more valuable information than the traditional chronic exposure tests used in risk assessment. However, the effects of repeated pulses were not investigated.