PARENT SESSION

TP12B Ecological Effects of Cholinesterase Inhibitors
B115 & B116
1:20 PM - 4:40 PM, Tuesday

() Pulse exposure to AChE inhibitors cause chronic effects in Daphnia magna.

Andersen, T¹, Wollenberger, L¹, Tjornhoj, R¹, Slothuus, T¹, Baun, A¹, ¹ Technical University of Denmark, Kgs. Lyngby, Denmark

ABSTRACT- Intermittent discharges of pesticides to the aquatic environment occur frequently, e.g. due to spraying or runoff during rain events, resulting in short-term high concentrations. Effects of such pulse exposures on aquatic organisms are rarely described. Therefore, we developed a pulse exposure method studying acute as well as chronic effects of the two model compounds dimethoate and pirimicarb (both acetylcholinesterase inhibiting pesticides) towards Daphnia magna during an observation period lasting 21 d after exposure. Test organisms were exposed to dimethoate (10, 20, or 30 mg/l) for 1, 2, 2.5, or 3 hours and pirimicarb (40, 70, or 100 g/l) for 1, 2, 3, 4, or 6 hours, respectively After these single pulse exposures the organisms were transferred individually to clean test medium and mortality, immobilization, recovery of mobility, body size, time for first brood as well as number of offspring were observed daily. Almost all animals were immobile directly after exposure, but had regained their mobility after 3 d (92% recovery for pirimicarb; 70% for dimethoate). Even short pulses (2 h) of dimethoate (30 mg/l) and pirimicarb (100 g/l) significantly reduced the number of offspring. For both chemicals, all the exposed groups showed a delay in the time for the first brood. A 3-h pulse of 30 mg/l dimethoate affected the growth of D. magna. The observed reduction of body size became less pronounced for longer post exposure periods. However after 21 days, exposed animals were still significantly smaller than the animals in the control group. In conclusion, pulse exposures to the two AChE inhibiting pesticides caused not only short-term immobilization, but also long term adverse effects in D. magna.

Key words: Crustacean, Pulse exposure, Acetylcolinesterase inhibitor, Chronic toxicity