RP10 Aquatic Ecotoxicology
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(JAR-1117-826307) Impacts of brief malathion exposure on olfactory, brain, and liver acetylcholinesterase activity in striped bass.

Jarrard, H¹, Metcalf, B¹, ¹ Department of Biology, Washington College, Chestertown, Maryland, USA

ABSTRACT- Numerous organophosphate (OP) pesticides inhibit acetylcholinesterase (AChE) activity in teleost brain (BR) and liver (L), and are correlated with increased mortality and behavioral alteration over standard testing durations of 24-96 hours. AChE activity in the teleost olfactory system (olfactory rosette, OR, and olfactory bulb, OB) can also be inhibited by these pesticides, even with brief exposures. This inhibition may be correlated with neurophysiological and behavioral impairment affecting behaviors reliant on a functional sense of smell (such as predator avoidance). In this preliminary range-finding study, we investigated the effects of brief exposure (4 hours) to the OP pesticide malathion on BR, L, OR, and OB AChE in the striped bass (Morone saxitilis). Furthermore, because this teleost inhabits coastal bays/estuaries often experiencing hypoxic conditions in summer months due to eutriophication, malathion exposure (0.25X, 0.5X, and 1X the 96hr LC50) occurred in either normoxic (5.8-7.3 mg/L O2) or hypoxic (1.35-3.5 mg/L O2) conditions. Seven exposure groups were pulse-exposed in flow-through tanks: Control (0 g/L malathion, normoxic), Low, Medium, and High-dose Normoxic (60, 120, and 240 g/L malathion), and Low, Medium, and High-dose Hypoxic (same malathion doses). Flash-frozen tissues were then collected and AChE activity measured. In results, all doses examined significantly reduced AChE activity relative to controls (one-way ANOVA, Dunnetts post hoc, 0.05 level): BR AChE activity was reduced to 10-42 % of control values, while L, OR and OB AChE activity was reduced to 4.9-9.4 %, 34.5-63.3 %, and 15.6-40 % of control values, respectively. No significant differences were observed between normoxic and hypoxic conditions at different doses, although effects may have been masked by the substantial AChE inhibition caused by the initial doses used. In summary, these results show that brief exposures to malathion profoundly impact olfactory, brain, and liver acetylcholinesterase activity, and potentially, dependant behaviors.

Key words: olfaction, organophosphate, hypoxia, teleost