Cholinesterase activity and behavior in chlorpyrifos‐exposed Rana sphenocephala tadpoles

Abstract

Recent studies have found a correlation between organophosphate (OP) pesticide exposure and declines in amphibian populations. We evaluated the hypothesis that this relationship is driven by behavioral changes in developing larvae. Specifically, we examined how exposure to a common OP pesticide, chlorpyrifos, influenced cholinesterase (ChE) activity, mass, and swim speed in Rana sphenocephala tadpoles. We also determined how the presence of natural pond sediments in exposure chambers influenced response to the pesticide and how mass and survival were affected when tadpoles were exposed to an invertebrate (odonate) predator in addition to the pesticide. Mass and swim speed were measured after 4- and 12-d laboratory exposures to 1, 10, 100, and 200 microg/L of chlorpyrifos in test chambers that either did or did not contain pond sediments. These same parameters also were examined in mesocosms dosed with 200 microg/L of chlorpyrifos to evaluate responses under more environmentally realistic conditions. The effect of the invertebrate predators on survival and/or growth of tadpoles was evaluated in the mesocosm study and in separate laboratory experiments. In laboratory tests, no pesticide-induced mortality was observed; however, tadpole ChE activity in the two highest concentrations was significantly lowered, with a longer exposure duration further decreasing activity (maximum inhibition, 43%). Mass also was lower at higher concentrations, but this effect was not enhanced with longer duration of exposure. Reductions in ChE activity of tadpoles exposed in mesocosms were similar to those observed in laboratory experiments for the first 4 d. Tadpole swim speed and survival in the presence of a predator were not affected, with the latter largely resulting from pesticide-induced predator mortality.

Esterase inhibition in tadpoles of Scinax fuscovarius (Anura, Hylidae) as a biomarker for exposure to organophosphate pesticides

“…It is possible that the diazinon sub-lethal concentrations tested allowed animals to recover esterase activity over time, which would be not possible with doses higher than LC 50 values, but this remains to be tested. Widder and Bidwell (2006) tested lower OP doses (100 and 200 µg/l chlorpyrifos) for 4 and 12 days in R. sphenocephala (L. sphenocephalus) tadpoles, and also observed a dose-responsive AChE inhibition. With respect to CbE, there are no reports on this enzyme in tadpoles, so comparisons can not be done.…”

“…Gurushankara et al (2003) observed a decrease in food consumption, growth and development in Limnonectus limnocharis tadpoles exposed to increasing concentrations of the OP malathion. Widder and Bidwell (2006) also reported lower body mass for Rana sphenocephala tadpoles, after chlorpyrifos (OP) exposure. According to Relyea (2004), malathion was moderately toxic for six tadpole species, with LC 50 values ranging from 1.25-5.90 mg/l according to the exposure period, but some species can be more susceptible than others to this compound.…”

“…Widder and Bidwell (2006) studied how chlorpyrifos exposure influenced cholinesterase (ChE) activity in R. sphenocephala tadpoles, verifying significant ChE inhibition after 12 days of exposure to 100 and 200 μg/l. They also observed a dose-dependent ChE decrease in four different tadpole species exposed to sublethal concentrations of chlorpyrifos (Widder and Bidwell 2008).…”

Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States

“…Similarly, locomotory behavior of mosquito fi sh, Gambusia affi nis , was affected by exposure to 60 μg CPY L −1 for 20 d (Rao et al 2005 ). Although exposures to concentrations of CPY of 100 and 200 μg L −1 caused depression of whole-body AChE (≈60% of controls) in tadpoles of Rana sphenocephala , there were no effects on swim-speed or vulnerability to predation (Widder and Bidwell 2006 ).…”

Combined Effects of Atrazine and Chlorpyrifos on Susceptibility of the Tiger Salamander to Ambystoma tigrinum Virus

“…Chlorpyrifos is the most widely used insecticide in the United States and, although targeted to act on insect nervous systems (Kiely et al, 2004), it also is known to alter nervous function in amphibians (Colombo et al, 2005). These effects result in both behavioral modifications and a reduction in growth (Widder and Bidwell, 2006). Chlorpyrifos also has a large range of lethal concentration (LC 50 ) values ranging from 1 to 3,000 lg/L for differing amphibian species (Barron and Woodburn, 1995).…”