Hatching success and pesticide exposures in amphibians living in agricultural habitats of the South Okanagan Valley, British Columbia, Canada (2004-2006)

Abstract

In 2004 to 2006, in the Okanagan Valley, British Columbia, Canada, we measured pesticides, water chemistry, and hatching success of Great Basin spadefoot (Spea intermontana), Pacific treefrog (Pseudacris regilla), Western toad (Bufo boreas), and Columbia spotted frog (Rana luteiventris). Predator-proof cages containing Gosner Stage 4 eggs were placed in ponds in nonagricultural reference sites in conventionally sprayed and organic orchards. Seventeen pesticides were detected in ponds in sprayed orchards but occurred at low concentrations (ng/L) except for diazinon (1,410 ng/L). Chloride, sulfate, conductivity, nitrate, and phosphorus showed significant differences among sites. Spadefoot mean hatching success ranged from 0 to 92% among sprayed orchards, whereas the range was 48 to 98.6% among organic orchards and 51 to 95.5% among reference sites. Mean hatching success for Pacific treefrog was 22.1 to 76.1% among sprayed orchards, whereas the range was 83.4 to 97.1% among reference sites. Although sample sizes were small and replication was low, we found that trends in hatching success of eggs of Western toad and Columbia spotted frogs were consistent with the other species. Variables that correlated negatively with amphibian hatching success included 12 pesticides and seven water chemistry parameters. However, stepwise regression found that, in 2005, atrazine accounted for 79% of the variation in spadefoot hatching success and, in 2006, atrazine, total nitrate, and chlorpyrifos accounted for 80%. For Pacific treefrog there were no significant correlations with pesticide concentrations; rather, hatching success correlated with water chemistry parameters. The present study also emphasizes the variability in species sensitivity and importance of incorporating water chemistry into the interpretation of water quality for amphibians.