Comparing the impacts of sediment-bound bifenthrin on aquatic macroinvertebrates in laboratory bioassays and field microcosms

• Bifenthrin exposure reduced C. tepperi emergence in laboratory bioassay.
• Abundance of many invertebrate taxa decreased at comparable concentration in microcosms.
• Early emergence of exposed Chironomus species in laboratory and field microcosm.
• Laboratory bioassays can accurately predict field response of other species.

We conducted two laboratory bioassays and two field microcosm exposures with bifenthrin (a synthetic pyrethroid) in order to evaluate the capacity of single-species laboratory bioassays to predict lethal and sublethal impacts on aquatic invertebrates in microcosms. For the laboratory species, Chironomus tepperi, larval survival was reduced by 24% at 53.66 µg/g OC, while adult emergence was reduced at concentrations of 33.33 µg/g OC and higher, with a 61% decrease at 77.78 µg/g OC and no emergence at 126.67 µg/g OC. The abundance of several other microcosm taxa was reduced in the microcosms at a similar concentration range (33.33 µg/g OC and above), however there was no impact on the abundance of the congeneric species, Chironomus oppositus. The differences in impacts between test systems were potentially due to both differing species sensitivity and the interaction of ambient temperature with bifenthrin toxicity. Bifenthrin also was associated with early emergence of Chironomus sp. in both test systems, at concentrations of 10 µg/g OC and higher (laboratory) and 43.90 µg/g OC (microcosm), and with a significant decrease in the proportion of C. oppositus males in a microcosm. These findings indicate that while laboratory bioassays accurately predict many impacts in the field, there are some limitations to the predictive capacity of these tests.