Relative toxicity of bifenthrin to Hyalella azteca in 10 day versus 28 day exposures
Authors: Anderson Brian S , Phillips Bryn M , Voorhees Jennifer P , Petersen Megan A , Jennings Lydia L , Fojut Tessa L , Vasquez Martice E , Siegler Catherine , Tjeerdema Ronald S 
Published: January 2015

Abstract
Many watersheds in the Central Valley region of California are listed as impaired due to pyrethroid-associated sediment toxicity. The Central Valley Regional Water Quality Control Board is developing numeric sediment quality criteria for pyrethroids, beginning with bifenthrin. Criteria are being developed using existing data, along with data from 10 d and 28 d toxicity tests with Hyalella azteca conducted as part of the current study. A single range-finder and 2 definitive tests were conducted for each test duration. Median lethal concentrations (LC50s), as well as LC20s and inhibition concentrations (IC20s) were calculated based on measured whole sediment bifenthrin concentrations and interstitial water concentrations. Sediment LC50s were also corrected for organic C content. Average LC50s were not significantly different in 10 d versus 28 d tests with H. azteca: 9.1 and 9.6 ng/g bifenthrin for 10 d and 28 d tests, respectively. Average LC20 values were also similar with concentrations at 7.1 and 7.0 for 10 d and 28 d tests, respectively. Bifenthrin inhibition concentrations (IC20s) based on amphipod growth were variable, particularly in the 28 d tests, where a clear dose-response relationship was observed in only 1 of the definitive experiments. Average amphipod growth IC20s were 3.9 and 9.0 ng/g for 10 d and 28 d tests, respectively. Amphipod growth calculated as biomass resulted in IC20s of 4.1 and 6.3 ng/g for the 10 d and 28 d tests, respectively. Lack of a clear growth effect in the longer term test may be related to the lack of food adjustment to account for amphipod mortality in whole sediment exposures. The average C-corrected LC50s were 1.03 and 1.09 μg/g OC for the 10 d and 28 d tests, respectively. Interstitial water LC50s were determined as the measured dissolved concentration of bifenthrin relative to interstitial water dissolved organic carbon. The average LC50s for dissolved interstitial water bifenthrin were 4.23 and 4.28 ng/L for the 10 d and 28 d tests, respectively. In addition, a set of 10 d and 28 d tests were conducted at 15 °C to assess the relative toxicity of bifenthrin at a lower temperature than the standard 23 °C test temperature. These results showed that bifenthrin was more toxic at the lower temperature, with LC50s of 5.1 and 3.4 ng/g bifenthrin in 10 d and 28 d tests, respectively. Amphipod growth at 15 °C after a 28 d exposure resulted in the lowest effect concentration of all experiments conducted (IC20 = 0.61 ng/g). This article discusses how bifenthrin dose–response data from 10 d and 28 d exposures inform development of sediment quality criteria for this pesticide for California Central Valley watersheds. Integr Environ Assess Manag 2015;11:319–328. © 2015 SETAC
Key Points
Sediment toxicity due to pyrethroid pesticides, in particular bifenthrin, is widespread in California and has lead to statewide regulatory actions to reduce pyrethroid loading in watersheds. The Central California Water Board is developing sediment quality criteria for bifenthrin and other pyrethroids. The process for developing sediment quality criteria requires acute and chronic toxicity data for a number of species and the results of the current study provide 10d and 28d data for bifenthrin using the amphipod Hyalella azteca in sediment, and sediment interstitial. Pyrethroids are more toxic at colder temperatures, so data are also provided for acute and chronic tests conducted at two temperatures. Results showed little difference in response between 10d and 28d tests conducted at the standard test temperature, and more toxicity at the lower temperature. The paper discusses how these results will be used in the development of sediment quality criteria for bifenthrin.