Piperonyl butoxide enhances the bioconcentration and photoinduced toxicity of fluoranthene and benzo[ a]pyrene to larvae of the grass shrimp ( Palaemonetes pugio)

Abstract

Piperonyl butoxide (PBO) is a commonly used synergist in many pyrethroid formulations due to its ability to interfere with cytochrome P450 (CYP) monooxygenases. Because PBO can co-occur in the estuarine environment with polycyclic aromatic hydrocarbons (PAHs), a class of compounds metabolized by CYP isozymes, the overall objective of this study was to investigate the influence of PBO on the bioconcentration and photoinduced toxicity of two common PAH contaminants, fluoranthene (FLU) and benzo[ a]pyrene (BaP), on the larvae of the grass shrimp ( Palaemonetes pugio). PBO alone was not particularly toxic to grass shrimp larvae. In dark exposures and under simulated sunlight (UV-A = 211.0 ± 7.0 μW/cm 2, UV-B = 9.8 ± 2.4 μW/cm 2), 96-h LC 50 values were similar (814.4 and 888.6 μg/L, respectively), suggesting that PBO toxicity is not enhanced in the presence of sunlight. The presence of sublethal concentrations of PBO in single PAH toxicity tests increased the bioconcentration of the two tested PAHs, and these increases were greatest at the lowest tested PAH concentrations. Mean bioconcentration factors (BCF) at the three lowest FLU and BaP treatments increased 14.3- and 7.1-fold, respectively, in the low PBO (127 μg/L) exposure compared to that of the no PBO exposure. Under simulated sunlight, PBO exposure also increased the photoinduced toxicity of the two tested PAHs, and this increase occurred in a PBO concentration-dependent fashion. For FLU, 96-h LC 50 values decreased from 2.35 μg/L in the absence of PBO to 0.76 μg/L in the high PBO (256 μg/L) exposure. For BaP, 96-h LC 50 values similarly decreased from 1.02 μg/L in the absence of PBO to 0.30 μg/L in the high PBO exposure. The presence of PBO also influenced the PAH tissue residue–response relationship, but in different ways for FLU and BaP. For FLU, slopes of the tissue residue–response relationship decreased in the presence of PBO, and for BaP, there was a trend towards increased slopes in the presence of PBO. These results demonstrate that sublethal levels of PBO increase the bioconcentration and photoinduced toxicity of certain PAH in grass shrimp larvae, and underscore the need to consider the potential for PBO to synergize the toxicity of co-occurring environmental contaminants in future risk assessments.