Assessing joint toxic effects of arsenate and perfluorooctane sulfonate on earthworm by combining integrated biomarker response and mixture toxicity indices

Abstract

Arsenic and perfluorooctane sulfonate (PFOS) are widely distributed pollutants in the soil environment and could coexist as mixture, but little studies have been reported about their combined toxicity to terrestrial invertebrates. In the present work, we exposed earthworm Eisenia fetida to sub-lethal levels of arsenate (As(V)), PFOS, and their mixture for 30 days. Multiple biomarker responses and bioaccumulation of the two toxicants in the organisms were analyzed to assess the joint toxicity of As(V) and PFOS. Bioaccumulation analysis results demonstrated that the coexistence of As(V) and PFOS in soil could increase the bioavailability of As(V) while decreasing the bioavailability of PFOS. As the level of exposure increased, significant variations were observed in all of the biomarkers analyzed, indicating growth inhibition and oxidative damage. The multiple biomarker responses were summarized by using the Integrated Biomarker Response (IBR) index, and significant dose–response relationships were found in treatments of As(V), PFOS and As(V)/PFOS mixture. Then the toxic interaction between As(V) and PFOS was assessed by combining IBR and two mixture toxicity indices, Effect Addition Index (EAI) and Concentration Addition Index (CAI). Results showed that the joint toxicity of As(V) and PFOS depended on the exposure concentration of As(V). The combined pollution of PFOS with lower concentration of As(V) led to synergistic interaction at the whole range of effect levels, while that with higher concentration of As(V) resulted in the toxicity interaction changing from antagonism to synergism as the effect level increased. As(V) was the main toxicant that caused adverse effects on earthworm biomarkers and affected the joint toxicity of As(V)/PFOS mixture. This study, for the first time, provides valuable toxicological data for the risk evaluation of combined toxicity of As(V) and PFOS in the soil environment. Moreover, this work indicates that the integration of IBR index and EAI/CAI could be an effective and practical method for the characterization of toxicity interaction within binary mixture systems.