Bioaccumulation of sediment-associated substituted phenylamine antioxidants in Tubifex tubifex and Lampsilis siliquoidea.

Substituted phenylamine antioxidants (SPAs) are additives in a variety of commercial polymers (e.g., lubricants, plastics, etc.). Based on their physicochemical properties, if SPAs were to enter an aquatic system, they would likely partition into sediment and have the capacity to bioaccumulate in biota. This study investigated the potential of four sediment-associated SPAs, diphenylamine (DPA), N-phenyl-1-naphthalene (PNA), N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine (DPPDA), and 4,4'-methylene-bis[N-sec-butylaniline] (MBA) to accumulate in the tissues of freshwater mussels (Lampsilis siliquoidea) and oligochaete worms (Tubifex tubifex). Mussels and worms were exposed to sediment spiked with individual SPAs for 28 d. The concentration of SPAs was measured in the gill, gonad, and remaining viscera of the mussels and entire body of the worms. The majority of biota-sediment accumulation factors (28-d BSAFs) for the different tissues of mussels were < 1. The highest concentrations of SPAs were consistently observed in the gill tissue of mussels relative to the gonad and viscera. The 28-d BSAFs for DPPDA and MBA for worms were < 1, and for DPA and PNA, they ranged from 0.38-2.13 and 1.54-33.24, respectively. The higher 28-d BSAFs observed for worms compared to mussels were likely because worms are endobenthic and feed on sediment-associated organic matter. PNA and DPPDA have similar octanol-water partition coefficients (Kow) but greater 28-d BSAFs were observed for PNA compared to DPPDA for both species. This observation provides evidence that biota may be able to metabolize and/or excrete SPAs with similar physicochemical properties at considerably different rates. The 28-d BSAFs observed for sediment-associated SPAs are lower than those typically required for a chemical to be classified as bioaccumulative.