Uptake and elimination of per-and polyfluoroalkyl substances in earthworms exposed to spiked artificial soil or aqueous medium.

Abstract

We investigated the accumulation of per- and polyfluoroalkyl substances (PFAS) in earthworms (Eisenia andrei). Uptake kinetics and bioaccumulation factors (BAFs) were determined using a mixture of 16 PFAS by exposing earthworms to spiked artificial soil for up to 28 d. Two treatments were used, with the low treatment targeting environmentally relevant concentrations. The concentrations of PFAS remained relatively unchanged during the exposures and statistically significant rates of uptake were estimated for most individual PFAS. For the 0.01 mg/kg treatment (target concentration of each PFAS), steady state was reached for all PFAS except PFHpS, PFHxS, PFOS, PFTeDA, and PFTrDA. For the 0.01 mg/kg treatment, bioaccumulation factors (BAF; kg/kg-dry wt.) ranged from 4 to 49 for most PFAS, but were higher for PFHxS (72), PFTeDA (271), and PFUnA (299). Organic-carbon-normalized BAFs were within the range of published values. The BAF values increased with increasing length of the alkyl chain for perfluoroalkyl carboxylic acids (PFCAs), but not for perfluoroalkyl sulfonic acids (PFSAs). Uptake rates and BAFs were lower for the 1 mg/kg treatment, typically by over one order of magnitude, likely because of sublethal physiological impairment. Fast and steep decreases in tissue concentrations of PFAS occurred when earthworms were transferred to clean soil, even for long chain PFAS, overall agreeing with previous reports. However, measured elimination rates were faster than predicted from the uptake experiments and the causes remain unknown. Bioaccumulation of PFAS was also investigated in exposures to aqueous medium for up to 7 d to derive bioconcentration factors (BCFs). Comparison of BCFs and BAFs suggests that uptake from soil may have higher relevance compared to dermal uptake from porewater for long-chain PFCAs and PFSAs.