The objectives of this project are to: (1) determine bioaccumulation dynamics (uptake, elimination) of individual per- and polyfluoroalkyl substances (PFASs) from complex mixtures across representative environmental conditions, and (2) determine uptake and elimination rates of PFASs in the benthic organism, Hyalella azteca, and a common fish model (Pimephales promelas) when exposed to simulated groundwater while varying environmental complexity (e.g., pH, salinity). These bioaccumulation dynamics will be modeled using a non-linear one-component uptake equation or two compartment model. The results will be determined for both whole-body accumulation and plasma accumulation. Analysis of PFASs will include branched and linear congeners as well as a suite of target PFAS analytes.

The approach will be to expose a common benthic invertebrate, H. azteca, and a common fish model, fathead minnows (P. promelas), to PFAS across gradients of environmental complexity. The reason for choosing H. azteca and P. promelas is that they are widely distributed across North America and are thus routinely employed for environmental assessments of effluent discharges, surface water quality and specific chemicals. Furthermore, all experiments will be carried out with sub-lethal PFAS concentrations, informed by initial toxicity studies following United States Environmental Protection Agency methods. This approach will ensure that PFAS levels do not interfere with uptake or elimination kinetics.

In the event that steady state is not achieved in the exposure experiments, the project will use the kinetic based approach to bioaccumulation factor (BAF) determination:

BAF = k_uptake / k_elimination

The uptake (k_uptake) and elimination (k_elimination) rates for specific PFAS molecules can be determined regardless of steady state conditions.

Analysis of PFAS will be conducted using authentic standards relative to mass-labeled standards by liquid chromatography tandem mass spectrometry (LC/MS/MS). Multiple reaction monitoring (MRM) will be used to determine the area of each analyte in samples and standards using established transitions from parent to daughter ions. Quantification will employ the relative response factor (RRF) method from calibration standards. Because there are several precursor PFAS compounds for which we do not have authentic standards, let alone mass-labeled standards. For compounds where a standard is not commercially available, an RRF of a similar compound will be used to estimate its mass. The electrochemical formulation of several PFAS resulted in both branched and linear isomers. Preliminary studies by principal investigator have shown that branched chain perfluorooctanesulfonic acid (PFOS) accumulates preferentially to linear PFOS in Japanese quail. Therefore, branched vs. linear bioaccumulation is hypothesized to differ in H. azteca and fathead minnow models as well.

This project will yield high quality, kinetic-based BAF values for a variety of PFAS with a common model aquatic invertebrate and a vertebrate across gradients of environmental complexity. It will further determine body burden and plasma binding in fish. These novel efforts will afford a unique opportunity to test assumptions, strengths and limitations of existing models, and derive improved predictive bioaccumulation tools for PFAS at contaminated sites. Successful completion of this project will provide improved predictive models to estimate uptake and elimination of PFAS in widely distributed, ecologically important invertebrate and fish models across environmentally relevant gradients.