Projects

Impacts of PFAS contaminants on oyster health and food safety

End Date: 1/31/2022

Abstract

The proposed study focuses on an area along the Alabama Coastline with extensive public oyster reefs, Alabama Marine Resources Division oyster material plantings and a nascent off-bottom oyster aquaculture industry. The main goals are to characterize seasonal cycles in PFAS concentrations in water and sediment, characterize PFAS body burden in bottom and off-bottom oysters, and examine the effects of PFAS on oyster health.Methodology will employ respirometry, valveometry, and state-of-the-art chemical analyses. Results will be incorporated into an existing DEB model for the eastern oyster to predict effects of PFAS on oyster health. Information regarding PFAS occurrence in water, sediment, and oysters will be disseminated to management agencies tasked with regulating/determining locations for oyster restoration, public harvest and commercial aquaculture operations. Identification of PFAS hotspots and seasonal patterns, coupled with effects on oyster health can be used to identify sites in need of restoration and protection from PFAS contamination.

Objectives

  1. To monitor seasonal concentrations of PFAS in, and near, Mobile Bay in relation to oyster beds and off-bottom farms.
  2. To assess current PFAS body burden of wild and cultured oysters in Mobile Bay.
  3. To determine the effects of PFAS on oyster energetics, stress indicators and short-term bioaccumulation.
  4. To provide practical information and recommendations to managers and oyster farmers regarding siting of oyster beds and farms.

Methodology

To examine PFAS physicochemical and temporal behavior in coastal systems near Alabama oyster reefs and farms, we will collect water and sediment samples >4 times/year from multiple sites in Mobile Bay, Portersville Bay, and Grand Bay. Samples will be analyzed using state-of-the-art PFAS methodology developed by our research team and described in Mulabagal et al. (2018).

To test whether PFAS body burden increases with oyster size and whether this relationship differs between on and off-bottom oysters, we will collect oysters from public oyster reefs and research off-bottom oyster farms. PFAS tissue concentrations will be analyzed and regressed against oyster height and mass. Relationships will then be compared between on and off-bottom oysters.

To test whether oyster stress indicators increase with increasing PFAS exposure in the field we will analyze field collected oysters for condition indices, stress protein concentrations and pathogen (dermo) prevalence. These stress endpoints will be regressed against mean PFAS concentrations in water, sediment and oysters to determine relationships between PFAS exposure, body burden and stress indicators.

To test for dose response relationships between PFAS concentration and oyster energetics, behavior and stress indicators, we will conduct a series of laboratory experiments utilizing standard respirometry, valveometry and molecular chaperone assays. Results will show whether respiration rates, incidence of valve closure and tissue concentration of HSP70 increase in a predictable fashion with increasing PFAS concentrations.

To test for the importance of obtained information to choice of sites for oyster harvest, restoration and farming, we will synthesize our results using a combination of dynamic energy budget (DEB) and Bayesian structural equation modeling (BSEM). Results will provide critical insight as to whether observed levels of PFAS in the environment and oyster tissues are cause for concern and which locations and location types are at lowest/highest risk.

Rationale

Per- and polyfluoroalkyl substances (PFAS) are contaminants of increasing concern in North America, with Alabama being a recognized hotspot. Recent sampling by the PIs revealed elevated PFAS concentrations in waters near the mouth of Mobile Bay and Dauphin Island where public oyster reefs and Alabama Department of Marine Resources oyster material planting is widespread. If PFAS bioaccumulate in oyster tissues, oysters harvested from polluted water raise food safety concerns. Conversely, if oysters clear pollutants rapidly from their tissues, energetic costs of depurating PFAS may negatively affect oyster health and susceptibility to disease. Similarly, if exposure to PFAS causes oysters to close their valves and cease filtering, bioaccumulation potential is reduced, but reduction in feeding would reduce energy intake with expected reductions in growth and reproduction.

Effects of PFAS exposure on bioaccumulation and oyster health are not well understood.

Some previous studies have shown little to no evidence of PFAS bioaccumulation in bivalves (including oysters) due to effective but energetically expensive defense mechanisms, such as the MXR system. However, other studies have shown elevated concentrations of PFOS (a type of PFAS) in Gulf of Mexico oysters, with Alabama oysters ranging from <50 to 545 ng PFOS/g dry weight in the 1990s. In fish, concentrations of 50 and 545 ng PFOS/g dry weight translate to consumption advisories of one meal per week to one meal per month, respectively. Thus there is a great need to understand both the bioaccumulation potential for Gulf oysters as well as the effects of PFAS exposure on oyster health. Knowledge of PFAS concentrations, effects and bioaccumulation in relation to oyster beds and off-bottom oyster farms are of particular importance to conservationists, oyster farmers and oyster consumers.