Fate and Effects of PFOS and PFOA in Saltmarsh Ecosystems

We are studying widespread industrial chemicals known as PFAS (per- and polyfluoroalkyl substances) that contaminate the environment. While we know PFAS are in rivers, we need to understand how these substances affect sensitive coastal areas, such as salt marshes, which are critical nurseries for marine life. Our project investigated how two common chemicals (PFOS and PFOA) moved through and impacted a simulated salt marsh ecosystem that included water, mud, plants, and animals. Our results show current safety guidelines may not protect all organisms, especially bottom-dwelling shrimp and clams, suggesting that existing environmental regulations may need to be updated to better protect estuarine life.

Why We Care
Per- and polyfluoroalkyl substances (PFAS) are known as “forever chemicals” because they resist natural breakdown and persist indefinitely in the environment. These widely used industrial compounds are now found everywhere, including in our oceans and estuaries, which are vital habitats for commercially and recreationally important species. While extensive research has focused on freshwater systems, we know much less about how PFAS affect complex marine and estuarine ecosystems, like the salt marshes that line our coasts. These coastal areas are crucial for fisheries and provide natural storm protection. Understanding the movement and impact of PFAS in these environments is essential to protect coastal resources, seafood supply, and the public health of coastal communities.

What We Did
We conducted a controlled, long-term study using simulated salt marsh ecosystems, known as mesocosms, to investigate two of the most common and historically relevant PFAS: perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). We exposed a variety of native salt marsh organisms—including fish, shrimp, snails, clams, and amphipods—to environmentally relevant concentrations of these compounds, both individually and as a mixture. Our primary goal was to track where these chemicals end up—in the water, the sediment, or the animals and plants—and to determine which species are most vulnerable to them. This work provides critical data needed by environmental managers, including state and federal agencies, to make informed decisions about regulating PFAS contamination in estuaries. The research was conducted in collaboration with partners at the University of South Carolina.

What We Found
Our findings revealed significant differences in how PFOS and PFOA affect various salt marsh species:

• • Vulnerable Species Identified:

– Amphipods, small crustaceans that live in the sediment, were the most sensitive organisms tested, showing nearly 100% mortality even at relatively low levels of PFOA.
– Grass shrimp, a key food source for many larger fish, also experienced high mortality (66%) under high PFOS exposure.
– Hard clams, a major economic resource, showed significant mortality when subjected to a high level of PFOA.

• • Resilient Species:

– Fish and mud snails showed no significant effects on survival, indicating a high degree of resilience to the tested PFAS concentrations.

• • Widespread Ecosystem Impact:

– A significant reduction in periphyton (the microbial film on surfaces that forms the base of the food web) chlorophyll-a was observed across all PFAS treatments, pointing to a broader impact on primary productivity and overall ecosystem health.
– The sensitivity of benthic species like amphipods and clams to PFOA could lead to indirect impacts on higher trophic levels.
– We observed sublethal stress in organisms like grass shrimp, where key biomarkers for oxidative stress were significantly reduced, suggesting the chemicals may cause harm even when not immediately lethal.

• • Chemical Movement:

– PFOS showed a greater tendency to stick to sediment and accumulate in the tissues of plants and animals compared to PFOA.
– For several species, including fish, PFOS tissue concentrations and bioconcentration factors (BCFs—a measure of how much a chemical concentrates in an organism relative to the water) were higher than PFOA, suggesting PFOS poses a greater risk for bioaccumulation in the food web.

Benefits of Our Work
The results of this study have direct, applied relevance for environmental regulation and resource management:

• • Protecting Coastal Ecosystems: The findings highlight that current acute aquatic life criteria set by the Environmental Protection Agency (EPA) for PFOA may not be fully protective for sensitive benthic invertebrates like amphipods, which play a crucial role in sediment health and nutrient cycling.
  • Informing Regulatory Decisions: This work provides critical, marine-specific data to federal and state regulators (e.g., EPA, NOAA, state environmental departments) needed to develop and refine standards for PFOA and PFOS in estuarine and saltwater environments, ensuring the protection of vulnerable species.
  • Safeguarding Seafood: By tracking the bioaccumulation potential (BCFs) of these chemicals in species like clams and fish, we provide essential information for understanding potential exposure routes and risks to the seafood supply.

Next Steps
To build on these vital findings, future research should focus on:

• • Developing Chronic Criteria: Working toward developing appropriate chronic criteria for PFOA in estuarine environments, as acute testing may underestimate the long-term ecological risk.
  • Understanding Exposure: Investigating the relative importance of ingestion (eating contaminated food or sediment) versus direct water uptake as the key exposure route for bioaccumulation in different species.
  • Long-Term Fate: Conducting a more comprehensive analysis of the full mass balance, including measuring concentrations in deeper sediment layers and in the entire plant root system to better predict the long-term persistence and fate of PFAS in salt marshes.
  • Mechanisms of Harm: Further exploring the mechanisms behind the observed impacts on periphyton, a critical foundational food source in the ecosystem.