Minnesota Pollution Control Agency

Perfluorooctane sulfonate (PFOS), a member of the per- and polyfluoroalkyl substances family, is highly bioaccumulative and remains a persistent public health concern for consumers of wild freshwater fish. However, testing fish tissue for PFOS is time-consuming and costly, and it requires fish mortality. To reduce these costs by furthering the understanding of controls on PFOS bioaccumulation, we analyzed 3,831 paired fish tissue and surface water grab samples collected between 2006 and 2023 from 185 sites in Colorado, Minnesota, and Wisconsin, United States. We found that surface water samples reliably predict PFOS concentrations in fish filets. Species-averaged tissue PFOS scales log-linearly with water PFOS (R2 = 0.49). Adding fish taxonomy modestly improves fit (R2 = 0.69), while fish length, feeding guilds, and habitat preferences contribute little compared with water concentration. Decision tests tied to common fish consumption advisory targets (3.9-200 ng/g) yield surface water thresholds of ∼2.3-26.2 ng/L and strong classification abilities (AUC 0.85-0.97). We posit that surface water PFOS is a practical, defensible proxy for fish PFOS that can accelerate protection while improving efficiency. Regulatory agencies could adopt a tiered framework using surface water PFOS concentrations to triage waterbodies for fish sampling, thus reducing costs, limiting fish mortality, and enabling timely, consistent advisories.

Applying biosolids as a soil amendment for crop production is a common practice, raising concerns about the introduction of per- and polyfluoroalkyl substances (PFAS) into soils and crops at application sites. We investigated the impact of biosolids application on PFAS concentrations in agricultural soils and crops at three different farms that received biosolids from three different wastewater treatment plants in Minnesota. At each farm, three fields were identified: one with no history of biosolids application, one with past biosolids application, and one with biosolids application in the study year (2023). Biosolids; soils; and corn (Zea mays), rye (Secale cereale), and soybeans (Glycine max) were analyzed for PFAS. Biosolids-amended soils showed a greater number of PFAS, as well as higher total PFAS concentrations than fields that had never received biosolids or had not received biosolids in recent years. Several PFAS, including perfluorooctane sulfonate (PFOS), were found to accumulate in corn, especially in the stalks and leaves (stover). PFAS were also found in rye, but not in soybeans. Bioaccumulation factors for crops were calculated for perfluorobutane sulfonate (5.0-5.2, corn stover), perfluorobutanoic acid (0.57, rye, and 7.0-7.7, corn stover), perfluoropentanoic acid (0.34, corn stover), and PFOS (0.03, corn stover). Crop and soil results were used to perform a human health risk assessment using a simple exposure model to estimate PFOS concentration in beef and milk. Hazard quotients were >1 for both adults and children based on 90th percentile consumption rates, indicating a potential for human health risk in the modeled scenario.

Wildfires can disrupt carbon transport from land to water, but how lake carbon cycling responds to fires remains unclear. Here, we analyzed the concentration and dominance of the main carbon forms in total carbon pools in 54 lakes (34 burned, 20 control) across 3 regions of Quebec, Canada and Minnesota, USA from recent wildfires ( < 1 – 3 years). Lakes in burned watersheds had up to double the dissolved organic carbon concentrations of control lakes, and the fire effect was most apparent when accounting for climate and landscape drivers (e.g., catchment to lake area ratio) of lake carbon cycling. The greater quantity and dominance of dissolved organic carbon in burned lakes over other carbon forms with different turnover rates and fates suggest a potential fire-mediated carbon export up to several years post fire with a yet undetermined fate in northern forested watersheds and with important implications for regional to global carbon budgets. Wildfires can increase lake carbon concentrations by up to double, mostly in the form of dissolved organic carbon, according to analyses of carbon in fire-disturbed and control lakes across Quebec and Minnesota.

Environmental health concerns over per- and polyfluoroalkyl substances (PFAS) have prompted public health laboratories to pursue monitoring studies determining PFAS occurrences. Select laboratories have begun implementing non-targeted analysis (NTA) methods to address the disparity between the few (< 100) PFAS typically measured using targeted analyses and the thousands of known PFAS. While NTA can provide a more comprehensive understanding of PFAS occurrence, significant barriers prevent its widespread adoption in public health laboratories. Notable barriers include a lack of harmonized guidance, standardized methods, and workflows that enable robust NTA application. EPA’s Office of Research and Development has been working to overcome these barriers as part of technical collaborations with state environmental and public health laboratories. As a product of these efforts, ORD has developed the ENTAiLS Toolkit, a publicly available compilation of best practices and an open-source data processing workflow for PFAS NTA studies. The ENTAiLS Toolkit offers NTA practitioners comprehensive guidance and integrated tools that can aid the identification and characterization of PFAS in drinking water resources.

Chlorinated ethenes are common contaminants in aerobic water-supply aquifers, and they can form large dilute plumes. Often, concentrations attenuate naturally along the flow path, and the bulk first-order rate constant for attenuation with travel time in the aquifer (k na) can be used to determine whether the concentrations at a point of compliance will be below the cleanup goal. If concentrations are below the goal, k na provides the U.S. EPA the first line of evidence for Monitored Natural Attenuation (MNA) as a remedy. However, monitoring wells may fail to sample important areas of a plume; thus, the first line of evidence alone is often not convincing for MNA acceptance. Consequently, there is a need for methods that provide additional lines of evidence to support the use of MNA in aerobic water-supply aquifers. A recently developed 14C-assay addresses this gap by directly quantifying natural abiotic degradation of chlorinated ethenes through the accumulation of radiolabeled polar products. Specifically, the assay provides rate constants for abiotic degradation within 6 weeks, offering both a quantitative measure of degradation (the second U.S. EPA line of evidence for MNA) and proof that contaminants are being transformed (the third line of evidence). Here, the 14C-assay was used to evaluate abiotic degradation at three sites. At one site k na was 0.89 +/- 0.094 per year. The rate constant for abiotic TCE degradation in a 14C-assay using sediment from the site was 0.27 +/- 0.11 per year, and the rate constant for cDCE degradation was 1.57 +/- 0.39 per year. These results demonstrate that the 14C-assay can provide robust additional lines of evidence supporting MNA in aquifers where abiotic degradation would otherwise be overlooked.