PFAS precursors at military sites may contaminate groundwater

Earlier this year, the US Environmental Protection Agency (EPA) proposed new regulations on maximum allowable levels of per- and polyfluoroalkyl substances (PFAS), commonly known as forever chemicals, in drinking water. However, a recent study led by the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has found that the draft standards fail to account for half of the PFAS compounds present at contaminated sites across the United States. The study, published in the journal Environmental Science & Technology, raises concerns about the potential health risks associated with these unregulated PFAS compounds.

PFAS are a group of chemicals used in various products, including fire retardant foams. They have been accumulating in the environment since their invention by Dupont in the 1930s and widespread manufacturing by 3M starting in the 1950s. Exposure to certain PFAS compounds has been linked to a range of health issues, such as cancer, immune suppression, diabetes, and low birth weight in infants.

PFAS compounds exist in two forms: precursor compounds and terminal compounds. The EPA’s draft drinking water rules only address six terminal compounds that do not break down naturally in the environment. However, precursor compounds can undergo transformation into terminal forms through biological or environmental processes. Many precursor compounds are not regularly monitored, and none are currently regulated.

The US military, particularly the Navy, is the largest global user of fire-retardant foams containing PFAS, known as aqueous film forming foam (AFFF). These foams, containing high levels of PFAS, have been used for fire training drills and firefighting on military bases worldwide. Consequently, AFFF use has become a major source of PFAS contamination in drinking water.

The Harvard study highlights that numerous PFAS precursor compounds present in AFFF are challenging to measure. The research demonstrates that these precursors slowly transform into PFAS compounds of health concern at sites contaminated with AFFF, contributing to further contamination downstream. Many of these precursors are not accounted for in standard analytical methods.

Using a method previously developed in the Sunderland lab at Harvard, the research team modeled the expected persistence and contribution of these precursors to groundwater contamination. The study specifically examined two newly regulated PFAS chemicals, perfluorohexane sulfonate (PFHxS) and perfluorobutane sulfonate (PFBS), at a military base on Cape Cod, Massachusetts. The researchers discovered that microbial precursor biotransformation in the soil sustains the contamination of PFHxS and PFBS. These precursors remain in the soil, leaching into groundwater in terminal form at concentrations thousands of times higher than the safe levels established by the EPA.

These findings underscore the need for comprehensive monitoring and regulation of PFAS compounds, including both precursors and terminal forms, to effectively address the contamination and associated health risks.

According to the researchers’ computer model and field data, widespread contamination of drinking water supplies near military facilities with PFAS is projected to persist for centuries if no remediation measures are taken. Despite the existing contamination of nearby aquifers, a significant portion of PFAS compounds remains in the surrounding soils. This highlights the urgent need for advancements in remediation technology capable of effectively addressing both precursor and terminal compounds. As current regulations focus solely on terminal compounds, the effectiveness of existing remediation technologies in addressing precursors is unknown.

The study’s findings suggest that elevated PFAS exposure downstream of over 300 US military facilities that have used fire-fighting foams could also persist for centuries. The researchers expressed concern that the role of PFAS precursors in sustaining hazardous contamination levels at Joint Base Cape Cod might lead to underestimated exposure risks at numerous other sites where these compounds are not measured.

The public comment period for the EPA’s draft PFAS drinking water regulation is set to close on May 30. While a positive step, it is important to note that there are thousands of PFAS chemical structures, with several hundred already detected in the environment, highlighting the complexity of addressing the issue, as mentioned by Sunderland.

In a related study also published in Environmental Science & Technology, Sunderland’s group found that the number of military fire training areas within a watershed serves as a good indicator of PFAS contamination in a community’s drinking water supply. However, some groups face higher risks than others, as an upcoming publication by the Sunderland lab will document significant sociodemographic disparities in PFAS exposures and proximity to PFAS sources across the United States.

The study’s additional authors include Colin Thackray and Chad Vecitis from Harvard, Craig Butt from AB Sciex LLC, and Denis LeBlanc and Andrea Tokranov from the US Geological Survey.

Source: Harvard John A. Paulson School of Engineering and Applied Sciences

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