Identifying and Managing Aqueous Film-Forming Foam-Derived Per- and Polyfluoroalkyl Substances in the Environment.

The use of aqueous film-forming foam (AFFF) has resulted in the widespread occurrence of per- and polyfluoroalkyl substances (PFAS) in groundwater, drinking water, soils, sediments, and receiving waters throughout the United States and other countries. We present the research and development efforts to date by the Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP) to measure PFAS in the environment, characterize AFFF-associated sources of PFAS, understand PFAS fate and behavior in the environment, assess the risk to ecological receptors, develop in situ and ex situ treatment technologies for groundwater, treat soils and investigation-derived wastes, and examine the ecotoxicity of PFAS-free fire suppression formulations. Environ Toxicol Chem 2021;40:24-36. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Partitioning of poly- and perfluoroalkyl substances from soil to groundwater within aqueous film-forming foam source zones.

Metadata from on-going site investigations at U.S. Air Force sites impacted by Aqueous Film-Forming Foam (AFFF) were used to evaluate primary factors that affect transport of poly- and perfluoroalkyl substances (PFAS) within source zones. Soil-to-groundwater ratios (γSoil-GW) were calculated for each site and PFAS as an empirical transport metric and regressed against select soil chemical and physical properties, as well as relevant interactions thereof, using analysis of covariance (ANCOVA). Total organic carbon and percent total clay content were significant covariates and best fit log-transformed γSoil-GW with a parallel lines model. Regression parameters were used to derive apparent KOC estimates for 15 perfluoroalkyl acids, perfluorooctane sulfonamide, and the 6:2 and 8:2 fluorotelomer sulfonates, which were bimodal where significant differences were primarily observed between PFAS with fewer than 8 perfluorinated carbons (including perfluorooctoanoic acid; PFOA) and those with 8 or more (including perfluorooctane sulfonate; PFOS). Surprisingly, clay content was observed with a negative slope (i.e., γSoil-GW decreased with increasing clay content), which may reflect greater retardation at more permeable sites due to air-water interfacial partitioning. Further analysis demonstrated that γSoil-GW is also affected by the degree of flushing in a way that suggests mass transfer (as opposed to hysteretic desorption) primarily controls mass discharge at poorly flushed sites. Overall, this meta-analysis demonstrates that PFAS retention in soil is significant, but depends on a combination of fundamental partitioning mechanisms that may not be predictable in all cases based on transport models that assume an equilibrium condition.

Chlorinated ethene source remediation: lessons learned.

Chlorinated solvents such as trichloroethene (TCE) and tetrachloroethene (PCE) are widespread groundwater contaminants often released as dense nonaqueous phase liquids (DNAPLs). These contaminants are difficult to remediate, particularly their source zones. This review summarizes the progress made in improving DNAPL source zone remediation over the past decade, and is structured to highlight the important practical lessons learned for improving DNAPL source zone remediation. Experience has shown that complete restoration is rare, and alternative metrics such as mass discharge are often useful for assessing the performance of partial restoration efforts. Experience also has shown that different technologies are needed for different times and locations, and that deliberately combining technologies may improve overall remedy performance. Several injection-based technologies are capable of removing a large fraction of the total contaminant mass, and reducing groundwater concentrations and mass discharge by 1 to 2 orders of magnitude. Thermal treatment can remove even more mass, but even these technologies generally leave some contamination in place. Research on better delivery techniques and characterization technologies will likely improve treatment, but managers should anticipate that source treatment will leave some contamination in place that will require future management.

Dermal bioavailability of benzo[a]pyrene on lampblack: implications for risk assessment.

Lampblack is the principal source of contamination in soils at manufactured gas plant (MGP) sites where oil was used as the feedstock. Risks and cleanup criteria at these sites are determined primarily by the total carcinogenic polynuclear aromatic hydrocarbon (PAH) content, particularly the concentration of benzo[a]pyrene (BaP). Dermal contact with soils at oil-gas MGP sites is a significant component of the overall risks. Seven samples were collected from oil-gas MGP sites and the steady-state dermal fluxes were measured over 96 h in vitro. The standard dermal bioassay technique (in which 3H-BaP is added to the soil matrix) was modified to allow direct measurement of the dermal absorption of the native BaP in the samples. The experimentally derived dermal absorption factors for BaP were 14 to 107 times lower than the default assumption of 15% over 24 h (55-fold lower on average). The dermal fluxes were correlated positively to the total BaP and total carbon concentrations. The measured dermal absorption factors were compared to the default risk-assessment calculations for all seven samples. The calculated excess cancer risk was reduced as a result of using the measured absorption factors by 97% on average (with reductions ranging from 93 to 99%). This work indicates the risks at oil-gas MGP sites currently are overestimated by one to two orders of magnitude, and provides a protocol for the testing and data analysis needed to generate site-specific cleanup levels.

Improving risk assessments for manufactured gas plant soils by measuring PAH availability.

Remediation of soils at oil-gas manufactured gas plant (MGP) sites is driven primarily by the human health risks posed by the carcinogenic polycyclic aromatic hydrocarbons (PAHs), particularly benzo[a]pyrene (BaP), that are associated with lampblack residues. Although PAHs on lampblack are tightly sorbed, risk assessments do not account for this reduced availability. A multi-investigator study of 7 oil-gas MGP site soil samples demonstrated that the dermal and ingestion absorption factors are far lower than current default assumptions used in risk assessments. Using these sample-specific absorption factors in standard risk assessment equations increased risk-based cleanup levels by a factor of 72 on average (with a range from 23 to 142 times the default level). The rapidly released fraction of the BaP in each sample, as measured by supercritical fluid extraction, was closely correlated (r2 = 0.96) to these calculated cleanup levels. The weight of evidence developed during this research indicates that the risks posed by PAHs on lampblack are far less than assumed when using default absorption factors and that a tiered evaluation protocol employing chemical analyses, chemical release data, and in vitro bioassays can be used to establish more realistic site-specific criteria.