The objective of this Statement of Need (SON) is to seek fundamental or applied research to further improve our understanding of the ecological toxicity of per- and polyfluoroalkyl substances (PFAS) at sites impacted by aqueous film-forming foam (AFFF), particularly those PFAS that are less characterized due to historical limitations in analytical methods. In addition, this SON seeks to develop methodologies that are able to more accurately and efficiently assess ecological toxicity. Specific objectives include:

• Broaden our understanding of which PFAS in the environment contribute to ecological toxicity in terms of their potential persistence and bioaccumulation. In particular, utilization of structure-activity relationships is of interest, to capitalize on extensive data available for a subset of PFAS. Assessing the applicability of such approaches across multiple geographies, habitats, regions, matrices, and environments is of interest.
• Develop new methodologies to assess the biological effects of PFAS (e.g., in silico, in vitro, in vivo, and in situ) at different levels of biological organization and under different exposure scenarios.

One or more of the objectives listed above can be addressed in a single proposal. Research and development activities at laboratory-, bench-, and field-scale will be considered, although work does not necessarily have to culminate in a field-scale effort. Proposers must provide the rationale for the selected PFAS proposed for further study. Proposals focused on PFAS for which extensive data already exist are not of interest.

Substantial work has been conducted to understand the toxicity, bioaccumulation, and biomagnification of specific PFAS, and work with mixtures is ongoing. Proposers are encouraged to demonstrate in their proposal a thorough understanding of the state of the science and clearly illustrate how their proposed work will build on previous efforts.

Addressing the research needs described above offers the potential to provide additional, more accurate data to support site conceptual models at PFAS-impacted sites.

While structure and physical/chemical properties are similar among some PFAS, diversity is greater than across other chemical groups where methods of generalization have been effectively demonstrated. Opportunities to more efficiently improve our understanding of PFAS include the use of new methods, identifying potential biomarkers and mechanisms for environmental screening and monitoring, and synthesizing data across studies. Current ecotoxicology data emphasize aquatic receptors and the first characterized PFAS. Expanding testing is important, but will be time consuming and expensive. New approaches may help reduce the time and expense of expanding the understanding of PFAS. In addition, new methodologies for ecological toxicity assessment could be helpful in facilitating a broader understanding of PFAS in general, particularly if they can be linked to higher biological order effects, from tissue to whole organism to population effects.

Studies have demonstrated that complex mixtures of PFAS are common at impacted sites. In some cases, the less understood PFAS can represent a significant fraction of the total organic fluorine (TOF) among impacted media. Identifying a subset of indicator chemicals is an approach that has been used to assess other groups of chemicals that have similar structures, physical/chemical properties, and mechanisms of toxicity (e.g., PAHs or PCBs). Additional research could assess whether a group of indicator PFAS could be utilized in this manner as well. Recent data from the U.S. Environmental Protection Agency is building on such an approach for PFAS (Patlewicz et al., 2024). The use of a subset of representative PFAS as indicators of total PFAS content offers the potential to improve site conceptual models, ultimately facilitating management and remedial actions at sites impacted with complex mixtures of PFAS.

The cost and time to meet the requirements of this SON are at the discretion of the proposer. The two options are as follows:

Standard Proposals: These proposals describe a complete research effort. The proposer should incorporate the appropriate time, schedule, and cost requirements to accomplish the scope of work proposed. SERDP projects normally run from two to five years in length and vary considerably in cost consistent with the scope of the effort. It is expected that most proposals will fall into this category.

Limited Scope Proposals: Proposers with innovative approaches to the SON that entail high technical risk or have minimal supporting data may submit a Limited Scope Proposal for funding up to $250,000 and approximately one year in duration. Such proposals may be eligible for follow-on funding if they result in a successful initial project. The objective of these proposals should be to acquire the data necessary to demonstrate proof-of-concept or reduction of risk that will lead to development of a future Standard Proposal. Proposers should submit Limited Scope Proposals in accordance with the SERDP Core Solicitation instructions and deadlines.

Patlewicz, G., R.S. Judson, A.J. Williams, T. Butler, S. Barone, Jr., K.E. Carstens, J. Cowden, J.L. Dawson, S.J. Degitz, K. Fay, T.R. Henry, A. Lowit, S. Padilla, K. Paul Friedman, M.B. Phillips, D. Turk, J.F. Wambaugh, B.A. Wetmore, and R.S. Thomas. 2024. Computational Toxicology, 31, ISSN 2468-1113, https://doi.org/10.1016/j.comtox.2024.100327