The U.S. Environmental Protection Agency (EPA)’s Science Advisory Board (SAB) panel on biosolids held its last meeting on July 5th to finalize their report to EPA. The 36-page draft report includes comments, suggestions, and recommendations for the EPA on its biosolids risk assessment framework. The SAB biosolids panel was created in 2022 and was charged with reviewing EPA’s proposed methodology for screening and assessing contaminants in biosolids for their risk to humans and the environment. EPA’s stated goal for this panel was to help modernize, standardize, and streamline the biosolids risk assessment process.

The panel’s work got underway in earnest back in March 2023. In addition to a peer review of EPA’s overall risk assessment approach, the SAB was asked to review EPA’s Biosolids Screening Tool (BST) for its scientific credibility and usability. The BST will be used for screening-level assessments of contaminants in biosolids.

The meetings have been moderated and the panel has been supported in its work by EPA’s Designated Federal Officer, Dr. Shaunta Hill-Hammond. The meetings were run by the Biosolids Panel Chair, Dr. Sylvie Brouder who is a Professor and Wickersham Chair of Excellence in Agricultural Research under the Department of Agronomy at Purdue University. At the latest meeting, the panel of experts went through the draft report section by section, with the goal of reaching consensus on the report text and recommendations. Dr. Brouder was also looking for high-level comments from the panel to include in the cover letter to EPA Administrator Michael Regan. She also wanted to enhance the citations and examples provided for consideration by EPA in the report’s appendix.

Different panel members had taken the lead on compiling and writing comments prepared by small subgroups of panel members who worked together on designated sections of the report. The panel also reviewed and discussed the draft User Guide for the BST and had numerous suggestions for improvements. The panel’s preliminary draft report can be found here.

The SAB’s draft report was organized into sections reflecting the panel’s charge from EPA to answer the following questions on the screening level methodology:

1. Does the SAB find that the application of the PICS (Public Information Curation and Synthesis) process to the chemicals found in biosolids is sufficient to identify the chemicals that should move to a deterministic screening-level risk assessment?

2. Does the SAB find the selection process for models within the BST to be appropriate for the exposure pathways for a screening-level risk assessment?

3. Are the receptors contained in the BST appropriate for a screening-level risk assessment for human health and aquatic and terrestrial wildlife?

4. Several screening parameters are set to health-protective, high-end values (e.g., concentration of chemical in biosolids, drinking water ingestion rates), but others are set near the central tendency for that parameter (e.g., bioaccumulation factor). Does the SAB agree that these metrics generate reasonable high-end exposure estimates appropriate for screening for human health and aquatic and terrestrial wildlife?

5. EPA proposes to evaluate three locations that have different meteorological characteristics (wet, median, dry). Are these three geographic exposure scenarios appropriate for this screening level risk assessments?

6. EPA has developed four scenarios for the screening-level risk assessment, including specific pathways. Are the pathways for exposure simulated in the BST appropriate for a national screening-level risk assessment?

7. Does the User Guide describe how to use the BST for screening at an appropriate level of detail?

On EPA’s refined risk assessment model, the SAB panel had to answer the following charge questions:

1. Are there any additional existing data sources on exposure that can be used as model inputs for Monte Carlo simulations?

2. Are there alternative transport models that EPA should consider for the refined biosolids risk assessment?

3. Are there additional scenarios for biosolids management that the EPA should consider for refined assessments?

Panel member Dr. Drew McAvoy, a professor of engineering at the University of Cincinnati, commented that criteria for soil mobility, sorption and attenuation are not reflected in the model parameters. There will be additional recommendations to come on this issue.

A theme repeated over and over again was “compounding conservatism,” with the panel concerned that the EPA models are layering conservative assumptions on top of conservative assumptions resulting in probable overestimating of risk.

The gist of the draft cover letter, relative to the panel’s charge, is that the panel finds the PICS process is “sufficient” if the recommendations of the SAB are followed. It will include the major concerns and critical points the SAB wants to make about the biosolids risk assessment framework. One of the main concerns expressed by almost everyone on the panel is that the EPA needs to consider the biosolids matrix and how PFAS behave in that matrix, which is different from other matrices.

Both WEF and NACWA provided written comments on the draft SAB report. NACWA’s comment letter was 13 pages and arrived in time for the panelists to read it before the July 5th meeting. During that meeting, several panelists cited points made by NACWA, including:

• “The framework needs an off-ramp for chemicals where a risk assessment would be unwarranted or provide meaningless results. The off-ramp is particularly relevant for chemicals (e.g., pharmaceuticals) that are intentionally ingested in food and consumer products.”

• “A risk assessment off-ramp is also necessary for chemicals that are present in biosolids at or below background soil concentrations.”

NACWA suggested the use of Reasonable Maximum Exposure (RME) versus the Highly Exposed Individual (HEI) receptor that is in the screening-level risk assessment model. NACWA also questioned the weighting of various criteria in the model and the role of geography or regional differences in climates, soils, and management practices. King County (Seattle, WA) Department of Natural Resources and Parks’ Wastewater Treatment Division submitted written comments in the same vein.

The full SAB Biosolids Panel will need to approve the final peer review report and cover letter and will be sending it to EPA Administrator Regan in the very near future. It’s not clear what happens with the report or whether or not EPA must make any changes as a result. The minutes from the July 5th biosolids panel meeting are supposed to be posted soon at Meeting | US EPA.