Grantee Research Project Results

Final Report: Fate and Transport of Unregulated Organic Contaminants in Biosolids - Development of a Human and Environmental Exposure Risk Framework

EPA Grant Number: R840247
Title: Fate and Transport of Unregulated Organic Contaminants in Biosolids - Development of a Human and Environmental Exposure Risk Framework
Investigators:
Institution:
EPA Project Officer:
Project Period: September 1, 2021 through May 13, 2025
Project Amount: $1,498,000
RFA: National Priorities: Evaluation of Pollutants in Biosolids (2020) RFA Text |  Recipients Lists
Research Category: Water Quality , Water , Water Treatment

Objective:

We propose a transdisciplinary and highly innovative project to develop a flexible framework for the prioritization of biosolids-associated organic contaminants (BOCs). The objectives are to 1) characterize the occurrence, fate, and transport of BOCs after land application of biosolids; 2) model BOC exposures and perform hazard and risk assessments to identify high-priority BOCs; and 3) utilize an array of communication channels to translate our findings and methodology for the wastewater and agriculture communities, regulators, and the general public.

Summary/Accomplishments (Outputs/Outcomes):

Objective 1

Sixteen biosolid samples from U.S. and Canadian treatment facilities were analyzed using advanced non-targeted mass spectrometry. A total of 451 features were prioritized based on their consistency across samples and quality control criteria. Identification confidence was assigned using Schymanski et al.’s five-tier scale, with the majority of features (over 75%) remaining unidentified (Level 4 or 5) due to limited spectral database coverage.

• 26 compounds were confirmed via reference standards (Level 1).
• These included pharmaceuticals (e.g., carbamazepine, citalopram), flame retardants, plasticizers (e.g., bisphenol A, S, and F), and fragrances.
• An additional 47 compounds were assigned Level 2a confidence via spectral library matches (e.g., indole, diphenhydramine).

Using the EPA’s Hazard Comparison Module (HCM), 89 identified BOCs were assessed across 19 endpoints. A quality-adjusted hazard scoring system prioritized compounds for chronic human exposure, short-term exposure, and ecological toxicity:

• Top chronic risk: Ketoconazole, p-cresol, phenolphthalein
• Top acute risk: Clorophene, indole, thymol
• Top ecological risk: Fludioxonil, ketoconazole, triclocarban

Data gaps for several endpoints (e.g., chronic aquatic toxicity) remain a major limitation, with many compounds excluded due to insufficient data.

43 prioritized BOCs were spiked into biosolids and incubated with sandy-loam soil for 30 days. Results revealed:

• 19 compounds underwent biodegradation (e.g., methylparaben, bisphenol A).
• 2 compounds were degraded via both biotic and abiotic processes.
• 11 compounds could not be quantified due to analytical interference.
• 9 compounds showed no degradation, indicating persistence (e.g., carbamazepine, fluoxetine).

Untreated biosolids were exposed to active soil for 60 days:

• 1,038 features were evaluated; 171 had tentative structural matches.
• Only 20 Level 2 compounds significantly decreased (e.g., bisphenol A, amphetamine).
• 112 compounds showed no significant change, confirming persistence.
• 15 compounds increased over time, likely due to the breakdown of larger parent compounds.

Together, these findings suggest that a substantial portion of BOCs in biosolids are recalcitrant under common soil conditions.

Lettuce, tomato, and carrot plants were exposed to four psychoactive pharmaceuticals (e.g., carbamazepine, fluoxetine) in hydroponic systems:

• 45 metabolites were detected and structurally characterized.
• Observed metabolic pathways included Phase I (oxidation, epoxidation) and Phase II (glucosylation, acylation).
• Metabolites like epoxycarbamazepine, nortriptyline, and norfluoxetine may retain psychoactivity or pose new toxicological risks due to increased lipophilicity.

Lettuce and tomato were grown in biosolid-amended soil spiked with mixtures of 40 BOCs:

• 10 compounds were detected in lettuce leaves; 8 in roots.
• Carbamazepine and spectinomycin reached higher concentrations in leaves than in soil.
• Fludioxonil and tris(2-chloroisopropyl)phosphate accumulated more in roots.

A Maryland field site was used to compare plant uptake in biosolid-amended vs. control plots:

• Crops included lettuce, tomatoes, potatoes, corn, onions, and green beans.
• No significant differences in plant BOC content were observed between treated and untreated plots under typical application conditions.
• This suggests minimal risk of plant uptake at environmentally relevant BOC concentrations.

Overall, the outcomes of Objective 1 highlight the need for expanded regulatory monitoring, improved contaminant prioritization frameworks, and refined biosolid application guidelines to protect environmental and human health.

Objective 2

Prior biosolids risk assessments have not considered key receptors that are likely to be highly exposed relative to the general population. The reason for their exclusion is a lack of exposure data, particularly for biosolids and soil exposures among those that apply biosolids and or work on farms where biosolids have been applied. Prioritization schemes that do not consider these occupational exposures are subject to uncertainty and run the risk of missing chemicals that contribute substantially to worker risk (but may be less important for more distal receptors). To this end, we accomplished the following during the award period:

• We built on qualitative research into farm worker soil exposures to develop quantitative soil contact exposure factors and exposure estimates that are relevant to farmer working on land amended with biosolids. These data are directly applicable to modeling quantitative BOC exposures for farmers.
• We conducted qualitative interviews with biosolids applicators to map out the types of tasks involved in biosolids loading, transport, and land application to scope the activities that contribute to BOC exposure. This work led to the discovery and documentation of previously unknown high biosolids-exposure relevant tasks (cleaning and maintenance of equipment in the field) that would have been otherwise missed in risk assessments (and lead to underestimation of BOC exposures for these receptors).
• Based on the findings of the biosolids applicator qualitative interviews, we designed a quantitative survey to determine the frequencies and durations of these tasks (and other relevant detail about the work) in order to develop quantitative exposure factors for the biosolids applicator receptors. The survey has been conducted with applicators, but data collection is underway for these persons. With the completion of this survey, these exposure factors can be used to improve the confidence in our exposure assessment in support of the risk prioritization of BOCs.

The majority of identified BOCs lack traditional toxicological metrics that would enable them to be considered in quantitative risk assessment - many of these chemicals have little or no toxicological information. Despite this, they may contribute to health burdens and need to be considered in efforts to prioritize BOCs for regulatory consideration or other potential interventions. For this reason, we focused our efforts on development of approaches for the most data-poor chemicals which previously would likely have been ignored in prioritization scheme. We leveraged computational toxicological approaches to provide a way to assign hazard information to these low-information BOCs in hopes that a comprehensive prioritization scheme can place BOCs into tiers; these tiers can facilitate ranking among chemicals with comparable levels of toxicological characterization.

For these data poor chemicals, we developed a hazard prioritization framework and a customized read-across workflow to support chemical risk assessment in complex exposure scenarios. The framework organizes hazard assessment into three domains: exposure scenario, chemical occurrence, and potential adverse effects. A four-step process, incorporating EPA’s Hazard Comparison Module (HCM), was used to generate composite scores for individual chemicals, facilitating prioritization despite data gaps. To address limitations in existing tools like GenRA, a customized, R-based read-across workflow was developed to infer toxicity of data-poor chemicals using structurally similar analogues. This approach incorporated additional filtering based on physicochemical properties and structural alerts, improving prediction reliability and reducing subjectivity. The workflow was piloted using contaminant data from a parallel study, demonstrating feasibility for early-stage screening and adaptability across environmental media. Although not fully applied to biosolids before the grant ended, the methods provide a scalable, transparent, and data-driven foundation for prioritizing chemical hazards with differing levels of toxicological information and uncertainty.

Objective 3

Outreach activities involved meetings with the stakeholder advisory board to link project outcomes to practical needs. Research conducted as part of Objective 1 has been published in peer-reviewed publications (see list of publication). Several manuscripts related to Objectives 1 and 2 are currently in preparation.

Future Activities: In the next monitoring period we will continue the laboratory experiments to assess biotransformation, leaching, and plant uptake, translocation and metabolism of BOCs. These laboratory experiments will be used to inform our interpretation of results obtained from our first field study that was conducted during this monitoring period. We will also conduct further analysis of biosolid samples in order to quantify the concentration of priority BOCs identified in the project. We will further conduct a second field study to evaluate groundwater leaching under field conditions. The data that we expect to generate in the next reporting period will be used for the further development and refinement of the hazard and risk prioritization framework.

References:

Publications

Newmeyer, M.N., Lyu, Q., Sobus, J.R., Williams, A.J., Nachman, K.E., Prasse, C. (2024). Combining non-targeted analysis with computer-based hazard comparison approaches to support prioritization of unregulated organic contaminants in biosolids. Environmental Science & Technology, 58 (27), 12135–12146.

Brueck, C.L., Xin, X., Lupolt, S.N., Kim, B.F., Santo, R.E., Lyu, Q, Williams, A.J., Nachman, K.E., Prasse, C. (2024). (Non)targeted chemical analysis and risk assessment of organic contaminants in darkibor kale grown at rural and urban farms. Environmental Science & Technology, 58 (8), 3690-3701.

Presentations

Newmeyer MN, Lowe CN, Black GP, Charest N, Sobus JR, Williams AJ, Prasse C. Implementing a chemical space mapping tool to improve interpretation of nontargeted analyses of biosolids: A proof-of-concept study. American Chemical Society Spring 2023 Meeting, March 2023, Indianapolis, IN and Virtual.

Newmeyer MN, Lupolt SN, Williams AJ, Nachman KE, Prasse C. Characterizing biosolids-associated organic contaminants (BOCs) to support human health risk-based prioritization. American Chemical Society Fall 2023 Meeting, August 2023, San Francisco, CA and Virtual.

Demo R, Prasse C, Nachman KE, Lupolt S. Qualitative characterization of exposures to biosolids among biosolids applicators. Oral presentation at the International Society for Exposure Science Annual Conference; Montreal, Quebec; October 2024.

Lupolt SN, Gillooly S, Simones T, Nachman KE, Smith A. Farmworkers are not construction workers: development of a farmworker scenario to support the derivation of soil screening levels for per-and polyfluoroalkyl substances (PFAS). Oral presentation at the International Society for Exposure Science Annual Conference; Montreal, Quebec; October 2024.

Prasse, C., Human and Environmental Exposure Framework for Biosolids. 4^th EPA New Approach Methods Conference, November 2024, Research Triangle Park, NC.

Prasse, C., Combining non-targeted analysis with computer-based hazard comparison approaches to support prioritization of unregulated organic contaminants in environmental media. NACRW annual meeting, July 2024, Ft. Lauderdale, FL.

Journal Articles:

No journal articles submitted with this report: View all 8 publications for this project

Supplemental Keywords:

measurement methods; environmental chemistry; organics; human health

Progress and Final Reports:

Original Abstract

2022 Progress Report

2023 Progress Report

2024 Progress Report