W5170: Beneficial Use of Residuals to Improve Soil Health and Protect Public, and Ecosystem Health

(Multistate Research Project)

Status: Active

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SAES-422 Reports

Annual/Termination Reports:

[01/04/2025]

Date of Annual Report: 01/04/2025

Report Information

Annual Meeting Dates: 05/19/2025 - 05/20/2025
Period the Report Covers: 10/01/2024 - 09/30/2025

Participants

Brief Summary of Minutes

Accomplishments

Accomplishments <ol> <li>Objective #1-  Evaluate the short- and long-term fate, bioavailability and persistence of emerging contaminants with an emphasis on per- and polyfluoroalkyl substances (PFAS), microplastics, metals, and pathogens in residuals, reclaimed water, and amended soils to aid in assessing and minimizing environmental and human health risks from their application at a watershed scale.  Specific tasks: i) Quantify and evaluate the uptake, accumulation and transport of emerging contaminants in residuals, wasteways and residuals- and wastewater-treated soils (e.g., agricultural, urban and brownfields); ii) Predict the long-term bioavailability, persistence and toxicity of emerging contaminants in residuals- and wastewater-amended soils; iii) Evaluate ecological effects of emerging contaminants from soils amended with residuals and reclaimed wastewaters; and iv) Evaluate long-term effects of residuals and wastewater application on the emergence/spread of antibiotic resistance.  Research for this objective was conducted by members from CO, WA, GA, MN, FL, AZ, PA, HI, IN, OH, KS, and TX.</li> </ol> Per- and polyfluoroalkyl substances (PFAS) To answer the question: “Is land application of municipal biosolids a significant source of PFAS human exposure via groundwater?”, a national collaborative project through the University of Arizona was initiated to evaluate the incidence and mobility of PFAS through soil following land application of biosolids. The goal of PHASE 1 of the project was to sample soil and analyze for PFAS from land application sites across the U.S., with different soils, depths to groundwater, and variable climates. Additionally, measured PFAS concentrations in groundwater beneath the land application sites allow for paired data sets of soil and groundwater concentrations. Ultimately these field data allow for validation of a screening level risk assessment model to predict the risk of PFAS leaching and subsequent groundwater contamination. This approach will allow for site specific evaluation of land application sites nationally with respect to the issue of human PFAS exposure. Thus, both well managed land application sites, and any sites contributing to groundwater contamination can be identified. Overall, this project benefits wastewater utilities and farmers across the U.S. It also benefits the public at large by reducing the extent of a human PFAS exposure via groundwater contamination. To date, samples from 23 sites have been collected from 17 different states across the U.S., making the project truly national in scope. Samples of surface and subsurface soil samples, biosolids samples, and wherever possible, groundwater samples have been collected. All samples were analyzed for PFAS analytes. Data showed that mean and median values of soil PFAS analytes were less than or close to soil screening levels that are protective of groundwater contamination. These data will ultimately be used as inputs for modelling efforts to predict the risk of PFAS leaching to groundwater. The above work in AZ has been supported by several W5170 members, including those in Washington State.  Much of the focus of the WA work on PFAS in biosolids has been extension and outreach focus with multiple columns in Biocycle, a trade journal and an op ed piece in a national farming magazine.  The focus of these pieces was to put science and risk analysis surrounding the presence of PFAS in biosolids into non- scientific language.  These columns also discussed and analyzed a series of articles in the New York Times that presented a highly biased and alarmist perspective. The Pennsylvania State University (PSU) conducted a preliminary greenhouse study to identify the uptake of PFAS into hemp from soils that had been spray-irrigated by treated wastewater for more than 40 years. Five varieties of hemp were investigated, including two that were harvested for grains, two that were harvested for fiber, and one that was harvested for CBD oil. Results found that none of the varieties were good accumulators of the 5 PFAS currently regulated in drinking water, with uptake < 1% of the PFAS in wastewater-irrigated soil. However, hemp does show potential to be a good accumulator of PFPeA and PFBA, which will be assessed in a subsequent greenhouse study. Overall results appear to suggest that hemp can likely be grown safely in biosolids-amended fields, given the low uptake. PSU completed the data analysis from a greenhouse study to: (1) quantify the relative importance of root uptake versus foliar sorption of PFAS in corn and orchard grass; (2) assess any potential plant health effects of PFAS-impacted wastewater irrigation may have; and (3) determine the implications for bioaccumulation into the food chain. The greenhouse study was comprised of four treatments for each forage crop: (1) PFAS-containing agricultural soil watered with treated wastewater; (2) PFAS-containing agricultural soil watered with tap water; (3) control soil watered with treated wastewater; and (4) control soil watered with tap water. Results suggested that foliar sorption was an unlikely contributor to PFAS concentrations in crop tissue. Root uptake was identified as the predominant uptake pathway. PFAS were detected more frequently in orchard grass samples compared to corn silage samples. Additionally, corn exhibited a lower uptake of long-chain PFAS compared to grass. Overall, no plant health effects on growth attributable to PFAS concentrations were observed.  PSU continues to work on a site that has received biosolids for nearly 50 years, focused on quantifying PFAS concentrations within the field and in riparian buffers. PFAS concentrations appear to decrease across the buffer. Additional PSU work has focused on PFAS in living filters and a community science-based project of PFAS in private wells across PA. Studies in Florida have continued to focus on the retention-release behavior of PFAS in biosolids and, upon treatment with various sorbents including drinking water treatment residuals. Few effects on PFAS mobility were observed when amending biosolids with a suite of amendments at amendment rates below 10% wt/wt.  Experiments investigating the trophic transfer potential of PFAS in simulated terrestrial food chains are ongoing.  An experiment characterizing uptake and elimination of PFAS in earthworms from PFAS contaminated soil is nearing completion.  This work will also relate PFAS uptake in invertebrates to tissue lipid/protein content and compare results to another already published study that investigated the trophic transfer of PFAS from tomato to tobacco hornworm. Research in Colorado has aimed at combining targeted and non-targeted PFAS analysis to propose degradation pathways, and explore how these are affected by parameters such as biosolids composition and PFAS structure, and pyrolysis temperature when pyrolyzing biosolids. The PFAS content of biosolids before and after pyrolysis at 300-700°C, either unmodified or amended with a) distinct PFAS compounds that may shed light on differing transformation pathways or b) natural minerals that may catalyze PFAS transformation, were studied. To gain a better understanding of PFAS fate, targeted PFAS analysis was supplemented with non-targeted methods (QTOF analysis, extractable organic and inorganic fluorine analysis, TGA-GC-MS and TGA-FTIR analysis), as knowledge to date relies almost exclusively on targeted analysis. Finally, PFAS leaching from biosolids and biosolids-derived biochars was examined to compare the environmental exposure potential associated with land application of either substance. Results showed that at temperatures as low as 300°C, pyrolysis successfully removed >97% of the PFAS mass, which may allow the production of higher-quality biochar at lower energy investment and without compromising environmental safety. Studies at the University of Georgia have continued research on electrochemical oxidation of perfluoroalkyl substance (PFAS) using porous Magnéli phase titanium suboxide (TSO) anodes as an innovative technology to destroy PFAS in wastewater.  Specifically, University of Georgia participants have prepared TSO anodes doped by sintering that improved their service life as well as EO performance in terms of PFAS degradation. Their study revealed the mechanisms of the performance enhancement and provides understandings to guide further improvements of the TSO anodes via doping (Sui et al., 2025). The team has also systematically assessed the impact of anions commonly present in natural waters on EO performance in terms of PFAS degradation (Wang et al., 2024). In addition, they are in the process of evaluating an approach based on enzyme-catalyzed oxidative humification reactions (ECOHR) to remediate PFAS in biosolids.  University of Georgia W5170 members have also participated in studies to survey the occurrence, fate, and removal of PFAS in both the water streams and biosolids in municipal wastewater treatment plants via systematic sampling and analysis of wastewater and biosolid samples from multiple treatment plants of different scales and involving different treatment processes (Kim et al., 2024; Oza et al., 2024).  They also participated in a study to assess the bioaccumulation of PFAS in a model soil organism caenorhabditis elegans, and to evaluate the impact on their learning and memory by early life exposure to individual and mixture PFAS (Currie et al., 2024). Work in Minnesota focused on three wastewater treatment plants (WWTP) and on-farm trials to monitor the occurrence of PFAS in soil and crop plants.  Within each WWTP location, three grower fields were selected: Field 1, where there was no record of biosolids application biosolids, Field 2 where biosolids were applied at least two years prior to 2023 (historical) and Field 3 where biosolids were applied either the fall or spring prior to planting based on available N content (current season).  Biosolids applied varied with location, and included aerobically digested, class A dried biosolids; aerobically digested class A liquid biosolids, and anaerobically digested class B liquid biosolids.  Crops grown at each location were: Field 1 - rye, corn, or soybeans; Field 2 - soybeans; Field 3 - corn.  Within each location, soil were sampled from 0-1, 1-2, and 2-3 foot depths prior to planting.  Soils were collected again at the three depths in June, from the 0-1 and 1-2 foot depths in August, and all three depths after crop harvest.  Samples underwent PFAS analysis using EPA method 1633.  Crops were hand harvested from the three sites within each field near the areas where soil samples were collected.  Harvested tissue also underwent PFAS analysis using EPA method 1633 and to UMRAL for total elemental analysis.  Minnesota results indicated that PFAS concentrations in biosolids varied with WWTP and in general higher concentrations in biosolids resulted in higher concentrations in soil.   Soil PFOS was detected in all fields with biosolids applied in the current year.  Highest concentrations were found with anaerobically digested biosolids. Highest soil PFOS concentrations were at the surface (0-1 ft), ranging from less than 1 ng/g up to 12 ng/g.   PFOS concentrations decreased at lower soil depths and as the season progressed.   Low amounts of PFOS were detected in fields that had no record of biosolids application (0.04- 0.11 ng/g).   Like PFOS, PFOA was detected in all fields with biosolids applied in the current year with highest concentrations resulting from application of anaerobically digested biosolids.  Concentrations ranged from < 0.1 ng/g to 1.0 ng/g and they tended to decrease with depth and as the season progressed.  Like PFOS, PFOA concentrations were detected at low levels in fields that had no recorded biosolids application, and concentrations were less than 0.2 ng/g.  At concentrations less than 0.6 ng/g, PFBA was detected in fields that had no history of biosolids application and sometimes were higher than in fields that had received biosolids.   PFBS was detected in fields that had a history of biosolids use and in fields with biosolids applied in the current year.   Results of this study demonstrate that the fate of PFAS in the soil environment may be linked to biosolids application but that for some compounds, other pathways also need to be considered.  Analysis of corn grain, corn stover, and soybean grain tissues revealed no detectable PFAS in soybean or corn grain.  PFOS, PFBA, PFPeA, PFBS, were detected in corn stover primarily in plots applied with liquid biosolids.   These results suggest that further testing is needed if stover is used for animal feed.   Under the conditions of this study and the PFAS concentrations in the biosolids applied, animal consumption of corn and soybean grain does not appear to be a health risk when biosolids are applied at agronomic rates. Purdue University researchers finished and published our comparative PFAS in biosolids analytical methodology as well as our investigation on PFAS dynamics within the solids stream processes in treatment of wastewater, specifically anaerobic digestion (AD), thermal hydrolysis (THP), autothermal thermophilic aerobic digestion (ATAD) and storage nitrification-denitrification reactor (SNDR).  Ongoing field studies include both historically applied and first-time biosolids applications on the west coast, east coast and Midwest fields, to  evaluate the persistence and transport of PFAS. Biosolids contained 50 to 75% precursor PFAS for which almost all the fluorotelomer precursors degraded to PFCAs within one year after application and primarily ECF-precursors remaining. Overall, long-chain PFAS predominantly persist in the upper 60 cm likely due to primarily organic carbon (OC) content given the high OC levels in the 0-30 cm depth (~15%) and the 30-60 cm depth (~5%) from annual biosolids applications annually (for up to four decades). No PFAS reached the DLD groundwater monitoring well above EPA April 2024 MCLs except PFOA at 39 ppt. Transport modeling of the field site in collaboration with Kurt Pennell at Brown University has been completed and is being written up. Additional work from Purdue University has focused on a 1-year feed grass greenhouse study (closed pots – no leachate exited the pot) using PFAS-contaminated soils from Maine in which the effect of three different application rates of high carbon wood ash plus a no ash addition on PFAS uptake was evaluated over multiple harvests. PFAS uptake in all treatments decreased from the first to third harvest and then increased consistently through the next 5 harvests. Uptake was not directly correlated to potential evapotranspiration rates (estimated from temperature, growing degree days) indicating other factors such as increased root mass and root exudates facilitated PFAS uptake. PFAS translocation factors decreased in all high carbon treatments with the 6 wt% ash treatment performing the best. A soybean greenhouse study (closed pot - no leachate exited the pot) using PFAS-contaminated soils from Indiana was conducted using six soybean plant genetic varieties as well as one treatment involving 3 wt% high carbon wood ash to evaluate where PFAS translocate into the soybean plant and if sorbents will alter uptake. Three pairs of soybean genetic varieties were selected for their genetic variations contributing to drought tolerance mechanisms or final bean protein/oil ratio to better understand mechanisms that may drive or reduce PFAS uptake in plants. At senescence, the beans, pods, leaves, and stems of the soybean plants were extracted and analyzed for PFAS. PFAS uptake into the bean had negligible bioaccumulative PFOS and EtFOSAA which were present at several hundred ppb in the soil, nor was PFOA taken up into the bean whereas substantial concentrations of C4 and C5 perfluoroalkylcarboxylic acids. PFAS accumulation in soybean plant tissues was greatest in leaves, followed by stems, and bean pods. PFOS only appeared in plant tissues with stomata indicating that transpiration is the primary mechanism of uptake. The high carbon wood ash treatment also reduced PFAS accumulation into soybean seeds demonstrating their potential as a management strategy contaminated agricultural lands. The Ohio State University is studying the transport of PFAS from biosolids in 12 soils with a range of properties important to absorption of PFAS .  This is a laboratory study using packed columns and USEPA Method 1340 which requires collection of 9 eluates per soil/biosolid.  Most, but not all, of the column studies have been completed.  Additional studies are focused on various biosolids and rates, and their effects on PFAS concentrations in soils and uptake in barley and corn plant components (e.g., stalks, leaves, grain).  A subsequent study is focused on the ability of ~ 50 different biochars to sorb/desorb PFAS. Other unregulated organic contaminants The University of Florida developed a method for the extraction of microplastics from drinking water treatment residuals and used this method to extract and characterize the amount of microplastics in a small but representative number of drinking water treatment residual samples. Ca-DWTRs contained very little microplastics contamination compared to Al- and Fe-DWTRs. Purdue University completed and published work on comparative biosolids analytical methodology for other unregulated organic compounds (UOCs), e.g., personal care products, pharmaceuticals, etc.). They also finished our UOC comparative fate during AD and with addition of THP prior to AD. In addition, ongoing field studies include both historically applied and first-time biosolids applications on the west coast, east coast and Midwest fields, to  evaluate the persistence and transport of UOCs.  Only a handful of UOCs persisted after one year of being land-applied, which included the pharmaceuticals miconazole (antifungal), fluoxetine (antidepressant) and diphenhydramine (antihistamine), personal care product chemicals tonalide (perfume) and nonylphenol, and the opioid methadone. The University of Cincinnati wrote up a report on the prioritization scheme for identifying the highest priority organic compounds in biosolids amended to agricultural fields. Briefly, a total of 910 chemicals known to be present in biosolids were screened to 125 priority UOCs. These 125 UOCs were then prioritized as high and low priority based on mobility, persistence, bioaccumulation, and toxicity. The carcinogens, endocrine disruptors, and the top 50 compounds that appeared in five prioritization scenarios were categorized as high priority. This represented 47 of the total UOCs evaluated. The remaining 78 UOCs were categorized as low priority. The 125 priority UOCs from this evaluation were also compared to other biosolids priority lists (Higgins et al. prepared for the Water Environment Research Foundation; wca Environment Ltd. prepared for the Scottish EPA; ToxStrategies Inc. prepared for the Texas Commission for Environment Quality). Eight UOCs from this study were present in two of the three other priority lists. These compounds included BDE-47, BDE-207, BDE-99, Tonalide, Sulfanilamide, Ofloxacin, Triclocarban, and Triclosan.  The University of Cincinnati also continued progress on a risk calculator model for biosolids amendment to agricultural soils. Modeling code for plant uptake, beef and milk accumulation, and vadose zone leaching has been developed. Additional modeling for chicken and egg exposure, surface runoff and fish exposure, and groundwater transport with drinking water exposure are in the process of being developed. Also, effects data are being gathered (cancer and non-cancer) and preliminary risk calculations are planned for the highest priority UOCs over the summer of 2025.   <ol> <li>Objective #2-  Evaluate and optimize the uses and associated environmental benefits of residuals and wastewaters applied to various ecosystems (e.g., agricultural, urban, recreational, forest, rangeland, mine-impacted, other anthropogenic) on soil physical, chemical, and biological properties and plant nutrition, health, and yield. Specific tasks: i) Quantify the effects of biosolids and other municipal, industrial, and agricultural residuals on indicators of soil health; ii) Quantify the effects of biosolids and other residuals on pollutant (metals/metalloids) availability, assimilation, phytotoxicity and remediation; and iii) Develop and evaluate treatment strategies of residuals and wastewaters to reduce contaminant or pathogen loads. Research on this topic was conducted by members from CO, WA, GA, MN, FL, AZ, PA, HI, IN, OH, KS, and TX.</li> </ol>  Soil health and soil carbon benefits Work in Washington State has focused on the impacts of biosolids for dryland wheat production.  The emphasis of the research has been on understanding benefits associated with use of biosolids in lieu of conventional fertilizer.  Our work has shown that use of biosolids provides persistent benefits with increased soil carbon and yields observed seven years after biosolids applications ceased (Singh et al., 2024).  We have also considered biosolids as an example of a circular nutrient economy.  For the latter, we have quantified the economic benefits to participating farmers on a per ha basis, as a result of reduced fertilization costs and increased yields (Brown et al., in review). The University of Florida completed a series of column experiments investigating the impact of amending a high Ca, high P “legacy” ranchland soil with a suite of different a P-immobilizing agents, including waste residuals and commercially-available mixtures (Objective #2). This work was funded by the St. Johns River Water Management District. Experiments were conducted to simulate both a permeable reactive barrier approach (PRB; where a barrier layer is placed within the column) as well as an “Add/Mix” approach (i.e., adding an amendment to soil and homogenizing it).  Al-DWTRs outperformed even commercial reference formulations. This work, featured in various presentations during the project year as well as being published in a MS thesis late last year, is currently being prepared for publication in a peer-reviewed journal. Kansas State University researched simultaneous recovery of P (Ca-phosphate precipitation) and N (sorption using clays or struvite precipitation) from swine wastewater using a laboratory- and field-scale treatment train centered around anaerobic membrane bioreactor (AnMBR) to assess the efficiency of an innovative configuration of AnMBR technology in combination with constructed wetlands (CWs) systems, providing a sustainable and resilient management system for agricultural wastewaters. Water quality Texas A&M projects were conducted to examine the impacts of an extreme flooding event on surface water quality and the potential for photocatalytic disinfection of E. coli in water. The first study examined microbial fecal indicators in Houston, TX following Hurricane Harvey where some areas received >150 cm of rainfall within a few days. Surface water samples were collected at six locations in the southeastern Houston area immediately before and after the hurricane and then every 1 to 2 weeks thereafter over a 2-month period. Total E. coli numbers were determined and water samples were analyzed via quantitative real-time PCR (qPCR) for general and source-specific total Bacteroidales and human Bacteroidales markers, and digital PCR (dPCR) for antibiotic resistance genes (ARG) and a plasmid (pBI143) associated with human waste. SourceTracker2 was used to determine human source contributions based on metagenomic analysis of PCR-amplified 16S rRNA gene fragments. Samples collected immediately after the hurricane had elevated levels of E. coli, ranging from 488 to 1,733 CFU 100 ml−1. After 1 week, E. coli levels decreased to <100 MPN 100 ml−1. Total Bacteroidales numbers were elevated immediately following the hurricane and remained high for 12 days. Human-source contributions, as assessed by PCR methods and metagenomic analysis, peaked within 12 days after the hurricane consistently across all sampling sites. Multiple regression analysis of environmental parameters, copies of ARG and pBI143, and metagenomic data confirmed that human waste caused the dramatic, short-term, high levels of fecal contamination of floodwaters generated by Hurricane Harvey. Fecal indicators approached normal background levels approximately 3 weeks after the rainfall ended.  The second study evaluated the use of TiO2 nanowire porous foams for photocatalytic disinfection of water. Use of the foams led to a 2–3-log reduction of E. coli in a span of 180 min when ultraviolet-A (UV-A) light was employed for photoactivation. More importantly, the photocatalyst foams were easily recoverable from water via mechanical separation, which in this study led to a recovery of 98–99% of the TiO2 nanowire photocatalysts. This strategy allows for further optimization of both the process kinetics and the total amount of photocatalysts needed for water remediation through optimization of the porosities and the geometries of the foams and ensuring that all the photocatalyst surfaces remain accessible to both the pollutants and light. Biochar studies The University of Hawaii created a biochar made from invasive tree species, mainly leucaena (Leucaena leucocephala L.) at pyrolysis temperatures around 350 – 400 oC. Subsequently, two types of compost were prepared with and without 5% biocchar and were amended to a nutrient-poor weathered soil in Oahu, Hawaii. Sweet corn (Zea mays L.)  was grown as a test crop. Preliminary results showed that the  biochar-assisted compost had more microbial activities (higher CO2 production) and matured about 2 weeks faster than the compost without biochar. Importantly, corn grew much better, yielded larger ears than the no biochar treatment. This work helped control invasive trees, protect local environment and profit farming operations.  Urban soils Dr Brown (University of Washington) and Dr. Hettiarachchi (Kansas State University) co-authored a paper considering the benefits of green space in urban areas (Brown and Hettiarachchi, 2025).  Green space here included urban agriculture.  The potential risks associated with contaminants (Pb and PAH) in urban soils was discussed.  Use of municipal biosolids and residual based composts as tools to both reduce the concentration and bioaccessibility of contaminants as well as to enhance plant growth in urban soils was a focus of the work. Dr. Hettiarachchi (Kansas State University) collected data from child lead poisoning prevention programs in Kansas City, MO, and Kansas City, KS, as well as brownfields programs. The data indicated that a significant number of residential properties tested contain lead (Pb) above the EPA level for child play areas (400 mg/kg). In situ stabilization of common soil contaminants, such as Pb, using soil amendments primarily focuses on reducing human health and environmental risks by inducing biogeochemical reactions that convert soil contaminants into forms with low bioavailability. Kansas State University personnel have been conducting field-based research studies at seven vacant lot sites in Kansas City, MO residential neighborhoods, using phosphorus and other soil amendments, including locally available Class A biosolids, since the summer of 2022. Results have demonstrated that P fertilizers, such as ammonium polyphosphate, and Class A biosolids amendments help to reduce the bioaccessibility of Pb in soils (measured using both PBET at pH 2.5 and USEPA’s IVBA at pH 2.5 methods) with relatively higher Pb bioaccessibilities (> 15-20% of the total Pb was bioaccessible at the beginning). Results also showed that it was challenging to reduce bioaccessibility further when soils have inherently low bioaccessible Pb (i.e., only <10-15% of total Pb in the soil is bioaccessible). The team is also verifying these reductions by studying changes in soil Pb speciation using X-ray absorption spectroscopy and currently in the process of establishing field sites in Kansas City, Kansas.

Publications

Impact Statements

The beneficial reuse of biosolids and municipal wastewater in agricultural activities is of growing importance to meet the need of increasing populations, but its acceptance is limited by some trace constituents in these materials, for example PFAS and other unregulated organic compounds (UOCs), e.g., personal care products, pharmaceuticals, etc.). The continued W5170 research is leading towards development of innovative technologies to mitigate heavy metal contamination, PFAS and other UOCs, including novel amendments, electrochemical approaches, enzyme-based processes, and pyrolysis techniques. The results provide a basis for design and optimization of the novel processes that can mitigate the constituents that limit the beneficial reuse of biosolids and wastewaters and thus reduce their environmental loads. These novel technologies are expected to have long-term impacts in beneficial reuse of biosolids and wastewater. In the meantime, we have conducted systematic research to investigate the occurrence of PFAS in water recovery facilities and assessed their toxicity potentials. The results provide useful information for knowledge-based environmental risk assessment and policy making in relation to PFAS contamination. WWTPs, farmers who receive biosolids, consultants, agricultural professionals, and the broader public will learn how biosolids application for crop production affects the fate of PFAS, UOCs, and metal compounds in soils, crops, and risk of groundwater contamination. The data generated will be used to help state agencies improve their PFAS transport and health risk models and develop policy on land application of biosolids.