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Fate and occurrence of unregulated organic chemicals (UOCs) in municipal, agricultural, and aquatic systems
Organic chemicals have become ubiquitous pollutants of aquatic and terrestrial ecosystems. Pharmaceuticals, chemicals in personal care products and/or consumer goods, illicit drugs, agrochemicals, industrial chemicals, and fire retardants like per- and poly-fluoroalkyl substances (PFAS) are all organic chemicals. These compounds have both unidentified toxicological risks and often well-known impacts on wildlife and humans. While most organic contaminants remain unregulated, select compounds are regulated albeit with regulations differing vastly among countries. As climate change exacerbates droughts, flood events, and access to water sources, understanding unregulated organic chemicals (UOCs) will continue to be a priority for managing freshwater resources and implementing sustainable agricultural approaches. Water resource recovery facilities (WRRFs) are essential infrastructure that restrict the contamination of receiving waterbodies. Biosolids can be recovered as an excellent fertilizer source by WRRFs; however, land-applied biosolids can serve as an unintentional conduit of UOCs to agricultural systems. Many developing nations do not have the infrastructure or a robust and enforceable regulatory framework to protect water resources from contamination. However, even countries with robust infrastructure are faced with many challenges surrounding UOCs management as WRRFs are not designed for removal of UOCs. This dissertation aims to fill existing data gaps by 1) evaluating the concentrations and seasonal variation of UOCs in a riverine ecosystems of Northern Pakistan receiving untreated sewage; 2) reviewing PFAS occurrence with a focus on primarily land-applied sources in an agricultural setting with a spotlight on uptake mechanisms; 3) optimizing and validating extraction and analysis methods for UOCs in biosolids with a focus on two different extraction approaches; and 4) quantifying UOC concentrations in sewage sludge for typical anaerobic digestion and Cambi thermal hydrolysis with anaerobic digestion and comparing concentrations both pre- and post-treatment and between the final products (Class B and Class A biosolids).
The Swat and Kabul Rivers of Northern Pakistan served as a study site to evaluate UOC concentrations in freshwater ecosystems receiving untreated sewage and municipal solid waste. The region consisted of a primarily river-based economy that had been coping with anecdotally reported fish declines. Due to the known impacts of pollutants on aquatic ecosystem health, evaluating UOC concentrations served as one aspect of a multifaceted collaboration aimed at elucidating the drivers of the regional fish declines. Water samples were collected during the high flow summer season (2018) and the low flow winter season (2019) in both the Swat and Kabul Rivers. Samples were analyzed for 67 compounds via liquid chromatography tandem quadrupole time-of-flight mass spectrometry (LC-QToF). In the mountainous Swat River, ∑plasticizers and caffeine were reported up to 7379 ng/L and 8453 ng/L, respectively. Four phthalates were reported with 100% detection frequency (DF) in both seasons with Bis (2-ethylhexyl) phthalate detected at the highest concentration in the SWAT river during the winter. Similarly, plasticizers and caffeine were identified in the Kabul River up to 722 ng/L and 2081 ng/L. Detection of pharmaceuticals decreased due to dilution during the high flow seasons in both the Swat (DF: 10-100% in summer and 70-100% in winter) and Kabul (DF: 0-11% in summer and 0-78% in winter) Rivers. The reported UOC concentrations remain below those reported to cause adverse effects by ecotoxicological studies. This information was provided to regional policy makers and stakeholders.
PFAS are a family of persistent chemicals found in biosolids of which agriculture may serve as an exposure route. Thus, a review was written to serve as a foundation to further understand the sources and fate processes of PFAS in agricultural systems along with the mechanisms and implications of plant-uptake. This review included additional PFAS than the narrow subset that had previously been the focus of researchers. Short-chain PFAS were identified to uptake in plants readily due to active and passive translocation processes. Additionally, the contributions of PFAS precursors in the rhizosphere as a long-term source of PFAS was introduced. The limitations of study design were discussed, as greenhouse studies and hydroponic studies predominately contributed to available knowledge. The need for comprehensive field studies was established as a prominent data gap along with the continuing need for studies to cover the complex range of different PFAS as opposed to a select few.
Analytical methodology greatly restricts the number and physiochemical diversity of UOCs that can be assessed by studies. Prior to the introduction of broadly applicable instrumental analysis like high resolution mass spectrometry (HRMS), methods that targeted a specific subset of compounds were common. However, due to their specificity current sample preparation methods are not well-suited to more advanced HRMS techniques like data independent acquisition. Moreover, biosolid matrices are especially challenging to analyze and require rigorous clean-up. Therefore, two common approaches to UOC extractions were adapted for biosolids and validated. The EPA method 1694 was adapted as the basis of the method implementing solid phase extraction (SPE) as the primary clean-up approach. The second extraction method implemented a dispersive SPE approach using an EMR-Lipid sorbent to remove matrix interferences. EMR-Lipid was chosen as the process is both simple and quick compared to solid phase extraction and the sorbent seemed well-suited to clean-up the biosolid matrix. Both methods used ENVI-Carb™ SPE cartridges (100 mg) as a second clean-up step prior to the final evaporation procedure. The method validation evaluated the impacts of component recovery and matrix effects (suppression and/or enhancement) for each method for 126 compounds. Both methods could extract 34 compounds in addition to 37 that were extracted independently with HLB-SPE and 19 that were extracted with EMR-Lipid. Tetracyclines, estrogens, and compounds with early elution profiles were not optimized due to the limitations of the chromatography and the objective of creating a comprehensive and simplified workflow. For 70% of the compounds the average extraction recovery was 100 ± 50%. Ninety compounds were suitably recovered from biosolid samples using both the HLB-SPE (n=61) and EMR-Lipid (n=29) extraction protocols. Using the optimized methods, 75 UOCs were detected and reported between the two biosolid composites used for this validation.
The optimized extraction methodology was then applied to assess the changes in biosolid UOC concentrations as the result of WRRF treatment. This research was novel due to the breadth of UOCs monitored and the unique opportunity to monitor UOCs as major infrastructure investments were made to update an anaerobic sewage sludge stabilization process. Biosolids were collected pre- and post-treatment for five months in 2019 for a typical anaerobic digestion (AD) process resulting in Class B biosolids. Over the next year, a Cambi thermal hydrolysis process (THP) was implemented at the same WRRF to increase the treatment capacity and the biogas production. Biosolid collection from the THP system was also conducted for a five-month period beginning in 2021 once the criteria for Class A biosolids was satisfactory. Composites of the collected biosolids were made to assess UOCs. Of the UOCs (n=90) assessed, 91% were detected in at least one of the sample composites while two thirds were detected in over 80% of the composites. Complete removal was observed for 11% of compounds in AD and 17% of compounds in THP. Plasticizers including BPA, NP, OP, and some phthalates were detected at the highest concentrations and exceeded method reporting limits. Additional compound classes reported in Class A and Class B biosolids included antihistamines, antimicrobials, analgesics, antidepressants, a fragrance, cannabinoids, organophosphate flame retardants, and substances controlled by the US drug enforcement administration.
This research has utilized a multifaceted approach to decrease the data knowledge gap on anthropogenic-derived UOCs to inform UOC management. These contributions include the first study evaluating UOCs in aquatic ecosystems of Northern Pakistan, broadening the current understanding of PFAS fate and plant uptake in agricultural systems, optimizing a comprehensive methodology that can be used to assess UOCs in biosolids, and comparing the UOCs in the production of class A and class B biosolids. The presence of phthalates at high concentrations in both rivers of Pakistan and biosolids indicates that this compound class should be prioritized and merits continued monitoring. The synthesized review focused on PFAS in agricultural systems revealed that while controlled laboratory or greenhouse studies have merit, comprehensive field studies are lacking to provide clarity on PFAS fate and their relative risk in agricultural systems, which also applies to other UOCs. Method optimization specific for quantifying UOCs in biosolids, which enabled evaluating UOC presence and changes in WRRF processes, will facilitate future research on further understanding UOC fate both in our WRRFs and after land application. Finally, evaluating UOC occurrence and changes during anerobic digestion and thermal hydrolysis processes for the same municipal waste stream provided a unique perspective on how these two treatment processes alter UOC concentrations in biosolids. Moreover, these findings contribute to the limited data on UOCs in biosolids that are intended for use as fertilizers.
This work was funded in part by support provided by the Purdue Research Foundation, the Department of Agronomy at Purdue University and the USDA National Institute of Food and Agriculture Hatch Funds under Accession No. 1006516.
United States Department of State and the United States Agency for International Development (USAID) under the Pakistan - U.S. Science & Technology Cooperation Program
Purdue Andrews PhD Fellowship
Purdue Bilsland Dissertation Fellowship
VA Hampton Roads Sanitation District (HRSD)
- Doctor of Philosophy
- West Lafayette