Honglin Chen

Project title: Evaluation of Health Impacts of Land-Applied Biosolids due to Presence of Phthalates and Per- and Polyfluoroalkyl Substances (PFAS) in Washington State

Degree: MS (Applied) | Program: Applied Toxicology (App Tox) | Project type: Project
Completed in: 2021 | Faculty advisor: Christopher D. Simpson


Biosolids are nutrient-rich residual organic matter derived from wastewater treatment. The majority of biosolids in Washington are land applied, with the remaining landfilled or incinerated. In land application, biosolids are mostly applied on agricultural lands or forests as a soil amendment and fertilizer. There are nine metals, Salmonella spp., enteric viruses, and viable helminth ova that are regulated in biosolids by federal and state legislation. Depending on the treatment process that is applied to reduce pathogens, biosolids are identified as either Class A or Class B. Concerns have arisen about the presence of other potentially harmful chemicals in biosolids due to increasing amounts of scientific studies that reveal the health impacts of exposure to such chemicals. Many organic chemicals have been detected in biosolids and this paper is focused on two of them: phthalates and per- and polyfluoroalkyl substances (PFAS). Phthalates are plasticizers widely used in different products such as polyvinyl chloride (PVC), vinyl flooring, and personal care products. Studies have shown that chronic exposure to phthalates can adversely affect the reproductive system, child growth and development, and may result in cancers. Phthalates are biodegradable in the environment. PFAS are a diverse group of persistent compounds that are not readily biodegradable. They are used in fire-fighting foams and other industrial applications but also in consumer products including non-stick cookware, textiles, food wraps, and cosmetics. Long-term exposure to PFAS is linked to possible liver damage, suppression of the immune system, low birth weight, and decreased fertility. Furthermore, studies have shown that long-term exposure to a specific PFAS - perfluorooctanoic acid (PFOA) can possibly cause testicular and kidney cancers. A literature review was conducted to assess the prevalence of phthalates and PFAS in biosolids and their potential exposure risks to human health. PubMed, PubChem, and Google Scholar were the databases used in the literature search. Keywords were determined prior to the literature search. Based on titles and abstracts, articles were selected for further review. There is limited data available on the levels of phthalates and PFAS in land-applied biosolids. Based on the limited data, some studies suggest plant uptake and migration of phthalates and PFAS to groundwater. Overall, it is difficult to conclude whether the presence of phthalates and PFAS in land-applied biosolids would pose adverse effects on human health.