New research from Johns Hopkins University reveals that fertilizers made from wastewater treatment leftovers may contain potentially harmful organic chemicals. The study, published in Environmental Science & Technology, offers a comprehensive look at the chemical makeup of biosolids across North America and could help regulators identify which compounds need closer scrutiny.
Biosolids, the treated remnants of sewage sludge, are widely used as fertilizers on agricultural lands, golf courses, and landscaped areas. While rich in nutrients, these materials may harbor traces of pharmaceuticals, industrial chemicals, and fragrances that could pose risks to human health and the environment.
Uncovering Hidden Hazards in Biosolids
The research team, led by Carsten Prasse, an assistant professor in the Department of Environmental Health and Engineering, analyzed 16 biosolid samples from wastewater treatment facilities in nine U.S. and three Canadian cities. Their findings included traces of bisphenol A (BPA), a common plastic component, and carbamazepine, a medication used for epilepsy and bipolar disorder.
“We’ve been relatively in the dark when it comes to possible organic hazards in biosolids, and we need to know if there are any smoking guns that we’re unaware of,” Prasse said. “Regulators need to know what these types of fertilizers are made of to determine how they can be responsibly used.”
The team identified 92 compounds present in 80% or more of the samples. They then cross-referenced these chemicals with the EPA’s CompTox Chemical Dashboard to identify those most likely to pose threats to human health or the environment.
Balancing Benefits and Risks
Despite the potential hazards, biosolids offer several advantages. They’re rich in nutrients essential for plant growth, require less energy to produce than synthetic alternatives, and help wastewater facilities generate revenue while reducing waste sent to landfills or incinerators.
In 2022, more than half of the 3.76 million tons of biosolids produced in the United States were used to fertilize various landscapes. While direct contact with biosolids is likely limited to occupational exposures, the broader population could be exposed to contaminants absorbed by crops grown in such fertilizers.
Matthew Newmeyer, a research associate at the Bloomberg School of Public Health and first author of the paper, emphasized the need for further investigation: “We’re not saying that these compounds pose a risk right now, because we haven’t done a formal risk assessment. We’re saying that these have a potential to be problematic and we need more information in order to make sure these biosolids are safe.”
The research team plans to measure the identified compounds in biosolids and vegetables grown in biosolid-amended soil to determine if their concentration levels warrant concern. They’re also investigating risks to farmers, landscapers, and composters who work directly with biosolids.
As the use of biosolids continues to grow, this research provides a crucial first step in ensuring their safe application. By identifying potential contaminants, the study paves the way for more targeted regulations and safer practices in the use of these recycled fertilizers.
