(Bloomberg) -- The Environmental Protection Agency doesn't know if the treated sewage sludge that farmers use as fertilizer is safe, according to a report from its internal watchdog.
The treated sewage known as biosolids is chock full of nutrients, which is what makes it so good at enriching soil. But it also can be chock full of pollutants, from heavy metals such as mercury and arsenic to pharmaceutical compounds, flame retardants and disease-carrying organisms.
And the EPA doesn't know enough about hundreds of pollutants found in the material, the agency's inspector general said in a report Thursday.
The EPA's controls over using biosolids as fertilizer are "incomplete" or have "weaknesses" and "may not have fully protected human health and the environment," said Jill Trynosky, a project manager with the inspector general's office. "The EPA is unable to state whether, and at what level, the pollutants found in biosolids pose a risk to human health or the environment," Trynosky said in an agency podcast describing the investigation.
The biosolids at issue are a byproduct of wastewater treatment -- essentially the residue that is left over after wastewater is cleaned at facilities nationwide. That sewage sludge can be sent to incinerators or landfills -- or it can go through additional treatment to remove pollutants and to make it less attractive to vermin, effectively transforming it into biosolids that can be applied to farmland as fertilizer.
Nearly half of the biosolids generated in the U.S. ultimately are applied to the land, according to the EPA.
The agency oversees the practice, with requirements to test for nine specific heavy metals, including arsenic and mercury, research additional pollutants that may need regulation and pare pathogens from the material.
Although the EPA has consistently monitored biosolids for those nine regulated substances, the agency lacks the data or tools needed to determine the safety of hundreds of other pollutants found in the material, the inspector general found. And while the EPA is reviewing additional pollutants, the agency hasn't always completed those assessments in a timely manner, the watchdog said.
According to the probe, the risks of at least 352 pollutants found in biosolids haven't been fully assessed by the EPA. And at least 61 of them have already been deemed hazardous by another federal agency or program.