
Decoding the EPA’s Draft Sewage Sludge Risk Assessment

Scott Grieco
This article was written by Kleinfelder Vice President and National PFAS Lead Scott A. Grieco, PhD, PE
The U.S. Environmental Protection Agency (EPA) released its draft sewage sludge risk assessment for PFOA and PFOS on January 14.
What are PFOA and PFOS?
PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) are both types of per- and polyfluoroalkyl substances (PFAS), a very large and resilient family of chemicals with unique properties whose prevalence in the environment have emerged as a worldwide priority for human health and the environment.
Why is this risk assessment important?
The draft sewage sludge risk assessment is just that — a risk assessment — to determine whether contaminants at a site are of concern to human health and the environment. It is not a limit or guidance value.
Each human health risk assessment is unique to the situation and population being assessed. The EPA stated that the draft risk assessment focused on people living on or adjacent to impacted properties; thus, it is not a risk assessment of PFAS in sewage sludge (i.e., biosolids) relevant to the vast majority of people (the general population).
What was considered in the assessment?
Three scenarios were considered:
The first scenario modeled direct food consumption (dairy, meat, eggs, or produce) from a farm property or runoff-impacted adjacent surface waters (e.g., fish in an adjacent stream). This would potentially include residences on the farm or people living near the farm whose diet primarily comes from that particular farm or adjacent stream.

The second scenario considered biosolids in an unlined or clay-lined disposal unit (sewage sludge monofill). The exposure scenario in this case would be drinking contaminated groundwater sourced near the disposal site.
The third scenario considered communities living near a sewage sludge incinerator.

What was determined?
For Scenario 1, the modeling suggests human health risk when drinking contaminated milk (32 ounces per day), consuming contaminated fish (one to two servings per week), or eating one serving per day of produce for an extended duration of time. It stresses that the risk analysis showed concern when the majority of the individual’s diet comes directly from a single impacted farm and/or adjacent surface water.
Conversely, the risk assessment did not consider occasionally consuming products from the target property, nor having a diverse selection of food. For example, the vast majority of Americans consume food from the grocery store, which is sourced from multiple locations, both domestically and internationally (for instance, my blueberries come from Peru, Mexico and Canada depending on time of year), or produced from blended sources (i.e., milk, juices, etc.). It also did not consider PFAS applied to non-food crops (grain, fuel, or fiber).
For unlined and clay-lined surface disposal sites (Scenario 2), there can be exceedances of the risk thresholds for the drinking water pathway. This would, of course, be highly dependent on the specifics of annual precipitation and depth to groundwater.
The draft risk assessment for Scenario 3, the incineration scenario, does not provide quantitative risk estimates due to significant data gaps related to the extent incineration in a sewage sludge incinerator destroys PFOA and PFOS and the health effects of exposure to products of incomplete combustion, if present.
What does all of this mean?
For the industry:
- Risk assessment values are not guidance values. These represent site-specific or, in the case of the EPA publication, hypothetical conditions.
- This would be the first step of many toward any kind of regulation of PFAS in biosolids at the federal level.
- Industry professionals should voice their concerns or support through the public comment period.
- Individual states will continue to take action and develop policy in light, or in lieu, of this risk assessment. Several states have numerical guidance values and several more states have (or are proposing) biosolids application moratoriums.
- Although this information is directed at the wastewater utility, it will very likely be beneficial to support further EPA action related to establishing Effluent Limitation Guidelines to support reduction of PFAS discharges into the wastewater system. It may also support further PFAS bans in consumer products and drive product substitution and beneficial replacement chemistry. This will allow the utility to benefit from multiple avenues of source reduction.
For the individual:
- This draft risk assessment focused on a specific and narrow population of people that EPA considers most likely to be exposed to PFOA or PFOS from the land application of biosolids.
- The majority of food produced in the U.S. is not grown on fields where sewage sludge is land-applied.
- Consider that organic farms are not allowed to use municipal biosolids, so organic produce, cattle, and dairy limit potential exposure.
- The EPA did NOT estimate risk associated with occasionally consuming products or drinking water impacted by land application of contaminated sewage sludge, nor foods that come from a variety of sources.
Learn more
Kleinfelder helps organizations across the country and around the world address their PFAS challenges, providing field services, engineering and scientific consulting, packaged treatment systems, and construction services to meet the unique needs of each client. Learn more about our solutions here.
Read the official press release on the U.S. EPA’s site, “EPA Releases Draft Risk Assessment to Advance Scientific Understanding of PFOA and PFOS in Biosolids,” here.