Lessons from PFAS Risk Assessment Projects

By the GHD PFAS Working Group

Per- and polyfluoroalkyl substances (PFAS) encompass a family of thousands of man-made chemicals that contain a fluorinated carbon backbone. PFAS came into common use in the 1950s and '60s and have been used in hundreds of industrial processes and consumer products. They are considered useful because they are resistant to heat, water and oil. PFAS have been used in non-stick cookware, grease-resistant paper, fast food wrappers, microwave popcorn bags, stain-resistant carpets and fabrics, water-resistant clothing, cleaning products and personal care products.

PFAS are also used in industrial processes and are a component of many of the firefighting foams used by the military, airport authorities, and local fire and rescue agencies. To date, use of these foams has most often been implicated when PFAS is found in groundwater, or the environment.

At the 2018 Real Property Institute of Canada (RPIC) Federal Contaminated Sites National Workshop (FCSNW) conference in Toronto, Ontario, GHD risk assessor Ian Collins presented a paper on the topic, Risk Assessment and Management of PFAS: Australian Lessons for Canadian Projects.

What is risk assessment?

Human health and ecological risk assessment evaluates whether a chemical in the environment may pose potential health risks to people and the environment, respectively. In this context, a potential health risk is identified when exposure to a chemical is high enough relative to the negative effects of the chemical that health consequences may occur.

In Canada, human health and ecological risk assessment for federal contaminated lands is conducted under the Federal Contaminated Sites Action Plan (FCSAP). Under this, guidance on human health risk assessment is provided by Health Canada, and guidance on ecological risk assessment is provided by Environment and Climate Change Canada.

Risk assessments for humans and the environment completed according to these guidance documents share several common elements, including a formulation of the problem, assessments of exposure and of toxicity, and a characterization of risk. A public communication strategy, forming part of risk management planning, is also developed in tandem with these other steps.

PFAS risk assessment projects in Australia by GHD, which was founded in 1928, provide valuable insight into common risk assessment elements to consider when planning such projects in Canada.

Science will advance when formulating the problem

At the problem formulation stage of a risk assessment, risk assessors will identify the chemicals to be investigated (sources), who might be exposed to them (receptors), and how those exposures might occur (pathways). During this process, risk assessors compare the amounts of the chemicals on a contaminated site to levels that government agencies indicate are acceptable (Tier 1 values). Those chemicals under investigation that are of greatest concern, i.e., those that exceed the Tier 1 criteria, are subjected to a quantitative site-specific risk assessment.

Australian entities have been proactive in their approach to investigate sites potentially impacted by PFAS, and these investigations have been undertaken around the country since at least 2013.

Globally, and in Australia specifically, the acceptable levels for PFAS have changed very quickly over the past two years as new scientific research about the toxicity of PFAS has become available.

Results of Tier 1 screening in 2017 may have indicated that a contaminated site in Australia was not a location of potential concern. However, when compared against the most recent criteria released in 2018, a site-specific risk assessment may be warranted, given the increased conservatism of the new screening levels.

Risk assessments that use these levels for decision making may, therefore, need to be re-evaluated as the ever-advancing pace of research provides new toxicity information on PFAS.

In a similar way, as the measure- ment technologies used by laboratories continue to improve, PFAS are being detected in environmental samples at lower and lower concentrations. A risk assessor who concludes that PFAS are not a concern because they were not detected in an environmental sample may not adequately characterize risk due to the reduced limits of reporting (LOR) and reduced Tier 1 screening criteria currently available.

Being prepared for these eventualities is essential when conducting risk assessments for PFAS. Acknowledging the pace of change in available toxicity information and discussing this issue as an uncertainty are musts for completing risk assessment reports. GHD has learned that changes in toxicity information, lab measurement technologies and acceptable levels can understandably promote mistrust, anger and anxiety in the affected community. Being open about these issues when talking with the public, is also essential.

Measure accurately and don’t model when assessing exposure

At this stage of a risk assessment project, a risk assessor estimates the magnitude of each exposure to the chemicals. Human exposures and ecological exposures are estimated in the same way, accounting for time spent in the contaminated area, eating crops or garden produce from the area, drinking water, contact with soil, inhaling air, etc.

In order to make good estimates of exposure, accurate and precise measurements of the amounts of the chemicals in the environment are needed. Because PFAS are present in many consumer goods, from clothes to food wrappers, as well as some types of sampling equipment, PFAS cross-contamination during sampling or laboratory analyses can be an issue. A robust Quality Assurance/Quality Control (QA/QC) program is an important part of the risk assessment process so the results are reliable and repeatable.

For example, GHD has adopted sampling guidelines from Australian governments, such as making sure to wash new clothes at least six times before wearing them to sample PFAS at a job site. In addition, GHD recommends thoroughly investigating how potential sample contamination may occur by using several types of blank samples in the QA/QC program.

Once amounts of the chemicals of concern have been measured in the environment, risk assessors may use mathematical models to determine how the chemicals might move through that environment. For example, such a model might provide an estimate of how much of a chemical would be found in a fish that swims in contaminated water, or how much would be found in a bird that eats that fish.

Currently, though, there is a lack of understanding of how PFAS behave in a food chain, although scientists have measured PFAS in birds, mammals and fish. The existing models are thus not reliable, and for risk assessment purposes, it is recommended to measure PFAS in living tissues, rather than trying to use an uncertain and unreliable model.

Conclusion

“Ultimately, the rapid pace of change in science, technology and government regulations, along with transparency about the challenges at hand, is what makes the risk assessment and management of PFAS an evolving challenge. GHD’s continued approach is to work diligently with the community, government agencies and industry to communicate the challenges of PFAS and to provide risk assessments that can be reliably used to make decisions moving forward,” concluded Collins.

For more information, email: ian.collins@ghd.com.