PFAS in Biosolids: The Risk to Soil Invertebrates

WHAT IS PFAS?

Per- and polyfluoroalkyl substances (PFAS) are a group of over 4000 man-made chemicals utilized since the 1950’s in a range of industrial and commercial applications. The compounds are present in products used throughout our daily lives, from the food wrappers in our garbage, to the kitchen appliances in our cabinets, and the cosmetics in our bathrooms. Despite their various uses, there has been growing concern over the past few decades surrounding the potential risks associated with PFAS exposure, in part because of their slow degradation time, giving them the nickname “forever chemicals”. More and more studies are finding negative consequences associated with PFAS which has led to the phaseout of some of the longer chain, more high-profile chemicals. The problem is that the majority of PFASs, specifically the shorter-chain compounds, remain unregulated in Canada and continue to be used.

PFAS AND BIOSOLIDS

Biosolids are treated residual solids produced by wastewater treatment plants. As a way to promote a circular economy, this product can be applied to agricultural fields as an alternative to fertilizers due to its high nutrient content. Although there are substantial benefits that come from the use of biosolids, they have been shown to be a source of PFAS to terrestrial environments. This is because wastewater treatment plants lack the technology to properly get rid of these chemicals, so as humans continue to use them, they are able to travel from influent to the effluent and biosolids. Their frequent detection in biosolids has raised concerns over their negative effects and accumulation potential in the plants and animals that reside in the fields where they are being applied.

LEFT: A tractor with equipment used to spread liquid biosolids across an agricultural field. RIGHT: A pile of pelletized biosolids to be applied to a famers field by tractor

PFAS TOXICITY EXPERIMENTS

The purpose of our experiments is to determine the risk posed by PFAS in agricultural fields due to biosolid application. The first step was to quantify the amount of PFAS present within agricultural fields in Southern Ontario. Several fields, both with and without biosolids, were sampled and the collected soil was sent for analysis to determine what PFASs were present and at what concentration.

A student walking around a farmer’s field to collect soil samples using a corer

The second step is to determine the impact of PFAS on soil invertebrates. Experiments will specifically focus on earthworms (Eisenia fetida) because of their importance in terrestrial ecosystems. Not only do worms help cycle nutrients and promote soil fertility, but they serve as a food source for several other organisms and can impact the food web.

A handful of earthworms (Eisenia fetida)

Based on current literature and the results from soil sampling, commonly detected, understudied PFASs will be the primary contaminants used for our research. Reproduction toxicity tests will be carried out to find out how these chemicals affect earthworm survival and their ability to produce offspring.