2025 AIChE Annual Meeting

Microplastic Sorption Can Lessen Impacts of “Forever Chemicals” on Soil Protists

With the increasing demand for disposable and low-cost goods, the use of plastics and thereby the amount of microplastics in the environment has been growing. Microplastics (MPs) absorb contaminants, thus, as microplastics are transported through the environment they carry absorbed contaminants with them. The impact of this pollution displays itself all throughout the environment, affecting the various microorganisms of the soil ecosystem, including soil protists. Protists regulate the soil bacterial population through grazing and transport which in turn also modulates soil fertility and plant productivity. Soil protists are also a significant food source for larger microorganisms, and as hydrophobic contaminants are known to bioaccumulate up the food chain, these contaminants can ultimately reach higher order predators such as humans while beginning at soil protists. Due to the hydrophobicity of microplastics, these HOCs can adsorb onto the surface of the plastic, now making the plastic their carrier. In particular, MPs can accumulate persistent, bioaccumulative, toxic compounds (PBTs) such as PFAS. Here we measure lethal and sub-lethal toxicity of PBTs to soil protists with and without co-exposure with MPs. Our hypothesis is that MPs absorb labile BPTs and reduce their bioavailability to protists, thus reducing the apparent toxicity of the compounds. Colpoda Steinii, a large soil ciliate, was selected as the model soil protist due to its ubiquity, ease of culture, and MP accumulation capacity. Polyethylene spheres (diameter range 1 to 5 micrometers), were selected as the model MP because it is the most commonly used plastic in the world, being both lightweight and versatile. The PBT compound selected as a model contaminant was perfluorooctanoic acid (PFOA), a so-called “forever chemical” known to have harmful health effects including birth defects and cancer. In order to test the impact of PFOA and MPs on soil protists, the protists were exposed to aqueous solutions containing PFOA only, PFOA plus MPs, and MPs alone as a control. The number of living and active protists was measured after 24 h exposure. Preliminary results suggest MPs can sequester PFOA and may be protective for protists when present in combination with PBTs. In addition, other potential PBTs are also being evaluated in addition to PFOA. These results point to the sometimes counter-intuitive impacts of environmental contaminants being present in combination, rather than in isolation. Through modeling the environmental fate and transport of both HOCs including PFOA and MPs, including their interaction, we can better understand their detrimental effects on the environment. Better understanding can lead to management practices aimed at mitigating adverse effects on a global scale.