Combined toxicity of perfluorinated compounds and microplastics on the sentinel species Daphnia magna: Implications for freshwater ecosystems

Persistent chemicals from industrial processes, particularly
perfluoroalkyl substances (PFAS), have become pervasive in the environment
due to their persistence, long half-lives, and bioaccumulative properties.
Used globally for their thermal resistance and repellence to water and oil
PFAS have led to widespread environmental contamination. These compounds
pose significant health risks with exposure through food, water, and
dermal contact. Aquatic wildlife is particularly vulnerable as water
bodies act as major transport and transformation mediums for PFAS. Their
co-occurrence with microplastics may intensify the impact on aquatic
species by influencing PFAS sorption and transport Despite progress in
understanding the occurrence and fate of PFAS and microplastics in aquatic
ecosystems, the toxicity of PFAS mixtures and their co-occurrence with
other high-concern compounds remains poorly understood, especially over
organisms’ life cycles. Our study investigates the chronic toxicity of
PFAS and microplastics on the sentinel species Daphnia, a species central
to aquatic foodwebs and an ecotoxicology model. We examined the effects of
perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and
polyethylene terephthalate microplastics (PET) both individually and in
mixtures on Daphnia ecological endpoints. Unlike conventional studies, we
used two Daphnia genotypes with distinct histories of chemical exposure.
This approach revealed that PFAS and microplastics cause developmental
failures, delayed sexual maturity and reduced somatic growth, with
historical exposure to environmental pollution reducing tolerance to these
persistent chemicals due to cumulative fitness costs. We also observed
that the combined effect of the persistent chemicals analysed was 59%
additive and 41% synergistic, whereas no antagonistic interactions were
observed. The genotype-specific responses observed highlight the complex
interplay between genetic background and pollutant exposure, emphasizing
the importance of incorporating multiple genotypes in environmental risk
assessments to more accurately predict the ecological impact of chemical
pollutants.