The Challenge Posed by Emerging Environmental Contaminants: An Assessment of the Effectiveness of Phenoxyethanol Biological Removal from Groundwater through Mesocosm Experiments

The occurrence of emerging pollutants (EPs) such as pharmaceuticals and personal care products (PPCPs) has raised serious concerns about the possible adverse effects on ecosystem integrity and human health. Wastewater treatment facilities appear to be the main sources of PPCPs released in aquatic environments. This research examines the effectiveness of groundwater microbial community activities to remove phenoxyethanol (Phy-Et), currently exploited as a preservative in many cosmetic formulations at a maximum concentration of 1% but which has shown, at higher levels of exposure, adverse systemic effects on animals. Mesocosm experiments were carried out for 28 days using two different concentrations of the substance (5.2 mg/L and 27.4 mg/L). The main results obtained through chemical and microbiological investigations revealed a significant Phy-Et reduction (≈100% when added at a concentration of 5.2 mg/L and ≈84% when added at a concentration of 27.4 mg/L), demonstrating that some autochthonous microorganisms in the analyzed samples played a “key role” in removing this compound, despite its proven antimicrobial activity. Nevertheless, the decrease in the “natural attenuation” efficacy (≈16%) when using higher concentrations of the chemical suggests the existence of a “dose-dependent effect” of Phy-Et on the process of biodegradation. Biomolecular investigations carried out through next-generation sequencing (NGS) revealed (i) the presence of a significant fraction of hidden microbial diversity to unravel, (ii) variations of the composition and species abundance of the groundwater microbial communities induced by Phy-Et, and (iii) a biodiversity reduction trend correlated to the increase of Phy-Et concentrations. Overall, the preliminary information obtained from the experiments carried out at the laboratory scale appears encouraging, although it reflects only partially the complexity of the phenomena that occur in natural environments and influences their “auto-purification capability”. Accordingly, this research paves the way for more in-depth investigations to develop appropriate tools and protocols to evaluate the occurrence and fate of Phy-Et in nature and assess the impact of its release and the effects of long-term exposure (even at low concentrations) on ecosystems and health.