Parabens removal from wastewaters by microalgae – Ecotoxicity, metabolism and pathways

Abstract

The presence of emerging contaminants (ECs) in aquatic systems and, particularly, in wastewater (WW) has become a major concern over the past years. Among these contaminants, parabens, belonging to the group of endocrine disruptors, are used on a daily basis as preservatives and constantly enter the environment, being called pseudo-persistent contaminants. Parabens have the potential to bioaccumulate and can be toxic to aquatic species. Unfortunately, the traditional methods used in wastewater treatment plants (WWTPs), namely the adsorption process, activated sludge and advanced oxidation processes (AOPs) are not effective in removing this type of contaminants. These treatment methods generate wastes with high concentrations of parabens adsorbed in activated carbon, large amounts of activated sludge containing parabens and/or chemically unstable by-products. To overcome these limitations, microalgae-based bioremediation has aroused great interest as an effective and sustainable process where parabens can be used in the microalgae metabolism as a carbon source (diauxic growth). However, several factors that affect microalgae growth and, consequently, their bioremediation capacity, must be considered for effective implementation of this biological treatment. This study reviews the impact of parabens on aquatic environments (ecotoxicity, bioaccumulation and persistence) as well as the limitations of the current methods applied in WWTPs considering the removal mechanisms and by-product formation. Moreover, it also addresses the metabolic pathways and the environmental factors (i.e. carbon and nutrients concentration, irradiation, photoperiod, pH and temperature) that can affect the parabens removal. As such, this review provides a set of conditions that can influence microalgae-based bioremediation, highlighting their ability for parabens removal and the requirement for supplementary research.