Combined nanoTiO2 and nitrogen effects on phytoplankton: a mesocosm approach

Abstract

The aquatic ecosystem is the ultimate sink for consumer and industrial waste discharge that contains nanometals such as titanium dioxide nanoparticle (n-TiO2). In this environment, nutrient availability and nanometals influence phytoplankton community structure and function. In a mesocosm experiment, we evaluated the interactive effect of n-TiO2 (48 mg L−1) and two nitrogen (N) levels (limited, LN; and replete, HN) on the phytoplankton community structure (biomass, species diversity and richness, algal species divisions), biochemical composition (carbohydrates, proteins, and lipids), and antioxidant response (peroxidase activity, POD). n-TiO2 decreased total phytoplankton biomass, and its combination with HN led to the highest decrease. Species diversity was not affected by N level, n-TiO2, and their interaction, while species richness decreased in combined n-TiO2 and HN treatment. All these recorded effects of n-TiO2 on the phytoplankton community structure were enhanced by increasing temperature over time. LN initially reduced phytoplankton carbohydrate content but increased by the presence of n-TiO2 and its interaction with N levels. Total protein and lipid content were not affected by n-TiO2 or its interaction with N levels. POD activity was increased by the interaction between n-TiO2 and the N levels tested. Our results indicate that the influence of n-TiO2 on the phytoplankton community was dependent on the concentration of N. Also, phytoplankton carbohydrate content and community structure varied with increasing water temperature. A few species thrived concerning biomass during exposure to the LN + n-TiO2 (Scenedesmus quadricauda, Coelastrum reticulum, and Microcystis sp.) and HN + n-TiO2 (Microcystis sp.) treatments. Members of the Chlorophyta were generally susceptible to the presence of n-TiO2 regardless of the N level. Thus, the presence of n-TiO2 in aquatic ecosystems can alter phytoplankton community structure and dynamics.