Abundance and distribution of microplastics in benthic sediments and cladocera taxa in a subtropical austral reservoir.

Abstract

The pollution of the environment by microplastics has become a global issue to ecosystems. The presence of microplastics in aquatic ecosystems poses threats to biota such as ingestion, slow reproduction, and death. The present study assessed the abundance and distribution of microplastics in benthic sediments and Cladocera taxa in a subtropical austral reservoir. A Pearson's correlation analysis was used to assess the relationship between microplastic abundance and physicochemical variables such as pH, salinity, temperature, resistivity, oxygen potential reduction, conductivity, total dissolved solids, and Chlorophyll–a. Cladocera taxa were also collected and placed in a labelled test tube, where they were digested using 50ML Hydrogen peroxide. The findings of this study generally showed high densities of microplastics during the cool-dry season for both sediments and Cladocera taxa. Microplastic shapes were dominated by fibres and the colour scheme was dominated by transparent. For sediments, the abundance of microplastics negatively correlated with only three physicochemical variables: chlorophyll–a concentration, temperature, and resistivity, during the hot-wet season. Whereas it positively correlated with pH and salinity. For Cladocera, the abundance of microplastics positively correlated with only two physicochemical variables: conductivity and salinity, during the cool-dry season. High microplastic abundances were recorded during the season of high rainfall, indicating that the Nandoni reservoir has multiple sources of microplastic pollution. The Luvuvhu River is a major source of microplastic pollution, as it feeds large amounts of water into the reservoir during rainy season. Rain also contributes to microplastics in the reservoir by washing contaminants from surrounding terrestrial environments into the reservoir. As more studies focuses on quantifying microplastic pollution in oceans and rivers, the present study highlights the significance of including reservoirs as mechanisms for microplastic retention. The study also highlights a base for identifying and addressing the issue of microplastic pollution and its effect on reservoirs and the biota found within the reservoir. 3 It will also help all stakeholders (e.g., community members, conservationists, and institutions) to come together to discuss and provide possibly solutions for microplastic pollution locally and internationally. More studies, especially laboratory experimental studies should be conducted to measure the uptake of microplastics by Cladocera taxa. Additionally, scientists should publicise their findings to the general public in order to increase awareness about microplastic contamination and to spur action to reduce or eliminate plastic pollution of freshwater environment.