Occurrence of microplastics in the effluent of wastewater treatment plants : growing threat to the environment?

Abstract

Microplastics have become an emerging environmental concern. Plastic production is increasing on an international scale. Some of the plastic produced ends up in the environment as a persistent pollutant. This issue has first been raised by scientists decades ago. While consequences of macroplastics are well studied, adverse effects of microplastics are still not completely understood. Former studies focused on the occurrence and impact of microplastics in marine ecosystems. Recently, a shift towards presence and effects of microplastics on freshwater systems could be observed. In order to rate the risk, microplastics are posing to those habitats, also sources and the amount of microplastics emitted to freshwater systems have to be investigated. Wastewater treatment plants are thought to be a main contributor to microplastic pollution in freshwater systems. However little data is available on the contamination of effluent water with plastic particles in the size range below 5 mm. This is true for all countries, including Austria. Sampling and analytical methods differ widely between studies and there is still no agreed standardized analytical method. A common approach to sampling and analysing microplastics not only in wastewater is a prerequisite in order to compare data from different sources. This study intends to provide a snap shot of microplastics occurring in the effluent of an Austrian wastewater treatment plant on the one hand side. On the other hand two different methodologies to quantify microplastics were used and compared. Whilst the first methodology is based on visual inspection, the second approach is based on an elemental analysis. In 14,5 m3 of water a total of 126 microplastic particles (>1mm, <5mm) was found. Microplastics occurred in all the samples taken. Visual inspection turned out to be the favoured methodology to detect microplastic particles in wastewater samples, as the use of threshold values for the elementary analysis are not suitable for the proof of microplastic particles in wastewater.