Distribution of microplastics present in a stream that receives discharge from wastewater treatment plants.

The presence of microplastics (MPs) in freshwater systems that receive discharge of urban effluent implies a great environmental impact. In order to be able to generate proposals that solve this problem, it is necessary to know in detail the contributions of different MPs sources. The aim of this work was to study the contribution of urban sewage discharge to MPs pollution in a stream that runs through a medium-sized city. The spatial distribution of MPs with sizes between 100 µm and 1.5 mm present in surface water was measured and their characteristics, dimensions, shapes and identification were determined. Physical-chemical parameters of the stream water were measured, and a decrease in water quality was found due to wastewater treatment plants. The main source of MPs was effluent from the plants (97% of the total MPs), while the rest came from storm drains and discharge of tributaries. The maximum concentration of MPs found was around 72,000 MP/L (equivalent to 53 million MPs/s), at a point after discharge from both plants. Around 70% of MPs correspond to microfibers with a mean length of around 300 µm and a mean width of around 15 µm, and they are mainly polyethylene fibers. The remaining 30% of MPs are particles with lengths of around 140 µm. The transport of MPs between a point located after discharge of the plants and another point located about 3 km further on was studied, and no significant variation was found in the concentration of MPs. Electrical conductivity was used as a conservative tracer of MPs concentration. This work presents for the first time a detailed analysis of different contributions of MPs to a freshwater system in South America, which receives discharge of wastewater treatment plants, evidencing its important role in pollution.

Study of a stream in Argentina with a high concentration of microplastics: Preliminary analysis of the methodology.

This study presents for the first time results about the microplastic concentration and their origin in a stream of the Pampas region in Argentina, receiving wastewater of an intermediate city. The most appropriate procedure to analyze and quantify the microplastics in the studied system is the use of an oxidative digestion process using a 30% H2O2 solution to eliminate the organic matter in the samples. A high quantity of MPs, on the order of millions of microplastics per m3 of water, was estimated in the Langueyú stream. 56% of the microplastics correspond to fibers with diameters between 10 and 15 µm and lengths less than 500 µm, while 44% are fragments with sizes of tens of micrometers. Raman microspectroscopy was used to identify the type of fibers. The characteristics of the microplastic fibers released in a wash load test are comparable with those observed in the Langueyú stream, in particular, the average sizes and the distribution of the diameters of the MPFs are similar. The processes in the sewage treatment plant, prior to their discharge in the stream, would affect the color of the fibers and their length.