OCCURENCE OF MICROPLASTICS AND ESTIMATION OF SOURCES TO RIVER WATER IN KATHMANDU CITY, NEPAL

Abstract

 Recently, microplastics (MPs) have been getting attention worldwide due to its potential for environmental impacts. However, one of the challenges of MPs studies is the comparison of various studies is difficult because there is no authorized method for measuring MPs. It is important to understand the characteristics and sources of MPs pollution in each region in order to reduce the load of MPs. In this study, we reported that the occurrence of MPs in road dust and river surface water in Kathmandu city, Nepal as an example of developing countries in Asia. In addition, we compared these results with that in Da Nang City (Vietnam) and Kusatsu City (Japan), which were conducted in the same way by authors. The results showed that the average MPs concentrations were 25.7~339 pieces/m² (n=4) in road dust and 600~45, 600 pieces/m³ (n=5) in river surface water (Bagmati River and Bisunumati River). In terms of composition, polyethylene and rubber plastics accounted for 40 % and 18 % of all MPs in road dust, while 70 % of MPs in river surface water were detected as acrylic plastics. The average sizes of MPs were significantly larger (p<0.01) in river surface water (median: 432 μm) than those in road dust (median: 309 μm). As a result, it was suspected that one of the main sources of MPs in river surface water in Kathmandu City is untreated wastewater. Therefore, it was expected that MPs concentrations would decrease after completion of wastewater treatment plant construction.