Microplastic occurrence in bed sediment and African catfish in Johor urban rivers

Abstract

Microplastics (MP) are plastic particles with size less than 5 mm and have been widely investigated for their occurrence in marine environments. Contrariwise, data on the abundance, sources and impact of MP to aquatic biota in freshwater ecosystems are still scarce. Previous studies were usually focused on spatial analysis to compare the MP concentration between different sites. In this study, the abundance of MP in bed sediment and fish community in Skudai and Tebrau River was temporally investigated. Sediments were collected across a seven-month sampling period. Meanwhile, fish were caught all year round from September 2017 until August 2018. In-situ water quality parameters were also recorded throughout the sampling process. The inspection of MP particles was carried out under compound microscope with 40x magnification. The type of plastic polymer was analysed using attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. The abundance of MP in sediment was in the range of 206.6 ± 79.6 (mean ± SE) to 813.4 ± 13.0 particles per kg dry weight (d.w.) in Skudai River and 286.6 ± 102 to 1020 ± 81.6 particles per kg d.w. in Tebrau River. There was a significant difference at 95% confidence interval in the abundance of MP between both rivers. The significant difference in the abundance of MP was also observed during March 2018. Six edible fish species were identified in Skudai River such as African catfish, Clarias gariepinus, tilapia, Oreochromis mossambicus, climbing perch, Anabas testudineus, Pangasius catfish, Pangasius hypophthalamus, beardless barb, Cyclocheilichthys apogon and marble goby, Oxyeleotris marmorata. However, only African catfish was caught in Tebrau River. Overall, 326 individuals were obtained from both rivers. The study has shown that a significant difference in the ingested MP was found among three fish species namely African catfish, climbing perch, and Pangasius catfish. Since African catfish was the most abundant fish found in both rivers, thus further investigation on the ingestion of MP by 287 individuals of this species was carried out. The study found that there was a significant difference in the MP ingested by African catfish between monsoon and transitional period. The study also showed a moderate strong correlation between the ingested MP and Fulton??s condition. Interestingly, polyethylene and polypropylene were the most dominant polymers found in both sediment and fish samples. The relationship between the abundance of MP and water quality parameter was analysed via generalised linear model with Poisson regression. Three statistical models were developed to determine the relationships of MP from sediment and water quality parameters. In general, only TDS showed the positive relationship. When water quality parameters were paired with monsoon seasons, only turbidity and TDS influenced the abundance of MP. Meanwhile, both studied rivers and TDS have affected the abundance of MP in sediment when the model combines water quality parameter and sampling sites. Conversely, a model for the MP ingested by African catfish that combines water quality parameter and monsoon showed that only TDS influenced the number of MP. Overall, MP were found persistence in both studied rivers. All studied species ingested MP and the temporal retention of MP ingestion by African catfish indicated that fish could be a suitable indicator of regional MP pollution. The study also successfully proposed Poisson regression model in generalised linear model (GLM) on the MP pollution data.