Microplastics (MPs), as an emerging global pollutant, have attracted considerable attention due to their widespread contamination and profound ecological impacts. Fish, as one of the most diverse groups of aquatic organisms, is a sensitive indicator of MPs contamination in aquatic ecosystems. Hainan Island which is located in the tropical and subtropical zone is rich in freshwater fishery resources. Due to the impact of human activities, freshwater fishes in Hainan Island are facing the threat of MPs pollution. Wanquan River is the third largest river in Hainan Island and is facing eutrophication, heavy metals, organic pollutants and MPs pollution. However, the contamination status of MPs in the gastrointestinal tract (GI) of fish from Wanquan River and the effects of feeding habits and spatial distribution on the abundance and characteristics of MPs in the gastrointestinal tract of fish have not been reported. In the present study, 11 representative sampling sites along the upstream, midstream, and downstream sections of the Wanquan River, covering both urban residential areas and natural watersheds were selected. Fish samples were collected using trawl nets from July to September 2021. All samples were immediately transported to the laboratory and stored in a freezer for subsequent analysis. In the laboratory, the surface of the fish was rinsed, and the GI tracts were carefully viscerated and weighing. The GI tracts samples were digested with potassium hydroxide and the supernatant was filtrated with 0.45 μm glass fiber filters. For the insoluble materials such as sediment in the digestion solution, saturated zinc chloride solution was added for flotation, and the flotation supernatant was filtered with 0.45 μm glass fiber filters. Fourier transform infrared spectroscopy (FTIR) was used to identify the composition of the MPs. The results showed that a total of 213 fishes spread over 34 species were collected and MPs were detected in 85.0% of the GI tracts of fishes. The average abundance of MPs was 3.15 ± 1.70 individuals/fish and this was consistent with the economic development level in Wanquan River basin. The MPs in the GI tract of fishes were mainly <1.0 mm (78.6%) transparent (46.0%) fibers (74.6%) due to their widely present in the environment, easy to be ingested, and difficult to be excreted. FTIR results showed that most MPs were made up of polypropylene (35.8%) and polyethylene (25.4%). With good temperature resistance and corrosion resistance, PP and PE have becoming the main components of carpets, industrial fabrics, fishing gear, shipping ropes, etc. Thus, PP and PE have been widely detected in aquatic ecosystems due to their durability and widespread useage. Principal component analysis showed that transparent/blue fibers with 0.5-1.0 mm contributed the most to the abundance of MPs in the GI tract of fishes. Strengthening the control of urban waste, fishing supplies and agricultural waste were the key to reduce the MPs pollution in the Wanquan River. The abundance of MPs varied with feeding fish and followed the order, molluscivorous (7.33 individuals/fish) > pelagic carnivorous (6.83 individuals/fish) > benthic carnivorous (4.33 individuals/fish) > detritivorous (3.36 individuals/fish) > crustaceavorous (3.15 individuals/fish) > insectivorous (2.40 individuals/fish) > epiphytivovrous (2.30 individuals/fish) > herbivorous (1.89 individuals/fish). The abundance of MPs in the GI tract of fish was affected by several factors, such as the pollution status of MPs pollution in foraging areas or habitats, the abundance of MPs in fish prey, fish predation frequency, factors of the fish itself (e.g. body weight, body length, body shape, gut structure, etc.), retention time of MPs in the GI tract of fish, and the excretion rate of MPs by the GI tract. From upstream (2.67 ± 0.43 individuals/fish) to downstream (3.81 ± 0.39 individuals/fish), the abundance of MPs in the GI tracts of fish in the Wanquan River showed a gradually increasing trend. This was related to the increasing urbanization and industrialization in the downstream areas and thus the increased input of MPs in downstream. The proportion of red/yellow/blue fragments and thin film MPs with size >1.0 mm increased, while the proportion of black fiber MPs with <1.0 mm decreased from the upstream to the downstream. This was related to the increase of shipyard, shipping, and tourism activities in the downstream of the Wanquan River. For individual fish species at different sampling sites, the abundance of MPs in the GI tracts of fish did not show a continuous increasing trend. This was because MPs in the GI tract of fish were mainly derived from the passive ingestion which was affected by many factors (e.g., feeding habits, intestinal structure, excretion ability, food intake, and the status of MPs contamination in the environment. The results of the present study not only provide data support for the risk assessment and control of MPs in fish of Wanquan River but also provide a scientific basis for the prevention and control of MPs pollution in freshwater rivers on Hainan Island. |