Microplastics in aquatic species of Anzali wetland: An important freshwater biodiversity hotspot in Iran

Abstract

Coastal wetlands are sensitive ecosystems that give habitat to large number of species. The extent of the impact of microplastic pollution in the aquatic system and humans is not known. In this study, the occurrence of microplastics (MPs) was assessed in 7 aquatic species from the Anzali Wetland (40 fish and 15 shrimp specimens), a listed wetland on the Montreux record. Specifically, the tissues analyzed were gastrointestinal (GI) tract, gills, skin, and muscles. The total frequency of MPs (all detected MPs in the GI tract, gill and skin samples) varied from 5.2 ± 4.2 MPs/specimen for Cobitis saniae to 20.8 ± 6.7 MPs/specimen for Abramis brama. Among all tissues studied, the GI tract of the Chelon saliens, a herbivorous demersal species, had the greatest level of MPs (13.6 ± 10 MPs/specimen). Significant differences (p < 0.05) were found between the abundance of MPs in different species, tissues, living domains and feeding habit types. The findings support that fish may uptake MPs through adherence in gills (respiration) in addition to ingestion. White/transparent and black/grey polyamide (PA) fibers were the most common type of MP which may be originated from municipal wastewater and intensive fishing activities. About 34% of the MPs were in the range of 250 μm-500 μm, and those >100 μm were not detected in muscles from the study fish. All species had unhealthy weight according to the Fulton's condition index (K). Positive relationships existed between biometric properties (total length and weight) of species and the total frequency of uptaken MPs, pointing to detrimental impact of MPs in the wetland.

Keywords: Anzali wetland; Demersal fishes; Herbivorous; Ingestion; Microplastic; Respiration.