Ecologically Safe Threshold Evaluation of Microplastics Contamination in Freshwater Ecosystems of South Asian...

Microplastics (MPs) pollution has become a global problem recently, and a wide range of aquatic biota are exposed to MPs in their natural habitat, leading to severe environmental risks. There are reports on ecologically safe threshold limit of MPs based on toxicity data; however, no report is available specifically for South Asian freshwater aquatic species until now. The present study attempted to enumerate the ecologically safe limits of MPs in inland aquatic ecosystems of South Asian countries (India, Bangladesh, Sri Lanka, Maldives, Nepal, Bhutan, Pakistan, and Afghanistan) based on species sensitivity. All benthic invertebrates demonstrated comparatively lower relative tolerance (T_rel) to MPs than the standard species. Fish species exhibited a wide standardized sensitivity (z = 3.71 to -0.35), followed by benthos (1.5 to -0.50), zooplankton (1.31 to -1.06), and phytoplankton (1 to -1). Species sensitivity distribution (SSD) curve estimated predicted no-effect concentration (PNEC) for phytoplankton, zooplankton, benthic animals, and fish as 0.012, 10.65, 1.38 × 10^-6, and 0.002 mg L^-1 with T. telescopium as the most sensitive species. The overall calculated PNEC based on the fifth-percentile hazardous concentration (HC₅) was 6.85 × 10^-6 mg L^-1. The study explored an ecotoxicological safety benchmark of MPs exposure to freshwater biota of South Asian countries, highlighting the need for more comprehensive MPs exposure studies with special reference to chemical types and size of MPs, robust and uniform methodology, and a wide range of aquatic species in the South Asian context.