Microplastic Contamination and Ecological Risk in Intertidal and Subtidal Crabs Uca perplexa (Decapoda, Ocypodidae) and Sesarma huzardii (Decapoda, Sesarmidae) from a Mangrove Estuary of the Niger Delta, Nigeria

Microplastics are currently the most pervasive environmental pollutant globally, permeating all environmental matrices and remotest part of the earth. Microplastic (MP) contamination assessment was carried out in two crab species, Uca perplexa (H. Milne Edwards, 1837) and Sesarma huzardii (Desmarest, 1825), inhabiting intertidal and subtidal zones of the Isaka Bundu tidal swamp, Niger Delta, Nigeria. This ecologically sensitive mangrove estuary is subjected to extensive anthropogenic pollution oil exploration, illegal refining, and domestic waste discharges. Crabs (n = 100), surface water, and sediment samples were collected from three stations representing varying pollution intensities and analyzed for microplastics. Microplastic quantification was performed via stereomicroscopy, followed by ATR-FTIR for polymer identification. Higher MP abundance was recorded in the sediments and intertidal habitats with female crabs generally having higher MP loads. U. perplexa showed marginally greater MP accumulation than S. huzardii. Fragments and fibres dominated MP shapes, with blue, red, and black being the most common colours. The predominant MP sizes ranged between 20–300 µm. Station 1 exhibited the highest contamination factor (CF), pollution risk index (PRI), and microplastic concentrations in both biotic and abiotic matrices. Hazard Index (HI) was uniform (21) across all sites, indicating similar polymeric risk profiles. The presence of high risk polymers such as polyethylene and ethylene vinyl acetate was also confirmed. Overall, the results indicated significant ecological risks posed by MPs to benthic invertebrates and indirectly to man in the estuarine system. This study stresses the urgent need for regulatory action, improved waste management, and continuous monitoring of microplastic pollution in Nigeria’s coastal environments. Polymer specific ATR-FTIR results provided the basis for ecological risk assessment calculations.