An Assessment of the Accretion Rate of Pollutants, Chemical Risk and Pollution Load Index on Microplastics in the Coastal Waters of Limbe-Idenau, Cameroon: Using Gravimetric Analysis

Floating MPs is a transboundary pollutant. Its transboundary nature and dynamics warrant deep know-how, not only on its transport and fate properties but also on understanding its mass change, which is a priority that needs relative addition for scientific dataset. This study highlights gravimetric analysis, another relevant technique to assess the accretion rate of pollutants, chemical risk and pollution load index on microplastics in the coastal waters of Limbe-Idenau, Cameroon. Sea-water samples were fished in five offshore distances in three distinct depth points in five purposive beaches on line transects. 9 samples/beach with 45/season amounting to 90 bottled water samples and each collected sample were stored in 1 L glass bottle for further analysis. Systematic sample filtration, content weighing and reweighing after oven drying, and plastic mass calculation were done, aided by 4X magnification for plastic characterisation. 178 MPs particles were identified with five unique particle weighs of 0.0000 g (150/0.0015 g), 0.001 g (20/0.02 g), 0.002 g (1/0.002 g), 0.003 g (5/0.015 g) and 0.011 g (2/0.022 g) weighing 0.605 g. The most frequently observed plastic was the 0.0000 g weighed particle with physical appearance of RWPP > IWPP > OWPP in all the sampled seawater. In terms of weighs MPs analysis, the dominant beach, offshore distance, size ranged, abundance/season and physical outlook parameters in particle/number were recorded as follows: LBD 1 (29.2%), 5 m offshore distance (59.6%), 1 - 1.5 m size ranged (55%) with mean size detection limits of 0.2 cm and dry season (77.5%). Lastly, the plastic physical outlook revealed that old weathered plastic particle, OWPP (51.1%) was dominant with large plastic mass loss experienced more during the rainy season. 0.011 g weight plastic showed the highest average mass loss/particle (17.2%). Evidence from this study has reaffirmed that mass gained by certain weightless plastic indicates their long-time existence, knowledge of distance from sourced and fragmenting capacity within the marine environment. Both CF (2.71) and PLI (1.47) show a level II risk factor meanwhile the RQ value indicates a low rate potential of risk of degrees of injuries or damages to both marine organisms and beach users which requires urgent environmental management and pollution control strategies.