A quantitative and qualitative assessment of microplastics collected at two public beaches along the east and south-east coast of Mauritius

Microplastics had been collected at two sites namely Trou d'eau Douce (TD) and La Cambuse (LC) public beaches, lying in the east coast and south-east coast of Mauritius, respectively, over 6 months from September 2019 to February 2020. The sizes of the latter varied from 180 µm to 4 mm. A higher amount of microplastics collected/6-kg sand sample was recorded at LC. Two-way ANOVA revealed that (1) there was a considerable gap in the variability regarding quantity and size distribution of microplastics on the two beaches. The post-hoc analysis showed that the majority of the microplastics at LC were > 1.40 mm, whereas the smaller plastic fragments < 1.40 mm were more dominant at TD. (2) There was a significant interaction between location and event (p value = 0.025). The post-hoc analysis showed that the torrential rain hitting the island prior to sampling week 7 had decreased the microplastic counts at both TD and LC, but not significantly. Interestingly, the two hurricanes, prior to weeks 8 and 9, had appreciably reduced the microplastic counts at TD and, on the other hand, there was an increase in the amount of microplastics at LC, but not to a significant effect. The chemical nature (qualitative analysis) of microplastics was determined by density flotation and FTIR spectroscopy. Microplastics at TD were exclusively high-density polyethylene (HDPE) in origin, whereas, at LC, microplastics were both HDPE and polypropylene (PP) in origin.