Quantitative analysis of the sized ranged plastic debris on beach shoreline along the Limbe Coastline, Cameroon

Abstract

In recent years, there has been increased interest in investigating the accumulation of plastic debris of mega‑, macro‑, meso‑, and micro-sized (4M’s) ranged particles that have been observed in beaches along the coastline. The abundance and distribution of different sized class plastic debris was quantitatively assessed in five sandy beaches along the coastline, Cameroon from March 2020 to October 2020. Duplicates of 2×2 m (4m2) quadrants were sampled in each beach/month with a total of 80 quadrants. Collected plastic samples were washed, sieved and dried. Particles of size, ≥ 2 mm, were sorted and measured using 30cm measuring ruler. The different sized class, were further counted and weighted as well. Overall, 12,822 particles by number and 530.59 g by weight with an average abundance of 40.07 items/m2(7.38–83.90 items/m2) and 1.66 g/m2 (0.62–3.37 g/m2) plastic debris was recorded. Plastic debris accumulation significantly varied temporally and spatially at p=0.05. ANOVA and Spearman’s rank correlation used shows linear relationships between the meso- and micro-sized classes. The large micro-sized debris concentration was strongly correlated with that of meso-sized classes for most material types, suggesting that the degree of contamination of large micro-sized class can be estimated from that of meso-sized class. Significantly higher plastic debris abundance was recorded in LDB sites. Furthermore, the highest abundance by weight was recorded in August and June numerically. More than 80% of plastic particles were between the size ranges of 5–20 mm by number of items and between 6 – 100 mm by weight in gram. Moreover, in all beaches micro-sized class plastics were dominant in terms number of items by 42.40% with fragmented debris type dominant, both in number of items and weight as 54.86% and 25.69% while meso-sized class plastics were 29.28% dominated by weight with fragmented debris type, the most prevalence both in number of items and weight as 46.11% and 26.18% respectively. On average, colour fractionation in the different sized ranged plastic debris revealed that coloured plastics were dominant with mean abundance of 80.45±18.17 items/m2and 2.58±0.68 g/m2. The shapes class also revealed that the irregularly shaped plastic debris dominated with average mean concentration of 47.24±20.40 items/m2 and 1.39±0.66 g/m2 and finally, the 0.0001 g weighted plastic debris was as well dominant with average mean concentration of 33.68±7.23 items/m2. Probably, the intense use of beaches for recreation and poor waste collection during the Covid-19 pandemic lockdown increased the potential for plastic contamination on these beaches. A comparative study should be done using different mesh sizes as the best option for plastic particle size determination.