Study on the Mass Concentration Distributions of Marine Microplastics in Estuaries and Coastal Areas

Marine microplastics are a global environmental issue, and understanding their distributions in estuaries and coastal areas is a critical prerequisite for the effective and sustainable management of microplastic pollution. Owing to the lack of methods that exist for quantifying microplastic content, characterizing the distribution of microplastics is difficult. The mass concentration of microplastics is an objective indicator that reflects their distribution. Therefore, a formula for calculating the microplastic mass concentration is proposed through the parameters of the number concentration, microplastic size, and mesh size, in addition to the proportions of particles with different sizes and shapes. On the basis of the large amount of existing measured data, the mass concentrations of microplastics in estuaries and coastal areas are calculated. It can be concluded that polypropylene (PP; 72%) and polyethylene (PE; 67%) are the most abundant microplastics in the ocean. Additionally, marine microplastics are more common in estuaries (102–103 mg/L) than in the open sea (0–10 mg/L). The maximum concentration of microplastics in surface water is approximately 8.0 g/L. Moreover, the concentration of microplastic pollution has significantly increased in areas surrounding sewage treatment plants and aquaculture farms.