Microplastics Dynamics in the Bathing Seawater Affected by the Ebb Tide in Zhanjiang Bay, China

At present, microplastics (MPs) pollution has attracted people’s attention, and MPs in seawater have caused great harm to the marine environment. Taking Yugang Park Beach (YPB) in Zhanjiang Bay (ZJB) as the research object, we studied the spatial and temporal distribution, composition, and inventory of MPs in the bathing seawater affected by the ebb tide by filtering the bathing seawater with a 45 μm stainless steel sieve. The results showed that the average abundance of MPs in the bathing seawater was 201.3 ± 183.0 items·m−3, with the highest at mid-tide, followed by high and low tides. The size of MPs in the bathing seawater was mainly 1–2 mm, with most being white (23.5%) and green (29.8%) MPs, and the largest proportion being foam (27.5%) and fiber (29.5%). The main polymer types were polypropylene (PP), polystyrene (PS), and cellulose (CE). Correlation analysis between MP abundance and their sizes showed that the abundance of 0.33–5 mm MPs was significantly and positively correlated with their sizes (p < 0.05). The average MP inventory was 3.2 × 106 items, with the largest at high tide, followed by mid and low tides. In conclusion, these results highlighted that tidal variations were the main factor causing the uneven distribution of MPs in the bathing seawater at YPB. This study provides theoretical support for future study of MP pollution in bathing waters, and the effect of tidal variations on MPs.