Seasonal Distribution of Microplastics in Farmed Mytilus galloprovincialis and Human Dietary Exposure

The seasonal distribution of microplastics, as a representative case, was examined in Mytilus galloprovincialis from a pilot farm in the Gulf of Naples (Italy). The influence of marine parameters on microplastic uptake rate was assessed. A destructive patented method was used, and two microplastic size classes (<10 µm; >10 µm) were defined. Estimated Daily Intakes were calculated for different age groups. Results showed a significant abundance of small microplastics (9683.92 ± 6911 vs. 41.85 ± 13.98). In mussels, the highest levels (19,738.13 ± 3406.04) were detected in summer, and the lowest in autumn (4145.56 ± 2364.93). Summer variations in seawater temperature, oxygen, and pH were significantly different from those in winter and spring. High exposure levels, mainly of microplastics < 10 µm, were observed in the elderly (318.08 ± 227.00), followed by adults (225.29 ± 160.78) and children (212.29 ± 151.50), with the lowest in teenagers (127.51 ± 91.00). Despite the high variability of factors influencing mussel filtration and microplastic uptake, the study provided data on the seasonal microplastic distribution pattern and a size-based screening exposure level. Results highlight the importance of geographic and seasonal conditions, and particle size in assessing microplastic exposure through farmed mussel consumption.