The Mediterranean Mussel Mytilus galloprovincialis as a Biomonitor for Microplastic Pollution

Microplastics are abundant and ubiquitous in marine environments, posing threats to ecosystem health and human well-being. Limitations in current quantification methods lead to unreliable data on concentrations of small microplastics (< 25 µm), which are likely to be the most hazardous. To predict ecological and sanitary risks associated with microplastic pollution, new measuring tools such as biomonitors are essential.

Marine mussels, as non-selective suspension feeders that filter large volumes of water, are already used as biomonitors for other pollutants and appear to be good candidates for monitoring microplastic pollution levels at sea. In this context, we investigated the uptake and depuration of microplastics by the Mediterranean mussel Mytilus galloprovincialis, the most widespread mussel species, across varying exposure concentrations and durations.

In a first experiment, mussels were exposed for 48h to increasing microplastic concentrations, ranging from 0 to 2000 MPs/L, followed by 48h of depuration in clean seawater. Results demonstrate a strong linear relationship between microplastic uptake and environmental concentration (R² = 0.91), with high depuration rates for all concentrations (92 ± 3%) after 48h in clean seawater. In a second experiment, mussels were exposed to a single environmental concentration of 200 MPs/L over various durations (24h, 48h, 72h, 10d, 20d, 50d, and 100d). Findings indicate a linear increase in microplastic content in mussels with exposure durations, and consistently high depuration rates (90 ± 6%) after 48h in clean seawater.

These results support the use of M. galloprovincialis as an efficient biomonitoring tool for assessing microplastic levels in marine environments. However, despite their strong depuration ability, microplastics tend to accumulate in mussel tissues over time. Limiting exposure durations in biomonitoring surveys is therefore recommended to prevent overestimation of microplastic concentrations in surrounding waters.