Contamination of mussels with microorganisms, metals, and biotoxins: a historical analysis from Portugal

Mussels (Mytilus spp.) are an important seafood product and a sentinel species for environmental contamination. This work aimed to analyze Portuguese monitoring data for mussels to identify seasonal and spatial trends in microbiological, biotoxins, and metal contamination. Data, from 2013 to 2025, were obtained from publicly available records from the official control program. Harvested mussels were generally safe for consumption, with most samples complying with microbiological Class A parameters (75.5%) and metals only exceeding regulatory limits once. Conversely, okadaic acid toxin group (i.e., diarrhetic shellfish poisoning toxins) exceeded limits in 19.5% of samples, identifying marine biotoxins as the greatest concern for mussel harvesting in Portugal. Microbiological contamination with Escherichia coli peaked in winter in estuaries and lagoons, while biotoxins peaked in summer in coastal areas. Both occurred most often in the North and Center regions, likely driven by rainfall-related inputs that may intensify under climate change-related extreme weather events. Therefore, harvesting restrictions did not only reflect food safety issues but also broader ecosystem contamination, requiring strengthened monitoring and mitigation measures to safeguard the ecosystem and public health.