Microplastics in Cetaceans Stranded on the Portuguese Coast

SIMPLE SUMMARY: This study characterises microplastics ingested by small cetaceans on the coast of Portugal. The intestine contents of 38 stranded cetaceans were processed in the laboratory to remove as much organic matter as possible from the samples and facilitate the detection of microplastics under a stereomicroscope. This study evaluated the possible influence of several biological and health variables (e.g., species, sex, body condition) on the amount of microplastics found in three small cetacean species, particularly on common dolphins, due to the larger number of available samples. Most of the analysed individuals had microplastics, with harbour porpoises revealing a significantly higher median number of microplastics than common dolphins, probably due to their different diets, use of habitat and feeding strategies. However, none of the other tested variables significantly influenced the number of microplastics in either all of the analysed species or in the common dolphin group. The relatively low numbers of microplastics found in the present study should not be enough to cause physical and chemical sublethal effects, although the potential effects of plastic-derived pollutants are not yet completely understood. Future monitoring of biota should rely on improved and standardised protocols for microplastic analyses. ABSTRACT: This study characterises microplastics in small cetaceans on the coast of Portugal and assesses the relationship between several biological variables and the amount of detected microplastics. The intestines of 38 stranded dead cetaceans were processed in the laboratory, with digestion methods adapted to the amount of organic matter in each sample. The influence of several biological and health variables (e.g., species, sex, body condition) on the amount of microplastics was tested in all analysed species and particularly in common dolphins, due to the larger number of available samples. Most of the analysed individuals had microplastics in the intestine (92.11%), with harbour porpoises revealing a significantly higher median number of microplastics than common dolphins, probably due to their different diets, use of habitat and feeding strategies. None of the other tested variables significantly influenced the number of microplastics. Moreover, the microplastics found should not be enough to cause physical or chemical sublethal effects, although the correlation between microplastic ingestion and plastic additive bioaccumulation in cetacean tissues requires further investigation. Future monitoring in biota should rely on improved and standardised protocols for microplastic analyses in complex samples to allow for accurate analyses of larger samples and spatio-temporal comparisons.