The invasive red swamp crayfish (Procambarus clarkii) as a bioindicator of microplastic pollution: Insights from Lake Candia (northwestern Italy)

Microplastic pollution has become pervasive. Identifying a bioindicator species to track the occurrence and ef-fects of microplastics (MPs) on ecosystems is crucial for determining their impact on the environment. The digestive tract of Procambarus clarkii was thought to be of interest for investigating MPs accumulation in freshwater organisms. Our hypothesis was that the same type of MPs found in abiotic compartments (water and sediment) could be found in P. clarkii, which would make it an ideal candidate for use as a bioindicator of MP pollution in freshwater ecosystems. Water, sediment, and P. clarkii specimens were collected from four sites in a lentic ecosystem (Lake Candia; northwestern Italy) for two consecutive years (2021-2022). The mean MPs abundance was 1.75 +/- 0.95 items/m3 in 2021 and 2 +/- 0.81 items/m3 in 2022 in the water samples and 6.75 +/- 1.5 items/kg and 8 +/- 0.81 items/kg in the sediment samples in 2021 and 2022, respectively. In 2021, the average was 0.06 +/- 0.07 items/g in the males and 0.05 +/- 0.05 items/g in the females; in 2022, the average was 0.04 +/- 0.05 items/g and 0.05 +/- 0.06 items/g in the males and the females, respectively. MP fibers and fragments (black, white, blue, light blue) of polypropylene and polyethylene terephthalate were found in the biotic and the abiotic compartments. The generalized linear mixed model revealed that the number of items/g was predicted only by total weight: the lowest number of items/g was recorded for crayfish with the highest weight probably due to the feeding habits of P. clarkii. Our findings suggest that the invasive P. clarkii (smaller individuals, in particular) could be a good candidate bioindicator for MP pollution since the same type of MP items were recorded in the abiotic compartments. Further research is needed to better understand the feeding behavior of P. clarkii and the dynamics of MPs in aquatic ecosystems.