Adverse effects of dietary virgin (nano)microplastics on growth performance, immune response, and resistance to ammonia stress and pathogen challenge in juvenile sea cucumber Apostichopus japonicus (Selenka).

Abstract

It has been well documented that micro- and nanoplastics are emerging pollutants in aquatic environments, and their potential toxic effects has attracted widespread concerns. Here, we evaluated the adverse effects of dietary polystyrene nanoplastics and microplastics (PS-N/MPs) on growth performance, oxidative stress induction, immune response, ammonia detoxification, and bacterial pathogen resistance of sea cucumber Apostichopus japonicus. After collection and acclimation, sea cucumbers were randomized into 3 groups (i.e., control, 100\xa0nm PS-NPs and 20\xa0µm PS-MPs at 100\xa0mg\xa0kg-1 diet) for 60-day feeding experiment. Every group contained 360 sea cucumbers which were equally divided into 3 aquaria as biological triplicates. The results showed that the specific growth rate and final weight of the sea cucumbers fed with diets containing PS-N/MPs were significantly lower than those of control group. Dietary virgin PS-N/MPs significantly increased the reactive oxygen species production and malondialdehyde content in coelomic fluid, causing oxidative stress and damage to the growth and development of A. japonicus. During the experiment, 100\xa0nm PS-NPs significantly induced the depletion in cellular and humoral immune parameters. The calculated IBR values based on multi-level biomarkers revealed the size-dependent toxic differences of PS-NPs >\xa0PS-MPs. The relative expression levels of GDH and GS mRNA showed first rise and then fall trends after exposure to ammonia, and 100\xa0nm PS-NPs had a more profound impact on suppressing ammonia detoxification compared with 20\xa0µm PS-MPs. Moreover, the expression of Hsp90, Hsp70, CL, TLR, and CASP2 genes were all down-regulated by ammonia exposure. Taken together of IBR results, ammonia stress test and pathogen challenge, we deduced that dietary 100\xa0nm PS-NPs are more potentially hazardous than 20\xa0µm PS-MPs. These findings provide valuable information for understanding the size-dependent toxic effects of PS-N/MPs and early risk warning on marine invertebrates.