Individual and combined effects of microplastics and cadmium on intestinal histology and microflora of Procypris merus

Microplastics (MPs) and their interactions with heavy metals have attracted considerable attention worldwide. In Guangxi, China, cadmium (Cd) pollution is ubiquitous in aquatic environments. Rice flower carp (Procypris merus) is popular in Guangxi, playing an important role in the economic development of the region. The effects of combined exposure to MPs and Cd on P. merus remain unclear consequently the present study was performed to determine the individual (500 µg/L Cd (Cd) or 500 µg/L MPs (MP)) and combined effects of MPs and Cd (500 µg/L Cd + 500 µg/L MPs (Cd + MP)) on the intestinal histology and microflora of P. merus after an exposure of 14 days. The intestinal structure was damaged in all treatment groups, and severe necrosis of the mucous layer was found in the MP and Cd + MP groups. Similarly, the number of goblet cells increased in all treatment groups, but was higher in the MP and Cd + MP groups. Alpha diversity indices of the gut microbiota were influenced by the individual or combined effects of exposure. At the phylum level, the abundance of Firmicutes was lower in MP group than Cd and Cd + MP group, and the Firmicutes/Bacteroidetes ratio was significantly decreased (p = 0.021) in MP group. At the genus level, Streptococcus, a genus that might be involved in controlling the incidence of intestinal inflammation, was also found to be significantly decreased in the MP group (p = 0.029). Consistent with these results, gut metabolic function was disrupted in the present study. Overall, the above results suggest that exposure to combined Cd and MPs could result in inflammatory disease in P. merus, which was potentially mainly due to MPs stress.