Ingesting Secondary Microplastics Induces Apoptosis Without Proliferation in the Daphnia magna Intestinal Epithelium

Microplastics in aquatic environments are a contaminant of emerging concern. The ingestion of primary and secondary microplastics (MP) by aquatic invertebrates have been previously shown to disrupt a wide range of physiological processes, but little is known about what drives these effects. We exposed Daphnia magna to secondary MP fibers in two 48 hour trials and investigated their impact on cellular apoptosis and proliferation in the intestinal epithelium. We hypothesized that ingestion of secondary MP would lead to increased apoptosis and cell proliferation in the intestine of D. magna. We found that D. magna readily ingest MP (< 240 μm) added to the culture medium. Using fluorescence microscopy, we observed a greater abundance of cells undergoing apoptosis in D. magna exposed to MP compared to the control. We did not observe a significant difference in proliferation of intestinal cells between groups. Our results suggest that ingesting secondary MP induces apoptosis in the intestinal epithelium of D. magna, leading to increased mortality and decreased growth and fecundity shown in previous studies. The present study provides a cellular basis for the negative effects of ingesting MP fibers in D. magna.