Effects of Polyethylene Microplastics Containing Benzophenone-3 on Daphnia Magna Population Dynamics Under Low Food Levels

Food levels play a vital role in zooplankton population dynamics. However, the effects of microplastics (MPs) on Daphnia magna populations at low food levels are not fully understood. In this study, we evaluated the effects of food levels and polyethylene MPs on the population structure of D. magna. To achieve this, D. magna populations were exposed to polyethylene MP fragments, MP fragments containing the ultraviolet stabilizer benzophenone-3 (MP/BP-3 fragments), and BP-3 leachate from MP/BP-3 fragments. The test duration was 42 days to observe the growth and decline of D. magna populations. The low food levels (2 × 105 cells/mL) significantly decreased (p <0.05) the population size and changed the population structure compared to the optimum food levels (5 × 105 cells/mL). In the low-food condition, treatments with both the MP and MP/BP-3 fragments significantly decreased (p <0.05) the population size in the decline phase compared with that in the low-food control group, but there was no difference in population size and structure between these two treatment groups. Notably, treatment with the BP-3 leachate delayed D. magna development and growth, resulting in a significant decrease (p <0.05) in population size during the growth phase. These findings suggest that BP-3 contained in MP/BP-3 fragments may not be available to D. magna. However, the mechanisms governing the interaction between MPs and BP-3 remain unclear and require further investigation.