Investigating the ecotoxicological effects of dimethyl phthalate (DMP) and polyethylene (PE) on the floating aquatic plant, Lemna minor.

Freshwater ecosystems are increasingly threatened by microplastics and their associated leachates; as significant producers in the freshwater environment, aquatic plants are at the greatest risk of emerging contaminants, threatening biodiversity, supportive and regulative ecosystem services. Given this, the aim of the present study was to identify and evaluate the dose-response effects of both dimethyl phthalate and polyethylene (30µm fragments), on the frond number, surface area, dry weight and chlorophyll content of Lemna minor . The results of this study indicated that while polyethylene did not consistently produce significant dose-response trends across the measured parameters, it did exhibit significant effects with respect to chlorophyll content (LOEC = 10 mg/L). Exposure to DMP caused significant (p < 0.001) effects on Lemna minor frond number and dry weight (LOEC = 10 mg/L). The combined exposure of DMP and PE revealed evidence of an interaction between the two contaminants, with notable effects on frond number and dry weights. Significant effects were also observed on chlorophyll content (LOEC = 50 mg/L of DMP when combined with both 10 and 100 mg/L of PE), supporting the hypothesis that a combination of the two amplify phytotoxicity. The findings of this study highlight the potential for microplastics and their associated leachates to disrupt plant growth, underlining the need for improved ecotoxicity assessments. The outcomes of this work contribute to a growing wealth of literature which aim to inform ecological risk assessments, supplement freshwater management plans and improve the health of our freshwater ecosystems.