Effects of Microplastic Contamination on the Aquatic Plant Lemna minuta (Least Duckweed)

Microplastics are widely spread in aquatic environments. Although they are consideredamong the most alarming contaminants, toxic effects on organisms are unclear, particularly onfreshwater plants. In this study, the duckweed Lemna minuta was grown on different concentrations(50, 100 mg/L) of poly(styrene-co-methyl methacrylate) microplastics (MP) and exposure times(T0, T7, T14, T28 days). The phytotoxic effects of MP were investigated by analyzing several plantmorphological and biochemical parameters (frond and root size, plant growth, chlorophyll, andmalondialdehyde content). Observations by scanning electron microscope revealed MP adsorptionon plant surfaces. Exposition to MP adversely affected plant growth and chlorophyll content withrespect to both MP concentrations and exposure times. Conversely, malondialdehyde measurementsdid not indicate an alteration of oxidative lipid damage in plant tissue. The presence of MP inducedroot elongation when compared to the control plants. The effects of MP on L. minuta plants were moreevident at T28. These results contribute to a better understanding of MP's impact on aquatic plantsand highlight that MP contamination manifests with chronic-type effects, which are thus detectable atlonger exposure times of 7 days than those traditionally used in phytotoxicology tests on duckweeds.