Exposure of Lemna minor (common duckweed) to mixtures of uranium and perfluorooctanoic acid (PFOA).

A variety of processes, both natural and anthropogenic, can have a negative impact on surface waters, which in turn can be detrimental to human and environmental health. Few studies have considered the ecotoxicological impacts of concurrently occurring contaminants, and that is particularly true for mixtures that include contaminants of emerging concern (CEC). Motivated by this knowledge gap, our study considers the potential ecotoxicity of environmentally relevant contaminants in the representative aquatic plant, Lemna minor (common duckweed), a model organism. More specifically, biological effects associated with exposure of L. minor to a ubiquitous radionuclide (uranium, U) and a fluorinated organic compound (perfluorooctanoic acid, PFOA, considered a CEC), alone and in combination, were monitored under controlled laboratory conditions. L. minor was grown for 5 days in small, aerated containers. Each treatment consisted of four replicates with 7 plants each. Treatments were: 0, 0.3, and 3 ppb PFOA; 0, 0.5, and 5 ppb U; and combinations of these. Plants were observed daily for frond number and signs of chlorosis and necrosis. Other biological endpoints examined at the conclusion of the experiment were chlorophyll content and antioxidant capacity. In single-exposure experiments, a slight stimulatory effect was observed on frond number at 0.3 ppb PFOA, whereas both concentrations of U had a detrimental effect on frond number. In the dual exposure experiment, the combinations with 5 ppb U also had a detrimental effect on frond number. Results for chlorophyll content and antioxidant capacity were less meaningful, suggesting that environmentally relevant concentrations of PFOA and U have only subtle effects on L. minor growth and health status.