Non-standard Physiological Endpoints to Evaluate the Toxicity of Emerging Contaminants in Aquatic Plants: A Case Study on the Exposure of Lemna minor L. and Spirodela polyrhiza (L.) Schleid. to Dimethyl Phthalate (DMP)

Emerging contaminants are targeted as primary pollutants of great concern for the ecosystem health. The evaluation of their effects on biota by non-destructive and reliable techniques is an issue receiving growing interest within the scientific community, particularly for plants. Beside commonly used proxies such as growth parameters and chlorophyll content, a set of non-standard endpoints has been proposed to be effectively used for the evaluation of the toxicity effects of xenobiotics on plants. Among them, chlorophyll fluorescence and leaf reflectance spectra analyses were reported as information-rich, non-destructive, and real-time mode technologies to assess the physiological status of plants. To verify their applicability for the ecotoxicology assessment in plants, a case study was set up by investigating the effects of dimethyl phthalate (DMP), an emerging contaminant in the aquatic environment, on two aquatic model plants (Lemna minor L. and Spirodela polyrhiza (L.) Schleid.), paralleling standard and non-standard toxicity endpoints. Results of a 7-day toxicity assay highlighted the effectiveness of chlorophyll fluorescence parameters and leaf reflectance spectra to assess the toxicity status of plants. Specifically, it was evidenced a lack of toxicity effects at 3 (DMP1) and 30 (DMP2) mg/L DMP in both Lemna and Spirodela plants, while at the highest DMP concentration (600 mg/L, DMP3), biometric and physiological endpoints revealed a toxicity status in both plant species, particularly in Spirodela. Thus, the performed case study evidenced the suitability of the targeted non-standard endpoints in assessing the ecotoxicity of DMP in aquatic plants, also contributing to shed light on the environmental risk posed by phthalates in the freshwater compartment.