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Dimethyl phthalate (DMP) is one of the most widely used plasticizers. Due to its anthropogenic inputs, DMP has become a serious contaminant in soils and water. Hydroponic experiments were conducted focusing on phytotoxic responses of rice seedlings (Oryza sativa L. cv. XZX 45) to 1,2-dimethyl phthalate. Relative growth rate (RGR) and water use efficiency (WUE) were measured as response endpoints to quantify the effective concentrations (ECs) of DMP to rice seedlings. As a comparison, acute phytotoxicity of dimethyl sulfoxide (DMSO) used as solvent media was also determined. Results showed that acute toxicity of DMP to rice seedlings was evident, but selected endpoints had different responses to DMP exposure. RGR of rice seedlings was more sensitive to change of DMP than WUE. EC-48 h values for 10, 20 and 50 % inhibition of the RGR were estimated to be 6.18, 38.41 and 329.41 lL for rice seedlings exposed to DMP, respectively, while smaller ECs were obtained for 96 h exposure.Results from phytotoxicity of DMSO demonstrated that the doses of DMSO used for dissolving DMP had a negligible effect on rice seedlings. In conclusion, DMP is problematic at relatively low concentrations for rice seedlings, and inhibitory effects are highly dependent on response endpoints and the duration of exposure period.

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