Comparative toxicity of the plasticizer dibutyl phthalate to two freshwater algae

Phthalate esters (PAEs), a family of emerging environmental contaminants, have been frequently detected in soils and water. However, intensive studies on the toxicity of PAEs have focused on growth response of terrestrial and aquatic animals, while only limited attention has been paid to aquatic plants, especially phytoplankton, the primary producer in aquatic ecosystems. Therefore, the acute toxic effects and underlying mechanisms of dibutyl phthalate (DBP) at different concentrations (0-20mgL^-1) on two typical freshwater algae (Scenedesmus obliquus and Chlorella pyrenoidosa) were investigated. The growth of S. obliquus and C. pyrenoidosa was conspicuously inhibited by DBP exposure at 2-20mgL^-1. The 96-h median effective concentration values (96h-EC₅₀) were 15.3mgL^-1 and 3.14mgL^-1 for S. obliquus and C. pyrenoidosa, respectively, implying that the spherical C. pyrenoidosa is more sensitive to DBP than the spindle-shaped S. obliquus. As expected from the damage done to cell organelles (i.e. cell membranes, chloroplasts, and protein rings), cell densities and chlorophyll content conspicuously decreased under DBP treatments. Moreover, the algal growth inhibition was closely linked to the increased production of intracellular reactive oxygen species and malondialdehyde content, indicating oxidative stress and lipid peroxidation in both algae. This was proved by the increased activity of antioxidant enzymes such as superoxide dismutase and catalase. Our findings will contribute to the understanding of toxic mechanisms in PAEs and the evaluation of environmental risks for primary producers in aquatic ecosystems.