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Background Phthalic acid esters (PAEs) are widely used plasticizer with a generally high environmental exposure level.PAEs cause reproductive and developmental toxicity in mammals.In this paper, the reproductive toxicity of DEHP, DBP, and DIBP were discussed using the model organism Caenorhabditis elegans to determine the sensitivity indices for evaluating the ecotoxicological effects of PAEs.Methods L4 C.elegans larvae were exposed to DEHP, DBP, and DIBP for 24 h to evaluate the LC50 of the compound and the changes in brood size and generation time.The effects of DEHP, DBP, and DIBP on the oogenesis of C.elegans were ascertained through oocyte and distal-tip cell (DTC) counting.Oocyte apoptosis and related mechanisms were further analyzed with different mutants.The total RNA of the nematodes was extracted, and real-time reverse-transcription PCR was employed to detect the expression levels of apoptosis-related genes (cep-1, cegl-1, ced-9, ced-4, and ced-3) after PAEs exposure.Results The LC50 of DEHP, DBP, and DIBP to C.elegans exceeded 100 mg/L.High PAEs exposure significantly reduced the brood sizes (P < 0.05) but not the generation time (P > 0.05) in comparison with the control group.A significant difference in oocyte numbers was found between the medium-or high-dose PAEs exposure group and the control group (P < 0.05).By contrast, no significant difference in the fluorescence intensity of DTCs was noted between the exposure and control groups.A significant difference in the number of apoptotic cells from the unilateral gonad ann was observed between the medium-or high-dose group and the control group (P < 0.05).Exposure of the nematodes to PAEs significantly increased the expression levels of cep-1, egl-1,ced-4, and ced-3 but significantly decreased that of ced-9.Fluorescence analysis of HUS-1 showed that PAEs exposure induced the over expression of the HUS-1 protein involved in DNA repair.Conclusions PAEs can cause reproductive toxicity by affecting C.elegans oogenesis.Oocyte number is an earlier indicator of reproductive toxicity than generation time and brood size.The decreased oocyte numbers in C.elegans when exposed to PAEs may involve the abnormal oocyte apoptosis induced by DNA damage.