Acute toxicity of typical environmental estrogens to the embryogenesis of the abalone Haliotis diversicolor supertexta
Student thesis: Doctoral Thesis
Environmental estrogens, a major class of endocrine disrupting chemicals, include a wide variety of domestic and industrial contaminants and cause significant toxicity. However, most previous studies focused on chronic rather than acute toxicities. The present study aims to investigate the acute toxicity of four typical environmental estrogens, namely nonylphenols (NPs), bisphenol A (BPA), 17α-ethynilestradiol (EE2) and 17β-estradiol (E2), to the embryonic development of a typical marine invertebrate, the abalone Haliotis diversicolor supertexta. The occurrence and distribution of the four target chemicals around the coastal areas of Shenzhen city, the main habitat of the abalone, were investigated. The concentration ranges of NPs, BPA, EE2 and E2 in seawater were 5.2-1176.8, 3.2-776.6, 4.8-268.9 and from not detected to 1.9 ng L-1, respectively. The acute toxicity of the target chemicals to the embryogenesis, the larval development and metamorphosis, of the abalone H. diversicolor supertexta was examined by a two-stage embryonic toxicity test. At the trochophore stage, the median effective concentrations after 12 hours (12-hour EC50) of NPs, BPA, EE2 and E2 were 1016.22, 30.72, 277.88 and 292.75 μg L-1, respectively. Using another experimental endpoint, the completion of metamorphosis, the 96-hour EC50 values of NPs, BPA, EE2 and E2 were reduced to 11.65, 1.02, 10.01 and 55.40 μg L-1, respectively. The diatom, the settlement substrate for the larvae undergoing metamorphosis, could accumulate target chemicals in both the cells and the extracellular polymeric substances, with bioconcentration factors in the range of 1879-2036, 237-256, 441-461 and 36-38 for NPs, BPA, EE2 and E2, respectively. Longer exposure time and magnified exposure concentration in the settlement substrate due to the bioconcentration in diatoms led to a higher sensitivity of the metamorphosed larvae to the target chemicals when compared with the trochophore. The hazard concentrations for 5% of the species after 96 hours (96-hour HC5) were 0.99, 0.18, 1.20 and 15.87 μg L-1 for NPs, BPA, EE2 and E2, respectively. The 96-hour HC5 values could be employed as the safety threshold for the metamorphosis of the abalone. Based on the safety threshold and the environmental pollution concentration of the target chemical in the environment, the risk quotients of NPs, BPA, EE2 and E2 were calculated to be 1.19, 4.31, 0.22 and 1.20×10-4, respectively. The probability of NPs and BPA to exceed the safety threshold and cause adverse effects on the metamorphosis of the abalone in 96 hours at a frequency of 2.1% and 9.6%, respectively, was higher that that of EE2 and E2. Results on the responses of functional proteins showed that typical endocrine estrogens could activate or inhibit the synthesis of certain functional proteins in the abalone larvae, affect the physiological functions and finally lead to the failure of metamorphosis, including energy and substance metabolism, cell signalling, formation of cytoskeleton and cilium, immune and stress responses. The present study demonstrated that NPs and BPA could cause acute toxicity to the embryogenesis of the abalone H. diversicolor supertexta at their currently detected environmental concentrations. This effect was further enhanced by their bioaccumulation in diatoms during the settlement of the embryos. Toxic mechanisms of the target environmental estrogens in the abalone embryos were partly elucidated on the protein level.
- Environmental aspects, Abalones, Embryology, Estrogen, Acute toxicity testing