Acute Toxicity Of Typical Environmental Estrogens To The Metamorphosis Development Of The Abalone Haliotis Diversicolor Supertexta

As a major class of endocrine disrupting chemicals, environmental estrogens include a wide variety of domestic and industrial contaminants, causing a great attention of toxicologists. However, most studies focus on the chronic toxicity rather than the acute toxicity, since the acute effective concentrations are much higher than the environmental pollution concentrations. The present study aims to investigate the acute toxicity of four typical environmental estrogens to the embryonic development of a typical marine invertebrate, the abalone Haliotis diversicolor supertexta.Occurrence and distribution of four target chemicals, 4-nonylphenol (4-NP), bisphenol A (BPA), 17α-ethynilestradiol (EE2), and estradiol (E2) were investigated around the coastline of Shenzhen city, serving as a main habitat of the abalone. In the seawater, 4-NP, BPA, EE2, and E2 ranged from 5.2 to 1176.8, from 3.2 to 776.6, from 4.8 to 268.9, and from not detected to 1.9ng/L, respectively. The acute toxicity of target chemicals to the embryogenesis, larval development and metamorphosis of the abalone H. diversicolor supertexta was examined by means of two-stage embryo toxicity test. At the trochophore stage, 12h-EC50 values of 4-NP, BPA, EE2, and E2 were 1016.22, 30.72, 277.88 and 292.75μg/L, respectively. With the completion of metamorphosis as another experimental endpoint, 96h-EC50 values of 4-NP, BPA, EE2, and E2 were reduced to 11.65, 1.02, 10.01, 55.40μg/L, respectively.As the settlement substrate for the larvae undergoing metamorphosis, the diatom could accumulate target chemicals in both the diatom cells and the extracellular polymer substances, with bioconcentration factors in the range from 1879 to 2036, from 237 to 256, from 441 to 461, and from 36 to 38 for 4-NP, BPA, EE2, and E2, respectively. Longer exposure time and magnified exposure concentration in the settlement substrate (caused by the bioconcentration) led to the higher sensitivity of metamorphosed larvae to target chemicals compared with the trochophore.The respective 96h-hazard concentrations for 5% of the species (HC5) were 0.99, 0.18, 1.20, and 15.87μg/L for 4-NP, BPA, EE2, and E2. The 96-HC5 value could be employed as the safety threshold for the metamorphosis of the abalone. Based on the safety threshold and the environmental pollution concentration of target chemical, the risk quotients of 4-NP, BPA, EE2 and E2 were 1.19,4.31,0.22 and 1.20×10-4, respectively. 4-NP and BPA had a probability to exceed the safe threshold and cause adverse effect to the metamorphosis of the abalone in 96h at a frequency of 2.1% and 9.6%, respectively, while EE2 and E2 had little probability to affect the metamorphosis of the abalone.Even though no estrogen receptor (ER) has been detected in invertebrates, typical endocrine estrogens could also activate or inhibit the synthesis of certain functional proteins in the abalone larvae without binding to ER. Based on the responses of functional proteins, typical endocrine estrogens could affect various physiological functions in the larvae as the same time and finally led to the failure of metamorphosis, including energy and substance metabolism, cell signaling, formation of cytoskeleton and cilium, immune and stress responses.