Summary

Endocrine disrupting chemicals (EDC) are as the name suggests chemicals   capable of affecting the endocrine system. High exposure to EDCs has been reported to result in feminisation, masculinisation, infertility and birth defects in species of fish, birds, reptiles and some mammals. To investigate the impact of certain endocrine disrupting chemicals that can enter the environment, Sydney rock oysters were exposed to 4-nonylphenol (1 and 100µg/L) and 17a-ethynylestradiol (5 and 50ng/L) in seawater over 8 weeks. Exposures were done to assess effects on reproductive state (vitellogenin induction and gonadal development) during reproductive conditioning. The chronic effects of these chemicals within the gonad were assessed via an estrogen receptor-mediated, chemical-activated luciferase reporter gene-expression assay (ER-CALUX®). We found that exposure to these chemicals did result in elevated estradiol equivalents (EEQ) in oyster tissue. EEQs were greatest in the 100µg/L 4-nonylphenol exposure (28.7 ± 2.3ng/g tissue EEQ) while 17a-ethynylestradiol at concentrations of 50ng/L were 2.2 ±1.5ng/g tissue EEQ. Results also suggested that  4-nonylphenol may be accumulated in oyster tissue and is partly resistant to biological breakdown; maintaining its potential for chronic estrogenic action, while 17a-ethynylestradiol, although exhibiting greater estrogenic potency on oysters possibly exerts its estrogenic action before being rapidly metabolised and/or excreted.

A new method was developed to assess the quantity of vitellogenin (egg protein) present in oysters using High Performance Liquid Chromatography (HPLC). Using this method, we found that exposure to both 17a-ethynylestradiol (50ng/L) and 4-nonylphenol (100µg/L) increased vitellogenin in females, whereas males exhibited increases in vitellogenin when exposed to 50ng/L 17a-ethynylestradiol only. Females exhibited greater vitellogenin responses than males at 50ng/L 17a-ethynylestradiol only. Microscopic examination of gonads revealed a number of individuals exhibiting intersex (having both male and female reproductive tissue) in 50ng/L 17a-ethynylestradiol exposures. Males in 1µg/L and 100µg/L 4-nonylphenol exposures and 5ng/L 17a-ethynylestradiol did not show the same degree of sperm development as that seen in untreated controls.