Analysing for xenoestrogens in the common cockle (Austrovenus stutchburyi) to determine the risk for human consumption

Abstract

Xenoestrogens are compounds that mimic the activity of natural estrogens and can interfere with the endocrine system. Several xenoestrogens have been linked to detrimental effects in wildlife and humans including reproductive abnormalities, cancer and abnormal behaviour. Some xenoestrogens are released into the environment by anthropogenic activities such as horticulture, or with industrial and domestic effluent. These xenoestrogens often end up in aquatic systems, particularly estuaries. The common cockle (Austrovenus stutchburyi) is an estuarine shellfish that is non-commercially harvested in New Zealand for human consumption. Cockles can bioaccumulate lipophilic compounds, including xenoestrogens, and could recycle them back into the food chain when humans consume them. This may pose a health hazard to population groups who regularly consume cockles, or for those potentially more at risk from estrogenic chemicals such as men, infants and the developing foetus. The main objective of this research was to determine the level of estrogenic activity in cockles collected from culturally-important areas in Otago harbour, plus additional sites in the Avon-Heathcote Estuary (Christchurch), and to assess this activity for the potential risk for human consumers.

Cockles were collected in December 2003 from five sites in the Otago Harbour and four sites in the Avon-Heathcote Estuary. The estrogenic chemicals (including natural steroids) were extracted from the cockles and analysed by two in vitro bioassays, the yeast estrogen screen (YES) and the estrogen receptor binding assay (ERBA), followed by chemical analysis by GC-MS. Prior to these analyses, the YES methodology had been developed and validated. This involved assessing the response of the assay to modifications of cell inoculum, growth phase or incubation temperature, and the effects of various solvents and the presence of lipids. A reproducible YES method was established to accept the shellfish extracts, but no estrogenic activity was detected. All extracts initiated a response in the ERBA, but the response was proportional to the original shellfish size and it was concluded that impurities were causing non-specific binding. The GC-MS was used to analyse for natural steroids (estrogens and ethynylestradiol) and xenoestrogens (bisphenol A, nonylphenol, polychlorinated hydrocarbons (PCBs) and organochlorines). There were unexpected problems with extract purification and derivitisation, and no steroids were detected (even in a spiked control), demonstrating that recovery for chemical analysis was poor. A few PCBs and DDE (all environmentally ubiquitous) were detected at very low concentrations. These provide some evidence that cockles are one route by which xenoestrogens are cycled back into the human food chain.

A full risk assessment was not possible in this project as the extent of the xenoestrogen hazard was not quantifiable. The diet is the main source of estrogenic chemicals for humans, and foods like shellfish may contribute an important part of xenoestrogen exposure. Future work to identify high-risk foods would benefit from careful development and validation of extraction procedures that retain the full range of estrogenic chemicals in a food and respond well to purification and concentration. The bioassays, with some improvement in sensitivity, could then be successfully used as a screening tool.