Pollutant threat to oyster industry

A study published today reveals that a common industrial chemical causes sexual deformities in oysters, producing large numbers of hermaphrodite animals. The chemical, nonylphenol, is a breakdown product from a surfactant widely used in detergents, dispersing agents, herbicides, spermicides and cosmetics.

Dr Helen Nice who undertook this study at Royal Holloway, University of London, says, ‘Our results may cast doubt on the widespread use of this chemical in many human products including contraceptive spermicides.’

Nonylphenol is a known endocrine disrupter – chemicals that interfere with the hormones of animals. It is discharged through sewage effluent and is therefore widespread in the aquatic environment.

Dr Nice, together with supervisors Professor Mike Thorndyke, Dr. Mark Crane and Dr. Dave Morrit, worked in collaboration with Seasalter Shellfish, a commercial oyster hatchery at Whitstable in Kent. She exposed oyster larvae, Crassostrea gigas, to environmentally realistic levels of nonylphenol, the breakdown product of a surfactant.

Her research shows that developing embryos and larvae exposed to levels as low as 0.1 microgrammes per litre experience delays in development, show abnormalities in the shell hinge and increased death rates. Nearly a third of the larvae that survived treatment with the pollutant developed into hermaphrodite adults (both sex organs present). But there were no hermaphrodites in the control oysters that were not exposed to the pollutant. Oysters are known for their ability to change sex from one season to the next, but they are either male or female, not bisexual.

These adverse effects are seen even when oysters are exposed to levels well below those currently considered safe. The Environment Agency has set current recommended safe levels in both fresh and marine water at an average of 1.0 microgrammes per litre, ten times higher than used in this work.

The implications for oyster cultivation are that bisexual animals self fertilise, producing offspring that do not survive to breed themselves.

Dr Nice says: ‘The Pacific oyster plays a vital role in many food webs and is commercially important worldwide. These results are worrying, not only because of the damage to the oysters themselves, but also because this chemical may well be affecting other organisms sharing their environment. The findings reported here resulted from brief, single exposures to nonylphenol at critical periods in the animals’ development. It is vital when chemicals are screened, that the effects on vulnerable developmental stages should be considered. We clearly need further research to find out exactly what harm this chemical does and if it can harm people.’