Hormone causing fish sex change may lead to new sewage treatment technology

The sustainability of fish populations in England and Wales could be being put at risk from oestrogenic hormones in water discharged into rivers from sewage treatment works, says the Environment Agency following the publication of research by scientists at Brunel and Exeter Universities. As a consequence, the Agency has said that the situation requires serious consideration of changes to sewage treatment technologies.


On 17 March, the BBC’s Country File programme revealed the contents of a leaked report stating that the artificial female hormone used in the human contraceptive pill – as well as natural female hormones – could be responsible for reducing the fertility of male fish (see related story). The programme also implied that there could be a further connection with declining human male fertility.

The Environment Agency has now published the full report, the latest information from the organisation’s on-going research into endocrine disrupting substances.

The research reveals that there is evidence of harm to male fish, including the production of eggs within their reproductive organs – known as the intersex condition, and the development of female reproductive ducts. Effects can occur at very low concentrations of oestrogenic hormones, and a combination of hormones can also have an additive effect, causing greater effects than they would have had individually. In particular, 17á-ethinyloestradiol – the hormone from the contraceptive pill – can cause effects in fish at concentrations of less than one part per billion.

Effects on of the hormones were studied in roach and gudgeon in 10 river catchments, with the effects being greater in roach. Comparison of gamete quality of both wild males and females from sites exposed to effluent from sewage treatment works showed that there was a progressive decrease in the overall quality of gametes, with increased levels of the intersex condition. Older male fish from areas known to have been exposed to effluent also showed delays in seasonal sexual maturation prior to spawning.

However, although around 50% of males in the Rivers Aire and Nene were found not to produce sperm in one spawning experiment, the results cannot be taken as characteristic of all lowland rivers, as spawning rates depend on a number of local risks, says the Environment Agency.

Fish kept in large aquaria and exposed to sewage effluents showed similar effects, and juvenile fish developed non-reversible feminisation of reproductive ducts and altered hormone levels even with only three month’s exposure.

Studies on wild fish also revealed that older fish are more severely affected by the intersex condition than younger individuals, suggesting that it is continued exposure to oestrogenic hormones that drives the condition. The research also suggests that the production of female ducts is a one-off process in early life.

“While we do not know what impact oestrogenic substances might have on the long term viability of some wild fish populations, we believe there is now sufficient evidence of harm to fish to develop a risk management strategy for oestrogens in sewage effluent,” said the Environment Agency’s Head of Chemicals, Steve Killeen. “The strategy may require changes in sewage treatment practices, possibly meaning the development of new technologies for some sewage treatment plants. However, not all fish populations will be affected so action has to be carefully targeted according to risk.”

Research published by the Environment Agency in September last year revealed that downstream of sewage treatment works in two rivers, the Nene and Lea, concentrations of oestrogens were highly variable, affected by the half lives of the different hormones. The most rapid biodegradation of one hormone, 17â-oestradiol, occurred in downstream urban/industrial stretches of rivers. Sorption of the hormones into sediments was also found to be an important route for their removal.

More research has to be done to discover the actual consequences on the sustainability of fish stocks due to these effects, says the Environment Agency. The Agency is calling for a collaborative programme with the water industry to develop a common approach to assess the effects of the hormones, identify priority treatment works, and to evaluate the effectiveness and costs of treatment. This should consist of an initial study on the feasibility of risk management options throughout 2003-4, followed by detailed studies on the implementation of these in 2005-7.

“We need to be confident that potentially major investment in treatment options will be effective,” said Killeen. “The environmental benefit – the degree to which damage to fish can be reduced – will have to justify the cost.”

The Agency was keen to point out that the research did not generate any information relevant to public health.

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