A scientist is warning the increasing amount of oestrogen excreted by dairy cows is a "ticking time bomb" for the New Zealand environment.
Oestrogen is a natural compound excreted by humans and animals in urine and faeces and can enter rivers and lakes. It has been documented in Europe as causing deformities in fish which can harm reproduction.
Northcott Research Consultant scientist Grant Northcott said the so-called "gender bender chemicals" change the male fish more into a female fish which can prevent them from breeding.
Dr Northcott said the rapid expansion of the dairy industry over the past decade means dairy cows were excreting increasing amounts of oestrogen into the environment.
"Our research has shown that within intensive dairy farm catchments there is a background concentration of oestrogenic steroid hormones and oestrogenic activity that is sourced from the on-land activities - being dairy farming.
"So we know they are there, we know the concentration range at which they are present and although it is very low - it's down in the parts per trillion range - these chemicals are so biologically active, they have such a high biological potency, that even at these very, very low concentrations they are still able to [have]an impact on aquatic fish that are exposed to them," he said.
Dr Northcott said oestrogens were starting to show up in bore waters in intensive dairying areas.
"I think it is a ticking time bomb. The research we have done shows they are present, they are essentially there at background levels.
"We've done work in other parts of the country, particularly Canterbury, where some bore waters from shallow ground aquifers from dairy farm catchments were sampled and we measured low concentrations of these chemicals and oestrogenic activity in these shallow groundwater aquifers."
Dr Northcott said oestrogen levels in parts of New Zealand were similar to Europe where many studies had shown fish were being deformed, but worryingly no studies had been done here into the effect of oestrogens on native fish.
In New Zealand there did not appear to be specific targeting of oestrogen pollution in dairy farm waste treatment, but in the United States where cows were concentrated in indoor housing they had an advanced system for processing manure into reusable energy.
But University at Buffalo researcher Professor Diana Aga found oestrogens largely survived that process, and because they were not regulated it was not something farmers thought about.
She said the study underscored how far waste treatment techniques on dairy farms had fallen behind the times.
"These chemicals are actually called micro-pollutants because compared to nitrogen they are at low levels and their effects are quite different in terms of pollution. Right now there are a lot of studies about oestrogen but at this time, while the Environmental Protection Agency is aware of this they are just starting to make regulations about what to do and it's a slow process.
"There are no maximum contaminant levels for example, so in that case that's what I mean by not regulated," Professor Aga said.
The Ministry for the Environment says endocrine disruptors in waterways, such as oestrogen, are among a range of emerging environmental issues it is monitoring.
The ministry said in a statement the information it had to date suggested it was not such a problem here as it was in Europe.
"This is because we don't have the same level of landfill leachate, high population densities and high volumes of sewage discharges to inland waterways, which appear to be the main source of endocrine disruptors in water ways overseas."
The ministry said assessing exposure to endocrine disruptors, and hence the health and environmental significance of these chemicals, was a challenging, specialist, and emerging field.
Grant Northcott said animal waste was also a recognized source of endocrine disruptors according to overseas studies, with that research showing the subsequent impact on waterways within intensively farmed agricultural catchments.
Dr Northcott said his research was completed eight years ago and it had been hard to get funding to continue the work.
"Intensification of dairy farming has continued at pace, so the environmental risk posed by the oestrogenic steroid hormones will have increased over the intervening period," he said.