Showering, brushing your teeth, and going to the toilet can wash dangerous contaminants into waterways that can disrupt fish reproductive systems and make them unafraid of mortal predators, scientists have found.

A growing array of household products, including soap, toothpaste, moisturisers, drugs, and cleaning products could be unsettling the ultra-sensitive marine ecosystems of New Zealand rivers and coastlines, the researchers say.

The products often contain preservatives, anti-bacterial compounds, or pharmaceuticals that are designed to penetrate living cells.

But when they're washed into the environment, even minuscule concentrations can upset hormonal signals in organisms bodies, affect reproduction or growth.


"It can even mean [fish] or organisms are no longer scared of predators, or they become disinterested in looking after their eggs or nests. The effects are wider-ranging and serious," said University of Canterbury environmental chemist Dr Sally Gaw ahead of a public lecture on her studies tonight.

A recent US study into the presence of pharmaceuticals in freshwater areas receiving sewage effluent found evidence of the Prozac in fish brains.

It found minnows became aggressive, anti-social and sometimes homicidal.

"Tiny concentrations can impact on fragile ecosystems," Dr Gaw said.

"One drop in 20 Olympic swimming pools can still be environmentally relevant.

"Some of the ingredients in the female contraceptive pill, present in very low concentrates in the environment, can have effects on aquatic organisms."

While there's been widespread research internationally on these emerging contaminants, little is known on their impact to the New Zealand environment.

Dr Gaw and her team of PhD students are already looking into a range of contaminants, including the impact of hair products and different metals in the environment.


"We need to find out what the issues are for New Zealand," she said.

"We want to provide really good information to the regulators so they can make the right decisions."

Sewage discharges are a major source of emerging contaminants entering coastal waters, Dr Gaw said.

And current sewage treatment processes were not designed to remove the dangerous contaminants.

Measures to reduce the impact of emerging contaminants in the marine environment will involve a combination of improved treatment at wastewater plants and regulatory controls for high risk chemicals, Dr Gaw says.

It's not just the impact on the environment, which is of concern either.


Dr Gaw says the presence of antibiotics and antimicrobial compounds in the environment is a public health issue too, with the potential for the development of antibiotic drug resistance in bacteria.

"We're getting better at finding these chemicals, but in the what-if and does-it-matter questions, we are still lagging behind a bit."