Intersex fish and superbugs: Kiwis warned to watch what they flush

Kiwis are being urged to think twice about what they flush, rinse, and wash away, with scientists concerned it could cause fish to “gender bend” and create superbugs.

A 2017 University of Exeter study found a fifth of the male fish in United Kingdom rivers had become intersex, some even laying eggs, because of chemicals in human wastewater – including hormones from contraceptive pills.

Researchers from the Nelson-based Cawthron Institute have been conducting ongoing research into the same problem in the Waikato River.

Environmental toxicologist Dr Louis Tremblay said New Zealand’s wastewater issue was not as severe as the UK's, where the ratio of wastewater to water was about 50 per cent.

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“Our towns are quite coastal, so most of our discharge is into the ocean, although there are a few catchments like the Mataura River in Southland, which Gore for example feeds into.”

Tremblay said the hormones in birth control were more active than natural oestrogen, so even at a lower level, the risk of it having an impact on waterways was “very high”.

“While the concentrations might not be as high, they can still have long-term implications.”

Unfortunately, human wastewater was not the only contaminant our freshwater species had to contend with.

Chemicals like bisphenol A (BPA), which was used in plastic containers and drink bottles, mimicked natural oestrogen, he said.

“It makes its way into waterways through litter, and the BPA is not chemically bound to the plastic fibres, so it leaches into the water.

“In early life stages, fish are more sensitive and hormones play a big role … this is what causes that gender bender in fish – the early exposure to oestrogen turns them female.”

The biggest impact, as researchers discovered in Waikato, was farm runoff.

“Dairy shed effluent is probably a bigger risk than the pill here in NZ.

“Those large herds of milking cows – sometimes thousands – release a less active form of oestrogen, but there is a lot of it.”

Tremblay said he would be interested in carrying out the research in other high dairy catchments, like Canterbury.

But in the meantime, other wastewater issues were slipping through the cracks, he said.

“Things like antibiotics, when they get into the environment ... germs get exposed to them and only the most resistant ones survive.

“They become superbugs.”

The main source was wastewater, both from hospitals and general use, he said.

“We use a lot of drugs, and every pharmaceutical we use has an impact on the environment.

“They’re not digested too fast by design, so a lot is excreted from the body, and a lot can survive the sewage treatment system.”

New Zealand’s wastewater facilities include primary and secondary treatment phases, which involve removing solids, then using biological methods to absorb nutrients.

“But for many chemicals, the efficacy of the treatment is not that good. Tertiary level technologies are available, but they’re very expensive.”

Tremblay said a lot of councils around the country were due to upgrade their systems.

“They’ve got an opportunity to help strip those chemicals out.”

Individuals could be part of the solution too.

The Cawthron Institute launched a community engagement project seven years ago to get people to look twice at what chemicals were in their usual garden and household products.

“We love those scented, coloured liquid body washes and things like that, but really, a bar of Sunlight soap would do the same thing.”

The onus also sat at corporate and Government levels, he said.

“Water quality across New Zealand is continuously degrading … Government bodies have a role to play, to make sure policies are in place to improve the situation.”

Tremblay said he was often left feeling frustrated.

“We do all this monitoring, but where do we put the stake in the ground?

“We can be witnesses to what’s happening, or we can take responsibility. The Government is us, and they will have to respond if we make demands as a community.”