NZ scientists say seaweed cure for methane emissions comes up short

An Australian scientist believes he has the answer to stopping cows burping out methane into the atmosphere - by feeding them seaweed.

But New Zealand climate scientists have discounted the idea because it might destroy the ozone layer, and because the seaweed is a known animal, and a suspected human, carcinogen.

Australian CSIRO scientist Rob Kinley has discovered a red seaweed of the Asparagopsis family - which grows in the top half of the North Island - cuts methane emissions in stock completely if fed as 1 per cent of their diet.

The discovery, Kinley said, could be a "game changer" when it comes to global warming.

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Scientists have sounded the alarm over surging global methane levels, and speculate that agriculture may be the main source of the additional methane that has been recorded in the last 10 years.

Kinley thinks it could take anywhere from three to five years to get a commercial animal feed to market. He says the biggest challenge will be growing enough seaweed.

He said he had been trying to get New Zealand scientists interested in his work for some time, and was in discussions with an aquaculture entrepreneur in the North Island who was keen to grow the seaweed.

However, scientists from New Zealand's Pastoral Greenhouse Gas Research Consortium (PGGRC) and James Cook University in Queensland studied the use of seaweeds in livestock five years ago.

Like Kinley, they noted it drastically reduced methane emissions.

But they also realised there was a hitch: like all seaweeds, the Asparagopsis seaweed produces a chemical called bromoform which leaks into the atmosphere and reduces the Earth's protective ozone layer.

Dr Andy Reisinger, the deputy director of the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC), said seaweed production of bromoform "would present a high risk of bromoform leakage into the atmosphere, which would be impossible to control fully in a seaweed farm".

He said the main mitigation effect did not come from the seaweed itself but from the bromoform that the seaweed produces.

Because it was a simple enough chemical to produce in a laboratory, it would be easier to administer it to animals via a bolus rather than go to the trouble of growing seaweed.

"That would allow a much more accurate dosing and would avoid all the potential negative environmental side-effects of large-scale seaweed production," Reisinger said.

He also raised the issue of the potential for the chemical to turn up as a residue in food.

He gave the example of how, as soon as residues of the nitrification inhibitor DCD (dicyandiamide) had been detected in food, it was banned outright.

"Given that experience, I for my side cannot imagine that the NZ industry (or any other industry that seeks to trade based on attributes of quality and safety, let alone 'clean and green' production) would support widespread use of bromoform in its production chain," Reisinger said.

Kinley rejected the carcinogen fear. The only study that tested bromoforms on animals was where mice were force fed the chemical at levels 1500 times what livestock would be fed - "guaranteed to cause some problems at that level".

Regarding bromoforms destroying the ozone layer, Kinley said their role was not yet well understood.

"At some point we have to make judgment calls. I know it's not good to replace one problem with another but the problem of bromoforms haven't been quantified whereas the benefits of the seaweed are far reaching."

Meanwhile New Zealand scientists are working on a number of methane-reducing projects which are showing promise. They include:

* a vaccine that will inhibit methane by 20 per cent, although success is at least a decade away;

* a methane inhibitor or chemical compound fed to animals. This would be administered as a slow release tablet which kills the methanogens in an animal's stomach;

* breeding low emission cattle and sheep. Selective breeding could reduce methane emissions from animals by 10-20 per cent without harming production, but it would take time;

* low emission animal feeds.