A scientist has slammed ACT leader David Seymour's comments about killer reusable shopping bags, labelling them as irresponsible.

Photo: VNP / Daniela Maoate-Cox

Mr Seymour said the government's decision to ban single use plastic bags could be killing up to 20 New Zealanders a year.

He said research in the US showed that people using reusable bags were susceptible to diseases such as campylobacter from chicken.

In August, the government announced it would rid the country of thin plastic bags by July next year.

Mr Seymour said the decision was made too hastily and was putting New Zealanders at risk.

He admitted pollution in the world's oceans needed to be addressed but he said the blame for that lay with African and Asian countries, not New Zealand.

"The problem of New Zealanders letting go of their plastic shopping bags and them ending up in the ocean is a problem but an absolutely tiny one.

"It's not a problem that justifies the level of inconvenience and potential public health danger that comes from a ban on plastic bags."

Mr Seymour is basing his claims on 2013 research from George Mason University that found five people a year died in San Francisco from food related infections such as E coli and campylobacter after using reusable bags contaminated with the disease.

San Francisco banned non-compostable bags in 2007. The research found 97 percent of shoppers did not regularly wash their bags.

It concluded that any health costs associated with the ban of plastic bags in San Francisco wiped out any savings from reduced litter.

However, Professor Siouxsie Wiles at Auckland University told Checkpoint this research had already been debunked.

"So it's written by two professors of Law and Economics who are not microbiologists or public health experts.

"They've taken a data set around people who are hospitalised or deaths in San Francisco and looked at before plastic bags were banned and then afterwards. They've then drawn a bunch of conclusions which if anybody in public health looked at would say no, not true at all."

Dr Wiles said Mr Seymour does have a point, albeit misguided.

"I do think we need to have a little bit more education about how people should be using their [reusable] bags and how you should be treating certain food groups.

"But to take - I'm not even going to call it a study - to take this information and then draw the conclusions that the researchers have is irresponsible actually."

Fellow food microbiologist at Massey University Jon Palmer said that there was a risk to reusing bags that previously contained meat, however there were solutions.

"We freeze it, so all chicken is sold frozen, none of it is sold fresh, that would reduce the risk of contamination. Or we allow plastic bags only for meat products so we can keep our chicken products in a separate bag away from fresh produce," he said.

David Seymour said he was happy to be proven wrong but until then, he would stick to his message.

"I use plastic bags, they're very convenient. You know what I do with them once I'm done with them? I just don't put them in the ocean."

"This is actually a policy that will mean a whole lot of people who wouldn't have otherwise chosen to use re-usable bags are forced to use them because there are no other options and that's when you get problems.

"If we're going to be good environmental custodians, if we're people who care about the future of our planet to use the best evidence, the best science when we make policy decisions."