The near-fatal poisoning of a NSW Central Coast man with severe autism who drank a cocktail of highly toxic herbicides left in an unmarked drink bottle has sparked fresh calls for a nationwide ban on Paraquat.

Damien Terry's survival, after accidentally drinking a combination of the commercial weed killers Paraquat and Diquat, has been described as nothing less than "miraculous".

The 21-year-old and his carer were visiting a sports oval on Mangrove Mountain in August, when he suddenly started vomiting uncontrollably shortly after returning from the disabled toilet.

He had been poisoned after accidentally sipping the chemicals, which he found in an abandoned soft drink bottle.

Safety warnings displayed on all Paraquat products include that it must be labelled clearly and not placed in drinking containers.

Doctors at Gosford Hospital told his family to prepare for the worst.

"The doctors basically said to us that Damien probably had 12 hours to live," said Mr Terry's mother, Julie Terry.

"Their words were 'nobody' survives from ingesting Paraquat.

"Obviously you go into a state of shock. Damien looked quite well, although he was vomiting quite significantly, he looked well so it was hard to comprehend that he was as ill as he was.

The herbicide Paraquat was left in an unmarked drink bottle. ( ABC News: Mary-Louise Vince )

"At that point ... they just said he would have massive organ failure and I just asked them to keep him as comfortable as possible."

Family speaking out after ordeal

After two agonising weeks in hospital not knowing whether Mr Terry would pull through, he is now on the road to recovery and his family wants to speak out about the dangers of Paraquat.

It is a highly effective weed killer commonly used by farmers across Australia but is also extremely toxic: it only takes a few sips to kill a person and has no antidote.

In 2015, a Queensland farmer died after the deadly herbicide accidentally sprayed into his mouth when he was filling a pressure back-pack pump spray.

Paraquat has caused thousands of deaths worldwide and is banned in more than 30 countries including China, Cambodia and across the European Union.

There is also a debate about its links to Parkinson's disease.

The poison has been under review by regulator, the Australian Pesticides and Veterinary Medicines Authority, since 1997 due to health and environmental concerns, with a final determination due next year.

Damien's parents, Julie and David Terry, want Paraquat banned in Australia. ( ABC News: Mary-Louise Vince )

The Terrys want a major crackdown on its use and availability but are ultimately seeking a nationwide ban.

"It defies logic in my mind that this is available over the counter for anybody to purchase," Ms Terry said.

"Everybody knows these days that health and safety is a very common agenda for all of us in the workplace so I feel a bit disillusioned that the authorities didn't keep an eye on that."

Support for the campaign

The Terrys call is one that is strongly supported by the National Toxics Network.

"It beggars belief a pesticide of this toxicity would ever be used in a public facility, let alone decanted into a drinking bottle," said environmental campaigner Jo Immig.

"What it really illustrates is the failure of risk management when it comes to highly dangerous pesticides.

"It's been banned by 32 other countries and it's high time the regulator put the needs of people and the planet first ... it's just a very highly toxic chemical that has no place in common use in Australia today."

Newcastle University environmental contamination expert Professor Ravi Naidu has also questioned why the herbicide was anywhere near the sports ground.

"When Paraquat is applied, that time and at least for 20 days children should not be exposed at all. If they're exposed then it poses risk," Professor Naidu said.

He said a national ban on Paraquat would hurt the agriculture industry but agrees it should be more tightly regulated.

Damien Terry is lucky to be alive after swallowing the herbicide Paraquat which was left in an unmarked drink bottle. ( ABC News: Mary-Louise Vince )

"I think the best way forward would be restrictive availability and therefore farmers must demonstrate they have a farm and a need for that and only the amount they need should be available."

Investigation could take up to three years

A New South Wales Environment Protection Authority (EPA) investigation is underway into the poisoning, which could take up to three years.

An EPA spokeswoman said any pesticide misuse resulting in harm to human health is extremely serious.

She said the authority was looking at a range of offences under the pesticides legislation, with a maximum penalty of $60,000 for an individual and up to $120,000 for a corporation for each offence.

Central Coast Council has declined to comment while the incident is being investigated.

Four months on, the Terrys' lives are returning to normal but they are determined make sure other families are spared the same trauma.

"[Damien's] recovery has been miraculous — there's no other word for it. He should be gone," Ms Terry said.