By PRATCH RUJIVANAROM
Paraquat is the most deadly herbicide used in agriculture, the medical experts on toxicology and neurology emphasised, with a death rate from direct exposure as high as 40 per cent. Long-term exposure can cause serious incurable brain diseases such as Parkinson’s disease, dementia, and has been connected to cancers. A widely used pesticide in the agricultural sector, paraquat is also known to the general population by its commercial name, Gramoxone.
An intense debate about whether to ban paraquat in Thailand is underway among stakeholders. One side argues that it is too harmful for people’s health to allow further usage, while the other side counters that the health threats could be easily avoided and that it is the cheapest option for killing weeds.
It has been known for more than 20 years that paraquat is among the most poisonous chemicals, said Dr Thiravat Hemachudha, a neurology professor in the Faculty of Medicine at Chulalongkorn University. Repeated scientific and medical research studies have confirmed the chemical’s long-term toxicity, including its contribution to untreatable brain disorders and likely link to cancers.
Dr Thiravat Hemachudha
“There is tremendous scientific proof from around the world confirming the connection between prolonged paraquat exposure and neurological diseases,” is how Thiravat summed up the research. “The research included rigorous studies using both long-term monitoring of those who were regularly exposed to paraquat, and laboratory testing at the gene level.”
He revealed that research in 2006, which monitored and studied a group of people regularly exposed to paraquat over a period of nine years, concluded that prolonged exposure to this harmful herbicide increased the risk of suffering from Parkinson’s disease by 70 per cent.
Moreover in 2013 there were more than 100 published papers proving the connection between paraquat and Parkinson’s disease, and by last year it was widely accepted that paraquat could cause serious neurological diseases, he noted.
Thiravat recalled his time studying at the renowned Johns Hopkins Hospital in the United States, where in 1985 he attended a lecture about the “prodrug” (a biologically inactive compound that can be metabolised in the body to produce a drug) MPTP, which at the time was used as a substitute for heroin. MPTP was found to cause acute Parkinson’s disease, as it destroys the neurology cells in the brain, Thiravat said
“Surprisingly, the chemical structure of MPTP is very similar to paraquat,” said Thiravat.
Paraquat is also well-known for its acute poisoning when consumed or after direct skin exposure. Dr Suda Vannaprasaht from the Faculty of Medicine at Khon Kaen University said that consuming only 10 to 20 millilitres of 20 per cent diluted paraquat could kill, while this chemical is also corrosive to skin and can cause lesions. Due to its corrosive effect on skin, it was suspected that the high prevalence of Necrotising fasciitis, a flesh-eating disease detected by Assoc-Professor Puangrat Kajitvichyanukul from Naresuan University during her research on the use of agricultural chemicals in Nong Bua Lamphu, was a result of a high intensity of paraquat contamination in the local water sources.
A paper by Dr Winai Wananukul, head of the Faculty of Medicine at Ramathibodi Hospital’s Poison Centre, found paraquat to be far more poisonous than other widely used herbicides, such as glyphosate, chlorophenoxy, and chloroacetanilide. Winai’s paper noted that up to 40 per cent of those who are exposed to this chemical would die, while the other herbicides have death rates around only 1 or 2 per cent.
Based on the accumulated evidence, Thiravat concluded that paraquat is too dangerous to be used in Thailand and has suggested that authorities find better and safer alternatives to this harmful herbicide.
“More than 48 countries including our neighbours, Laos, Cambodia and Vietnam have already banned paraquat,” he stressed.