In many developing countries in the Asia-Pacific region, suicide is the leading cause of death in young and middle-aged adults. Half to 2/3 of these suicides are committed by intentional pesticide ingestion.
In a new study, researchers from Sri Lanka and Australia are calling on the World Health Organization (WHO) to impose more stringent pesticide bans and change its classification system to one based on human toxicity studies rather than animal models. The researchers believe this combination of actions will reduce suicides in Asia by one-third—and they have the evidence to back it up.
The researchers began their long-range study in March 2002, ending in December 2019. In 2002, there was an average 260,000 suicides year in Asia Pacific due to intentional pesticide poisoning. However, after five of the most toxic agents were banned from 2008 to 2011, the number of total suicides dropped by almost half to 150,000.
The decline was noticeable in Sri Lanka, where the scientists were working with 34,902 patients who presented with possible or known pesticide self-poisoning over the 17-year period.
Before they were banned in 2008 and 2011, respectively, anticholinesterase insecticides and the herbicides paraquat, MCPA, propanil and glyphosate accounted for 83% (19,295) of hospital admissions and 96% (1,727) deaths for which specific toxins were identified. In the years since the ban, the researchers recorded only 59 poisonings due to those toxins.
However, according to the study, there remain five commonly ingested agents that have greater toxicity than those previously banned. Profenofos, carbosulfan, propanil, quinalphos and fenobucarb have caused 24% of deaths since 2013, while accounting for only 13% of all pesticide poisonings.
This is where the researchers have identified discrepancies in WHO classifications of pesticide hazards. Study author Michael Roberts, research chair of therapeutics and pharmaceutical science at the University of South Australia, says this is because the classifications are based on animal doses rather than human data.
“If human data for acute toxicity of pesticides was used for hazard classification and regulation worldwide, it would prevent many deaths and have a substantial impact on global suicide rates. Instead, WHO classifications are largely based on animal median lethal doses. This method ignores the differences between species and how they respond to treatment, and the formulations used,” said Roberts.
The study data not only supports banning the five previously mentioned pesticides, but all other pesticides that possess fatality rates above 5%, too. In their overall analysis of patients who intentionally ingested pesticides, the research team identified many variations—across all categories and indications—that had a demonstrable case fatality of less than 5%.
“This result would be a currently achievable benchmark to set for a pesticide formulation to establish categorization as highly or extremely hazardous (WHO class I), or as a highly hazardous pesticide as defined by the Food and Agriculture Organization of the United Nations and WHO, with the resulting regulatory consequences,” the study authors explain.
If a 5% global benchmark is set, Roberts predicts pesticide-induced fatal poisonings across Asia could fall by more than 50%, with total suicides in the region decreasing by at least one-third.