Weeding out a killer pesticide

By Tim Connell

EACH year, it’s estimated that hundreds of thousands of people in Asia and other parts of the world consume something poisoned with insecticide and die.

Many of them take their own lives by directly ingesting insecticide. It is a socially devastating endemic that disproportionately affects poor communities in rural areas, particularly in Asia.

While researchers acknowledge they can’t know the exact number of suicides, or the number of attempts, the World Health Organisation says that between 60 per cent and 90 per cent of the suicides in China, Malaysia, Sri Lanka and Trinidad and Tobago in the decade to 2006 were by insecticide ingestion.

The scale of the tragedy is depicted starkly in a study in the journal BioMed Central, which “conservatively” estimates that more than 258,000 people die from insecticide self-poisoning each year or, accounting for corrections to India’s data, perhaps more than 371,000.

It is, then, a method used in a third of the world’s suicides, and the single biggest cause of suicide.

One class of insecticide is a common ingredient in the deadly trend, but a new study based on research by the CSIRO offers hope that soon, it will no longer be a death sentence.

A swift, silent killer

Organophosphate, or “OP”, insecticides are highly effective at killing pests that eat crops.

They are also chemically similar to nerve agents such as Sarin and VX, are listed among the Australian government’s Chemicals of Security Concern for use in scenarios such as terror attacks, and are cheap and readily available across swathes of rural Asia and the developing world.

When a person ingests an OP insecticide, it acts on the body’s nervous system and triggers acute respiratory and cardiovascular failure within hours.

Generally, there is little that a first responder can do. The current treatments include administering oxygen, atropine and oxine, but the patient is usually dead before or soon after reaching hospital.

Big help from a little friend

In the war against OP insecticides in the natural environment, especially where they’re found in groundwater, CSIRO researchers had already identified a powerful, tiny ally.

Bioremediation is a way of detoxifying organic pollutants in the environment by using enzymes from bacteria. When it comes to this kind of clean-up work, enzymes boast an enviable list of attributes; they’re fast, non-toxic and good at targeting specific chemicals.

For the task of fighting OP pesticides in groundwater, the CSIRO scientists chose a specific enzyme called OpdA.

“We worked up some formulations of dissolving tablets” Dr Colin Scott, the leader of CSIRO’s Biocatalysis & Synthetic Biology Team, said.

“We formulated them like that so we could put them in a stream and they would dissolve over time, during the peak of contamination as the water off the field.”

The enzyme did its job. In the trials, the CSIRO team found it was able to degrade the insecticide pollutants in the stream in a matter of hours or minutes, depending on how much of the enzyme they used.

Unbeknown to the CSIRO team as they observed the success of those trials in contaminated water, international researchers already saw their work as medicine’s best chance of treating OP-poisoned humans.

An unintended consequence

The Australians’ success at cleansing OP pollutants from the environment caught the attention of Dr Michael Eddleston, the Personal Chair of Clinical Toxicology at the University of Edinburgh, and one of the world’s leading authorities on pesticides and self-harm.

A new study in the journal Clinical Toxicology involving Dr Eddleston, Dr Scott and other researchers from the CSIRO and the universities of Edinburgh and Munich examines how effective enzymes can be for treating OP poisoning in humans.

Building on their previous work, CSIRO scientists injected their same previously successful enzyme, OpdA, into human serum – or blood plasma – while researchers in the UK tested the enzyme on rats fed doses of OP insecticide.

“For the rat study, there was a really clear difference,” Dr Scott said.

“All of the rats that had the OP poisoning, but not the enzyme, died. And pretty much all the ones that had the OP poisoning and the enzyme survived. It is a really effective treatment.”

Further intravenous tests of the enzyme on OP-poisoned mini-pigs, conducted in Britain, were similarly resounding, Dr Scott said, leaving the researchers confident they now have the best treatment under development.

Follow-up tests on non-human primates found the enzyme solution itself did not have adverse side-effects on recipients.

“There are 200,000 people a year who are dying unnecessarily because there’s no treatment for this particular problem,” Dr Scott said.

Beyond the hoped-for human trials, a commercial partner would help with the logistics of getting a final version of the treatment to the people who the researchers say need it most.

It has already been a satisfying and surprising journey for Dr Scott.

“It’s not the outcome we were looking for at the start, but the fact our research could be used for another application that could make such a large difference to people’s lives and improve their lives, that’s something to be proud of.”

If you are thinking about suicide or experiencing a personal crisis help is available. Contact Lifeline on 13 11 14 (in Australia, 24 hours a day).