Published online 12 November 2009 | Nature | doi:10.1038/news.2009.1080


Environmental impact of cocaine strategy assessed

Studies measure effects of glyphosate-based herbicide on wildlife and human health.

cocaWhat is the environmental impact of herbicide spraying on coca fields?istockphoto

A controversial herbicide-spraying programme to tackle cocaine production in Colombia has few adverse environmental impacts. That's the conclusion of a suite of studies that marks the latest chapter in a bitter environmental debate over its benefits and risks — yet the studies' findings are already being challenged.

Spraying the herbicide glyphosate on coca plants is a key tool in the war on cocaine. The strategy, known as Plan Colombia, is supported by the United States but there have long been questions over the plan's impact on animal and human health in the region.

The latest assessment looks at the various environmental and ecological effects of glyphosate and surfactants that are used to increase the herbicide's potency. The surfactants increase glyphosate's solubility, helping it to penetrate plants' leaves.

Keith Solomon of the University of Guelph in Ontario, Canada, led a team working in Colombia, where researchers tested the effects of the glyphosate mixture using the same concentrations and formulations that are sprayed from planes and in the field. Of eight species of South American frogs studied, four showed some sensitivity to the herbicide mixture at concentrations below the application rate used in Plan Colombia, and four species remained unaffected1.

The researchers also found that frog larvae in small artificial ponds showed few toxic effects from glyphosate exposure, perhaps because of adsorption of both glyphosate and the surfactant to sediments and particulate matter in the ponds.

A summary paper2 of the work highlights the conclusion reached by Solomon and his colleagues — that glyphosate is the lesser evil compared with the bigger impact of coca farming, including deforestation and the use of pesticides. The results of the various studies are published in a series of articles in the Journal of Toxicology and Environmental Health.

Questions from the ground

But Rick Relyea of the University of Pittsburgh, Pennsylvania, a critic of both Solomon's research and Plan Colombia, says that the studies are flawed. For example, the pond studies of frogs, he notes, do not give enough information about the soils present to be sure that they were not adsorbing more of the herbicide mixture than would normally occur in the wild.

What's more, in one particular species of frog (Rhinella granulosa), about a third of adults died after being exposed to glyphosate at concentrations equivalent to field applications. Relyea notes that the research also confirms his own studies of how much glyphosate is sufficient to kill half the frogs in a population3 — a concentration known as the LC50.

"Everyone agrees on concentrations that cause toxicity," says Reinier Mann, an ecotoxicologist at the University of Technology in Sydney, Australia. "The argument is over whether the frogs are exposed to those concentrations."

The glyphosate–surfactant mixture could cause problems when it is sprayed in frog habitats, such as a rut in the road or a ditch beside a field, where some frog species live and reproduce in temporary shallow pools. "If those chemicals are being sprayed in those areas, then it is quite possible that you will get concentrations that cause toxicity," Mann says. The opposing view is that natural settings provide substantial dilution, he says, whether by water in running streams and deep lakes, or by soil adsorption that takes the compounds out of solution. "That's the sticking point," he says. "It's an old argument that will probably never be settled, I think."

That's bad news for Colombia's neighbour Ecuador, which continues to protest the aerial spraying of glyphosate around its borders. Ecuador is part of a coalition known as the Organization of American States, which funded Solomon's research in an effort to resolve the issue.

Humans at risk?

Solomon's research team also studied a cohort of almost 2,600 women from five different regions in Colombia, in a retrospective time-to-pregnancy study that did not establish a relationship between fertility problems and the coca eradication spraying4. The scientists say the glyphosate exposure may not have come from the Plan Colombia spraying, but from its use in sugar-cane plantations.


The team also tracked the health of 274 agricultural workers who had been exposed to glyphosate, and found no firm evidence of chromosomal or cellular damage5. This finding contrasts with earlier research6,7 that reported glyphosate had highly toxic effects on human cells in vitro.

Plan Colombia continues unabated, but still faces tough opposition. In October 2008, the US Government Accountability Office (GAO) reported to then-Senator Joe Biden (Democrat, Delaware) that coca cultivation was spreading and that the eradication programme was not working8. The GAO recommended that the US Congress should start pulling back funding for Colombia's military, which oversees Plan Colombia, and should look for alternative solutions such as persuading farmers to grow crops other than coca.

Despite this, a spokesman from the US state department says that the United States will support Colombia's government as long as it chooses to continue the herbicide-spraying strategy to tackle its cocaine problem. 

  • References

    1. Bernal, M. H., Solomon, K. R. & Carrasquilla, G. J. Toxicol. Environ. Health A 72, 966-973 (2009). | Article | PubMed | ChemPort |
    2. Solomon, K. R., Marshall, E. J. P. & Carrasquilla, G. J. Toxicol. Environ. Health A 72, 914-920 (2009). | Article | ChemPort |
    3. Relyea, R. A. & Jones, D. K. Environ. Toxicol. Chem. 28, 2004-2008 (2009). | Article | ChemPort |
    4. Sanin, L. H., Carrasquilla, G., Solomon, K. R., Cole, D. C. & Marshall, E. J. P. J. Toxicol. Environ. Health A 72, 949-960 (2009). | Article | PubMed | ChemPort |
    5. Bolognesi, C., Carrasquilla, G., Volpi, S., Solomon, K. R. & Marshall, E. J. P.J. Toxicol. Environ. Health A 72, 986-997 (2009). | Article | PubMed | ChemPort |
    6. Benachour, N. & Séralini, G.-E. Chem. Res. Toxicol. 22, 97-105 (2009). | Article | PubMed | ChemPort |
    7. Richard, S., Moslemi, S., Sipahutar, H., Benachour, N. & Séralini, G.-E. Environ. Health Perspect. 113, 716-720 (2005). | PubMed | ChemPort |
    8. US Government Accountability Office PLAN COLOMBIA: Drug Reduction Goals Were Not Fully Met, but Security Has Improved; U.S. Agencies Need More Detailed Plans for Reducing Assistance. Report GAO-09-71 (2008);


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  • #60086

    Shocking. Also, do you know what the growers do with the crops after they are sprayed? They harvest them as fast as possible, process them if needed (Coca) or not (Marijuana) and ship them to America. Then guess who ingests the herbicides? Keepin' America safe! This is not new. I think during Regan years, the CIA dumped really harsh herbicide on Columbia's mountains/forests rumored to contain coca farms. The area was completely depleted of plant life for two years. Since then, only coca grows there.

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