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 unaffected.

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 paper 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.