Concerned environmentalists in the United States have upped pressure on legislators to outlaw a widely-used insecticide, after waiting five years for a response from the country's Environmental Protection Agency.

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On Monday, activists made their case for an outright ban of Chlorpyrifos in court in Seattle. The Ninth Circuit Court of Appeals heard that EPA had failed to act on a petition submitted by three environment groups.

The Natural Resource Defense Council, Pesticide Action Network, and EarthJustice first called for a ban in 2007. Lawyers representing the groups said discoveries made in 2006 relating to the chemical's effects on workers exposed to the chemical and children exposed to drift make the case for a ban more compelling.  

Chlorpyrifos, a pesticide in the organophosphate family, commonly used on wheat and alfalfa in the US, is toxic to humans and exposure has been linked to development of autoimmune diseases. The chemical is also "acutely lethal" to aquatic life. Nevertheless, according to EPA it remains "one of the most widely used organophosphate insecticides" around the world.

EPA responded to the plaintifs at the beginning of the week, stating that complex health questions had led it to revisit regulations which could see new risk assessment procedure developed that would cover all organophosphate pesticides. The new regulations would relate to the risk from solid Chlorpyrifos preparations becoming a gas.

Use of Chlorpyrifos in homes in the US was prohibited in 2001, after its effects on the nervous system and foetal development were made clear, though it is still commonly used in agriculture. Since that time, EPA has also introduced guidelines intended to protect bodies of water from Chlorpyrifos used nearby.  

In the UK, the industry 'Say no to Drift' campaign celebrated its first year in effect last month. Chlorpyrifos manufacturer Dow AgroSciences welcomed the response from arable and horticultural producers to the voluntary initiative. The campaign involves using 'low-drift' spray nozzles and observing a 20 metre buffer-zone by water to minimise unintended effects of using the pesticide.  

The campaign organisaers aim to secure 100 percent of industry support for the campaign. Even so, the renewal process for products containing Chlorpyrifos is still pending. The chemical's manufacturers therefore hope that by voluntarily tightening application requirements, they can secure renewal and avoid action seen in the US.