Regulators in America and South Africa preparing to green-light 2,4-D crops

August 2012

Regulators in America and South Africa have been busy preparing to green-light a new range of herbicide-resistant GM crops. These plants are genetically transformed to be doused with a very old and much-used weed-killer commonly referred to as '2,4-D'.

A component of the infamous 'Agent Orange' defoliant used during the Vietnam war, the toxic potential of 2,4-D seems to have been eclipsed by the horrific, on-going, consequences of the other ingredients and the dioxin by-products. A search for safety data on 2,4-D turns up a torrent of tangential evidence which never manages to pinpoint harm, but is never convincing about safety either.

The main confounding factor is that '2,4-D' isn't just one substance. The term refers to a family of chlorinated phenol derivatives. Add to this that commercial formulations might include any one, or more than one chlorophenoxy herbicide, combined with a large proportion of “inert ingredients”. (Note that up until recently about 90-95% of 2,4-D weed-killers used globally consisted of two types, 'DMA' (a dimethylamine salt) and 'EHE' (an ethylhexyl ester). This situation is likely to change dramatically with the advent of GM 2,4-D tolerant crops.)

Most of the safety data are based on animal studies in which a range of species were fed on various different kinds of 2,4-D. Such studies have thrown up the possibility of damage to the thyroid, kidney, adrenals and ovaries or testes, reproductive, foetal and developmental effects, neurotoxicity,and interference with cell metabolism. There is mention of endocrine disruption, DNA, chromosome and cell membrane damage, and central nervous system toxicity.

With all that smoke, is it really possible there's no fire?

The only certain thing to emerge from these animal studies is that sensitivities to 2,4-D vary hugely with species. Actual relevance of any of them to humans is uncertain.

In the absence of direct experimentation, human safety data are based on chance events, chance recording of these events, and on who-knows-what version(s) of 2,4-D formulated into proprietary weed-killers with unknown other ingredients.

Cases of attempted suicide by drinking 2,4-D indicate that central and peripheral nerves are a major target.

There have been no reports of adverse effects from normal occupational exposure to 2,4-D: this could be because no harm's been experienced, because no one's asked, or because 'occupational exposure' involves so many other harmful agri-chemicals that no clear link to one specific one is ever possible. Despite this, some association between 2,4-D and non-Hodgkin's lymphoma and soft tissue sarcoma have been found (after Sweden banned the herbicide in the early 970s the incidence of these two cancers declined). Also, reduced sperm quality has been associated with the class of chemicals to which 2,4-D in all its forms belongs. In four US wheat-producing areas where there has been widespread use of chlorophenoxy herbicides, increases in birth malformations and adverse perinatal outcomes were observed.

There are no human data on chronic effects of 2,4-D other than epidemiological studies of cancer. Most assessments hedge their bets by describing it as “possibly carcinogenic”.

What we are left with is a mass of safety data, based on a whole lot of variables, and so many inconsistencies that no conclusion is possible. Traditionally, regulators and industry seem to have got away with using inconsistency as an excuse to assume safety in the absence of clear proof of harm.

The story of 2,4-D is shaping up to be very similar to that of Roundup herbicide for use on Roundup Ready GM crops. Roundup progressed from being 'safe as salt' in food and non-persistent in the environment, to being a recognised cancer-causing teratogen and disruptor of soil life. Like Roundup in its early days, 2,4-D has a reputation for safety, passing through the body unchanged and easily biodegradable. However, it does end up in drinking water (in the Northern Great Plains of Canada, 2,4-D was detected in 100% of the surface drinking-water supplies), and like Roundup it seems to accumulate in actively growing plant tissue which suggests that unprecedented high levels in GM food and feed are possible.

In laboratory studies, five main breakdown products of 2,4-D were identified: four of these are toxic. The 2,4-D which is 'safe' because it doesn't persist in the environment or in your digestive tract long enough to cause harm may simply be converted to another toxic material.

If the Roundup experience is anything to go by, applications of 2,4-D will jump 20-fold when GM crops resistant to the chemical get into full swing. This will be accompanied by a host of novel 2,4-D formulations and a host of novel 'inert' ingredients which are actually anything but 'inert'. For example, in response to bad press regarding 2,4-D contamination 100 miles away from its site of application, Dow AgroSciences, the company now commercialising these GM crops, has already rushed to conjure up a new formulation of 2,4-D which doesn't drift so easily when sprayed.


2,4-D seems to be just another Roundup but with more complexities, and more potential harm.

GM maize tolerant to 2,4-D passed through US Department of Agriculture hands early and 2012 and is currently being considered by regulators in South Africa.

Next in the pipeline is GM soya resistant to three herbicides, glyphosate (Roundup), glufosinate and 2,4-D all of which will be in your food.

What you can do

The African Centre for Biosafety has prepared a petition to the government of South Africa to reject 2,4-D resistant GM maize. You can help by adding your signature to this. Check it out at

  • Olympic Sponsor Speeds Up Pesticide Arms Race, GM Freeze Press Release, 2.08.12
  • Tom Philpott, USDA Prepares to Green-Light Gnarliest GMO Soy Yet, Mother Jones 18.07.12
  • 2,4-D Technical Fact Sheet, National Pesticide Information Center
  • 2,4-Dichlorophenoxyacetic acid,
  • Material Safety Data Sheets for: Amine 4 2,4-D Weed Killer; 2,4-D; 2,4-Dichlorophenol; 1,2,4-Benzenetriol; 2,4-Dichloroanisole; Chlorohydroquinone; 4-Chlorophenol
  • Prof. Joe Cummins, New GM Crops Tolerant To Old Toxic Herbicides a Step Backwards, Science In Society, #54, Summer 2012

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