Dow Chemical is developing corn and soybeans resistant to 2,4-D, a component of Agent Orange, the defoliant used in the Vietnam War.

Does this mean that Dow Chemical plans to use a component of Agent Orange as a weed-killer that its seeds will be resistant to? I'm sure they'll claim that 2,4-D is safe for all living creatures. But that is definitely not true:

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Acute toxicity
2,4-D is a WHO Class II 'moderately hazardous' pesticide. This places it in the same class as endosulfan, lindane, paraquat and toxaphene. It has an LD50 of 375 mg/kg in the rat with evidence suggesting a similar level of toxicity in humans(9).

Occupational exposure to 2,4-D has produced serious eye and skin irritation. Other symptoms of 2,4-D poisoning include nausea, weakness and fatigue, and in some cases neurotoxic effects including inflammation of nerve endings(10). Some medical reports from practitioners who have treated victims of acute exposure to 2,4-D mention severe and sometimes long lasting or even permanent symptoms. These include, as well as those listed above, diarrhoea, temporary loss of vision, respiratory tract irritation, confusion, numbness and tingling, bleeding and chemical hypersensitivity(11).

A recent review of 2,4-D by the UK Advisory Committee on Pesticides (ACP) noted that "Approval holders must generate a number of toxicology/operator exposure studies to allow a full risk assessment to be made."(12)

Chronic effects
It seems that long term exposure to 2,4-D can affect different animals in a wide variety of ways. Rats for example were found to be largely unaffected when fed moderately large amounts in their diet over long periods, although signs of kidney pathology were demonstrated. Dogs however died when fed smaller amounts over shorter periods. A human fed 16.3 grammes over 32 days showed severe symptoms of intoxication(13).

It also seems that the various chemical forms of 2,4-D can have different toxic effects. Acid, salt and various esters differ in all their measured toxic effects to some extent, but the majority of toxicity data relates only to the acid.

Cancer
Phenoxy acid herbicides have been linked with soft tissue sarcomas, but the UK ACP has concluded that 'the data do not suggest a positive link with 2,4-D'14 as have the Canadian authorities(15). However, the International Agency for Research on Cancer (IARC) has classified 2,4-D among the phenoxy acid herbicides MCPA and 2,4,5-T as a class 2B carcinogen-possibly carcinogenic to humans(16) (concluding that there was limited evidence in humans, inadequate evidence in animals).

The US authorities have also been reluctant to declare 2,4-D as a potential human carcinogen, but the US courts decided that a forestry worker contracted cancer and died as a direct result of his exposure to 2,4-D during the course of his work(17).

One concern about 2,4-D has related to dioxin contamination. 2,4-D was in the past frequently co-formulated with the herbicide 2,4,5-T. Production of 2,4,5-T was contaminated with the carcinogenic dioxin TCDD. Those who were exposed to the mixed formulations might therefore have been exposed to TCDD. The most notorious mixed formulation was Agent Orange, used first by the UK military in Malaysia and later extensively by the US military to defoliate jungle regions in Vietnam. In the UK, 2,4-D + 2,4,5-T formulations were in use until 1994(18). 2,4-D has been produced with contaminant dioxins, but not the harmful TCDD(19).

Reproductive effects
Abnormal foetal skeletal development, increased foetal mortality and other reproductive effects are fairly conclusively associated with exposure to phenoxy-acid herbicide and their dioxin contaminants(20).

2,4-D has also been classified as an endocrine disrupter(21), and significant chromosomal damage occurred in human cells cultured in the presence of 2,4-D. At the same time no evidence for mutagenicity has been found and 2,4-D did not damage DNA in human lung cells(22).

Fate in the environment
2,4-D has low soil sorbtion and a high potential for leachability(23). Indeed 2,4-D residues have been recorded many times both in water company monitoring programmes and by the UK Department of the Environment(24,25). It has also been detected in groundwater supplies in a number of US States and in Canada(26). In 1994, 3% of groundwater samples, and in 1995, 4% of surface water samples in England and Wales exceeded the EU standard(27).

Its high potential for water contamination has led to the inclusion of 2,4-D in the EC Priority Candidate List of chemicals to be considered for inclusion among the chemicals most tightly controlled to prevent water pollution. 2,4-D is also a priority candidate for inclusion in the UK Department of the Environment Red List which has a similar function.

Wildlife
Some formulations of 2,4-D are highly toxic to fish while others are less so. Aquatic invertebrates do not in general seem to be very sensitive to 2,4-D. Moderate exposure of honey bees to 2,4-D severely impaired reproduction. Toxicity to birds is low to moderate(28). However, the ACP noted "Insufficient data are available to fully assess the safety of in or near water uses to aquatic life" and "Approval holders must generate a number of studies using 2,4-D and its derivatives in order to allow a full assessment of the risk to wildlife to be made."

Conclusions
2,4-D is a pesticide that has been heavily used in agriculture all over the world for some fifty years or more. Alarmingly the ACP Evaluation has highlighted a large number of major data gaps-covering human health effects, aquatic and wider environmental risk. In addition to the number and the range of these data gaps, there continue to be concerns about long term adverse effects of 2,4-D on human health and water pollution.

2,4-D Fact Sheet

Nature bats last.

And I hope Ernie Harwell is calling the game. RIP Ernie.

Dan, clinging to the barest thread of on-topic.

A major concern about crops seeds that are genetically-modified to resist Round-up has been that the Round-up resistant gene could jump from the GM seed to the weeds. I wonder if that could be the case here.. not that Round-up resistance has evolved, but rather that it transferred from Monsanto-engineered seed to the weeds...

Just because it is...um..."major" doesn't mean it is possible. The more valid worry is just what it does to random gene expression.

Dan

The most colorful words in the english language don't describe how I feel about Monsanto...but if i were to write them, it would look much like this:

!@$#$%#&^%$ *&%^(*&^*) &^%*&$^&$#^% $@#&^%$ &^%*)(_ )*)+&_(*)*& %^*& ^%$ #^%$#%^# @$%@!#&^%$

So what I've been wondering is, what's the best organic method of killing giant dandelions in cracks? You can't pull them---they go in too deep and just snap off. I've tried vinegar but it just browns them and they come right back. Believe me, I'm anti-pesticide of any kind, but how are we supposed to keep a nice looking yard? I'd love some suggestions.

Anney: the study that the article you provided is based on identifies nine weeds that have shown Roundup reststance in some areas. The surprise to me is that this has shown up so quickly (we are now only 14 years after exposure began to GMO crops and, consequently, over-use of Roundup).

My next surprise is that only one resistant insect has shown up -- the pink cotton boll-worm (in India). Before GMOs were introduced, I assumed that insect resistance would show up faster than weed resistance because vegetarian insects have an evolutionary history of developing resistance to plant-produced toxins. Maybe the "refugia" policy really works, although I have read that some farmers are cheating.

An odd annecdote that I heard at the market last Saturday is that velvet leaf was rare in southern Michigan before attrazine was widely used; when attrazine became poular velvet leaf became common. If true, this shows how a paricular pesticide can provide an advantage for a potentially resistant weed by removing its competition. Regards, Peter.

Some may wish to follow the link below to an Opinion article that appeared in the Thursday, May 6, 2010 New York Times.
I know there are many misguided people that think that the glyphosates are the best thing since sliced bread and they are necessary while others of us know this is wrong and the manufacture, sale, and use of this should be banned.

kimmsr

I note that several of the commenters at the link you posted suggest alternating various herbicides to fool the "weeds" so that they don't develop a resistance to any one of them.

But I really wonder if this isn't just delaying the inevitable. Why won't the "weeds" just develop resistance to all of the herbicides eventually?

It seems to me that evolution could do just this since it's so efficient at creating functional complexity. And as was mentioned earlier upstream, there is a possibility of a genetic jump from one resistant weed to another, perhaps even in a chain reaction from the GM seeds the process was designed to protect. Not probable, someone said? Maybe not, but then I'd never predict what Nature can throw into the pot to right the imbalances that are done to her.

When it comes to GM agriculture, it seems that most of our fears appear to have materialized. The US Department of Agriculture does not require anything approaching the testing that is needed on GM crops or processes, and the US is where most of the GM processes are underway.

Why won't the "weeds" just develop resistance to all of the herbicides eventually?

They will. Such is the way of the world and the multifold issues with agriculture. It has been this way for 9000+ years and will be forever. Wait 'til man-made climate change really kicks in and we have to deal with lower soil moisture and greater swings in temp on top of all the invasives and pests. We'll be saying 'sustainable' and 'resilient' in every other sentence then.

Dan

Maybe I'll get some flak for this, but the root of the problem is the unsustainable meat consumption in Western society. That's what a lot of the corn and soybeans are grown for. It might be economically profitable for now, but we long ago crossed the limit of environmental sustainability.