Herbicide 2.4-D 720g/l; 860g/l SL agrochemical

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Herbicide 2.4-D 720g/l; 860g/l SL agrochemical

Introduction:
2, 4-D, its salts and esters are systemic herbicides, widely used for the control of broad-leaved weeds such as Plantago, Ranunculus and Veronica spp. In cereals and other crops at 0.28-2.3 kg/a. After dilution, it can be used to control the broad leaf weeds in the fields of barley, wheat, rice, corn, millet and Sorghum etc.
 

Use
The principal use is for the control of broad leaf weeds in cereal crops-including wheat, maize, rice and sorghum-and grassland and turf areas. It is also widely used in mixtures with other herbicides to provide weed control in forestry, orchards and non-crop areas, and for the control of aquatic weeds.

The phenoxy acid group of herbicides are probably one of the widest used herbicide chemcial classes. The US, South America, Europe and the former Soviet Union are major markets for 2,4-D-weed control on US wheat relies on little else-and global use is predicted to grow over the next decade(3). In the US where it was the third most used pesticide in the early to mid 1990s, over 31,000 tonnes of 2,4-D was used annually(4). In the UK it is among the top six herbicides used by UK local authorities, and it ranked seventh among herbicides used on grassland and fodder crops and twentieth among herbicides used in orchards in 1992(5,6). Overall the area of land treated with 2,4-D in UK agriculture (excluding amenity use) declined by 83% during the period 1984-1994(7).  2,4-D is also used widely in developing countries: India, for example, used 1,300 tonnes in 1994-5(8).

 

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.

 

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.