Aldicarb

Aldicarb is a carbamate pesticide that has been used around the world since the mid 1960s. Public interest groups consider it hazardous enough to include it in the Pesticide Action Network's Dirty Dozen list.

What is aldicarb
Aldicarb is a systemic pesticide (readily taken up by the roots and transferred around the plants) and acts as a contact stomach poison. Aldicarb is applied to the soil to control chewing and sucking insects (especially aphids, whitefly, leaf miners, and soil-dwelling insects), spider mites and nematode worms. It is used in production of in sugar beet, fodder beet, strawberries, potatoes, onions, hops, soya, citrus fruit, bananas, coffee, sorghum, pecans, cotton, and cane sugar.

Product
Union Carbide, the original patent holder, was the sole aldicarb producer until 1987, when the company sold its worldwide agrochemical division to Rhône-Poulenc (RP) of France. Today the chemical is still a major part of RP's sales strategy. In the first quarter of 1998, aldicarb sales were second only to RPs flagship insecticide fipronil(1).

Problems in production and transport
In 1984, the gas leak at a Union Carbide factory in Bhopal killed 3,000 local residents. The factory was making the carbamates aldicarb and carbaryl for the Indian cotton crop. Many thousands have since suffered respiratory ill effects. At the time of the gas escape, all safety systems designed to contain leaks were out of action(2).
    Eight months after the Bhopal disaster, a gas leak at a Union Carbide aldicarb factory in West Virginia, sent 125 people to hospital(3).
    In April 1994, a truck carrying 23,000 pounds (10,500 kg) of aldicarb crashed near Dallas, US, spilling the toxic pesticide and sending at least 17 people to hospital. The truck hit a traffic sign and burst into flames. Officials on the scene evacuated a five-mile radius around the incident site, including two schools and dozens of homes(4).

Usage
Data on pesticide usage by active ingredient is hard to come by. The US State of California is an exception, where all pesticide use is recorded. Here the use of aldicarb more than doubled between 1991 and 1997 from 190,707 pounds (87,000 kg) to 530,066 pounds (240,000kg)(5).
    In the UK, most aldicarb is used on potatoes, followed by sugar beet, carrots and parsnips. Overall, usage has steadily declined since the early 1980s, and in 1998 an estimated 56,500 kg was applied to a range of arable, fruit, glasshouse, vegetable and fodder crops(6). The market share of aldicarb used on potatoes is much higher in the UK than in any other EU member state(7).

Acute toxicity
As a member of the carbamate group, aldicarb is an anticholinesterase compound. This means it acts as a nerve poison by disrupting nerve impulses.
    The acute toxicity of aldicarb is probably the highest of any widely used pesticide in the UK(8) and the US(9). It is classified by the World Health Organisation (WHO) as a Class Ia 'extremely hazardous' pesticide. The acute oral LD50 (the dose required to kill half a population of laboratory test animals) for aldicarb is 0.93 mg/kg(10).
    The acute skin LD50 for male rabbits is 20 mg/kg(11). Rats were killed within five minutes by a dust concentration of 0.2 mg/litre air(12).
    The symptoms of aldicarb poisoning in humans are characteristic of other organophosphate and carbamate insecticides. In humans, signs of aldicarb poisoning include dizziness, salivation, excessive sweating, nausea, abdominal cramps, vomiting, diarrhoea, blurred vision, pin-point pupils, difficulty breathing and muscle twitching. Death follows if exposure has been high enough (at levels see above)(13).
    Atypical of carbamates in general, aldicarb is extremely toxic through both the oral and dermal routes. This is one reason aldicarb is only formulated in a granular mix (10-15% active ingredient) rather than as an emulsified concentrate or a liquid, as is the case with many other pesticides. Aldicarb is less toxic when administered in the dry granular form (lethal concentration (LC)50 in the range of 7.0 mg/kg). Despite this the US authorities still place aldicarb well within the range of category I 'highly toxic' poisons, and it has to carry the words 'Danger-Poison' on the label(14). In the UK by contrast the formulation is registered as: 'Toxic in contact with the skin, by inhalation and if swallowed'(15). In the US, a formulation that can contain up to 15% aldicarb active ingredient is used; in the UK the figure is only 10%. According Rhône Poulenc: "Temik 10G is marketed in the UK as a formulation which contains aldicarb at a concentration of 10% of the active ingredient. In addition aldicarb is made less hazardous formulating it as a solid granule formulation. For these reasons the product is classified by the Pesticides Safety Directorate as 'toxic'(16). According to WHO classification tables, a formulation containing 10% means the product is downgraded to Ib 'highly hazardous' from Ia 'extremely hazardous'(17).

Chronic effects
The International Agency for Research on Cancer (IARC) considers there is evidence of genetic mutation in animals(18). In the UK, the Advisory Committee on Pesticides reviewed aldicarb in 1994 and considered it is not a human genetic hazard(19).

Immunological effects
In 1986, epidemiologists in the US found that consumption of low levels of aldicarb contaminated well water was associated with one immune system abnormality (an indication of this is an increase in the number of 'T8 cells' [lymphatic white blood cells]). Tests in laboratory mice also found water contaminated with as little as one part per billion of aldicarb affected one parameter of immune function, the plaque forming cell response(20). The results of this study have been widely debated among regulators internationally.

Environmental fate
The potential exposure of aquatic animals is high due to aldicarb's solubility and mobility in soil. Aldicarb, applied to farm fields can be transported to aquatic areas through run-off, especially for sandy soils. Its half-life in water can be as long as a few months(21). There are long harvest intervals for aldicarb for treated crops because of environmental persistence. In the UK, the harvest interval for potatoes it is 8 weeks(22).

Wildlife
Aldicarb has a broad spectrum action and can affect a range of beneficial insects(23). It is also dangerous to animals, including game and wild birds, and fish or other aquatic life(24). The 96 hour LC50 for rainbow trout is 0.88 mg/l, and for blue-gill sunfish 1.5 mg/l. It is also toxic to bees(25).

Residues in food
In California during the mid 1980s there were a number of outbreaks of food poisoning involving water melons and cucumbers caused by aldicarb. The estimated doses of the residue ranged between 0.0011 and 0.06 mg/kg body weight, and most were well below the 0.025 mg/kg Lowest Observed Effect Level for blood cholinesterase depression (a measurement of adverse effects from aldicarb). Workers at the Californian Department of Health Services concluded from these cases that: "Aldicarb appears to be more toxic than previously suspected"(26).
    At least 30 people were poisoned in Ireland in May 1992 after eating cucumbers contaminated with aldicarb. The Irish Department of Agriculture took a week to identify the chemical, which was not approved for use on cucumbers(27). A further Irish incident occurred in 1993 when a boy, aged 15, fell ill during a football match. Doctors established that he had aldicarb poisoning after eating cucumber that had wrongly been applied by a local farmer(28).
    In the UK aldicarb residues have been found at levels below the maximum residue limit in citrus fruit. In 1995, one sample out of 71 imported oranges contained residues of aldicarb(29).
    Aldicarb residues in individual potatoes may exceed MRLs due to the factor of variability (see PN 43 p.7), even though the crop may have been treated in accordance with good agricultural practice(30).

Data gaps
In 1998 the European Commission Scientific Committee on Plants carried out a review of the health and environmental effects of aldicarb. It recognised that, across Europe as a whole, very little residue data is available.
    The committee outlined a number of data gaps in relation to dietary and environmental risk assessment:

• Further individual commodity residue data for the relevant crops should be generated from European field trials.
• The data available for aldicarb are not adequate to allow a comprehensive health risk assessment to be made for operator exposure.
• The risk assessment for the exposure of smaller sized birds to granules critically depends on the assumption that more than 99% of the granules are incorporated into the soil. Whilst this may be achieved under ideal conditions, the Committee believes that this high degree of incorporation is not consistently achievable under normal agricultural use. The Committee therefore advised that a reassessment is necessary
• The notifier (Rhône Poulenc) submitted no data on aldicarb and its metabolites (aldicarb sulfone and sulfoxide) relating to long-term toxicity for aquatic and soil dwelling organisms, and oral toxicity and exposure assessment for honey bees.

In conclusion, the Committee was not able to assess, from the data available, whether the use of aldicarb should continue pending the generation, submission and evaluation of additional data(31).

Developing country problems
Adverse effects of pesticides are often difficult to assess in developing countries. Groups participating in the international Pesticide Action Network (PAN) survey have identified aldicarb as 'known to have caused health or environmental problems' in Sudan, Colombia, Costa Rica and Ecuador(32).

A member of the Dirty Dozen
Aldicarb is one of the PAN's Dirty Dozen pesticides. PAN took this action because of the deaths, poisoning and environmental contamination in both developing and industrialised countries caused by this pesticide(33).

Regulatory action
In 1990 Rhône Poulenc announced a voluntary halt to the sale of Temik (aldicarb) in the US for use on potatoes because of concerns about groundwater contamination and because residue levels were significantly exceeding the maximum legally permissible residue limit. By 1992 the Environmental Protection Agency (EPA) approved the re-introduction of aldicarb on this crop in limited geographical areas. This decision was based on extensive data showing that new application technologies and other restrictions resulted in lower residues in food. Despite these controls, aldicarb remains in the EPA's intensive Special Review process because of continuing concerns of risks to groundwater. Indeed, aldicarb's use on potatoes is only approved in areas where the risk of groundwater is believed to be low(34).
    In 1997, the French Ministry of Agriculture introduced rigorous new measures requiring registrants of aldicarb-based insecticides to provide quarterly statements of amounts sold and their purchasers. Distributors of aldicarb also had to supply details of names, addresses and final destinations to French agriculture officials(35).
    As an anticholinesterase compound, aldicarb is being reviewed by the UK Pesticide Safety Directorate and the Health and Safety Executive.

Conclusion
One of the PAN Dirty Dozen, aldicarb has caused concern among public interest groups around the world since the mid 1980s. These worries appear to have been echoed by the European Union, which has come out with a series of important questions over the health and environmental effects of this chemical.
    Aldicarb is one of the few active ingredients that has been implicated in food poisoning in northern countries.
    As a matter of urgency, its use should be severely restricted, and more research should be initiated to find safer alternative methods of pest control. (By David Buffin)

References 
1. Agrow's Top 25-1998 edition, PJB Publications, 9 November 1998, p251.
2. B. Dinham, The Pesticide Hazard, The Pesticides Trust [now PAN UK], 1993, p32.
3. Aldicarb Spill in Texas, Global Pesticides Campaigner, Pesticides Action Network North America, 1994, Vol. 4, No. 2.
4. Ibid.
5. Summary of Pesticide Use Report Data 1997, Environmental Protection Agency, Department of Pesticide Regulation, California, June 1999.
6. Miles Thomas, pers. comm., Pesticides Usage Survey Group, Central Science Laboratory, 1999.
7. Opinion of the Scientific Committee on Plants Regarding Aldicarb, Consumer Policy and Consumer Health Protection, DG24, 18 December 1998.
8. Aldicarb, WRc, Marlow, Bucks, September 1995.
9. Aldicarb: Special Review Technical Support Document, US EPA, Office of Pesticides and Toxic Substances, Washington DC, 1998.
10. WHO Classification of Pesticides by Hazard 1998-1999, International Programme on Chemical Safety, WHO/IPCS/98.21.
11. C.D.S. Tomlin, The Pesticide Manual, British Crop Protection Council, 1997, pp26-28.
12. Ibid.
13. Aldicarb, EXTOXNET, Cornell University, US.
14. R. Whitehead (Ed.), The UK Pesticide Guide, British Crop Protection Council, 1999.
15. Ian Cockram, pers. comm., Rhône Poulenc, letter of 29 June 1999.
16. Op. cit. 10.
17. Aldicarb, WHO, Environmental Health Criteria, 121, International Programme on Chemical Safety, Geneva, Switzerland, 1991, pp69-70.
18. Occupational Exposures in Insecticide Application and Some Pesticides, IARC, Monographs on the Evaluation of Carcinogenic Risks to Humans, WHO, Lyon, France, 1991, Volume 53.
19. Evaluation on Aldicarb, Pesticides Safety Directorate, October 1994.
20. C. Cox, Aldicarb, Journal of Pesticide Reform, Summer 1992, Vol. 12, No. 2:31-35.
21. Philip Howard, Handbook of Environmental Fate and Exposure for Organic Chemicals, Vol. III, Lewis Publishers, 1991.
22. Op. cit 14.
23. Aldicarb, Data Sheet, WRc, Marlow, Buck, September 1995
24. Op. cit. 14.
25. Op. cit. 11.
26. L. R. Goldman, M. Beller, R. Jackson, Aldicarb Food Poisoning in California, 1985-1988 Toxicity Estimates for Humans, Archives of Environmental Health, 1990, 45,3:141-147.
27. Clare Heardman, pers. comm., Earthwatch, 1994.
28. Daily Telegraph, 7 July 1993.
29. Annual Report, Working Party on Pesticide Residues: 1995, MAFF/HSE, London, September 1996, p60.
30. Pesticide Residues in Food 1996, Aldicarb, FAO Plant Protection Paper 142, FAO, Rome, 1997.
31. Op. cit. 7.
32. D. Myers, The FAO Code: Missing Ingredients, The Pesticides Trust, 1989, p104.
33. Aldicarb Joins the Dirty Dozen, Pesticides Action Network North America, May 1989.
34. EPA Approves Limited Re-introduction of Aldicarb Use on Potatoes, 1992.
35. Agrow, No. 285, 25 July 1997, p8.

[This article first appeared in Pesticides News No. 45, September 1999, pages 18-19]