Pesticides - Some of its harmful effects on environment and health

Professor M Sumarjit Singh *

Pesticides are substances that are meant to control pests. The term pesticide includes all of the following: herbicide, insecticides nematicide, molluscicides, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, antimicrobial, fungicide, and lampricide.

The emphasis today is solely on productivity- high input in exchange for high returns and productivity (mostly diminishing now however for farmers worldwide). Four important considerations— what happens to the land, food it produces, the people who eat it and the communities which lose out— are overlooked.

The environmental impacts of pesticides are often greater than what is intended by those who use them. Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than target species, including nontarget species air, water, bottom sediments, and food.

Pesticide contaminates land and water when it escapes from production sites and storage tanks, when it runs off from fields, when it is discarded, when it is sprayed aerially, and when it is sprayed into water to kill algae. During spraying or dusting of pesticides only a small portion is adhered to the crop and rest either fall down or taken up into the atmosphere by the current or turbulence.

Volatilization is a major pathway for the loss of applied pesticides which depend upon the vapour pressure. The soil is contaminated with the pesticides either through deliberate application of them for controlling soil inhabiting pests or through run off from plants, and dumping of empty containers.

The amount of pesticides that migrate from the intended application area is influenced by the particular chemical’s properties: its propensity for binding to soil, its vapour pressure, its water solubility, and its resistance to being broken down over time.

Factors in the soil, such as its texture, its ability to retain water, and the amount of organic matter contained in it, also affect the amount of pesticide that will leave the area. Some pesticides contribute to global warming and the depletion of the ozone layer.

Several agricultural chemicals used for controlling various diseases, insect pests and weeds are highly toxic and their application adversely affects the soil micro flora and fauna. Prolonged persistence of these pesticides in soil is bound to lower the soil fertility both directly and indirectly.

List of pesticides/pesticides formulations banned in India

A. Pesticides banned for manufacture, import and use (27 Nos.)

1. Aldrin,
2. Benzene Hexachloride,
3. Calcium Cyanide,
4. Chlordane,
5. Copper Acetoarsenite,
6. Clbromochloropropane,
7. Endrin,
8. Ethyl Mercury Chloride,
9. Ethyl Parathion,
10. Heptachlor,
11. Menazone,
12. Nitrofen,
13. Paraquat Dimethyl Sulphate,
14. Pentachloro Nitrobenzene,
15. Pentachlorophenol,
16. Phenyl Mercury Acetate,
17. Sodium Methane Arsonate,
18. Tetradifon,
19. Toxafen,
20. Aldicarb,
21. Chlorobenzilate,
22. Dieldrine,
23. Maleic Hydrazide,
24. Ethylene Dibromide,
25. TCA (Trichloro acetic acid),
26. Metoxuron,
27. Chlorofenvinphos

B. Pesticide / Pesticide formulations banned for use but their manufacture is allowed for export (2 nos.)

28.Nicotin Sulfate,
29. Captafol 80% Powder

C. Pesticide formulations banned for import, manufacture and use (4 nos.)

1. Methomyl 24% L,
2. Methomyl 12.5% L,
3. Phosphamidon 85% SL,
4. Carbofuron 50% SP

D. Pesticide Withdrawn (7 nos.)

1. Dalapon,
2. Ferbam,
3. Formothion,
4. Nickel Chloride,
5. Paradichlorobenzene (PDCB),
6. Simazine,
7. Warfarin

List of pesticides refused registration

1. Calcium Arsonate,
2. EPM,
3. Azinphos Methyl,
4. Lead Arsonate,
5. Mevinphos (Phosdrin),
6. 2,4, 5-T,
7. Carbophenothion,
8. Vamidothion,
9. Mephosfolan,
10. Azinphos Ethyl,
11. Binapacryl,
12. Dicrotophos,
13. Thiodemeton / Disulfoton,
14. Fentin Acetate,
15. Chinomethionate (Moretan),
16. Chinomethionate (Morestan),
17. Ammonium Sulphamate,
18. Leptophos (Phosvel)

Pesticides Restricted for use in India

1.Aluminium Phosphide,
2.DDT,
3. Lindane,
4. Methyl Bromide,
5. Methyl Parathion,
6. Sodium Cyanide,
7. Methoxy Ethyl Mercuric Chloride (MEMC),
8. Monocrotophos,
9. Endosulfan,
10. Fenitrothion,
11. Diazinon,
12. Fenthion,
13. Dazomet
Source: Web portal of ‘Directorate of Plant Protection Quarantine & Storage, Faridabad’ as on 15.03.2011

Most of the insecticides, herbicides and fungicides used in agriculture and for domestic purposes belong to a class of pesticides called organophosphates. The most common organophosphates are malathion, chloropyrifos, dimetheoate and phosphamidon. These degrade fast and are fast-acting on the target pest. However, their toxicity is not specific to any particular pest, and lethal effects have often been observed in other non-targeted organisms, especially birds and humans.

Organophosphates trigger both leukaemia (cancer of the bone marrow) and lymphoma (cancer that originates in lymphocytes). Lymphoma is broadly divided into two categories- Hodgkin’s and non-Hodgkin’s lymphoma. It has been observed that these pesticides trigger non-Hodgkin’s lymphoma on a larger scale. Non-Hodgkin’s lymphoma poses a greater threat as it does not respond to treatments like chemotherapy and bone marrow transplant. (Dr. M.R. Ray, Head of the Experimental Haematology Unit).

Organophosphate pesticides also affect the nervous system by inhibiting acetylcholinesterase (AChE) enzyme activity. This enzyme breaks down the neurotransmitter acetylcholine. Change in AChE’s molecular configuration makes it impossible for it to function properly, causing acetylcholine to accumulate. This increases nerve impulse transmission, thereby leading to nervous system failure. The respiratory muscles are the most affected muscle group, whose paralysis often causes death.

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