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October 1992, Volume 42, Issue 10

Review Articles


Abdul Jabbar  ( National Agricultural Research Centre, Islamabad. )

The ever increasing demand for more food produc­tion has been met by adoption of better crop protection measures. Since world war II synthetic chemi­cals/poisons have been extensively used for the control of agricultural as well as household and medical insect pests. These poisons which otherwise are employed for human benefit can also be called as economic poisons. Pesticides used for the control of different insect pests are the major component of such economic poisons.
Genocide -. Terminal / Fatal
Suicide -. High doses —~ Terminal / Fatal, Occasionally
Low doses  Survive  Survive
Intentional -. Experimental—.. Volunteers
Poisoning~~—. (Therapeutical)-.. Patients
Unintentional   Accidental Fatal, Survive
Poisoning —. Occupational Survive with side effects

Environmental Survive with side effects
There is general concern on environmental pollu­tion and the chronic effects of pesticides. It is impossible in today’s society to avoid some sort of direct or indirect exposure to these chemicals. Contaminated diets are the main concern of the present day man throughout the world. The pesticides are used in one part of the world and then contaminated grains shipped and exported to the other part of globe. Similarly within a country the translocation of the food items (vegetables, fruits and grains) is on a massive scale. For example, survey of vegetables from markets far away from vegetable growing areas in Pakistan has revealed the presence of pesticide residues in many cases. Likewise the pesticides applied to crops can enter into the produce which when consumed by livestock can build up in milk and meat, eventually transferred into the human body. Moreover, con­taminated raw vegetables and fruits can also be a source of pesticide residues found in human tissues.
The entry of these pesticides in the body is by three routes, firstly oral (ingestion or drinking), secondly dermal (through the body contact) and thirdly inhalation (fumes). Individuals exposed to pesticides can be categorized into two major groups, i.e., high and low risk’ groups (Table I).


These could include insecticides (used for the control of agricultural, medical veterinary and household insect pests), fungicides (used for the control of various fungal diseases), acaricides (used for the control of mites), rodenticides (used for the control of rodents), nematicides (used for the control of nematodes) and herbicides (used for the control of weeds). Whereas in the world herbicide comprise 56% of the total pesticides used, the situation in Pakistan is entirely different. In Pakistan almost 85% of all pesticides used are insecticides, followed by 6-7% of fungicides and herbicides. The insecticides can further be classified into four major groups or classes. First and the foremost is the persistent class of organochlorine. DDT, BHC, Dieldrin are the famous insecticides belonging to this class. Organophosphorus insecticides are the other major group. These are less persistent and their primary mode of action is on the nervous system mainly inhibiting the acetyl cholinesterase enzyme. Malathion, methyl­parathion, diazinon, endosulfan, dimethoate, chlor­pyrifos, monocrotophos are some of the important members of this class. Third group is carbamate insec­ticides based on the carbamic acid. The most recently developed and least persistent of these insecticides belong to pyrethroids which are derived from the chrysanthemum. In addition to the natural group of insecticides collectively called pyrethrins some synthetic pyrethroids are also available in the market. Cyper­methrin, deltamethrin and fenvalerte insecticides avail­able in Pakistan belong to this class. These insecticides have quick knock-down effects and are most commonly used against the flying insects (e.g., as aerosols for the control of household insects like flies, mosquitos, etc.). Herbicides usage in Pakistan is increasing and hence posing a direct or indirect danger to our com­munity. Paraquat, diquat, diuron, metametron, phosalon, atrizine, 2,4-D and 2,4-T are the major her­bicides in use. Similarly zinc phosphide, aluminium phosphide, warfarin, racumin, bromodialone, brodifacoum and strychnine are major pesticides used for the control of vertebrate pests.


Extensive, ill planned and improperly applied pesticides can pose danger to our ecosystem. These can be source of our food chain pollution and a possible health risk. Although whole world is concerned about the problems due to excessive use of pesticides, but situation in developing countries is alarming as com­pared to developed countries. Survey of acute poisoning among agricultural workers in four Asian countries revealed organophos­phate compounds to be mostly responsible for poison­ing2. The pesticide poisoning in Malaysia was 53.6% of the total poisoning cases registered, in Sri Lanka 69.1%, in Thailand 22.7% with organophosphate insecticides and 25% with bipyridyls. In Indonesia copper compounds were responsible for 23.4% of the cases and organophos­phorus insecticides for 17.8%. In Afghanistan overall mortality rate was 6.2% due to accidental poisoning among children, organophosphorus insecticide poison­ing alone was responsible for 50% of total deaths3.


Organ chlorine residues are detected in measurable concentrations in various tissues of human beings because of the worldwide pollution of air, water, soil and foods. The concentrations vary from region to region according to chemical, climatic, socio- economic and geographic factors. Polluted air is carried over huge distances4 and some chemicals are found almost worldwide, e.g., hexachlorobenzene (HCB), which has been used as fungicide and is mainly emitted by chemical industries now5. In a study conducted in Karachi area by Mughal and Rehman6 more than sixty samples of human adipose tissue from the general population were analyzed for chlorinated compounds by colorimetric and chromatographic procedures. The average level of total DDT-equivalent was 25 ppm, total benzene hexachloride (BHC) was 0.48 ppm and dieldrin was 0.047 ppm. Values varied widely and the frequency distribution was posi­tively skewed. The tendency towards lower concentra­tions in females was due, perhaps, to their greater fatty pool distribution of residues. The concentration of p,p -DDD, an intermediary of DDT metabolism, was definitely higher in autopsy as compared to biopsy material due,  probably, to post-mortem anaerobic microbial metabo­ Krawinkel7 conducted a survey monitoring the organochlorine concentrations in human blood and fat tissue of patients of the Sandeman Provincial Hospital in Quetta, Balochistan (Table II).

Results of the analysis for HCH, DDT and DDE showed that there is a great range of interindividual differences whereas the HCH- and DDT/DDE- values each are concordant in the individual samples; probands with high concentrations of DDT/DDE in blood also have higher levels of DDT/DDE in fat tissues, high levels of DDT are associated with high levels of DDE. The concentration of pesticide-residues was not correlated with age or sex of the patients. The role of organochlorines as pathogenic agents is questioned as no obvious symptoms of chronic intoxica­tion of man have been reported excluding all other pathogenetic impacts. Pesticide residues in man extreme­ly vary from country to country, even from region to region6,9,12. Krawinkel7 further observed that except the median for r-HCH in fat tissue the median concentrations of all pesticides are much higher in Quetta than in Germany. The fact that no HCB was detected in any sample from Quetta is interesting. HCB is not applied locally and the global spread of HCB in the air alone does not cause a contamination of human blood and fat tissue as it could be suspected from the findings of other investigators13. Farvar14 reported that in 1970 in rural areas of Guatemala, where DDT spraying for malaria control has been carried on for some fifteen years, total DDT in human mother’s milk was found to be from 0.3 to 12.2 ppm. These figures suggest that Guatemalan infants were drinking from the breast at least 15 and perhaps nearly 500 times more than the acceptable daily intake of DDT established by the World Health Organization. Iranian samples of human milk obtained from areas sprayed by malaria eradication teams showed DDT concentrations of 0.4 to 2.5 ppm, which is 8 to 50 times higher than the permitted levels in cow’s milk sold in the United States15. In 1976 an epidemic of poisoning due to water-wet­table powder of malathion occurred among 5,350 spraymen.


In, 1970 mixers and 1,070 supervisors in malaria control programme in Pakistan. During the entire epidemic there were five deaths, but they occurred before special study began and details were not available. Three brands of malathion were in use which differed substantially in (a) toxicity to rats, (b) content of isomalathion and (c) the degree of inhibition of cholinesterase produced in spray men who applied them. Elimination of use of two more toxic preparations and special instructions on proper safety measures halted the epidemic. A major poisoning accident occurred in Multan in 1972 when workers with improper clothing were unload­ing a consignment of phorate under extreme summer conditions became ill and seven of them died. In the other instance survey of 200 employees of the Depart­ment of Plant Protection, associated with the flying and engineering unit of their aerial section, for cholinesterase activity in their blood showed that nearly 50% of them possessed low enzyme activity16.


The examples of accidental pesticide poisoning around the world are innumerable. In Pakistan there is lack of scientific information on the subject. Except the following reported cases most cases appear as reports in the press which need verification before acceptance and quotation. In summer of 1984 an epidemic of endrin poisoning occurred in Talagang District Auock. Acute convulsions were recorded in 194 affected persons in 18 villages. 70% cases were in the children of 1-9 years of age. Nearly 10% (19 out of 194) patients died. The epidemiology of the Talagang outbreak suggested that a shipment of food (possibly sugar) was contaminated en route to the city17. Some simple reported examples from throughout the world18 show how vulnerable and at what riskwe are. For example a man ate food accidentaly seasoned with as much as 15-30 ml of a powder allegedly mistaken for monosodium glutamate later identified as lindane (r­BHC). Four members of a family were poisoned after they have treated their living quarters by heating a pesticide dust on a hot plate. There was only one application. The symptoms of poisoning appeared six months later. The wife of an agricultural scientist used a small amount of a 10% granular formulation of aldicarb to treat the soil around rose bush at her home. Twenty-four days later, she showed the symptoms of poisoning after eating the 4 to 6 terminal leaves of a mint plant growing nearby to the rose bush. More than 150 school boys had to be treated for poisoning when they entered the cornfield near their school which had been sprayed with pesticides the previous day. The tragedy of Bhopal in India is still fresh in our minds. More than 2,000 people cUed after exposure to the fumes of methyl isocyanate gas leaked from the pesticide manufacturing plant of union carbide.


Table III gives the amount of pesticide which was either accidentaly consumed and the patients survived or deliberately given to volunteers and no ill-effects were observed. It also gives the values or limits which are supposed to be safe for the pesticide workers. Of course individuals would differ in susceptibility.

Table IV gives the symptoms which appeared after accidental or intentional exposure to larger amounts of pesticides. The treatment given is the one which was administered to these individuals and they recovered. In addition to the medical symptoms the laboratory studies on rats and other primates have shown that long term exposure to pesticides can lead to mutagenic, teratogenic, carcinogenic and hepatotropic effects.


1. Jabbar, A., Inayatullah, C., Bajwa, M.I. and Shah, A. Environmental considerations of pesticide production and usage in Pakistan. Country paper UNIDO/UNDP seminar, Jakarta, Indonesia, November 28-December 2, 1988, pp.1-35.
2. Jeyaratnum, A., Lun, KG and Phoon, W.O. Surveyof acute pesticide Poisoning among agricultural workers in fourAsian countries. Bull. WHO., 1987;65;521-27.
3. Cbaudhry, V.P., Jalali, J.A. and Haider, G. Spectrum of accidental poisoning among  children in Afghanistan Ann. Trop. Paediatr., 1987; 7:278-81.
4. Cohen, J.M. and Pinkerton, C. Widespread translocation of pesticides by air transport and rainout. Adv. Chem. 5cr., 1966;6O:163-76.
5. Zell, M. and Ballschmiter, K. Baseline studies on the global pollution II. Global occurrence of hexa-chlorobenzene (HCB) and polychlorocamphenes (toxaphene) (PCC) in biological samples. Z. AnnaiChem., 1980;300:387-402.
6. Mughal, HA. and Rabman. MA. Organochiorine pesticides contentof human adipose tissue in Karachi Arch. Environ. Health, 1973; 27:396-98.
7. Krawinkel. M.B., Plehn, Ga Kruse, H. and Kasi, AM. Organochiorine residues in Balochistan/Pakistan: blood and fat concentrations in humans. Bull Environ, Contam. Toxicol., 1989; 48:821-26.
8. Astolfi, E., Aifanso, A.H., Mendizabal, A. and Zubizaretta, E., Pesticides chlor\\\'s de Faccouchee etdu cordon oblical de nouveau-nes. J.Eur. Toxicol., 1974;7:330-38.
9. Siddiqui, M.K., Sexena, M.C. and Krishna Murti, Cit Storage of DDT and BHC in adipose tissue of Indian males. Int.J. Environ. Anal. Chem., 1981; 10:197-204.
10. Albert, L, Cebrian, M.E., Mendez, F. and Porules, A Organochioririe pesticide residues in human adipose tissue in Mexico; results ala preliminary study in 3 Mexican cities. Arch, Environ. Health, 1980;35(5):262-69.
11. Abbott, D.C., Collins, G.B., Goulding, Ft. and Hoodless, LA. Organochiorine pesticide residues in human fatin the United Kingdom 1976-77. Br.Med.J., 1981;283:1425-28.
12. Niessen, KH., Ramolla, 3., Binder, M., Brugmann, C. and Hofmann, U. Chlorinated hydrocarbons in adipose tissue of infants and toddlers: inventory and studies on their association with intake mother’s milk, Eur.J. Pediatr., 1984; 142:238-44.
13. Schauerte, W., Lay, J.P., Klein, W. and Korte, F. Long-term fate of organochiorine xenobiotics in aquatic ecosystem. Distribution, residual behaviour and metabolism of bexachlorobenzene, pentachloronitrobenzene and 4-chloroaniline in small experimen­tal ponda. Ecotoxicol. Environ. Safety, 1982; 6:560-69.
14. Farvar, M.T. Pesticides in developing countries. Institute of Electrical and Electronics Engineering Inc., document No.75CH 1004-1. Int. Conf, on environmental sensing and assesament (ICESA), 1975.
15. Farvar, M.C. Collection of human biological specimens in developing countries for monitoring organochlorine compounds. Proc. Int. Workshop on biological specimens. Oxford, 1971.
16. Rahman, A The effect of pesticides on professionally exposed personnel and users. Tech. Report. Jinnah Postgraduate Medical Centre, Karachi, 1982, pp. 1-70.
17. Rowley, D.L., Rab, M.A. Hardjotanojo, W., Uddle, 3. Burse, V.W., Saleem, 84., Sokal, D., Falk, H. and Head, S.L Convulsions caused by endrin poisoning in Pakistan. Pediatrics, 1987; 79:928-34.
18. Hayes, W.J. Pesticides studies in man. Baltimore, William and Wilkins, 1982, pp.284-435.

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