by Mr. Oscar Nieto-Zapata

The persistent organic pollutants (POPs) include a group of highly stable synthetic compounds utilized in agriculture as pesticides and in industry or generated inadvertently as by-products of combustion or industrial processes. They constitute a problem of world interest since they are highly persistent in the environment, moving to unsuspected sites far from their places of origin, where they accumulate in the tissues of most living organisms, poisoning humans and various forms of wildlife.

The impact on human health of the pesticides that have been internationally recognized as requiring immediate action--namely aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, toxaphene, and hexachlorobenzene--will be described below.

The chemical structures of the pesticide POPs generally correspond to those of aromatic chlorinated hydrocarbons, although some of them contain other elements, such as oxygen and sulfur.

In general, these pesticides are slightly soluble in water and are stable in the presence of sunlight, moisture, air, and heat, which makes them quite persistent in the environment. As a result, many countries allow their use exclusively in public health campaigns to combat insect vectors of diseases of epidemiological importance, for example, malaria and dengue. Other countries have prohibited or restricted their use.

In the countries where the use of these compounds has been limited or prohibited, their residues are still frequently found in food, especially of animal origin, precisely because they are very stable in the environment.

Listed below are some generic and commercial names of organochlorine pesticides:

1. Absorption Mechanisms

Organochlorine pesticides can enter the body through the digestive and respiratory systems or through the skin. In this latter case, the degree of penetration also depends on the type of compound in question. For example, the DDT is absorbed only slightly by the skin, while aldrin and endrin are absorbed more rapidly and in greater quantity. In addition, when these substances are dissolved in animal or vegetable fat absorption is even greater.

2. Mechanisms of Action on the Organism

The principal toxic action of POPs is on the nervous system; they interfere with the flow of ions through the membranes of the nerve cells, thus increasing the irritability of the neurons. They are, in addition, enzymatic catalysts.

Because, as already mentioned, POPs are only slightly soluble in water, when there is sudden exposure the blood is rapidly saturated and there is also reabsorption by the kidney. As a consequence of this saturation, these compounds accumulate in the fatty tissues and are thus able to cause chronic poisoning.

When a pregnant woman is exposed, the fetus also is affected, since POPs pass through the placental barrier. Newborns are affected even more by breast-feeding, because it is a significant path for excretion.

In addition, DDT, aldrin, chlordane, dieldrin, endrin, heptachlor, and mirex are capable of causing the production of some liver enzymes, which also metabolize some drugs.

These pollutants are eliminated slowly, through bile, feces, urine, and breast milk.

The early manifestations of acute poisoning (usually due to exposure to large quantities in a very short time) include an increase in sensitivity and a tingling sensation in the face (especially peribuccal) and limbs, although giddiness, lack of coordination, tremor, and mental confusion may also occur. In the case of ingestion, gastrointestinal irritation (vomiting and diarrhea) are presented.

In the most severe cases of intoxication, there are muscular contractions, followed by generalized convulsions (indistinguishable from those of a different origin), which appear early on and may recur periodically for some time. High concentrations of these substances increase cardiac irritability and may produce cardiac arrhythmias. Coma and respiratory depression may also occur.

Cyclodiene (aldrin, dieldrin, endrin, chlordane, heptachlor, and mirex) and toxaphene poisoning usually begins with sudden convulsions, without the initial symptoms mentioned above.

Exposure to vaporizables formulations may produce irritation of the eyes, nose, and oropharynx, symptoms that disappear upon suspension of the exposure.

The diagnosis of poisoning is based mainly on a history of exposure to some of the substances in this group of pollutants and the characteristics of the clinical picture, taking into consideration changes that may be present due to the concomitant action of the solvents and the possible confusion with convulsions of a different origin.

Laboratory Tests

The most sensitive laboratory tests for identifying the different types of POPs and the biological samples appropriate for their study are described below.

- Gas chromatography is utilized for identifying POPs or their metabolites (compounds formed within the organism) in blood samples, urine, stomach contents, stool, and other biological specimens. With the use of gas chromatography it is possible to determine the presence of these substances at concentrations much lower than those related to acute poisoning. As a result, a positive laboratory report alone does not constitute unmistakable evidence of poisoning. It should also be recalled that, given the high degree of persistence of POPs in the environment, it is quite probable that most, if not all, individuals have some level of one or more of them in their bodies.

- In DDT, dieldrin, and endrin poisoning, these substances can be detected as such in the blood. Due to the rapid transformation of aldrin into dieldrin in the liver, the latter could be found in cases of aldrin poisoning.

- DDE (metabolite of DDT), dieldrin, and anti-12-hydroxyendrin (metabolite of endrin) can be measured in the urine.

Prognosis

If the patient survives the convulsions, the possibilities of full recovery are good. However, in very severe cases there is a risk of secondary brain damage due to the prolonged lack of oxygen that may result from convulsions that are not quickly controlled.

These effects can be observed after a single exposure to a large nonlethal dose or after repeated exposures to doses that are usually low.

Skin

For the most part POPs produce a irritation in this organ known as chloracne. Laboratory animal exposure to endrin is associated with dermatitis and alopecia.

Reproductive impact

The reproductive impact of POPs include abortion, retardation of fetal growth, birth defects (teratogenesis), and an increase in mortality among the newborn of exposed mothers. Infertility and loss of libido have been reported in humans exposed to aldrin and dieldrin.

Mutagenesis and Cancer

Except for mirex and toxaphene (little studied), all POPs are mutagenic. All these pesticides are considered potential carcinogens of greater or lesser strength. Chlordane, DDT, heptachlor, and aldrin and dieldrin are associated with liver cancer. DDT is also associated with breast cancer and dieldrin with cancer of the adrenal glands. Most of the studies on which these conclusions are based have been carried out with laboratory animals.

Immune System

There have been reports immunosuppression (an effect associated with increases in cancer and infections) in people exposed to aldrin.

Other Effects

Other effects that are observed in the medium or long term after exposure to POPs may include, loss of appetite, weight loss, nausea, headaches, sleep alterations, signs that numerous peripheral nerves are affected, liver and renal damage, generation of liver enzymes (which can accelerate the metabolism of drugs and other products), cardiac arrhthymias, eye damage such as allergic conjunctivitis, blepharitis, and retinal angiopathy. Changes in personality and difficulties in concentrating have been noted in people exposed to heptachlor.

1. Arias J. et al. Plaguicidas organoclorados. Metepec, México: Centro Panamericano de Ecología Humana y Salud, 1990.

2. Cadavid S. "Insecticidas derivados clorados", in D. Córdoba, ed., Toxicología. Medellín, Colombia: Darío Córdoba, 1991.

3. Levine R.S., Davies J.E. "Toxicidad de los plaguicidas y modo de acción", in J.E. Davies, V.H. Freed, and F.W. Whittemore, eds., Enfoque agromédico sobre manejo de plaguicidas. Washington: Organización Panamericana de la Salud.

4. Levine R.S., Davies J.E. "Aspectos clínicos de la intoxicación aguda", in J.E. Davies, V.H. Freed and F.W. Whittemore, eds., Enfoque agromédico sobre manejo de plaguicidas. Washington: Organización Panamericana de la Salud.

5. Morgan D. Recognition and management of pesticide poisonings. Washington: U.S. Environmental Protection Agency, 1989.

6. Murphy S. "Toxic effects of pesticides", in C. Klaassen, M. Amdur, J. Doull, ed., Casarett and Doull's Toxicology. New York: Macmillan Publishing Company, 1986.

7. OPS. Criterios de Salud Ambiental 9, DDT y sus derivados. Washington: OPS, 1982.

8. WHO/FAO. Data sheets on pesticides No.1, Endrin. Geneva: WHO/FAO, 1975.

9. WHO/FAO. Data sheets on pesticides No.21, DDT. Geneva: WHO/FAO, 1976.

10. WHO/FAO. Data sheets on pesticides No.41, Aldrin. Geneva: WHO/FAO, 1979.

11. U.S. Department of Health and Human Services B ATSDR. Toxicological profile for endrin and endrin aldehyde (update). Atlanta: ATSDR, 1996.

12. U.S. Department of Health and Human Services B ATSDR. Toxicological profile for mirex and chlordecone. Atlanta: ATSDR, 1995.

13. U.S. Department of Health and Human Services B ATSDR. Toxicological profile for toxaphene (update). Atlanta: ATSDR, 1996.

14. Enviromental Health Center B National Safety Council. Http://www.nsc.org/ehc.

15. New Jersey Department of Health. ftp://alternatives.com/library/envchemh/chemh173, 286, 382.

16. Environment Canada. http://www.alternatives.com/libs/envcan.htm/pcdb.doc.

17. For the MSDS of aldrin, clordano, DDT, dieldrin, heptaclor, hexaclorobenzene, mirex and toxafene the folling electronic address was consulted: http://siri.org.

18. Henao S, Nieto-Zapata O. Curso a distancia sobre diagnóstico, tratamiento y prevención de intoxicaciones agudas causadas por plaguicidas. Guatemala: INCAP/ECO/UNED, 1993.