Basic Knowledge
(1) What are Organochlorines?
Organochlorines are chemicals in which carbon and chlorine are combined. Some
organochlorines are found in nature and some are byproducts of combustion
and industrial processes, but the vast majority may have been specifically
manufactured for a wide range of uses, including pharmaceuticals, pesticides,
plastics, and solvents. Most of organochlorines are Persistent Organic Pollutants
(POPs).
(2) What are Organochlorine pesticides?
The organochlorine pesticides being studied are aldrin, dieldrin, endrin,
endosulfon, heptachlor, DDT, hexachlorobenzene (HCB), mirex, technical hexachlorocyclohexane
(HCH), lindane, and toxaphene.
Canada was the first country to ratify the 1998 Protocol on Persistent Organic
Pollutants (POPs) under the UN Economic Commission for Europe's 1997 Convention
on Long Range Transboundary Air Pollution. This Protocol lists 16 POPs substances,
11 of which are pesticides. The 16 POPs now subject to international action
are:
- Pesticides: aldrine, dieldrine, endrine, chlordane,
DDT, heptachlore, hexachlorobenzene, mirex, chlordecone, lindane, toxaphene;
- Industrial Chemicals: PCBs, hexabromobiphenyl;
- Contaminants (by-products): dioxins, furans, polycyclic
aromatic hydrocarbons (PAHs).
- Aldrin and dieldrin
-
are the common names of two insecticides that are closely related chemically.
Aldrin is readily converted to dieldrin in the environment, so these
two closely related compounds are considered together by regulatory
bodies. Their toxicities do not differ significantly.
Aldrin and dieldrin were widely used from the 1950s to the early 1970s,
and their primary use was for control of corn pest. Aldrin has been
used as a soil insecticide to control rootworms, beetles, and termites.
Dieldrin has been used in agriculture for soil and seed treatment
and in public health to control disease vectors such as mosquitoes
and tsetse flies. Dieldrin has also had veterinary use as a sheep
dip and, along with chlordane, was used in the timber processing industry.
Persons could be occupationally exposed to aldrin and dieldrin from
inhalation and by absorption through the skin.
- Endosulfan
-
is an insecticide. It was first introduced in the 1950s. Although
it may also be used as a wood preservative, endosulfan is used primarily
on a wide variety of food crops including tea, coffee, fruits, and
vegetables, as well as on rice, cereals, maize, sorghum, or other
grains. Endosulfan is a highly toxic substance. The World Health Organisation
(WHO) classifies endosulfan as moderately hazardous, and the US Environmental
Protection Agency (US EPA) classifies it as highly hazardous pesticide.
Short-term toxicity is high, and influenced by the solvents and emulsifiers
used to dissolve it. Endosulfan is easily absorbed by the stomach,
by the lungs and through the skin, meaning that all routes of exposure
can pose a hazard.
- Endrin
-
is a rodenticide used to control mice and voles, and an insecticide
used on cotton, rice, and maize. Closely related to aldrin and dieldrin,
endrin is the most toxic of the three in the aquatic environment and
its metabolites are more toxic than endrin itself. In soils endrin
is extremely persistent, with a half-life as long as twelve years.
- Chlordane
-
is a broad-spectrum insecticide that has been used since 1947. It
was applied on corn, citrus, deciduous fruits and nuts, and vegetables.
Its use has recently been increasingly restricted in many countries,
and it is now used mainly to destroy termites by subsurface injection
into soil, and for fire ant control in power transformers.
Chlordane is very resistant to degradation. In experimental animals,
prolonged exposure in the diet causes liver damage. Chlordane produces
liver tumours in mice, but the weight of evidence indicates that it
is not genotoxic. Chlordane can interfere with cell communication
in vitro, a characteristic of many tumour promoters.
- Heptachlor
-
is a broad-spectrum insecticide, the use of which has been banned
or restricted in many countries. At present, the major use of heptachlor
is for termite control by subsurface injection into soil.
Heptachlor is quite persistent in soil, where it is mainly transformed
to its epoxide. Heptachlor epoxide is very resistant to further degradation.
Heptachlor and heptachlor epoxide bind to soil particles and migrate
very slowly. Heptachlor and heptachlor epoxide have been found in
drinking-water at levels of nanograms per litre. Diet is considered
to represent the major source of exposure to heptachlor, although
intake is decreasing.
Prolonged exposure to heptachlor has been associated with damage to
the liver and central nervous system toxicity.
- Dichlorodiphenyhricliloro-ethane (DDT)
-
is an inexpensive, persistent, broad-spectrum, nonsystemic ingested
and contact insecticide. From 1946-1972 DDT was the most widely used
agricultural insecticide in the world. DDT was commonly used to control
insect pests in gardens, orchards, agricultural crops and forests
and to control bloodsucking insects and disease vectors. It is still
widely used in tropical countries for disease vector control (malaria,
yellow fever, trypanosomiasis and typhus) because of its efficiency
as a broad-spectrum insecticide and low manufacturing costs.
DDT is highly persistent on solid surfaces and readily partitions into
animal fats where it has been demonstrated to bioaccumulate and biomagnify.
It has been reported in humans at levels which are of potential concern
to health.
Human exposure can result directly from spraying or through skin contact,
inhalation or from ingestion of contaminated foods. DDT and its metabolites
display acute and chronic aquatic toxicity, and mammalian chronic
toxicity and there is strong evidence of teratogenicity, mutagenicity,
and carcinogenicity.
- Hexachlorobenzene (HCB)
-
was introduced in the 1940s as a seed-dressing to prevent fungal disease
into several crops. HCB is also formed as a waste product in the production
of several chlorinated hydrocarbons and is found as a contaminant
in some pesticides. HCB has been detected in all environmental compartments.
HGB persists in the environment and has been shown to bioaccumulate
and biomagnify in the food chain.
In humans, HCB is easily absorbed to accumulate in fat tissues, and
persists for many years since it is highly lipophilic and resistant
to metabolic breakdown. Tissue residue surveys showed that HCB concentrations
have not declined since 1975 in some regions such as the Great Lakes
and suggest that concentrations may be increasing. HCB produces a
spectrum of biological and toxic conditions that are characteristic
of polyhalogenated compounds and is capable of enzyme induction and
disruption of endocrine control. HCB is toxic by all routes of exposure:
inhalation, ingestion and dermal contact. Nursing infants ingest 200
to 300 times the adult intake on a body-weight basis.
- Mirex
-
is a stomach insecticide that was used against fire ants, leaf cutters,
harvester termites, Western harvester ants, and pineapple mealybugs.
Also been used as a fire retardant in plastics, rubber, paint, paper
and electrical goods. Recently, the use of mirex has become increasingly
restricted or prohibited in many countries. Mirex is carcinogenic.
- Technical hexachlorocyclohexane (HCH) and Lindane
-
HCH, a pesticide introduced during the 1940s, has two technical grades:
technical HCH and lindane. Technical HCH contains only 10 - 12% of
the active ingredient, gamma-HCH, and is predominantly made up of
the non-insecticidal isomers alpha-HCH (60-70%), beta-HCH (5-12%)
and other minor components. Lindane is almost pure gamma-HCH, and
is used as an insecticide in agriculture for the control of lice on
cattle and grass grub in pasture, and for insect control on vegetables
and in orchards.
HCH enters the environment through direct application and through non-point
sources during manufacturing and disposal. Once in the environment HCHs
persist and have been show to bioaccumulate. HCHs is the most abundant pesticide
in the Arctic Ocean.
Dietary exposure is the primary route of human exposure where HCH is used
on plants and animals, since it is adsorbed from the gastrointestinal tract.
The estrogen effects of HCH and its adverse effects upon the male reproductive
system have been reported in a variety of animal studies. Because of concentrations
of this pesticide in human breast milk, nursing infants are at special risk.
- Toxaphene
-
is a complex mixture composed of many congeners with different chemical
properties. Toxaphene has been used against insect pests on cotton,
tobacco, forests, grains, ornamental plants and livestock. Toxaphene
is very persistent in the environment and is transported long distances
in the atmosphere.
Toxaphene is both acutely and chronically toxic to aquatic species
and wildlife. It has also been identified as a potential carcinogen.
Human exposure to toxaphene can induce neurological and respiratory
dysfunctions, heart dilations, brain haemorrhages and death.
(3) How did organochlorine pesticides get into the environment?
Organochlorine pesticides have entered the environment through industrial
discharges, the manufacture and use of organochlorine pesticides in agriculture
and industry, and disposal of organochlorine pesticides.
These organochlorine pesticides are chemically very stable, which means they
break down only very slowly and can remain in the environment for a long time.
Organochlorines which are stable and vapour-forming can be carried by air
currents for long distances. Eventually they condense and are deposited on
land and water, particularly in cold climatic regions.
Organochlorine residues have been detected in air, water, soil, sediment,
fish, and birds global wide. They have also been found in remote areas, such
as open oceans and polar regions.
If they contaminate the food supply of animals, the organochlorines become
more concentrated as they move up through the food chain. For this reason
the highest levels of organochlorines are found in species at the top of the
food chain: human beings, fish-eating birds and marine mammals. They build
up in the fatty tissue and stay in the body for a long time because they are
only slowly metabolised and excreted.
The organochlorine pesticides which have all four properties of persistence,
toxic, vapour-forming, and concentrating up the food chain (bio-accumulative),
are among the chemicals now referred to internationally as persistent organic
pollutants (POPs). These chemicals are a focus of international concern.
Created :
2002-08-21
Modified :
2002-08-21
Reviewed :
2002-08-21
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