Organochlorine Pesticides

Organochlorine Pesticides

Potential exposure

Organochlorine pesticides are one of several classes of insecticides, which

include the chlorinated ethane derivatives (DDT and methoxychlor), the

cyclodienes (chlordane, aldrin, dieldrin, heptachlor, endrin, and toxaphene), and

the hexachlorocyclohexanes (lindane). During the 1940s to the 1960s, the

organochlorine insecticides were used extensively in agriculture, soil, and

structure insect control, as well as in malaria control programs. However, due to

their long-term persistence in the environment and their tendency to accumulate

in biologic as well as nonbiologic media, the organochlorine insecticides were

replaced by the organophosphate insecticides for many uses in the early 1950s

(Klaassen, Amdur, and Doull 1986). DDT is one of the best known, cheapest,

and one of the most effective of the synthetic insecticides. The general

population has sustained exposure to DDT and its derivatives with storage of

some quantity of this insecticide in fatty tissues as a result of its introduction into

commerce in the mid-1940s. The USEPA has restricted the use of DDT in the

United States because of the ecological effects, potential effects of chronic

exposure and storage of low levels of DDT in humans, and the development of

resistant strains of insects. However, it is still used elsewhere worldwide.

Humans may be exposed to organochlorine insecticides in contaminated air,

soils, water, food, and breastmilk by inhalation, dermal contact, and ingestion

exposure routes.

The persistence of organochlorines in the environment varies with each

individual compound. Organochlorines, including aldrin, chlordane, endosulfan,

and heptachlor, are reported as ranging from moderately persistent, with

effectiveness ranging from 1 to 18 months, to persistent, retaining toxicity for

years, perhaps as many as 50 to 100 years (Briggs and Council 1992). Lindane,

DDT, DDE, DDD, dieldrin, endrin, and methoxychlor are persistent insecticides

(Briggs and Council 1992).

Physical and chemical properties of DDT

Property

Value

Molecular weight

354.5 g/mol

0.0031 mg/L at 25 C

Water solubility

8.3 10-6 mm Hg at 20 C

Vapor pressure

Koc

113,000 to 350,000

log Kow

6.91

3.8 10-3 atm-m3/mol at 20 C

Henry's Law Constant

Toxicity

In general, the organochlorine insecticides are considered to be less acutely

toxic, but have greater potential for chronic toxicity, than the organophosphate

D57

Appendix D Toxicological Profiles