Pesticide Residues in Mother’s Milk - Pesticides: Evaluation of Environmental Pollution - page 545

DDT elimination from the body can take some time; its half-life in humans is approxi-
mately 4 years. DDT's major metabolite, DDE, has a half-life of approximately 6 years. The
relative proportions of DDT and DDE detected in human tissues can be an indication of
the length of time since exposure (Salem and Ahmed 2002). In areas where DDT exposure
is recent, the DDE/DDT ratio is low, whereas in areas where substantial time has passed
since its use, the DDE/DDT value is higher. Levels of these contaminants in breast milk are
often six to seven times higher than in the blood.
Hexachlorocyclohexane : Hexachlorocyclohexane (HCH) is an insecticide made up of a
mixture of eight isomers. The components are 58%-80% of α-HCH, 5%-14% of β-HCH,
12%-14% of γ-HCH, 2%-10% of δ-HCH, and 3%-5% of other isomers (Chen et al. 2007;
Devanathan et al. 2009). Different isomer forms have different levels of persistence and
bioaccumulate in breast milk differently. The γ-isomer of HCH, also known as lindane, is
widely used as an insecticide directly applied to the body and scalp to treat head and body
lice. The β-isomer of HCH is the most persistent and bioaccumulative form (Salem and
Ahmed 2002; Ennaceur et al. 2007). The α- and γ-isomers of HCH are converted into the
β-isomer in organisms. The dechlorination rate sequence in HCHs is α-HCH>γ-HCH>δ
-HCH> β-HCH, in which the α-HCH is the most unstable isomer and has the fastest deg-
radation rate; γ-HCH in agricultural soils can be easily transformed into other HCHs by
decomposition or biotransformation; β-HCH is stable, with the lowest solubility, and does
not evaporate easily (Chen et al. 2007). As a result of this conversion, as much as 90% of
HCH detected in human tissues and breast milk is β-HCH (Sonawane 1995).
Chlordane : Chlordane (CHL), a mixture of more than 26 compounds, is an organochlorine
cyclodiene pesticide and typically consists of 15% cis-chlordane, 15% trans-chlordane, 9.7%
trans-nonachlor, 3.9% heptachlor, 3.8% cis-nonachlor, and other chlorinated hydrocarbons
and by-products (Solomon and Weiss 2002). Chlordane has been used as an agricultural
pesticide, on home lawns and gardens, and against termite control in buildings. Like most
POPs, the breakdown of chlordane once it has attached to soil particles or sediment is very
slow; in some cases, it has been found in the soil up to 20 years after the initial treatment.
Chlordane is rapidly metabolized in organisms into oxychlordane and γ-chlordane or into
impurities such as trans-nonachlor or cis-nonachlor. These breakdown products that per-
sist in the tissue of fish, birds, and mammals are found in breast milk (Kunisue et al. 2004b;
Tanabe and Kunisue 2007; Subramanian et al. 2007; Devanathan et al. 2009).
Heptachlor : Heptachlor is an organochlorine cyclodiene pesticide that has been used to
control termites and as an insecticide on seed grains and food crops. Heptachlor rapidly
oxidizes by both photochemical and biological processes to heptachlor epoxide, which is
extremely persistent in the soil. In some cases, trace amounts of heptachlor epoxide have
been found in the soil 14-16 years after application. Plants can draw heptachlor epoxide
directly from the soil, and the chemical bioaccumulates in animals (Solomon and Weiss
2002).
Dieldrin and aldrin : Dieldrin and aldrin are closely related organochlorine insecticides
that are extremely persistent in the environment. Both pesticides have been used in agri-
culture, and dieldrin was also used for vector control, veterinary purposes, and termite
control (Solomon and Weiss 2002; Mustafa et al. 2010). In both plants and animals, aldrin,
once present in soil or water, is transformed to dieldrin. Dieldrin breaks down very slowly,
does not easily evaporate into the air, and binds to soil particles. Plants take up aldrin and
dieldrin residues directly from the soil. In animals, including humans, dieldrin is stored
in the fat and leaves the body very slowly. Because of low water solubility and a tendency
to bind strongly to soil, both aldrin and dieldrin migrate downward very slowly through
the soil or into the surface water or groundwater.