Environmental Engineering Reference
In-Depth Information
from women makes it difficult to identify differences related to actual exposure conditions.
The wide variation in the methods of chemical analysis adopted in different studies across
the world hinders the comparison of data. So, it is perilous to extrapolate from the observed
levels of contaminants in breast milk around the world to predict potential health effects
or to declare specific levels as safe. Despite the difficulties in generalizing across studies,
heavier local use of contaminants is the major predictor of the levels of contaminants in
breast milk, but contamination is even detectable in the areas with no local use of chemicals
(Saeed et al. 2000). In general, ban on the production or use of POPs has been associated
with decreasing residues of these chemicals in breast milk samples over the subsequent
decades. The following sections review some of the data on specific chemicals to illustrate
time trends and regional differences in breast milk levels of OCP contaminants.
17.2 Characteristics of Organochlorine Pesticides
Organochlorine pesticides are a kind of synthetic chemical pesticides, which can be
divided into two groups: one takes benzene as the raw material and the other takes cyclo-
pentadiene. These pesticides are very stable. Both persistence and bioaccumulation are
strong. They are difficult to degrade naturally in the environment, and they can be a threat
to ecosystems and human health through evaporation, migration, food chain transfer, and
other pathways (Tan et al. 2008; Katsoyiannis and Salnara 2005).
The Stockholm Convention listed the OCPs among the POPs (Table 17.1; Wong et al.
2005). The Convention is a global treaty to protect human health and the environment
from POPs. These chemicals are difficult to degrade into less hazardous substances in the
environment. They are lipophilic compounds that tend to bioaccumulate in fatty tissues
through the food chain.
Dichlorodiphenyltrichloroethane : Dichlorodiphenyltrichloroethane (DDT) is a commercial
organochlorine insecticide that has been widely used on agricultural crops as well as for
vector control (Hui et al. 2008). Technical-grade DDT is a mixture of up to 14 compounds.
The active ingredient is p,p′-DDT (65%-80%). The other compounds include 15%-21%
of o,p′-DDT, up to 4% of p,p′-DDD, and other substances (Wong et al. 2005). DDT can
be degraded to DDD compounds under anaerobic conditions, while it can be degraded
to dichlorodiphenyldichloroethylene (DDE) under aerobic conditions (Chen et al. 2007).
These degradation products are more persistent than the parent compound and are bio-
accumulative, are transported over long ranges, and have adverse effects on humans,
animals, and the environment. DDT has been banned for all uses in 49 countries.
TABLE 17.1
Persistent Organic Pollutants Listed in the Stockholm Convention
Category
Chemical
Organochlorine pesticides
Aldrin, chlordane, dieldrin, DDT, endrin,
heptachlor, hexachlorobenzene (HCB),
mirex, and toxaphene
Industrial chemicals
Hexachlorobenzene and polychlorinated
biphenyls (PCBs)
Unintended by-products
Dioxins and furans
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