Biodegradation of organochlorine insecticide DDT

概要

1.1 Persistence Organic pollutants (POPs)
POPs are chemical pollutants that can persist in the environment for a long time, and this allows them to move into the
water, soil, sediment, and air, which enables them to accumulate to a point that is harmful to wildlife and human health.
These chemical pollutants are referred as persistent organic pollutants (POPs) (El-Shahawi et al., 2010). These pollutants
are organic compounds that are natural or anthropogenic chemicals that compose a combination of chemical and physical
properties such that, as soon as they are released into the environment, they remain as a whole for a long period of time,
since they are capable of withstanding chemical, photolytic and biological degradation (Buccini, 2006; El-Shahawi et al.,
2010) Compounds of this nature are highly resistant to degradation by biological photolytic and/or chemical means.
Recently, POPs have been a cause of concern because of their toxicity and tendency to accumulate in food chains. The
environmental impact is now more important than the total metal concentration.
The carbon–chlorine bond is very stable regarding hydrolysis and the more chlorine and/or functional groups present
the higher the resistance to photolytic and biological degradation. Since POPs disintegrate very slowly, there is a tendency
to be highly present in the environment for a long time, even if all emerging sources were eliminated immediately (ElShahawi et al., 2010; Satish et al., 2017). In the environment, POPs can be transported at low concentrations by moving
through fresh and marine waters. Since they are semi-volatile, they can be transported over long space in the atmosphere.
As a result of this action, there is a widespread distribution of POPs globally, which also involves regions where POPs have
never been in the application (El-Shahawi et al., 2010). It was so surprising to many people to see the high level of POPs
in the Arctic region of Alaska, because some of these pollutants have been prohibited from the United States and Canada
for many years. POPs move toward cold areas like Alaska and then sink because of the colder temperature. The
contaminants that is settled in this environment remain in place for a long period of time because the temperature does not
allow them to break down very easily. Due to this reason, they can transport through the air and water they finally deposited
into the soil and plants, making it easier to pass down to animals and humans. The persistence of these contaminants in the
Arctic region from very far sources first came to play in the late 1970s when pesticides were noticed in the polar bear fat
tissue, then later the presence of POPs in the atmosphere, their effect on wildlife and human health-a famous story in the
Arctic (El-Shahawi et al., 2010; Jacob, 2013). Thousands of POPs are derived from a particular member or family of
chemicals, for example, there are conceptually 209 polychlorinated biphenyls, which are different from each other based on
the chlorination and the position of the chlorine. As mentioned earlier POPs persist in the environment and they have long
lives in which they stay for a long time in the air, soil, and sediments. There hasn’t been any agreement among the
professionals on the meaning of persistence, how long the half-lives in a particular media are, or how it will take a pollutant
to exist in the environment before it can be named a “persistent” compound. Nevertheless, in practice, POPs can be
categorized among the compounds that could have a half-life of years or decades in the environment for a long period of
time (Gioia et al., 2007; Paknikar et al., 2005). POPs are fat-loving and water-hating chemicals, meaning they are lipophilic
and hydrophobic. These compounds tend to partition in solid state notable organic matter, which avoids the aqueous phase.
While in the organism, they partition into lipids rather than moving into the aqueous milieu of cells, and they become stored
in fatty tissue. POPs tend to enter into the gas phase under environmental temperatures. Therefore, they can volatilize from
soils, vegetation, and water bodies into the atmosphere. Since they are resistant to breakdown, reactions in the air travel a
long distance before it is being re-deposited. The pattern of Volatilization and deposition can be repeated many times,
leading to the fact that POPs could get accumulated in an area that is very far from where it is been used or released. POPs
can make a partition between particles and aerosols which depend on the physio-chemical properties of the chemical and
ambient temperature. The properties of POPs, which are stable and tend to form a gas under appropriate environmental
conditions, means that they are subjected to long-range atmospheric transport. The amalgamation of lipophilicity and
resistance to metabolism means that POPs have a higher propensity to accumulate in the food chain (X. ...

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