Persistent Organic Pollutants (POPs), Chlorinated Hydrocarbons (Organochlorides)

Persistent Organic Pollutants (POPs)

• POPs are defined as “chemical substances that persist in the environment, bioaccumulate through the food web, & pose a risk of causing adverse effects to human health & the environment”.
• Persistent organic pollutants (POPs) are chemicals of global concern due to their potential for:
  • long-range transport,
  • persistence in the environment,
  • ability to bio-magnify & bio-accumulate in ecosystems,
  • Have significant negative effects on human health & the environment.
• The most commonly encountered POPs are organochlorine pesticides, such as
  • Dichlorodiphenyltrichloroethane (DDT),
  • Endosulfan,
  • Polychlorinated biphenyls (PCB: resistant to extreme temperature & pressure. PCBs were used widely in electrical equipment like capacitors & transformers),
  • Dioxins (toxic by-products produced when organic matter is burned), etc.
• DDT was widely used a few decades ago as an effective pesticide & insecticide.
• It was later identified as POP, & its usage was phased out in almost all developed countries.
• DDT is banned for agricultural use in India; however, it continues to be used for fumigation against mosquitoes (disease vector control) in several places in India In India.

Stockholm Convention on Persistent Organic Pollutants

• It is an international environmental treaty.
• It came into effect in 2004.
• It aims to eliminate or restrict the production & use of persistent organic pollutants (POPs).

Chlorinated Hydrocarbons (Organochlorides)

• CHCs are hydrocarbons in which one or more hydrogen atoms have been replaced by chlorine E.g., DDT (dichlorodiphenyltrichloroethane), endosulfan, chloroform, carbon tetrachloride, etc.

Applications of Chlorinated Hydrocarbons (CHC)

• CHCs are used in the production of polyvinyl chloride (a synthetic plastic polymer used to make PVC pipes).
• Chloroform, dichloromethane, dichloroethane, & trichloroethane are useful solvents.
• These solvents are immiscible with water (not forming a homogeneous mixture when mixed with water) & effective in cleaning applications such as degreasing & dry cleaning.
• DDT, heptachlor & endosulfan are were widely used as pesticides.

Effects of Chlorinated Hydrocarbons (CHC)

• DDT accumulated in food chains & caused eggshell thinning in certain bird species.
• In India, traces of DDT spray used three decades ago can still be found on the walls of homes.
• DDT residues continue to be found in mammals across the planet.
• In Arctic areas, particularly high levels are found in marine mammals.
• The traces of persistent organic pollutant are found in the breast milk of several mammals.
• In females, the concentration is lower due to the transfer of the compounds to their offspring through lactation.