Persistent Organic Pollutants (POPs)
Persistence is an important characteristic of the environmental pollutants in an environmental medium (air/ water/ soil) or in a living tissue, in which the pollutants remain active for a longer time in a toxic form through chemical, biological, and photolytic processes.
Persistent organic pollutants (POPs) are organic compounds that, to a varying degree, resist photolytic, biological and chemical degradation.
Due to persistence, the pollutants are capable of long-range transport, bioaccumulation and biomagnification. Most of the POPs include pesticides, Industrial solvents, polyvinyl chloride, and pharmaceuticals. The Other words used are PBTs (Persistent, Bioaccumulative and Toxic) or TOMPs (Toxic Organic Micro Pollutants.)
Common Characters of the POPs
The persistent Organic Pollutants generally have __:
- Low Water solubility
- High lipid solubility: This property leads them to bioaccumulation in animal tissues.
- Semi volatile: The property of their physico-chemical characteristics that permit these compounds to occur either in the vapour phase or adsorbed on atmospheric particles, thereby facilitating their long range transport through the atmosphere
- The POPs with higher Molecular weights are more toxic and more persistent generally.
- Most of the POPs are halogenated and many have Chlorine as a component.
Bio-accumulation, Bio-concentration and Bio-magnification
The above three terms are different with each other.
- Bio-accumulation refers to increase in concentration of a substance in certain tissues of organisms body.
- While Bioaccumulation occurs when an organism absorbs a toxic substance from all sources at a rate greater than that at which the substance is lost. Bioconcentration occurs when an organism absorbs a toxic substance from ONLY Water at a rate greater than that at which the substance is lost.
- Please note that Bioaccumulation and Bioconcentration are synonymous except the difference of the source. Both Bioaccumulation and Bioconcentration occur in the same organism. But Biomagnification occurs across various trophic levels in a food chain.
Biomagnification refers to the is the INCREASE in concentration of the POPs such as DDT, that occurs in a food chain as a consequence of persistence, high lipid solubility and low water solubility. The substances become more and more concentrated in tissues or internal organs as they move up the chain. This is shown in the following picture:
In May 1995, the United Nations Environment Programme Governing Council (GC) started investigations on the POPs. The process began with 12 POPs which were most common at that time. They were called “Dirty Dozen”.
The Dirty Dozen are: Aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and toxaphene. The list enlarged later with inclusion of some more chemicals.
Stockholm Convention on Persistent Organic Pollutants
Stockholm Convention is first ever-concerted global effort on Persistent Organic Pollutants (POP). It was called in 1995 by UNEP. The convention calls to outlaw nine of the dirty dozen chemicals, limit the use of DDT to malaria control, and curtail inadvertent production of dioxins and furans. The convention listed twelve distinct chemicals in three categories in the beginning.
- Eight pesticides (aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene)
- Two industrial chemicals (poly chlorinated biphenyls and hexachlorobenzene)
- Two unintended byproducts (poly chlorinated dibenzo-p-dioxins and dibenzo furans, commonly referred to as dioxins and furans).
Countries are required to make efforts to identify, label and remove PCB-containing equipment by the year 2025, and manage the wastes in an environmentally sound manner, not later than 2028.
The Convention also seeks to continue minimization and, where feasible, ultimate elimination of the releases of unintentionally produced POPs, such as dioxins and furans. Stockpiles and wastes containing POPs must be managed and disposed off in a safe, efficient and environmentally sound manner, taking into account international rules, standards and guidelines. Each Party is required to develop a plan for implementing its obligations under the Convention.
India and Stockholm Convention
India is a party to the Stockholm convention since 2005. The Convention will enable India to participate in the It will also enable India to avail technical and financial assistance for implementing measures to meet the obligations of the Convention.
Stockholm Convention and Endusulphan
Endosulphan belongs to the organochlorine group of pesticides such as DDT. In pure form it exists as colourless crystals, slightly soluble in water, dissolves readily in xylene, chloroform, kerosene and most organic solvents and is a non-combustible solid. It is mixable with most fungicides and compatible with most pesticides
It is used as an organochlorine insecticide and acaricide (killing tickes and mites). It causes endocrine disruption and neurotoxic impacts. It is also supposed to be a genotoxic and may lead to genetic mutation, however, it has not been found to be a carcinogenic. Because of its threats to environment as a POP, it is banned in more than 63 countries but still is widely used.
Currently, a global ban on the use and manufacture of Endosulphan is being considered under the Stockholm Convention. India is the largest user of Endosulphan, and had sought a 10 year remission from ban. However, in 2011, the Supreme Court banned the use of Endosulphan due to some peculiar health impacts seen after aerial spray of in Cashew Plantations in Kerala. The court ordered a complete ban on the manufacture, sale and use of Endosulphan after a PIL had brought to the court’s notice the hazardous effects of the pesticide on human life as well as biodiversity in Kerala, Karnataka and other states.