By: Shankar dev
Basic info: (if you know these concepts you may skip)
Toxins enters the foodchain in two successive and interlinked phenomenon, which are
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost.
Biomagnification, is the increase in concentration of a substance that occurs in a food chain as we move over various trophic levels. Let uss see both the phenomenon in detail, (you may skip if you know this already). The trophic level of an organism is the position it occupies in a food chain.
- Level 1: Plants and algae make their own food and are called primary producers.
- Level 2: Herbivores eat plants and are called primary consumers.
- Level 3: Carnivores which eat herbivores are called secondary consumers.
- Level 4: Carnivores which eat other carnivores are called tertiary consumers.
For understanding the concept lets assume a hypothetical village, which has only the following
- 100 insects/worms/grasshoppers
- 10 cocks/hens
- 1 man
The man owns some land in which he cultivate rice. He uses 100kgs of DDT on his crops. Now while insects feed on the crops it consumes DDT along with crops. So lets have like this 100 insects consumed 100kgs of DDT, therefore 1 insect have consumed about 1kg.
Now the man’s 10 hen will eat all the 100 insects. As per logic by now, each hen should have 10kgs of DDT in their body. End of the day the man- tertiary consumer eats all his 10 chicks. So one chick=10kg, so 10 chick= 100kgs of DDT. By now the man should posses 100kg of DDT in his body. (catch the concept, forget all the logic).
We may notice that as we move up in trophic level (insect -> chicks->men), the volume of DDT per individual also increases. This phenomenon is called Bio-magnification. Bio-magnification occurs as a result of Bio-accumulation.. Now lets see what are POPs.
Persistent organic pollutants :
Persistent organic pollutants (POPs) are set of organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Due this resistance, they have been observed to persist in the environment, being capable of long-range transport, through Bio-accumulation and Bio-magnification and to have potential significant impacts on human health and the environment.
POPs circulate globally and chemicals released in one part of the world can be deposited at far distances from their original source through a repeated process of evaporation and deposition. This makes it very hard to trace the original source of the chemical.
POPs are highly toxic and exposure can take place through food habits, environmental exposure, or accidents. They negatively affect humans, plant and animal species and natural ecosystems. POPs are lipophilic (fat-loving), which means that they accumulate in the fatty tissue of living animals and human beings . In fatty tissue, the concentrations can become multiplied manifold times by up to
70 000 times higher than the background levels. As you move up the food chain, concentrations of POPs tend to increase so that animals at the top of the food chain such as fish, predatory birds, mammals, and humans tend to have the greatest concentrations of these chemicals = Bio-Magnification.
Exposure to POPs in humans can cause several negative health effects including
- Developmental changes
- Damage to the central and peripheral nervous systems
- Disruption of the endocrine, reproductive, and immune systems
- Other blood related disorders.
According to the U.S Environmental Protection Agency (EPA) there are links between POPs exposure and the increased frequency of diseases and/or abnormalities in wildlife species, including certain kinds of fish, birds, and mammals . The negative effects of pesticides in the marine and coastal environments include changes in reef community structure, such as decreases in live coral cover , damage to seagrass beds etc.
International Action on POPs
In 1995. the United Nations Environment Programme expanded its research and investigation on POPs with main focus on “Dirty Dozen”. These were a group of 12 highly persistent and toxic chemicals: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachlorobenzen, mirex, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and toxaphen. Many of the pesticides in this group are no longer used for agricultural purposes but a few continue to be used in developing countries.
There are also a number of International Conventions dealing with POPs :
Aarhus Protocol on Persistent Organic Pollutants: Was signed on 1998 in Aarhus,Denmark.. It is an addition to the 1979 Geneva Convention on Long-Range Transboundary Air Pollution (LRTAP).
The POPs covered under the Convention and the Protocol can be sub-divided into three main categories:-
1. Pesticides e.g. DDT
2. Industrial Chemicals e.g. Polychlorinated biphenyls (PCBs)
3. Unintentional by products e.g. Dioxins, furans
The Protocol and Convention establish strict international controls on production and use of intentionally produced POPs, export and import. It has 36 signatories but India is not a signatory.
Stockholm Convention on Persistent Organic Pollutants (POPs).: it Aims to reduce releases of POPs chemicals on a global basis. The convention entered into force on May 17th, 2004. the convention requires Parties to take measures to eliminate or reduce the release of POPs into the environment. The Convention is administered by the United Nations Environment Programme and is based in Geneva, Switzerland.
Rotterdam Convention on the Prior Informed Consent (PIC) : it lays a procedure for transport and trade of certain hazardous chemicals and pesticides . Aims to promote shared responsibilities in relation to importation of hazardous chemicals and contribute safe use. The Convention entered into force on 24 February 2004.
The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal. Aims to protect human health and the environment against the adverse effects resulting from the generation, management, transboundary movements and disposal of hazardous and other wastes. It has 170 Parties and came into force in 1992.
Convention on Long-Range Transboundary Air Pollutants (LRTAP), Protocol on Persistent Organic Pollutants (POPs). The aim of the Convention is that Parties shall endeavor to limit and, as far as possible, gradually reduce and prevent air pollution including long-range transboundary air pollution. The aim of the protocol on POPs is to control, reduce, or eliminate discharges, emissions, and losses of persistent organic pollutants. The protocol entered into force on 23 October 2003.
Globally Harmonized System (GHS) for Classification and Labelling of Chemicals. Is a Globally Harmonized System (GHS) of Classification and Labelling of Chemicals promoting standard criteria for classifying chemicals according to their health, physical and environmental hazards.
International Convention on the Control of Harmful Anti-fouling Systems on Ships. Aim to prohibit the use of harmful organotins in anti-fouling paints. Will enter into force on 17 September 2008.
The Vienna Convention for the Protection of the Ozone Layer & The Montreal Protocol on Substances that Deplete the Ozone Layer. Aims protect the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion. Entered into force on January 1, 1989.