One of the major challenges that the newly independent India faced was addressing the country’s public health issues. Malaria and other vector-borne diseases possessed a serious threat to public health.
To control insect pests and curb the spreading of such diseases, Dichloro Diphenyl Trichloroethane (DDT) was introduced in India in 1948. DDT soon gained immense popularity in India and was used widely in pest control, including in agriculture. However, in 1989, India banned the use of DDT in agriculture owing to credible scientific evidence of its harmful effects on health and environment. But it is used for pest control even today. In fact, in 2015, India, at the Stockholm Convention on Persistent Organic Pollutants (POPs) in Geneva, strongly opposed a deadline on a worldwide ban on pesticide DDT by 2020.
But why is DDT harmful?
DDT is a Class II insecticide, meaning it is moderately toxic. Studies have proved that DDT has serious implications on human and animal health. Low-to-moderate exposure (10mg/kg) may result in nausea, diarrhoea and irritation of eyes, nose or throat, while higher doses (16mg/kg) can lead to tremors and convulsions. It can even cause chromosomal damages in some cases.
Moreover, because of its non-biodegradable character, it can remain in soil or water for many years leading to a very dangerous and concerning process – biomagnification.
Biomagnification happens when toxic chemicals, like DDT, whose remains in the environment are consumed indirectly by organisms through food. When an organism in the higher food chain consumes the lower organism containing such chemicals, the chemicals can get accumulated in the higher organism. In other words, it travels through the food chain harming every single stratum. The concentration of these toxins or chemicals increases through the trophic levels of the food chain.
DDT and Biomagnification Credit: ResearchGate
K. G. Drouillard’s Encylopedia of Ecology defines biomagnification as “the condition where the chemical concentration in an organism exceeds the concentration of its food when the major exposure route occurs from the organism’s diet.”
Biomagnification Credit: Biology Junction
Biomagnification happens in all ecosystems and food chains. In aquatic ecosystems, toxins get consumed by smaller species like zooplankton, which are in turn consumed by smaller fishes. The toxins then travel through larger fishes and to humans and birds, in such a way that it affects every trophic level. These toxins, like DDT, which enter the animal or the human body through the food chain can get deposited as adipose tissues, which when oxidised, release the toxins into the body.
People often confuse biomagnification with another associated term, ‘bioaccumulation,’ and even use it interchangeably. But it is important to differentiate between the two. According to Biology Junction, an online biology magazine, ‘biological magnification specifically refers to increasing concentration of materials in each higher link in the food chain. However, bioaccumulation examines the increased presence of a particular substance inside a single organism.’
Bioaccumulation Credit: WWF
According to the Environmental Protection Agency of the United States, bioaccumulation occurs at the base of a food web, usually within primary producers like phytoplankton. These photosynthetic organisms absorb man-made chemicals called ‘Persistent Organic Pollutants’ (POPs), directly from the seawater and accumulate them in their bodies. The absorbed toxins build up in their tissues at a rate faster than they can be metabolised.
What causes biomagnification?
Even though biomagnification is a natural phenomenon, the condition is exacerbated by rapid anthropological activities like agriculture, mining and industrial activities.
Chemicals present in manures, beauty products, and cleaning products such as soap, can escape into the food chain and have an adverse impact on the health of humans and wildlife. According to Biology Junction, ‘Organic elements like phosphorus, nitrogen, and carbon are necessary for survival, but if they appear in excessive quantities in ecosystems, they may cause eutrophication.’
Eutrophication is a phenomenon when an organism that thrives in these conditions experiences exponential growth and suddenly has an overwhelming population. This can then lead to the disruption of its ecosystem, due to extreme competition for the available resources.
Agriculture and industrial activities
Industries and agriculture release toxic substances that are absorbed by the soil, lakes, oceans and rivers. This can include inorganic pesticides, fungicides, fertilizers and other toxic industrial waste.
Mining activities are responsible for the deposition of heavy metals like zinc or cobalt which pollute aquatic plants and contaminate water sources. Mining also generates large amounts of selenium and sulphide, which get deposited in water and adversely affect oceanic ecosystems and coastal regions.
Article by Gokul G. K.