Kolkata most polluted city in India

Kolkata is the most polluted metropolis in the country with its pollution levels recorded highest among eight tropical Asian countries, according to study.

The study, on distribution and identification of source of persistent organic pollutants (POPs) was conducted in eight countries - Laos, Cambodia, Vietnam, Thailand, Philippines, Indonesia, Malaysia, India and Japan.

According to the study, India has highest PAHs (polycyclic aromatic hydrocarbons), a carcinogenic persistent organic pollutants (POPs) as compared to cities of other countries, the research paper published in Marine Pollution Bulletin, an international scientific journal, said.

Among major metropolis in India, Kolkata was found to be the most polluted city with its pollution levels recorded highest among the eight tropical Asian countries, the research paper added.

The research was undertaken by Indian scientist Dr Mahua Saha at Japan-based Tokyo University of Agriculture and Technology.

"In urban areas, the highest PAHs were found in India with an average of 11300 nano grams per gram and the lowest in Malaysia which was 206 nano grams per gram," it said.

According to the researcher, results were alarming for a country like India as its pollution levels were high compared to other tropical Asian countries.

POPs are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes.

"Public concern about contamination by POPs exists due to the multitude of evidence showing the negative effects of POPs on human health and the environment.

Several compounds have been identified as hormone disruptors which can alter normal function of endocrine and reproductive systems in humans and wildlife. Cardiovascular disease, cancer, obesity, and diabetes have also been linked to POPs," she said.

During the nine-year long study, surface sediment samples from 174 locations of eight countries were analysed.

Saha said that after incorporation into the environment, PAHs usually do not dissolve in the water due to its hydrophobic nature.

"That is why it is found to be adsorbed on the solid material due to which the sediments were picked up for analysis," she said.

Combodia recorded second highest levels of PAH with 1760 nano grams per gram PAH content, followed by Vietnam with 1540 nano grams per gram, Philippines 1410 nano grams per gram, Indonesia 1300 nano grams per gram and Thailand with 1120 nano grams per gram.

The research further summed up that out of the eight countries, seven have petrogenic source which means pollution caused by petroleum products.

India is the only country which has pyrogenic that was created due to combustion.

Besides, surface sediment as samples, scientists also worked out on innovative environmental media like plastic resin pellets for measuring PAHs and other POPs.

"We collected the pellet samples. These pellets are found on the beach shores. They are usually spilled over from the ship during the transportation and are very easy to collect, preserved and transport to lab than any other media," Saha said.

The research was carried out under supervision of professor Hideshige Takada of Tokyo University of Agriculture and Technology.