(Image for representational purpose only) A study analysing the distribution of source of persistent organic pollutants (POPs) in eight countries -- Laos Cambodia Vietnam Thailand Philippines Indonesia Malaysia India and Japan-- found that India has highest PAHs (polycyclic aromatic hydrocarbons) a carcinogenic persistent organic pollutants (POPs) as compared to cities of other countries. (Read: Why does pollution cause cough?) The study published in the international scientific journal Marine Pollution Bulletin also revealed that among top metropolitan cities in India Kolkata is the most polluted with its pollution levels recorded highest among the eight tropical Asian countries. (Read: Diwali 2014: Delhi