The World Health Organization (WHO) has named mercury and lead in the list of top 10 most dangerous chemicals. Mercury is known to poison fish as well as those who eat them and it has been found that exposure to the chemical can cause death, the WHO has said. Children can develop neurological and behavioural disorders on inhalation and ingestion of mercury or a dermal exposure. Lead, meanwhile, can cause long-term harm in adults by increasing blood pressure and leading to kidney damage. It can also result in poor brain development and nervous system among young children.

The WHO has said that these chemicals are unsuitable for use, especially in crowded urban areas or in regions close to water bodies like the sea.

Sulphur, another common chemical in firecrackers, reacts with water to produce sulphuric acid, which is a harmful pollutant.

"Other than the noise that the crackers produce, triggering problems like annoyance, hypertension and stress, the chemicals in them cause huge air pollution. The chemicals react with air to form harmful gases, which deposit on soil, thus entering the crops we consume. Air pollution, particularly associated with large fireworks display, cannot be ignored. Emissions of respirable fine particles are at the level of injury to sensitive persons. If there is no rain or wind, these gases take longer time to clear," warn activists.

"This is shocking and a matter of concern. The public should be aware and mustn't buy crackers that have high contents of lead, mercury and sulphur as it will be harmful for them and their young ones. I request the government to look into this matter and take legal actions," said Sumaira Abdulali, convener of Awaaz Foundation.

"The harmful chemicals in fire crackers become oxides. Like nitrogen becomes nitrogen oxide, sulphur becomes sulphur oxide and so on; these are unhealthy pollutants that lead to itching of eyes, breathing congestion and severe throat pain," said G D Yadav, vice-chancellor of Institute of Chemical Technology.