Masks, gloves and other shields used by people who have not tested positive for Covid-19 or are not home quarantined should be kept aside for 72 hours and then thrown with other waste, a guideline by the Central Pollution Control Board in April says.

The Telegraph reported on Friday that the shields used by people who have not tested positive but could be asymptomatic carriers of the coronavirus were being thrown away with other waste materials every morning, putting garbage collectors and rag pickers at risk of contracting Covid-19.

Waste disposal experts are blaming improper disposal of Covid-19 gear to the absence of waste segregation at source in Calcutta.

A scientist with the central pollution board said on Friday that people should be careful not to throw masks and gloves before three days of last use. “We issued a guideline on what people who are not patients or home quarantined contacts of patients should do,” said the scientist.

“Used masks and gloves generated from... households should be kept in a paper bag for a minimum of 72 hours prior to disposal of the same as general waste,” states the central board’s guideline issued in April. “It is advisable to cut the mask prior to disposal to prevent reuse.”

The scientist said the 72-hour period was mentioned based on a study that the virus - SARS-CoV-2 - cannot survive on the material used for making single-use surgical masks for more than 72 hours.

Sourabh Manuja, a fellow at the Centre for Waste Management at The Energy and Resources Institute (TERI), said the study was published in the New England Journal of Medicine. “It said that the virus lives on plastic and stainless steel for 72 hours. The single-use surgical masks are made of polypropylene, which is a type of plastic. That is why one should not dispose of a mask at least 72 hours before the last use.”

“Latex gloves and face shields, too, are made of plastic. They should also be disposed of after 72 hours.”

Shahid Jameel, the CEO of DBT-Wellcome Trust India Alliance, said people should use cloth masks that can be washed and reused.

“In any case, a single-use mask will only add to the volume of waste. There cannot be a guideline for everything. People should apply their mind and use reusable cloth masks,” he said.

Jameel’s organisation works in biomedical, clinical and public health research and is funded by the Centre’s department of biotechnology and the Wellcome Trust of the UK.

Another waste management specialist said that before disposing, the mask should be kept aside in a safe place and not touched by anyone.