Environment Minister Robert Pickersgill says the National Environment and Planning Agency (NEPA) has determined that methylene chloride was the chemical pollutant in the atmosphere in the vicinity of the Central Sorting Office (CSO) last month.

In a release yesterday afternoon, Pickersgill said the finding was made based on air-quality sampling conducted by NEPA and the Ministry of Health, and analysed by Airzone One Limited in Canada.

"NEPA is continuing the investigation to determine the source of the pollutant," Pickersgill said.

Methylene chloride (or dichloro-methane) is an organic compound used mostly as a solvent.

In its natural form, it is a colourless liquid with an ethereal odour.

The substance caused several people to faint and sickened many others on February 28.

The police reported that around 60 people had to seek medical attention.