Residents living within a 2-5 kilometre radius of the burned-out Ming Dih Chemical Co factory in Bang Phli district of Samut Prakan have been allowed to return home after the Pollution Control Department (PCD) confirmed air quality in the area was at a safe level.
Provincial governor Wanchai Kongkasem said on Wednesday that all areas within that radius of the factory had been examined to ensure safety for when people returned.
The management team handling residual chemicals that contaminated an area 1km in radius immediately around the factory is also in talks with the provincial command centre, PCD, Department of Disaster Prevention and Mitigation (DDPM) and Oil and petrol giant PTT.
Mr Wanchai said they voiced concern over residual amounts of the industrial chemical, styrene monomer, in 2,000-tonne tanks that have yet to be cleared following the blaze. The residual chemical in surrounding areas must also be dealt with, he added.
Since the fire, the PCD has been working with the Ministry of Natural Resources and Environment to assess the impact on the environment. Since the contaminated water can be absorbed into the soil, Environment Minister Varawut Silpa-archa instructed the Department of Groundwater Resources to expedite quality checks on water sources both above ground and underground within a 12km radius of the factory.
Mr Varawut also said the PCD and provincial governor were in talks to determine whether to use organic peroxide to spray the styrene to prevent further fires.
Meanwhile, in a move to curb water contamination, the Office of National Water Resources secretary-general Somkiat Prajamwong said the Royal Irrigation Department would be instructed to close all floodgates in canals in adjacent areas to prevent widespread impacts. The PCD would also follow up with checks on water quality until the situation improves, he said.
Meanwhile, environmental expert Sonthi Kotchawat urged agencies to act quickly to contain the contamination, as the spread of styrene monomer in the environment is highly toxic to both humans and ecosystems.
Mr Sonthi warned that the major environmental concern, apart from health hazards caused by air pollution, is the contamination by toxic chemicals of surface water sources and groundwater.
When it rains, he said, rainwater will wash leaked chemicals from the burnt factory site as well as other fire-extinguishing agents into nearby canals. The rain will also mix with pollutants in the air, causing acid rain. This can contaminate wider areas beyond the factory site, with chemicals seeping into groundwater sources, and rendering them unusable.
"Styrene is a hazardous substance. It can destroy the ecosystem and cause cancer, so the PCD needs to act quickly to decontaminate the area," he said.