BANGKOK • Bangkok's air is full of toxic heavy metals, researchers have discovered, and it is contributing to year-round hazardous threats to public health.

The director of the Centre for Research and Development of Disaster Prevention and Management at Thailand's National Institute of Development Administration on Thursday called on the Thai authorities to set out standards for controlling the emissions of every hazardous heavy metal found in the air.

Dr Siwatt Pongpiachan said his studies have found that Bangkok air contains harmful levels of cadmium, tungsten, arsenic and polycyclic aromatic hydrocarbons (PAHs).

His two academic studies of the Thai capital city's air pollution revealed that within the very fine PM2.5 dust particles were at least 51 kinds of heavy metals, of which three - cadmium, tungsten and arsenic - were found at unsafe levels, according to World Health Organisation standards.

"Right now, Thailand has set a safe emission standard only for lead. Even though we have detected lead in the air, its concentration is still within the safe level, thanks to the authorities' measures to get rid of lead from vehicle fuels and control the emissions of lead into the environment," he said.

"We need a similar set of safe-emission standards for other kinds of heavy metals as many of these hazardous substances present very serious threats to human health in both the short and long term."

Studies conducted by environmental group Greenpeace have also noted another health threat from the toxic heavy metals found within PM2.5 particles.

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The studies found that PM2.5 dust particles are contaminated with toxic environmental substances. The tiny particles - it takes three of them to equal the width of a human hair - can pass through the body's dust protection system found in the respiratory tract, enter the bloodstream and reach the internal organs, delivering the toxic particles directly into humans.

Dr Siwatt said the studies found that levels of these airborne toxic substances did not change much from week to week throughout the year, indicating that the majority of pollution sources were from local areas of Bangkok.

"Even though weather patterns during this time of the year and the transboundary haze are partially contributing to the serious smog problem, the research studies indicate that the exhaust from traffic, factories and crematoriums are the true major sources of air pollution in Bangkok," he said.

He noted that the transport sector emits pollution in many ways, as the incomplete burning of fuel in the vehicles, especially those that use diesel fuel, emits a large amount of PAH.

These PAHs can cause cancer, while the city's traffic congestion also causes the level of tungsten in the air to rise significantly as drivers apply their car brakes - the heavy metal serves as a brake lining. Tungsten-contaminated PM2.5 are thus released into the air.

Meanwhile, cremation is a major source of air pollution and heavy metals, Dr Siwatt said.

Many parts of the human body, such as prostheses and tooth fillings, contain heavy metals and they are released into the environment during cremation.

"There are so many temples in Bangkok that cremate human bodies every day. Even though many of these temples' crematoriums have pollution filtering systems installed, not 100 per cent of heavy metals are filtered," he said.

THE NATION/ASIA NEWS NETWORK