A board at Central MTR station still shows air pollution data. Photo: Sam Tsang

Hazardous level of trace metals in Hong Kong’s air as scientists warn of health crisis

Scientists warn of potential public health crisis, with Chinese breathing in up to 20 times the amount of dangerous particles found in the US

The air in China contains 10 to 20 times more fine metallic particles than in the United States, according to scientists studying samples of air pollutants collected across the country, including Hong Kong.

The city's overall PM2.5 levels are lower than in most urban centres on the mainland, but it has a higher concentration of health-threatening trace metals, the scientists say.

Nearly 20 per cent of PM2.5 particle samples collected in the city carried metals such as zinc, a hazardous element that can permanently damage DNA.

While public attention is often focused on PM2.5 levels, scientists are more concerned with the particles' composition.

PM2.5 particles, the smallest measured, lodge deep inside lungs and are the most dangerous to human health.

Several teams of scientists have studied smog in China - including Hong Kong - and at least two detected heavy concentrations of trace metals. Excessive amounts of zinc and chromium are toxic and can lead to a wide range of problems, from premature ageing to cancer.

In extreme cases, high concentrations of airborne trace metals can even damage human DNA, heightening the risk of genetic conditions that can be passed on to future generations.

Scientists warn that without tighter environmental regulations, high trace metal levels could lead to a public health crisis.

Li Weijun , a professor of environmental science at Shandong University in Jinan , said: "While the general level of PM2.5 in China is five or six times higher than the US, the amount of trace metals could be 10 or even 20 times higher."

Since 2003, Li and his team have studied nearly every corner of China, from the grasslands of Inner Mongolia to Hong Kong's Victoria Peak, collecting samples and examining them under powerful electron microscopes.

They have built what is probably the largest data bank of airborne particles in China.

"Damage to health caused by fine particulates is not only determined by the quantity of particles, but also what type they are," Li said.

"Trace metals are the nastiest things in the air that can damage your health."

He said most of the PM2.5 pollution in Hong Kong could have come from power plants and factories in the Pearl River Delta.

"As long as you have a large number of factories in your neighbourhood, you will have the problem. But even the most advanced technology cannot remove these extremely small particles," he said.

In a research paper published last year in the academic journal Li's team found 105 micrograms of iron per litre of water in cloud on Mount Tai in Shandong and 90mcg on Mount Lu in Jiangxi . Similar samples gathered from Mount Elden in Arizona, in the US, contained only 5.6mcg.

Zinc concentrations were even greater in China, with 200-250mcg found on the two Chinese mountains, but no trace of the metal on Mount Elden.

Li said other metals or hazardous elements found in China's air included copper, magnesium, lithium, nickel, cobalt, arsenic and selenium. When mixed with water, zinc can enter human cells in the bloodstream or tissue.

With the help of oxygen, zinc can damage the structure of the DNA inside cells. Healthy cells have effective responses to repair most DNA damage. But certain damage, such as that caused by some trace metals, is irreversible.

Li said the findings show China is in urgent need of tighter and more effective environmental regulations. An air pollution researcher at the Chinese Academy of Sciences agreed, adding that the current situation could lead to a health crisis in the coming decades.

"Today the public is only warned about general PM2.5 levels. But people should know what these particles contain, and how they have very different health implications," said the researcher who refused to be named.

Sheng Zhiguo , a toxicologist at the State Key Laboratory of Environmental Chemistry and Ecotoxicology in Beijing, said certain medicines could lower the risk of irreparable DNA damage by slowing down the oxidisation process. But the scientists' concern was not limited to the present generation, he said.

"There are many discussions among the Chinese research community these days about the possible health impacts of smog.

"Some researchers fear that some genetic damage will be passed down to the next generations, and it will be difficult in a few decades from now to trace where they came from," Sheng said.

"We are facing probably the most sophisticated forms of air pollutants in history, but we still don't have many clues about their exact impact on our heath."


This article appeared in the South China Morning Post print edition as: Hazardous level of trace metals in China's air