久久亚洲国产成人影院-久久亚洲国产的中文-久久亚洲国产高清-久久亚洲国产精品-亚洲图片偷拍自拍-亚洲图色视频

Almost overnight, blue-green algae went from a little-known laboratory research topic to a national concern. The organism first bloomed last month, spoiling drinking water in Wuxi, East China's Jiangsu Province, creating a serious local health threat.

And while that crisis is yet to die down, the promulgation of a new standard for drinking water again focuses attention on the dangerous algae.

From July 1, microcystins, a type of natural toxin produced by blue-green algae, were added to a new list of water testing indicators. Water and aquatic products contaminated by microcystins are imminent perils to human health, scientists warn.

They say before the Wuxi water crisis, the Taihu Lake where blue-green algae bloom broke out had been long contaminated by microcystins.

The Taihu Lake is the third largest freshwater lake in China and located in the highly developed and densely populated Yangtze River Delta. In recent years, the lake has become increasingly polluted, with frequent and intense blue-green algae bloom in warm seasons.

On May 29, international academic journal Water Research published an article by Chinese scientists, warning that the Meiliang Bay of Taihu Lake was jeopardizing human health as an unsafe source of drinking water.

Dr Song Lirong at the Institute of Hydrobiology in Chinese Academy of Sciences (CAS), the paper's leading author, says: "During the season of algae bloom, water administration should frequent the monitoring of microcystins."

Song and his colleagues investigated distribution of microcystins in the Meiliang Bay between February 2005 and January 2006, and found the number of dissolved microcystins in most samples were several times higher than the standard recommended by the World Health Organization (WHO) guideline.

"Based on our finding, the lake currently is losing the original function as an important natural resource and natural filtering system," the authors wrote.

Another research team led by Dr Xie Ping at the Institute of Hydrobiology has also published similarly alarming findings over the past two years. Their research showed that many creatures in the Taihu Lake and Chaohu Lake, another large freshwater lake in East China, were seriously contaminated by microcystins. The affected aquatic life included Crucian carp, shrimps, snails and mussels.

Blue-green algae blooms containing microcystins are a problem worldwide, including in China, Australia, the United States and much of Europe.

Once ingested, microcystin travels to the liver, via the bile acid transport system, where most is stored though some remains in the blood stream and may contaminate tissue. Microcystin binds covalently to protein phosphatases thus disrupting cellular control processes.

The potential threat of microcystins aroused the attention of Chinese scientists more than two decades ago, when Professor Yu Shunzhang, former dean with the Public Health School of Fudan University, and his colleagues discovered that microcystins were rich in some pond ditches in Southeast China, which might be one of the factors causing a high incidence of liver cancer among local people.

"Our research initially suggests that microcystins are potentially carcinogenic. Of course, more research is needed on this aspect," says Yu.

The research team also conducted an epidemiological study in Taixing and Liyang, two cities in Jiangsu Province. They found local elementary students who drank from pond ditches were more likely to display abnormal liver performance than those who drank deep well water or tap water. "It implies that microcystins can cause liver damage," Yu says.

According to Xie, biological toxins like microcystins are more difficult to eliminate than many organic pollution.

"I'm afraid that water eutrophication will become more and more serious across China. As long as there were blue-green algae blooms, microcystins would be released continually," Xie says.

Neither regular water treatment technology nor water boiling can eliminate microcystins effectively. Studies show that microcystins can still be active even in temperatures of 300 C. Yu says activated carbon could remove more than 95 percent of microcystins in drinking water.

Some experts called for better monitoring and safety assessment on microcystins in drinking water and aquatic products in China.

To reduce risks of microcystins, the WHO published guidelines in 1998 for permitted maximum concentration of microcystins in drinking water.

China's newest drinking water standard issued by the National Standard Committee and the Ministry of Health this month stipulates a standard for microcystins consistent with the WHO guideline. That is, one microgram of microcystins per liter of water. But notably, microcystin is not an obligatory indicator in this new standard.

Yu, who was the only Chinese expert involved in compiling the WHO guidelines, says it is already known that microcystins disperse in aquatic products in many areas.

He recommends investigation into the distribution of microcystins in different aquatic products of different water areas. "Then we should evaluate the health risks," Yu says.

Xie calls for wider monitoring of aquatic products. "We should follow what we have done to standardize drinking water to establish a microcystin monitoring and assessment system for major aquatic products," he says.

"Only with this, we can learn what kinds of aquatic products are unsafe under the condition of eutrophication, and transmit the information to the public."

Xie adds that in China, freshwater products account for as much as 40 to 50 percent of all aquatic products. "In this case, there is a high possibility that microcystins will affect safety of aquatic food and health of Chinese people," he says.

But the scientists also say the public should not panic.

Song says algae blooms may also be caused by some nonpoisonous algae. And even where water contains high concentration of microcystins, some extensive water treatment measures can solve the problem.

In addition, only by consuming a large quantity of contaminated aquatic products over a long period of time can people damage their health.

(China Daily 07/04/2007 page19)