China has initiated a program to evaluate the ecological impact of the Songhua River water pollution in northeast China and put forward countermeasures, said a senior environmental official said in Beijing Tuesday.

The evaluation program is "an urgent and arduous job" that needs the joint efforts of related departments, said Zhu Guangyao, deputy director general of the State Environmental Protection Administration (SEPA).

More than 100 researchers from 20 institutions such as the Chinese Academy of Environmental Sciences (CAES) and the prestigious Qinghua University have been sent by the State Council, China's cabinet, to Jiamusi, a downstream city of the Songhua River in northeast China's Heilongjiang Province.

The program, initiated by the SEPA, is composed of 14 task forces that have been ordered to prepare plans to deal with issues such as the moving and transformation of pollutants, the absorption of pollutants after freezing, the stagnation of the pollutants, and their impact on the environment, drinking water and fishery security, said Liu Zhengtao, chief researcher of the CAES.

Some work involved in the program, including the calculation of the overall pollution, has been, said Liu, adding that they are mainly using stalks and straws for absorbing pollutants due to the high cost of activated carbon.

"Experiments have proven that stalks and straws contain a large amount of organic carbon and are very good for the absorption of nitrobenzene," he said.

Continuous monitoring has shown that the nitrobenzene density in the Songhua River has dropped by a large margin, said Zhu, also deputy head of the investigation team designated by the State Council to deal with the pollution crisis.

Explosions in a chemical plant on Nov. 13 in Jilin Province spilled a large amount of nitrobenzene into the Songhua River, causing a four-day water cutoff in downstream Harbin, capital of neighboring Heilongjiang.

The SEPA reported Tuesday that the nitrobenzene density has continued to drop at Jiamusi, some 244 km upstream from the city of Tongjiang, where the river joins the Heilongjiang River and flows into Russia.

The investigation team, formed on Dec. 6, is looking into the cause of the blast and how the benzene was discharged into the Songhua River without proper treatment.

It will also find out who should be held accountable for the accidents.

The chemical plant is under the Jilin subsidiary of the China National Petroleum Corporation.