China's environmental watchdog reports that the tail end of the chemical spill in the Songhua River will soon pass Jiamusi some 244 km downstream from the city of Tongjiang, where the river joins the Heilongjiang River and flows into Russia.

The report said measurements of nitrobenzene at Jiamusi at 4 AM Monday were 0.027 mg per litre. Meanwhile at Huachuan the chemical was measured at 0.174 and 0.145 mg per liter at 4 PM and 6 PM on Sunday. Huachuan is 202.8 km downstream from Tongjiang

Nitrobenzene density has been falling as the slick flows downstream due to evaporation and settling, said the State Environmental Protection Administration (SEPA).

The chemical spill is the result of an explosion at an upstream petrochemical plant last month. The SEPA has established 30 monitoring posts along the river.