Pollution levels in the Harbin section of the Songhua River fell slightly yesterday, one day after a toxic spill from a Jilin petrochemical factory started passing through the city. The State Environmental Protection Administration said nitrobenzene levels in the contaminated Harbin section of the river peaked at 33 times the safe limit late on Thursday night. About 7am yesterday, nitrobenzene levels had dropped to 28 times the safe limit, Xinhua reported. The readings were taken at Sujiatun, about 16km upstream from Harbin's water-collection point. Benzene levels at Sujiatun were within safe limits, said Xinhua, adding that the 80km spill was expected to take 40 hours to pass through the city. Repeated exposure to high concentrations of nitrobenzene can reduce the blood's ability to carry oxygen and may induce nausea, vomiting, and shortness of breath. The spill of more than 100 tonnes of toxic chemicals is expected to reach Jiamusi , a city of about 2.44 million people, in a week, Xinhua reported. But Jiamusi relies on groundwater for its drinking supplies, according to China Central Television. Xinhua quoted the Ministry of Water Resources as saying it was dealing with the crisis by increasing the flow from reservoirs to dilute the pollutants, stepping up monitoring, sending extra teams to Heilongjiang, and keeping neighbouring Russia notified. Meanwhile, thousands of tonnes of activated carbon have reached Harbin to help filter its water when mains supplies resume.