Thunderstorms over the remnants of the industrial complex have caused experts to raise concerns about further toxic pollution in the Chinese port city. Giant explosions razed the warehouse, killing 114 people.
Rainfall on Tuesday stifled recovery efforts after last week's deadly explosions and exposed Tianjin's population to dangerous chemicals, some of which could be ignited by contact with water.
The warehouse held around 700 tons of highly toxic sodium cyanide, an amount that violates safety rules. Officials fear that the water could further spread the chemicals, and are cleaning up a 1.8 mile (3 kilometer) radius closed to the public.
"We are paying high attention on the rain forecast for the coming couple of days," Bao Jingling, chief engineer at the Tianjin environmental protection bureau, told AFP.
When rain evaporates, there is also a risk that it could also disperse hazardous residues on the ground, which may set off chemical reactions and further explosions.
Hazardous contamination risk
Sodium cyanide is a poisonous white crystal or powder, used in industrial processes such as gold mining, as well as for gas executions in the US. It can create combustible substances when mixed with water.
According to the US Environmental Protection Agency, even exposure to lower concentrations can cause weakness, nausea and eye and skin irritations. Chronic exposure can impact the cardiovascular and central nervous systems.
While officials have declared Tianjin's water and air safe, locals and victims' families are doubtful.
Eight of 40 water testing points, all within the clean up area, showed excess levels of cyanide on Monday, with the highest exceeding 28.4 times official standards, said Bao. The hazardous substance was found at a further 21 points.
The engineer announced the agency would monitor the air at 18 testing points. He emphasized that the public would be immediately warned if excessive levels of cyanide were found.
Deputy national fire chief Niu Hueguang revealed that more than 40 toxic chemicals were being stored at the warehouse with a total volume of about 3,000 tons, as reported on the official website of the China Fire Services.
This number included 800 tons of ammonium nitrate, which can be used in explosives, and about 500 tons of potassium nitrate, used to make rocket fuel and fireworks.
Honoring the fallen
The rain fell as ceremonies were held for the victims of the explosion. By Tuesday, 114 people were dead, 57 were missing, and there were 31 unidentified bodies.
White flowers were laid across the town, the color of mourning in China. This is the first observance in the traditional 49-day mourning period in China. The demise is marked on the seventh day after the death, including the day of the event.
Firefighters were hard hit by the disaster, with 50 confirmed dead and another 52 missing. This is the deadliest episode for first responders in China's history. Around 1,000 responded to the blasts.
"There were many firefighters who went into the blast and sacrificed themselves," said Fan Jie, a mourner lighting candles for firefighters killed in the blaze. "So we're here today for them, to give thanks to them and grieve for them."
China is now investigating its chief of the State Administration of Work Safety, the ruling Communist Party announced on Tuesday. Yang Dongliang is "currently undergoing investigation" for suspected violations of party discipline and the law, the Central Commission for Discipline Inspection said in a statement on its website. It is one of the government agencies responsible for regulating companies that work with dangerous materials.
The Tianjin disaster ranks among the deadliest industrial accidents in China's recent history.