“Contrary to what was feared, no critical levels of dioxin and PCBs have been found,” Ulrich Quass of the environment department in North
Rhine-Westphalia told a press conference.
More detailed analyses are still under way, with the results expected next week, officials said.
Three people are confirmed to have died in the explosion on Tuesday at the Chempark complex in the city of Leverkusen, with two still missing but presumed dead.
The blast at a waste incineration site, which was heard several kilometres away and rattled the windows of nearby homes, sent a cloud of black smoke into the air.
It also triggered a fire in storage tanks for solvents that took firefighters hours to put out.
Police closed several motorways in the area and residents were told to stay indoors and shut their windows over concerns dangerous gases may have been released.
Officials on Friday warned residents to continue to avoid eating fruit and vegetables from their gardens and to keep children away from the city’s playgrounds.
“We do not yet know how long these measures will last because they depend on the progress of the investigation,” Quass said.
The cause of the explosion, which also injured 31 people, remains unknown.
The area where the blast happened, in Leverkusen’s Buerrig district, is a short distance away from Chempark’s main industrial park that houses numerous chemical companies including Bayer, Lanxess and Evonik Industries.
Police in nearby Cologne said Wednesday they are investigating unknown persons on suspicion of involuntary manslaughter and causing an explosion through negligence.