About half of those affected, including 19 children, were hospitalized following exposure to the smoke, emergency department spokesman Ihor Krol said. He said their lives were not in danger.
Independent Channel 5 television, without citing sources, reported that 72 people were hospitalized, and some residents and experts questioned the authorities' claims that people the 14 villages in the affected area were out of danger.
Concentrations of phosphorus residue in the air over two of the affected region's 14 villages, Anhelivka and Lisove, remained 23 times higher than normal, the Nature Ministry said early Wednesday.
Later in the day, however, the ministry said concentrations over the villages had decreased dramatically in a matter of hours and were within the range considered safe.
"It has dispersed. We cannot explain processes in nature," said a ministry spokesman who refused to give his name, citing the department's policy.
Zofia Kubrak, a chemistry and toxicology specialist at Lviv Medical University, contended that such a drastic decrease was impossible in light of the weather conditions.
"We have neither wind nor rain in the region. That just couldn't have happened," Kubrak told The Associated Press.
"It is a very serious accident which can have unpredictable consequences for people," she said.
Kubrak said that some people in the Lviv region complained of discomfort in the throat and mouth, which she said were typical symptoms of phosphorus poisoning.
"In our villages, half the population suffered strange headaches, and it was difficult to breathe. People's faces were baked," a red-faced woman identified only as Lyudmila told Channel 5 from a Lviv hospital where she brought her two small grandchildren.
"I was vomiting and had headaches," her granddaughter said.
But Krol said the health threat had dissipated. "The cloud of a toxic gas dispersed and there is no threat for people's lives," he said.
In the immediate aftermath of the accident, residents of the Lviv region were advised to stay inside and not to use water from wells, eat vegetables from their gardens or drink the their cows' milk.
But Deputy Prime Minister Oleksandr Kuzmuk, who traveled to the area, said on television Wednesday that tests showed it was safe to eat vegetables and drink well water.
Maria and Olexiy Moskva, a couple in the village of Ozhydiv, were not so sure.
"We don't wear gas masks, but just in case, we locked our cow in a shed and won't eat our apples or cucumbers," Maria Moskva said on Channel 5.
Emergency workers continued to sprinkle contaminated land with soda and sand.
The train, traveling from Kazakhstan to Poland, derailed near the city of Lviv, not far from the Polish border, and 15 of its 58 cars overturned, Krol said. Six of the tankers caught fire and a cloud of smoke from the burning phosphorous spread over a 90-square kilometer (35-square mile) area.
The highly toxic substance, which can catch fire spontaneously on contact with air at temperatures higher than 40 C (104 F), can cause liver damage if consumed.
Of the 11,000 people living in the contaminated area, 815 were evacuated, Krol said Tuesday. Media reports said that other people had left the villages amid health fears.
Prime Minister Viktor Yanukovych pledged to punish anyone found responsible for the accident.
The accident touched nerves still raw more than two decades after the catastrophe at the Chernobyl nuclear power plant.
Concerns about the government's response and openness linger from the 1986 explosion and fire at the Chernobyl plant in Ukraine, then a Soviet republic.
Moscow kept the world's worst civilian nuclear accident under wraps for days and played down the disaster long afterward.
Kuzmuk on Tuesday compared the disaster to Chernobyl and warned of unpredictable consequences, though he later backtracked on his remark.
Phosphorus compounds are chiefly used in fertilizers, although they are important components of pesticides, toothpaste, detergents as well as explosives and fireworks.
Source: International Herald Tribune