A train in New Jersey has derailed causing hazardous chemicals to spill, including vinyl chloride.
Short-term exposure to high amounts of that chemical can lead to dizziness, drowsiness and headaches, according to the Environmental Protection Agency.
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The Labour leader did not say whether he would maintain Britain's nuclear deterrent programme.
Ukip leader Paul Nuttall also said he would want to get rid of Sharia courts.
Over 40,000 people picked up their packs to take part in the annual marathon in the capital.