PARIS — Construction resumed at the Notre-Dame cathedral in Paris on Monday, weeks after authorities had shut the site down over worries about lead contamination linked to the fire in April.

The work restarted with stricter decontamination measures in place, but amid concerns that authorities still weren’t doing enough to contain the blaze’s toxic fallout.

Over 400 tons of lead roofing burned in the fire, releasing a cloud of lead particles into the air. City and national officials have been criticized for reacting slowly and failing to fully disclose the risk of contamination for people living or working in the area.

One environmental group has filed a lawsuit, accusing the authorities of minimizing the risks for cleanup workers, apartment dwellers and schools in the dense neighborhood around Notre-Dame. Some critics have accused the French authorities of rushing to meet the five-year deadline set by President Emmanuel Macron to rebuild the cathedral at the expense of safety measures.