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Houston Chronicle, Marie D. De Jesus, Associated Press
DuPont spokesman Aaron Woods speaks during a news conference about a hazardous chemical leak that killed four employees and injured one at the DuPont industrial plant in La Porte, Texas, Saturday, Nov. 15, 2014. The cause of the leak is under investigation.

LA PORTE, Texas — Records show dozens of minor or moderate state environmental violations over the past five years at a Houston-area chemical plant where four people died from toxic fumes this weekend.

Texas Commission on Environmental Quality records for the DuPont plant in La Porte list multiple incidents since 2009, but it has received a satisfactory rating from the state and holds more than 150 environmental permits.

The four employees died Saturday after the release of methyl mercaptan — a chemical used in the manfucture of insecticide and fungicide that causes eye and skin irritation and rapidly affects the respiratory system.

It's not clear how the chemical was released, and a team of investigators from the U.S. Chemical Safety Board entered the plant Monday.