Four workers have been killed and another injured after a chemical leak at the DuPont plant in La Porte, Texas, on the Gulf Coast early Saturdaya morning, officials said. The chemical, methyl mercaptan, which is used to make insecticides and fungicides, escaped into the air around 4 a.m. inside a building. It took about two hours to contain the leak, said a company official. "We know something wrong happened today and we are going to do the proper investigation to make sure it doesn't happen again," said company spokesman Aaron Woods. There were no details given about the employees who were killed, except to say they ranged from 40 years with the company to one that had been hired just eight months ago.