Mr. Dourson, 65, worked for the Environmental Protection Agency from 1980 to 1994, according to his résumé, starting as a staff toxicologist, preparing health assessments of various substances. He worked his way up over time, becoming chief of the pesticides and toxics team in 1989, supervising scientists who support the E.P.A.’s regulatory work. Mr. Dourson ultimately oversaw a team of scientists conducting risk assessments for the agency’s offices of water, solid wastes and air quality.

The following year he created a nonprofit consulting firm that became a line of first defense for companies facing health and safety challenges from the E.P.A.

Mr. Dourson has a popular sideline as a writer of books that combine Bible stories with his views on science. His series, “Evidence of Faith,” is an examination of the intersection of evolution and bible history.

At a time when the E.P.A. is in the early stages of putting in place Congress’s 2016 overhaul of the law governing toxic chemicals, Mr. Dourson’s nomination to become the agency’s assistant administrator for chemical safety has alarmed Democrats and some former E.P.A. officials.

“Dr. Dourson’s consistent endorsement of chemical safety standards that not only match industry’s views, but are also significantly less protective than E.P.A. and other regulators have recommended, raises serious doubts about his ability to lead those efforts,” said Senator Tom Carper, Democrat of Delaware, the ranking minority member on the panel that will assess Dr. Dourson’s qualifications. “This is the first time anyone with such clear and extensive ties to the chemical industry has been picked to regulate that industry.”