Mr Pruitt, a lawyer, is known for climate science denial and his own website described him as “a leading advocate against the EPA’s activist agenda”.
Despite this, Donald Trump chose him to run the agency.
While working as Oklahoma’s Attorney-General, Mr Pruitt has sued the agency several times and, since he was chosen by the new President, he has refused to say whether he will drop out of an on-going case against the agency even if he becomes its top official.
One of the 447 signatories of the letter to Congress, Judith Enck, who was appointed by Barack Obama to head an EPA regional office, told The Washington Post that Mr Pruitt’s appointment would be an “an unprecedented assault” on the agency’s primary function.
The letter said Mr Pruitt’s views and history of suing the agency “strongly suggest that he does not share the vision or agree with the underlying principles of our environmental laws”.
“Different administrators have come to different conclusions about how best to apply the law in view of the science, and many of their decisions have been challenged in court, sometimes successfully, for either going too far or not far enough,” it said.
“But in the large majority of cases it was evident to us that they put the public’s welfare ahead of private interests.
“Scott Pruitt has not demonstrated this same commitment.”
Mr Pruitt has in the past opposed the EPA’s attempts to control mercury pollution, power station carbon emissions, air pollution and water quality.
“Every EPA administrator has a fundamental obligation to act in the public’s interest based on current law and the best available science,” the letter said.
“Mr Pruitt’s record raises serious questions about whose interests he has served to date and whether he agrees with the long-standing tenets of US environmental law.”
Ms Enck, who only recently left the agency, told the Post she had not seen “the level of concern at EPA that I’m seeing today”.
She said Mr Trump’s decision to appoint Mr Pruitt was “an unprecedented assault on environmental protection, not just on EPA as an agency, but on our country’s ability to enjoy clean air, clean water and a logical agenda on climate change”.
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