Environmental Protection Agency Administrator Scott Pruitt said he would not participate in any cases in which Oklahoma is a party. (AP/Susan Walsh)

Environmental Protection Agency Administrator Scott Pruitt has recused himself from ongoing lawsuits against the agency that he participated in during his previous job as Oklahoma attorney general.

In a four-page document dated Thursday, Pruitt detailed a list of cases he said he planned to avoid during his time leading the agency he so often opposed while in Oklahoma. The cases include high-stakes litigation over the Obama administration’s Clean Power Plan and the controversial Clean Water Rule, both of which the Trump administration has said it intends to roll back.

Pruitt also wrote that he would recuse himself from a handful of cases involving clean-air regulations, methane regulations for the oil and gas industry and mercury standards for power plans. In addition, he said he would avoid participating in the legal cases involving a diesel emissions cheating scandal at Volkswagen AG.

“To demonstrate my profound commitment to carrying out my ethical responsibilities, while I am the Administrator of the [EPA], I will not participate in any active cases in which Oklahoma is a party, petitioner or intervenor,” Pruitt wrote in the memo, which was first reported by E&E News. “I understand that this commitment is longer than is required by the federal impartiality standards, but I am taking this action to avoid even the appearance of any impropriety under federal ethics or professional responsibility obligations.”

It remained unclear how Pruitt’s recusal would affect any of the ongoing litigation. The Trump administration has made clear that it intends to reverse many of the environmental regulations put forward under Obama, and it has asked courts in some cases to refrain from ruling on the active lawsuits while the agency revisits them.

Just last week, for instance, a federal court granted the administration’s request to suspend lawsuits against the Clean Power Plan rule — a regulation that would have limited carbon missions from power plants — signaling the likely end of President Barack Obama’s signature climate policy.

In addition, while Pruitt will recuse himself from working on any litigation in which he was involved, he is not recused from the rule making process at EPA. That means he will likely play a central role in the administration’s efforts to rewrite an array of Obama-era environmental rules.

As Oklahoma’s attorney general, Pruitt for six years repeatedly sued the EPA for its efforts to regulate mercury, smog and other forms of pollution. In all, he participated in more than a dozen lawsuits against the EPA during his tenure, challenging the agency’s authority to regulate toxic mercury pollution, smog, carbon emissions from power plants and the quality of wetlands and other waters. One of his key acts as attorney general was to establish a “federalism unit” to combat what he called “unwarranted regulation and systematic overreach” by Washington. On his Linked In page, Pruitt boasted of being “a leading advocate against the EPA’s activist agenda.”

That combative approach won him broad praise from fellow Republicans and the oil and gas industry. But it has made him despised by environmental advocates, who continue to criticize him for questioning the overwhelming scientific consensus around climate change, defending the interests of fossil-fuel firms instead of focusing on public health and presiding over potentially massive cuts to the EPA.

“The fact that Scott Pruitt has to recuse himself from so many cases, many of which are extremely high profile, is evidence that he shouldn’t be allowed anywhere near the EPA,” Naomi Ages, a senior climate campaigner for the environmental advocacy group Greenpeace, said in a statement. “Yes, Pruitt’s direct oversight has been curtailed, but now who is in charge of representing the people in these critical decisions?”

Given his litigious history with the EPA, the issue of whether he would recuse himself if he were made the agency’s leader came up during his Senate confirmation hearings.

Questioned by Sen. Edward J. Markey (D-Mass.) about whether he would avoid involvement in the cases he’d been party to while in Oklahoma, Pruitt at the time said he would rely on the advice of agency ethics lawyers.

“If directed to do so, I will do so,” he said.

“If you don’t agree to recuse yourself,” Markey said, “then you become plaintiff, defendant, judge and jury on the cases you are bringing right now as attorney general of Oklahoma against the EPA.”

In his memo this week, Pruitt said that so far during his time as EPA administrator, “I have not participated in any of the cases listed in this recusal statement officially at all and will continue to recuse for now.” He added that if he changes his mind, he would first check with ethics officials at the agency.

The memo also details a “screening arrangement”to ensure that Pruitt does not participate in matters related to the cases from which he recused himself. Under the arrangement, his chief of staff, Ryan Jackson, will “screen all EPA matters, including existing litigation” to determine if Pruitt’s involvement would violate his ethical obligations.