The Environmental Protection Agency has extended the comment period for a blood-thinning poison registered to kill prairie dogs.

The request for a 30-day extension in the comment period came from the poison's manufacturer, LiphaTech.

In a similar but separate case, involving Kaput-D, another blood-thinning poison that is being considered for registration, a request for an extension -- sought by the American Bird Conservancy -- was denied.

Both Kaput-D and Rozol have come under fire by environmental groups because of the danger of secondary poisoning to animals that feed on prairie dogs, most notably the black-footed ferret, ferriguinous hawk and bald and golden eagles.

The EPA opened comment periods on uses of both poisons in the wake of a series of complaints about the agency's action and the filing of a lawsuit.

In the case of Kaput-D, the World Wildlife Fund objected to its registration, prompting the EPA to take comments.

That decision, however, came shortly after the Defenders of Wildlife and Audubon of Kansas filed a lawsuit in federal court, challenging the EPA's decision in May to register Rozol.

Defenders lawyer Jason Rylander, who filed the lawsuit against the EPA, criticized the agency's decision to extend the comment for one poison -- at the behest of its manufacturer -- while denying a request made by an environmental group.

"EPA's pesticide  office continues to act as if it were wholly-owned subsidiary of the pesticide industry," Rylander said in an e-mail. "Extending the comment period at the request of industry shows that EPA is not serious about addressing its illegal registration of Rozol in a timely fashion."

In response, he said, Defenders and Audubon again formally requested that EPA rescind its May 13 registration of Rozol pending a complete review.

"Numerous conservation groups, the Western Association of Fish and Wildlife Agencies and the U.S. Fish and Wildlife Service have urged EPA to rescind its illegal registration of Rozol immediately," he said. "Time is of the essence, yet EPA has chosen instead to delay action on withdrawing this registration, which assures that tons of this poison could be sold and used this year with significant impacts to wildlife."  

EPA spokesman Dale Kemer was unsure exactly why a 31-day extension was granted in one case but not in another. The people responsible for the decision were not expected to be in the office until sometime later today.

In the case of the registration of Kaput-D, that comment period ended Oct. 23. Only 26 comments were posted after that deadline has passed, but a few additional comments have since trickled in.

Kaput-D contains the blood-thinning chemical diphacinone and the insecticide imidacloprid, designed to kill fleas that could harbor sylvatic plague, deadly to both prairie dogs and black-footed ferrets.

The comment period for Rozol -- containing the blood-thinner chlorophacinone --  was scheduled to end today, but it has been extended until Dec. 7.

So far in the Rozol case, fewer than 30 comments have been received.