Washington ? As BP moves to seal the Deepwater Horizon well permanently, more than 31,000 cleanup workers continue to rely on incomplete and at times misleading information about toxic exposure to the spilled oil in the Gulf of Mexico.

Public health officials say they face a daunting challenge: how to inform workers about the possible dangers when studies on the toxic effects of such a large spill have never been done.

Research has provided enough clues about some of the chemicals, however, that independent scientists and worker health advocates say that BP and the Obama administration should be more aggressive in warning workers about the possible long-term health effects of toxins, especially given complaints of worker illnesses that surfaced after the 1989 Exxon Valdez spill in Alaska.

“It’s sort of a legalistic framework that the government has adopted in saying there are not a lot of studies so we don’t know a lot,” said Dr. Michael Harbut, who specializes in occupational and environmental medicine and has treated oil industry workers.

“It’s true that there have not been extensive studies about crude oil dumping into the Gulf in the millions of barrels quantity and being mixed with dispersant,” he said, “but there are thousands of studies about what happens when people and animals come into contact with these chemicals, and those studies demonstrate that they are not benign.”

Two months into the response, however, administration officials decided that respirators weren’t needed for cleanup workers stationed nearby and on shore, because air monitoring didn’t detect levels of contaminants that were higher than federal standards.

The government did recommend that BP provide respirators to workers in the areas that were closest to the freshly spilled oil and to the vapors from burning it, but didn’t make it a requirement.

BP asserts that the air-monitoring data demonstrate that workers have little to worry about.

“The monitoring data shows that few people, if any, are exposed to levels of oil or dispersants that have even the potential to cause any significant adverse health effects,” the company said in a written response to questions from McClatchy Newspapers.

The reality is much more complicated, however, experts say.

Contract employees for Miller Environmental Services scrub a containment boom the old-fashioned way Thursday in Grand Isle, La.

Little information

Discerning the danger is difficult because the chemical soup that’s spreading throughout the Gulf is a mix of dozens of toxic materials that are hard to measure, including benzene — a carcinogen — and polycyclic aromatic hydrocarbons, some of which health officials have determined “may reasonably be expected to be carcinogens.”

The Labor Department said there was an “incomplete understanding about the human health toxicity” of the oil and dispersants. While noting that the aged and evaporated oil is “unlikely to pose an inhalation risk,” the government said that studies of tanker oil-spill responses had reported “adverse health effects.”

The records that are supposed to be the key sources for workers on the toxic chemicals shed little light on such questions.

For instance, the documents, written by BP, say that the crude from its runaway well contains some toxins — such as benzene, hydrogen sulfide and polycyclic aromatic hydrocarbons — but they don’t list toluene and xylene as other oil and gas companies do.

Although BP acknowledges in the records that animal studies have shown that crudes “possess carcinogenic activity to some degree,” it adds that only workers who practice “poor personal hygiene” and who are exposed repeatedly over many years “may potentially be at risk of developing skin cancer.”

The company adds that crude oil “has not been identified as a carcinogen” by government agencies.

Adam Finkel, a former regulatory and enforcement official with the Occupational Safety and Health Administration, said that the documents, known as material safety data sheets, were confusing and left out too much important information to be of any use to workers.

“The MSDS is not just a piece of paper. It is the rule,” Finkel said. “The employee is supposed to be able to learn about the harm. If you’re going to have a system that relies on these complicated documents, then at the very least they ought to be true and consistent.”

BP said the documents were sufficient for informing workers about the dangers and “are not intended as information packets for the general public.”

Jordan Barab, the Labor Department’s deputy assistant secretary for OSHA, said his agency didn’t scrutinize the BP documents closely because his inspectors didn’t rely on them to determine what to monitor in the Gulf. He said the agency was working on changing regulations that he said now allowed companies to file “everything from two pages that have nothing on them to 26-page MSDSs that nobody can decipher.”