A number of workers cleaning up the oil spill in the Gulf of Mexico have been fallen sick with flu- like symptoms, it was announced on Thursday.

More than a dozen workers were suffering from symptoms ranging from chest pain to dizziness, nausea and headaches, according to the Natural Resources Defense Council (NRDC).

The sick workers have been treated at local medical centers, the council said.

"Within the past week, we've seen a number of workers hospitalized. That's new," said Dr. Gina Solomon, a senior scientist with the NRDC.

The physical symptoms may be related with exposure to different chemicals emanating from the slick, health experts said.

"The reports that we've heard from hospitals and doctors have been (that the symptoms are due to) inhaled irritant exposure, but they've not gone so far as to say what exactly they think the responsible agent might be," Solomon said. "The workers are widely blaming the dispersants."

Dispersants are chemicals used for the oil clean-up. The solvent used after the massive 1989 Exxon Valdez oil spill off the Alaska coast, for example, was limonene, which can cause skin inflammation and asthma, said Robert Emery, vice president for safety, health, environment and risk management at the University of Texas Health Science Center at Houston.

"There's no doubt that people are getting sick out there (in the Gulf of Mexico)," Emery said. "The key question is what is it that is causing them to get sick."

BP's Deepwater Horizon exploded and sank in the Gulf of Mexico on April 20, killing 11 workers and spewing an estimated 21 million to 45 million gallons of crude oil into the water.

BP and the U.S. Coast Guard have said dehydration, heat, food poisoning or other unrelated factors may have caused the workers' symptoms.

The U.S. Environmental Protection Agency reported that it has detected some "odor-causing pollutants associated with petroleum products along the coastline at low levels." These chemicals could cause headache, nausea and throat irritation.