For reasons scientists cannot yet explain, Utah’s Great Salk Lake is laden with toxic mercury. Exactly where the poison is coming from, and how much danger it poses to the millions of migratory birds that feed on the Great Salt Lake, are now under investigation.

Three years ago, tests by the federal Geological Survey showed the lake had some of the highest mercury readings ever recorded in a body of water in the United States. The state warned people not to eat certain kinds of ducks because of the mercury.

The mercury may be accumulating naturally, from some as-yet-unknown source in the ground, or it could be the result of industrial pollution. Mercury released into the atmosphere from coal-fired power plants, gold mines, or industrial facilities may be settling in the lake.

Hannah Pingree was so alarmed when she learned she had dangerously high levels of mercury, arsenic and other toxic chemicals in her body that she took her case to the Maine state legislature and challenged chemical makers.

Hannah Pingree was so alarmed when she learned she had dangerously high levels of mercury, arsenic and other toxic chemicals in her body that she took her case to the Maine state legislature and challenged chemical makers.

Health officials have become uneasy about the growing demand for paddlefish caviar. A variety of toxins have been found in the fish eggs, including mercury, chlordane and cancer-causing polychlorinated biphenyls, or PCBs.

Kentucky, Indiana and Tennessee have issued advisories warning consumers to limit their consumption of paddlefish caviar from certain sources. But since the FDA does not require companies to list river of origin on labels, it can be difficult to know the source of caviar.

Linda Greer, health director for the Natural Resources Defense Council in New York, said consumers should avoid any foods containing PCBs. “There’s no safe level of exposure to a carcinogen,” she argues. “My advice would be to err on the side of caution and not eat the paddlefish caviar.”

Government researchers are pushing to test chelation therapy, an as yet unproven treatment on autistic children.

The treatment removes heavy metals from the body and is based on the theory that mercury in vaccines triggers autism. Many parents of autistic children attest to the success of the treatment, and the head of the National Institute of Mental Health now supports testing it on children provided the tests are safe.

For now, the proposed study has been put on hold because of safety concerns.

Any study of chelation in children would have to exclude those with high levels of lead or mercury, which would require treatment and preclude using a placebo.