Childhood cancer clusters discovered in the rural Kern County towns of McFarland and Rosamond some 25 years ago are among dozens of disease clusters in several states cited by environmentalists in a report released Monday.

While there's little new information in the report produced by the Natural Resources Defense Council and the National Disease Clusters Alliance, one of the aims of the effort was to compile wide-ranging data from 42 disease clusters in 13 states into a single document, said Dr. Sarah Janssen, a physician and senior scientist with the NRDC and a co-author of the report.

"We think these are probably just the tip of the iceberg," Janssen said of the 42 clusters the group documented.

The report concluded that federal authorities must do more to help investigate potential clusters, and devote more resources toward finding the causes.

"For most of these clusters, the cause is not known," Janssen said. "But it doesn't take away from the fact that families and communities are suffering a great burden."

Tuesday, the Senate Committee on Environment and Public Works will hold a hearing on disease clusters. Dr. Gina Solomon, another NRDC senior scientist and co-author of the paper, will testify, as will Erin Brockovich, whose story was portrayed by actor Julia Roberts in the movie about the industrial poisoning of a small town's water supply.

The childhood cancer cluster in McFarland came to light in the mid-1980s after five children were diagnosed with cancer, all within a nine-month period.

A study in 1986 found that the water, air and soil in McFarland were not contaminated by known carcinogens.

In 1991, a state-appointed scientific advisory committee said it could not find an environmental or lifestyle cause for the cancer.

When seven new cases of childhood cancer were discovered between 1990 and 1995, new investigations were launched. But subsequent investigations found no definitive link.

The cluster identified in Rosamond was just as frustrating -- and just as tragic. Eight children were diagnosed from 1975 to 1984, half of them with medulloblastoma, a rare form of brain cancer.

Although the state Department of Health Services found several locations in Rosamond that were contaminated with dioxins and other chemicals that cause cancer, they could not determine how the children could have come in contact with the chemicals.

Don Davis, the president of the Kern County Farm Bureau, said Monday he hadn't had a chance to look over the report, but he said the farm bureau supports science-based regulations that help ensure a clean environment and healthy foods.

"It is critical we maintain an abundant and safe food supply," Davis said.

But what he's seen too often when someone gets sick is American agriculture is assumed to be the cause.

"It's in our best interest to be highly regulated," Davis added.

But government regulations must be based on science and settled fact, Davis said, not on emotional appeals or assumptions.

In her blog Monday, Solomon writes, "Learning lessons from the disease clusters in communities around the country allows for the possibility of some good emerging from something that is otherwise very bad. I'm sure that every parent of a child with cancer or a birth defect would do whatever they can to help -- not only their own child -- but also help prevent other parents and children from having to go through such an ordeal by identifying causes and preventing future disease."