RALEIGH, N.C. - A long-awaited study by the U.S. Centers for Disease Control and Prevention shows a link between tainted tap water at a U.S. Marine Corps base in North Carolina and increased risk of serious birth defects and childhood cancers.

The authors of the study on Camp Lejeune released late Thursday by the CDC's Agency for Toxic Substances & Disease Registry warned it is based on a small sample size and cannot prove exposure to the chemicals caused specific individuals to become ill.

But the study did conclude that babies born to mothers who drank Lejeune tap water while pregnant were four times more likely than women who lived off-base to have such serious birth defects as spina bifida. Babies whose mothers were exposed also had a slightly elevated risk of such childhood cancers as leukemia, according to the results.

The study surveyed the parents of 12,598 children born at Lejeune between 1968 and 1985, the year most contaminated drinking water wells were closed. They reported 106 cases of serious birth defects and childhood hematopoietic cancers. Of those, researchers said they could obtain medical records to confirm the diagnoses in only 52 cases.

Epidemiologist Richard W. Clapp, who serves on a federal board that has reviewed the Lejeune contamination, said the links found through the study might "appear to be weak" due to the relatively small sample size. But he said the findings are important because they show strong evidence the water that Marines and their families drank, cooked with and bathed in might have made some sick.

"The fact that there was anything found is pretty important," said Clapp, professor emeritus at Boston University's School of Public Health. "This is an insensitive tool that we use here, these epidemiological studies. So the fact that they found anything is sort of remarkable."

The study looked back through time and was designed to see if there was a link between exposure to certain chemicals and certain health problems that developed later. This type of study is often used to investigate disease outbreaks, when health officials are trying to identify possible reasons for the illnesses.

There are no records to measure how much tainted water those surveyed consumed. Therefore, the study had to use complex modeling to gauge how much of the chemicals they could have been exposed to. The study also did not look at the health effects on adults that drank the water. More than 80 men with Lejeune ties have been diagnosed with an extremely rare form of breast cancer.

In the nearly three decades since the contamination was first disclosed to the public, military officials have repeatedly issued public statements downplaying health risks from drinking the tainted water prior to the closure of the most contaminated wells.

A brief statement issued Thursday by Lejeune spokeswoman Capt. Maureen Krebs contained no such disclaimers. It stressed that the water currently flowing from the base's taps is routinely tested and safe to drink.

"These results provide additional information in support of ongoing efforts to provide comprehensive science-based answers to the health questions that have been raised," the statement said. "The Marine Corps continues to support these initiatives and we are working diligently to identify and notify individuals who, in the past, may have been exposed to the chemicals in drinking water."

Krebs said Friday she could provide no comment about the new report beyond the written statement.

Records reviewed by The Associated Press show military authorities continued to rely on the wells for years after testing suggested the water was contaminated. The most highly contaminated wells were closed in 1984 and 1985, after a round of more extensive testing found dangerous concentrations of toxins associated with degreasing solvents and gasoline.

A prior CDC study cited a February 1985 level for trichloroethylene of 18,900 parts per billion in one Lejeune drinking water well -- nearly 4,000 times today's maximum allowed health limit of 5 ppb. Testing also found high levels of benzene, a fuel additive.

The ground water contamination was traced to two primary sources -- a leaky on-base fuel depot and a nearby dry cleaner. In prior public statements, Marine officials have emphasized the contamination that came from outside the base. But the newly released study found the greatest negative health impacts to be associated with benzene, which came from the on-base Hadnot Point tank farm built during World War II.

Last year, President Barack Obama signed the Camp Lejeune Veterans and Family Act to provide medical care and screening for Marines and their families, but not civilians, exposed between 1957 and 1987. The law covers 15 diseases or conditions, including female infertility, miscarriage, leukemia and multiple myeloma, as well as bladder, breast, esophageal, kidney and lung cancers.

The law was passed after years of advocacy by former Marines who blamed the contamination for negative health impacts, efforts that were often met with strong resistance from the Marine Corps.

Jerry Ensminger, a former Marine drill instructor, lost his 9-year-old daughter Janey to leukemia in 1985. He is among those with pending federal compensation claims have been on hold while waiting for the CDC research to be completed.

He said the study results are a vindication of what he's been saying for nearly 20 years, but they won't bring his daughter back.

"Nothing ever gives you comfort when you lose a child," Ensminger said Friday. "I think that's the worst thing that can happen to a human being ... to watch them go through the hell they go though. That's something that never leaves you."