Hunt Goes On for Cause of Brain Defects in Babies Born on Border : Anencephaly: Theories include chemicals emitted by factories, solvents in Gulf of Mexico, or fathers exposed to chemicals at work.

Tears flow into the Rio Grande from both sides of the border--from Teresa Salazar in Brownsville and from Faustina Rivera in Matamoros, two housewives in mourning.

In March, Salazar gave birth to a stillborn boy. In April, Rivera gave birth to a stillborn girl. Both children were anencephalic--they were born with undeveloped brains, with partly formed skulls.

“I felt responsible. . . . I thought it was my fault he was born that way,” said Salazar, months later.

Rivera never held her baby--”They didn’t let me see her. I wanted to, but they wouldn’t let me. I wanted to at least know her.” But her husband, Hermilo Mata, touched the child before she was buried.

“I felt . . . I don’t know . . . I felt something,” he said, pausing frequently as he groped for words. “I didn’t know why.”

These two families are not alone in their tragedies, or in their bewilderment. On both sides of the border, far too many children are being born with brain and spinal defects. And no one knows why.

Some say the cause is in the breeze--toxic chemicals emitted by factories on the Mexico side. Some say solvents in the water are to blame, or that the fathers were exposed to chemicals at work. Others point to the mothers’ diets.

But a yearlong medical investigation conducted by the Texas Department of Health and the U.S. Centers for Disease Control failed to find an answer; scientists said they could not determine any link between the defects and environmental factors.

“You’ve heard . . . about all the things that people are pointing the finger at as a cause,” said Dr. Dennis Perrotta, state director of epidemiology. “All of them, some of them, or none of them may indeed be true.”

The only point of agreement is that something is wrong.

Nationally, anencephalic births occur two to three times per 10,000 live births; the rate in Texas is three or four per 10,000. In Cameron County, surrounding Brownsville, the rate has been consistently higher since about 1986, and jumped to an average of about 14 per 10,000 around 1989.

A year ago, obstetrical nurses at Valley Regional Medical Center reported a horrific streak--three anencephalic births during a single 36-hour period.

In Matamoros, meanwhile, a similar escalation has been detected. In 1987, the rate was 3.2 per 10,000 births. The next year it increased to 5.3, and then to 11.8; for the last three years, it has been 15 or above.

There also have been increases in other disorders, such as spina bifida. These are neural tube defects, disorders involving the brain or spinal cord.

The disorders occur in embryos during the first 28 days of life, when the neural tube, a precursor to the spinal cord, is developing, said CDC epidemiologist Dr. Joe Mulinare.

“If the development does not occur properly . . . at the head end, then anencephaly occurs,” Mulinare said. “If the development does not occur properly at the lower end of the spine, then spina bifida occurs.

“Spina bifida can be very mild,” he said, “or it can be very severe.”

Anencephaly, however, is fatal. The babies are either stillborn or die shortly after delivery.

Studies have shown links--some say tenuous links--between xylene and toluene, common chemicals used in Matamoros factories, and neural tube defects.

A 1979 study showed a link between women who had babies with neural tube disorders and exposure to toluene and xylene. Another medical study suggested that fathers who were routinely exposed to solvents at work were at greater risk of producing anencephalic children.

A 1991 study conducted by the National Toxic Campaign Fund found high concentrations of xylene in canals around some Matamoros factories.

Samples collected at the discharge near one plant showed that the water contained 2.8 million parts per billion of xylene, more than 6,300 times U.S. drinking water standards. A sample from another plant had 23.2 million p.p.b., more than 52,700 times U.S. standards.

Marco Kaltofen, director of the Citizens’ Environmental Laboratory in Boston, said the compounds also evaporate readily, making exposure likely through the air as well through water.

Air sampling in Brownsville has also consistently detected toluene.

A private study group has mapped the anencephalic cluster in Brownsville and found that most of the mothers lived within a 2.4-mile radius of the river. There has also been a seasonal link; the clusters for the last two years have begun showing in the spring.

These are all tantalizing clues to the mystery, but for the moment they are nothing more than clues: “It may be that we will never really know,” said Dr. Tim Thurber, a pediatrician who is part of that group of local medical professionals who are trying to solve the puzzle.

Even as the search goes on, more hearts are broken. Long before her baby was due, Janet Ramirez had decided to name her Maria Guadalupe. But then, at five months, she and her husband learned that the baby was anencephalic.

The child was delivered stillborn after she underwent an induced labor at six months. Ramirez’s eyes mist over and she wipes them with her shirt as she recalls holding the dead baby.

“I didn’t want (the termination),” Ramirez said. “But the doctors said if I was going to go through the nine months I was going to suffer and so was the baby.”

“It was a shock,” she said. “My husband had a nervous breakdown. Because it was our first baby.”

“It was a shock,” she said again.