Brownsville, Texas – On a hairpin bend of the Rio Grande, where the south wind from Mexico carries the sweet smell of freshly cut sorghum and the stench of chemicals, something terrible befell Janet Ramirez.

The child she had prayed for, her first, was born dead with a tangled mass of nerve endings instead of a brain.

“I held her in my arms for ten minutes, and then my husband took her for half an hour. He didn’t want to let her go, but the man from the funeral home was waiting to take her away,” said Ramirez, 22, remembering last year’s birth of tiny Maria Guadelupe.

Here at the southernmost tip of Texas, mothers are giving birth to babies without brains at eight times the nationwide rate – more frequently than anywhere else in the United States and many Third World nations. Why this is happening remains a medical mystery. But local doctors and environmental activists believe the answer lies just across the muddy Rio Grande in Matamoros, Mexico, where a U.S.-led industrial boom has spawned widespread toxic contamination. Scientific studies conducted around the world have suggested that exposure to toxic chemicals, as well as heavy pesticide use or poor nutrition, can increase the risk of the birth defect, known as anencephaly.

A yearlong study of the Brownsville anencephalies released 11 days ago by state and federal health investigators failed to identify any cause, and additional studies are planned. Whatever the explanation, the ongoing search for answers has focused new attention on conditions along the entire 2,000-mile U.S.-Mexico border, where poverty is endemic, environmental enforcement is spotty and an industrial revolution in Mexican border cities is accelerating.

“We have been the forgotten corner of the country for so long, it’s amazing to us that people are starting to pay attention,” said Dr. Margaret Wells Diaz, the local physician who first detected the cluster of anencephalies. Ultimately, 24 were identified in 1990-91 . “I just wonder how many more babies are going to have to die before anything really changes,” she said.

Almost 10 million people live in a 130-mile-wide strip straddling the border from Texas to California – 95 percent of them jammed into 14 pairs of sister cities stretching from Brownsville-Matamoros to San Diego-Tijuana. The population has grown so quickly – by more than 60 percent in 10 years – that Mexican cities like Nuevo Laredo now use the Rio Grande as both an open sewer and a drinking water source. On the far wealthier U.S. side of the border, three-quarters of all households earn less than $ 12,000 annually, and about 215,000 people live in colonias, unincorporated shantytowns that usually lack running water or even primitive sewage treatment.

In recent years, a new element has been added to the Mexican side of this crowded, dirty landscape: export factories. Attracted by favorable Mexican tariff laws and wages of about $ 12 a day for skilled labor, U.S. companies in Mexican border cities now number roughly 1,800, with 20 percent more opening each year. The maquiladoras, as the foreign-owned factories are called, employ about 400,000 people. Many – including General Motors, Zenith and DuPont – are engaged in chemicals processing, electronics and other industries that generate hazardous waste. “There is no poverty in New York that comes even close to the absolutely horrendous conditions that many of these people have to live in,” said Stuart Shalat, an environmental epidemiologist at Texas A&M University. Shalat, who investigated the Love Canal toxic waste site a dozen years ago for New York State, says the border’s environmental problems are “much more severe. You have terrible public health conditions and a polluted environment from multiple sources.”

On a 102-degree afternoon earlier this month, Matamoros’ huge manufacturing parks were a blurred image of poverty and industrial blight. Children who live in nearby shacks swam in a drainage ditch that serves several factories. Some young boys played stickball across a dirt road from an insecticide plant and one that makes ammonia.

Jesus Moreno, 20, lives in Colonia Chorizo, so named because it is shaped like a long Mexican sausage. In front of his family’s two-room shack, three orange chemical drums have been set up to catch water for bathing. A few hundred feet away, across a railroad track, is a factory where workers make pentachlorophenol, a highly toxic wood preservative that contains dioxin and has been banned in some European countries.

“When the wind blows toward us, the gas burns in our throats and we all have to leave the colonia. The children can’t stand it,” said Moreno, a laborer in the sorghum fields.

The factory, known as Productos de Preservativos, is owned by a subsidiary of Houston-based KMG Bernuth. Company officials did not return phone calls.

“It makes me very angry that these companies would come down here and take advantage of our ignorance. Why don’t they respect our lives?” said Maria Guadelupe Torrez, 46, who works for a foundation-funded group seeking better conditions for workers, mostly women, in Matamoros’ maquilas.

Torrez was employed for 18 years by a now-closed electronics manufacturer in Matamoros, and eventually learned that the liquid she was using to clean her hands and clothes was the solvent methyl chloride, which the U.S. Environmental Protection Agency has labeled a potential carcinogen that causes such things as frost bite, eye damage, slurred speech and comas.

Torrez made her discovery only after tearing the safety label off a drum, sneaking it out of the plant and giving it to a U.S. social worker who translated the warning into Spanish. “Nobody told us,” she said.

To health officials who are trying to determine why anencephalies are so common in Brownsville and other towns in Cameron County, the industrial boom on the opposite side of the river is an obvious, if unproven, suspect.

“Until proven otherwise, my money is on the maquilas. I feel absolutely certain that’s what it is,” said Diaz, the doctor. Based on the U.S. average, Cameron County would have expected about three anencephalies to be born in 1990-91 – as many brainless babies as were delivered during a single 36-hour period at one Brownsville hospital. It’s uncertain how many anencephalic babies have appeared in Matamoros, but Mexican health officials have suggested that the numbers are high there, too.

Anencephaly’s cause lies somewhere in the delicate chemistry of early fetal development, scientists say. Between the 18th and 28th day after conception, a groove-shaped mass of nerves along the embryo’s back closes into a tube. When the bottom part of the neural tube fails to close, the spinal cord remains exposed and the baby is born with spina bifida, which generally is not fatal. When the top of the tube does not close, most or all of the brain fails to develop, and the anencephalic fetus usually dies in the womb or in the first minutes after birth.

“Something is causing this, and some of the strongest evidence supports non-genetic factors. There is clearly evidence that there’s a role for environmental factors” such as nutrition or exposure to pesticides or other pollutants, said Lowell Sever, a staff scientist at the Batelle Pacific Northwest Laboratory in Richland, Wash., and a specialist in perinatal epidemiology.

Pesticide use and spina bifida were linked in a 1988 study in Nova Scotia. And a 10-year-old Australian survey showed that neural tube defects were highest for embryos conceived during the Southern Hemisphere’s summer months of December, January and February, when the dioxin-containing pesticide 2,4,5-T is most widely used. Exposure to solvents may be a more likely cause of neural tube defects than pesticides, some studies have suggested. In 1990, the Texas Department of Health found that fathers working as painters are 3 1/2 times more likely to conceive babies with neural tube defects, compared with the statewide average. Men exposed to pesticides at their jobs were only slightly more likely than average to father children with neural tube defects.

All of these environmental risk factors are in view from the front porch of Janet Ramirez’ small home near the Rio Grande. When she looks out her torn screen door and across the river into Matamoros, the smokestacks of maquiladora auto-parts manufacturers and chemical processors loom over the fields of sorghum and corn. When the wind blows northward, as it usually does, the smell of those factories is sometimes noticeable. Tank cars from Matamoros carrying hydrofluoric acid, a volatile toxic chemical, regularly roll past on a nearby railroad spur, within about 50 feet of her house.

In addition, crop dusters sometimes spray the sorghum fields with pesticides, and one of the most common in subtropical South Texas is 2,4-D. While there is conflicting research on whether 2,4-D is dangerous, the evidence is stronger on 2,4,5-T, which has been banned in the United States as a suspected carcinogen but is still used in Mexico.

Nutrition also is a risk factor because the diets of many Mexican-Americans are usually light on the leafy vegetables that contain folic acid and heavy on corn tortillas that are susceptible to aflatoxins, a mold linked to liver cancer. A major study last year showed that giving mothers large doses of folic acid starting one month before conception cut the chance of anencephaly by as much as 70 percent.

But the newly completed study, conducted jointly by Texas’ health department and the U.S. Centers for Disease Control, found no clear evidence that any particular factor is linked to the Cameron County anencephalies. The study, which compared parents of the 24 anencephalic infants to parents of healthy children, included questionnaires and blood and urine tests. But it excluded air or water sampling, or testing of anencephalic embryos’ tissue.

“It certainly can’t be called a complete study,” said Gregoria Rodriguez. She is helping Brownsville’s public-health clinic organize a locally controlled study that will include environmental sampling and a more detailed questionnaire. “The river [Rio Grande] is just a line on a map. It doesn’t mean anything. But they didn’t even try to look at what’s happening across the river.”

It’s hard to even guess how much pollution is coming from the maquiladoras because, unlike in the United States, companies in Mexico are not required to disclose how much pollution they emit or how much waste they generate.

But there is considerable anecdotal evidence that illegal dumping is widespread on the Mexican side of the Rio Grande.

Under Mexican law, maquila waste products generated by raw materials imported from the United States are supposed to be returned to the United States. But the U.S. Customs Service reports that only about two trucks and two rail cars daily cross the border from Mexico carrying hazardous material.

“The truth is, we have absolutely no way of knowing how much of this stuff is staying in Mexico,” said Ernest Tijerina, U.S. Customs’ chief inspector in the Port of Brownsville. “We don’t know where it’s going.”

“I’ll tell you where it’s going,” said Domingo Gonzalez, a Brownsville activist with the Boston-based National Toxics Campaign. “It’s going into the air, into the water, into the soil. It’s being dumped.” As recently as May, soil samples collected outside several Matamoros factories by Gonzalez, and analyzed by the Boston group, detected toxic solvents at concentrations hundreds of times above U.S. limits.

Lately, Mexican officials, embarrassed by news reports about the Brownsville anencephalies and worried that environmental criticism could jeopardize congressional approval of the proposed North American Free Trade Agreement, have tried to look more aggressive in policing the maquilas.

Mexico’s environmental secretariat, which had been part of the country’s housing agency, was given independent status late last month. And the new secretary, on one of his first trips from Mexico City, visited Matamoros and announced a new get-tough policy with the maquiladoras. Just before he arrived, five maquilas were ordered closed for environmental violations.

A few days after the secretary left, all five factories were allowed to reopen, after their managers signed agreements promising improvements. “It’s mostly for show,” said Rodriguez, who is writing her doctoral dissertation on health problems in the maquiladoras. “In Mexico, there’s a phrase for this that translates as ‘the diplomacy of the brassiere.’ On the outside, it looks beautiful, but on the inside it’s oppressive.”

In Matamoros, Mexican environmental officials declined to comment. But the general manager of the Matamoros Economic Development Council said his nation is serious about improving its environmental enforcement. “There may have been some companies who said let’s move down here to Matamoros because the laws aren’t enforced, but that’s changing now. We don’t want the pollution here,” said Luis Elicondo Martinez.

For Mexico, the maquilas are a source of almost $ 4 billion annually in hard currency, and, compared to other parts of the country, also provide jobs at relatively high wages. “It all depends on what you’re looking at. These companies can go to Reynosa [a nearby Mexican city] and pay $ 6 a day instead of $ 12 here in Matamoros. Or they can go to China and pay 15 cents an hour,” said Fred Quintana, executive director of the Matamoros Maquila Association.

The prospect of a free-trade agreement that would further reduce trade barriers has border-area health officials particularly concerned, although the Bush administration argues that foreign investment attracted to the area by the trade agreement will lead to improved environmental conditions.

“As bad as things are now, they are likely to be worse with the trade agreement. Some cities on the Mexican side will double their population within 10 years, and that will bring many more problems with pollution,” said Dr. Geraldo De Cosio, deputy chief of the El Paso field office of the United Nations Pan American Health Organization.

The Bush administration, which is planning a post-Election Day push for congressional approval of the free-trade deal, has promised to take another look at birth defects throughout the border as part of a two-year environmental assessment to be conducted by the United States and Mexico.

That assessment is part of a broader plan, finalized in February, that calls for Mexico to invest at least $ 460 million over three years for environmental improvements along the border. The United States agreed to spend $ 240 million next year and unspecified amounts in future years.

But federal officials have estimated that it will cost at least $ 750 million simply to bring minimally acceptable sewage and water systems to Texas colonias.

That kind of money seems remote from the daily lives of border women like Teresa Salazar, 28, of Brownsville. Last summer, her doctor told her the fetus she was carrying had a condition she had never heard of – anencephaly – and that she would have to choose between an abortion or a stillborn delivery. She chose the abortion.

“It was a shock, because my husband and I really want children,” said Salazar, who lives in a small house amid corn fields. “At first, I thought it was my fault, and I told my husband we could separate so he could have children . . . Then they told me this was happening to other women here, and I wanted to know why. But nobody could tell me why.”