The research from a University of Cincinnati scientific team on the packaging chemical adds to the growing body of scientific evidence indicating that it should not be used for food contact materials.

BPA works by disrupting the important effects of estrogen in the developing brain, the University of Cincinnati team, headed by Scott Belcher, reported.

BPA shows negative effects in brain tissue "at surprisingly low doses". they say in two articles in the December 2005 edition of the journal Endocrinology.

"In the face of more than 100 studies published in peer-reviewed journals showing the detrimental effects of BPA, the chemical industry and federal regulatory agencies have resisted banning BPA from plastics used as food and beverage containers, despite the fact that plastics free of BPA and other toxic chemicals are available," Belcher stated.

BPA is used in the production of epoxy resins and polycarbonate plastics. The plastics are used in many food and drink packaging applications. Resins are commonly used as lacquers to coat metal products such as food cans, milk container linings, bottle tops, water supply pipes and dental sealants.

"While plastics are typically thought of as being stable, scientists have known for many years that the chemical linkage between BPA molecules was unstable, and that BPA leaches into food or beverages in contact with the plastics," he stated.

Scientific research has often implicated BPA in disease or developmental problems. The chemical has long been known to act as an artificial estrogen, the primary hormone involved in female sexual development.

BPA has already been shown to increase breast cancer cell growth. In the January 2005 edition of the journal Cancer Research, another University of Cincinnati research team reported that it increased the growth of some prostate cancer cells as well.

Warnings about other possible long-term health risks associated with fetal exposures to BPA have also been discussed in recent scientific literature.

Belcher and his colleagues worked with rats at a period in their development equivalent to the third trimester of human fetal development through to the first few years of childhood.

Although best known for its function as a female sex hormone, Dr. Belcher explained, estrogen also has very important roles in the developing brain of both males and females.

In the absence of estrogen, Dr. Belcher said, BPA alone was found to mimic the actions of estrogen in developing neurons. Very low doses of BPA completely inhibited the activity of estrogen. Because estrogen normally increases the growth and regulates viability of developing neurons, he said, these results support the idea that BPA may harm developing brain cells.

While high doses cause little effect, analysis of cellular and molecular markers of estrogen signaling revealed that near-maximal effects of BPA on rat brain neurons not only occurred "at surprisingly low" doses of 0.23 parts per trillion, they also happened in a matter of minutes, Belcher stated.

"From other studies it's clear that these low concentrations are in line with human fetal exposures, and at levels one might even see in the water supply," he stated.

This "low-dose" effect of BPA is troubling, since its maximum effects occur at the level typical of human exposure. This means that the harmful effects of BPA could easily be missed using standard approaches for determining the risks of chemical exposure, he stated.

"These are important considerations in view of the widespread presence of low concentrations of BPA in the environment," he stated.

Earlier research, which showed estrogens could control the survival of maturing neurons in the brain region involved in movement and coordination. Belcher and his co-workers found the effects of estrogen were the same in both males and females.

"Estrogen's actions on these neurons appear to be a double-edged sword," he stated. "During certain periods of development estrogen can kill specific subsets of neurons, but at a later developmental stage it actually appears to increase their viability."

Disruption of either of these actions of estrogen could be considered potentially harmful, he added.

"We have now shown that environmental estrogens like BPA appear to alter, in a very complicated fashion, the normal way estrogen communicates with immature nerve cells," Belcher stated. "The developmental effects that we studied are known to be important for brain development and also for normal function of the adult brain."

What remains unclear is how the inappropriate hormone signaling, or blocking the normal signaling at a critical time during development, will influence humans in later life.

"These new studies are also the first to show that estrogen's rapid signaling mechanisms are active in the developing and maturing brain in regions not thought to be involved with sexual differences or reproductive functions," Belcher stated.

As reported earlier in FoodProductionDaily.com, US scientists from Tufts University School of Medicine in the US reported during the summer that low doses of BPAcould be a contributing factor to the development of breast cancer in women.

BPA was first shown to be oestrogenic in 1938, in a study using rats. In a 1993 study BPA was found to be oestrogenic in the human breast cancer cell, the scientists state. Another 1995 study found that the liquid in some cans of tinned vegetables have been found to contain both BPA and and the related chemical dimethyl bisphenol-A.

The highest levels of BPA were found in cans of peas. BPA was also found in the liquid from cans of artichokes, beans, mixed vegetables, corn and mushrooms. All liquids which contained BPA were found to be oestrogenic to a human breast cancer cell, the scientists reported.

In 1997 researchers Fred vom Saal and others at the University of Missouri-Columbia concluded that BPA was harmful to humans and that its use should be banned. They noted that BPA is also used in the manufacture bottles, from which it leaches at an increasing rate as the bottle ages.

BPA was first identified in the 1930s. In the 1950s, chemists linked BPA together to create polycarbonates and companies began using the chemical in plastics production. BPA is now one of the top 50 chemicals being produced in the US.

A study from a group of German researchers released in September provided the first direct evidence that human exposure to BPA in Europe is very low and is, at most, in a range similar to the levels reported in other parts of the world, according to a chemicial industry site.

The research was sponsored by UBA (Umweltbundesamt), which is the German Federal Environment Agency.