March 31, 2003 -- A chemical used in plastic baby bottles -- and many other food and beverage containers -- causes genetic damage in mice, a new study suggests. But the plastics industry says there is no cause for alarm.
The damage is seen in egg cells of female mice. When these cells try to divide, their chromosomes don't line up right. In humans this results in spontaneous abortion, birth defects, or mental retardation, says genetic abnormalities expert Patricia A. Hunt, PhD, of Case Western Reserve University School of Medicine.
In studies published in the April issue of the journal Current Biology, Hunt and colleagues showed that very low doses of a common plastics ingredient may cause these effects. They also found that dangerous amounts of the chemical -- known as BPA -- can seep out of used plastic bottles.
"The effect we saw is pretty dramatic," Hunt tells WebMD. "We were stunned by how low a dose it took. I am becoming pretty convinced there are significant effects [of BPA] at pretty low exposures. I can't say how scared you should be because our studies don't say anything about humans. But that's why we study animals. We assume the processes are pretty well the same in humans."
The chemical is known as bisphenol A or BPA. It's found in all kinds of common products, mostly polycarbonate plastics. Nearly all plastic baby bottles in the U.S. are made of this kind. So are many common food containers, water storage bottles, aluminum can linings, and even some kinds of dental sealants.
Other animal studies have linked BPA to low sperm count, hyperactivity, early puberty, obesity, small testes size, and enlarged prostates. But Hunt's is the first study to suggest that BPA can affect future generations.
Frederick S. vom Saal, PhD, professor of biology at the University of Missouri inColumbia, has studied BPA for many years. He says that some 40 studies show that polycarbonate plastics are dangerous. Hunt's findings scare him most of all.
"What is so important about this finding is we are talking about something that causes spontaneous abortions of babies," vom Saal tells WebMD. "And then there is the horrifying fact that babies are born with these chromosomal abnormities. ... This is a higher level of concern, a major new finding of a really profound adverse effect of this chemical in mice that were just drinking out of old baby bottles."
The findings also frighten Vom Saal's colleague, reproductive endocrinologist Wade V. Welshons, PhD.
"We found bad effects of fetal exposure to BPA, but that is something a pregnant woman can avoid. When my wife was pregnant, we did try to avoid it," Welshons tells WebMD. "But Hunt's study shows exposure may be unavoidable. It is shocking."
Hunt didn't intend to study BPA. She was studying egg development in mice. Suddenly, she started finding genetic defects in eggs from mice that were supposed to be normal. Nearly a year's work was destroyed. Finally, she found the cause. The mice were housed in polycarbonate plastic cages. They drank from polycarbonate bottles. Both had accidentally been washed in a floor cleaner that made them degrade faster.
When Hunt's research team exposed new plastic bottles to floor cleaner, they gave off lots of BPA. Sure enough, they found, BPA by itself caused the genetic changes. But then they found that the bottles gave off BPA much more easily than they'd suspected.
"No, it doesn't take washing the bottle with floor soap," Hunt says. "As these products get reused, they start to leach BPA. The part that will make your hair stand on end is baby bottles. They are made of polycarbonate plastic. People who use them say that after just washing them in the dishwasher they see these same changes in the bottles. When we see bottles start to turn cloudy, they are leaching. And when they get sticky, they are giving off a lot of this stuff."
The plastics industry says there is nothing to be alarmed about. Large studies of BPA show no effects on animals or on their offspring, says Steven Hentges, PhD, executive director of the polycarbonate business unit of the American Plastics Council. Hentges represents the makers of polycarbonate and BPA.
Hentges says there are three things to know about the Hunt study:
- It doesn't actually demonstrate any health hazard. It only looked at the genetic effects of BPA on mice, and not at whether it caused reproductive problems or deformed embryos.
- The techniques used in the study don't necessarily predict actual harm in animals or humans.
- The study does not show that the effects seen are relevant to humans.
"There has been a lot of research on the subject of BPA," Hentges tells WebMD. "It is very reassuring research. It give us confidence that BPA does not cause reproductive problems. The bottom line is when you look at the whole package of BPA studies, you don't see any bad health outcomes. There have been no reproductive problems of the type you might expect from what Hunt and co-workers report."
That may not be true, say vom Saal and Welshons. People are reaching puberty earlier. Men have lower sperm counts. There's an epidemic of obesity. Could some of this be related to the millions of tons of BPA generated each year?
"There is already enough environmental exposure to lead to problems in humans," Welshons says. "In a recent study, fetal umbilical blood shows higher BPA levels than we generated in mice. Human exposure levels are already high."
"The horrifying thing is that it looks as though these effects in the Hunt study and other studies happen at lower doses than what is actually found in human fetal blood -- umbilical cord blood," vom Saal says. "That is pretty stunning. That is an alarm. It needs to be the basis for a very serious re-evaluation of the potential for human harm of BPA."
Hentges points to large studies -- including one published last year by the Research Triangle Institute -- that fail to show any effect of BPA on animals, their organs, their genes, or their offspring. Vom Saal and Welshons say that all such studies have been paid for by industry sponsors and all are flawed. Hentges says it is the smaller studies that are flawed.