Abigail Goodman and Marc Lifsher, The Los Angeles Times

There's growing unease among parents and experts about the potential effects of plastic chemicals on the young.

Thirteen-month-old Solange Dorsainvil plays with toys made from wood and cloth, drinks from a Swiss-made aluminum sippy cup and teethes on kale stems and celery.

Her life is as plastic-free as her mother, Celina Lyons, can make it.

Celina, a Berkeley-based acupuncturist, has become increasingly worried about the possible toxic effects of plastics. "I remember hearing — I don't remember when — that my Nalgene [water] bottle was no longer safe," Lyons said. Once pregnant, she stopped storing food in plastic and cut back on plastic wrap. She sought plastic baby bottles free of a chemical called bisphenol A and teething rings free of chemicals called phthalates. (She failed to find the latter.)

"It's hard to just be a relaxed parent," Celina says. "You want to do what you can to make things as safe as possible."

More and more consumers — new mothers are leading the pack — are expressing concern about potentially toxic chemicals in plastic products. Baby blogs are abuzz with warnings about chemicals in baby bottles and toys. Retailers say that demand for glass baby bottles is higher than it's been in decades and that shoppers are snatching up bottles and training cups made from plastics without bisphenol A. California lawmakers have taken notice: Last week, the state Legislature passed a bill to ban certain phthalates in plastic items meant for children younger than 3.

Recent widely publicized studies have shown that plastics are not only ubiquitous in the environment (marine researchers have shown that plastic debris outweighs zooplankton in remote parts of the Pacific), but are found in the bodies of nearly all Americans too. Scientists have hypothesized that chemicals in certain plastics may be linked to such conditions as asthma and even obesity. But most of the research, and the strongest evidence, points to effects that certain plastics chemicals appear to exert on the reproductive system. Findings are still considered preliminary (existing studies are small and few), but reports are enough to make consumers ask: Are plastics safe?

"Unfortunately," said Dr. Philip Landrigan, a pediatrician and chairman of the department of community and preventive medicine at the Mount Sinai School of Medicine in New York, "we're in the terrible position of having to say that we mostly don't know."

Antonia Calafat, a lead research chemist at the Centers for Disease Control and Prevention, has spent the last several years measuring levels of phthalates — chemicals used to make plastics pliable — in the U.S. population. The chemicals, studies show, appear in nearly all Americans.

But while phthalates and other chemicals used in plastics have been shown to be toxic to animals, "in humans, the data are still inconclusive," Calafat said.

In fact, when it comes to humans, the data are nearly nonexistent. Very little research has examined the health risks associated with consumer use of plastics. And because of suggestive evidence from studies of lab animals, much of that research has focused largely on chemicals in two types of plastics: those marked with recycling No. 3 and No. 7.

PVC ingredient a problem

Plastic No. 3, polyvinyl chloride or PVC, was one of the earliest plastic chemicals to be linked to cancer. Studies dating back to the 1970s showed that PVC factory workers suffered an increased risk of a rare form of liver cancer — an effect that had been demonstrated earlier in animal experiments.

The toxic agent, it turned out, wasn't the finished product; it was a PVC building block, a chemical known as vinyl chloride monomer. Vinyl chloride monomer poses no threat to people who use finished PVC products. (The monomer, unlike a PVC product, is small enough to be inhaled; in the body, it gets broken down into chemicals thought to damage genetic material.) More recent research, however, indicates that other components of PVC — phthalates — may pose health risks to the end users of the plastic.

Phthalates are added to normally rigid PVC to make soft products, including the plastic bags that store blood, plasma and intravenous fluids; feeding, breathing and dialysis tubes; catheters; respiratory masks; and exam gloves. Phthalates are also found in children's toys, vinyl floors, wallpaper, shower curtains, vinyl bibs and countless cosmetics, including lotions, shampoos and nail polish.

About a decade ago, CDC researchers figured out how to detect small levels of the breakdown products — or metabolites — of phthalates in human urine. Since then, they've been monitoring levels of the chemicals in Americans and collaborating with academic researchers to find possible associations between phthalate levels and disease.

In laboratory animals, high doses of phthalates cause a conglomeration of health effects that suggest the chemical may either block the activity of male sex hormones (such as testosterone) or hamper their synthesis in the developing embryo. The so-called phthalate syndrome in lab rodents is characterized by lowered testosterone levels; a shortened distance between the anus and scrotum; testes that fail to descend; reduced sperm counts; and defects in the urethra, prostate and seminal vesicles.

The evidence from animal studies on one particular phthalate, DEHP, was enough to spur the Food and Drug Administration in 2002 to issue a notification advising healthcare providers to avoid using intravenous bags, tubes and other devices containing DEHP when treating premature babies, adults undergoing dialysis, heart transplant recipients and women pregnant with male fetuses. DEHP, the notice stated, had been shown to leach out of medical devices into stored liquids, like blood, plasma and intravenous fluid.

In the years since the FDA's notice, evidence on the effects of phthalates in humans has been accumulating. Studies have shown that the more treatment newborns in intensive-care units receive, the higher the phthalate levels in their bodies. CDC chemist Calafat collaborated with Harvard University public health professor Russ Hauser and others on studies correlating levels of phthalates in the body with decreased levels of thyroid hormone, increased DNA damage in sperm and lowered concentration of sperm.

In a study of men seeking fertility diagnoses at a Massachusetts hospital, for example, men with the highest levels of a particular phthalate (monobutyl phthalate) were more than three times as likely to have a low sperm count than men with the lowest levels of the phthalate. A separate study of men at a Massachusetts infertility clinic found that men with higher levels of mono-(2-ethylhexyl) phthalate had about 50% more sperm DNA damage than men with the lowest bodily levels of the chemical.

Other studies on phthalates imply the chemical may affect other bodily systems too. Scientists at the National Institute of Environmental Health Sciences demonstrated a link between phthalate exposure and decreased lung function in men. In Sweden, researchers compared the levels of phthalates in the dust in the homes of children with asthma and without; levels of butyl benzyl phthalate in dust were 25% higher in the homes of children with asthma than in homes of children without asthma.

At the University of Rochester School of Medicine and Dentistry in Rochester, N.Y., researchers found that among men enrolled in a large national health study, waist circumference was roughly 1 1/2 to 3 inches bigger in men with the highest levels of several different phthalates than in men with the lowest levels of the chemicals. A measure of insulin resistance, a common indicator of diabetes, was also higher in the men with the highest phthalate levels.

But the first indication of a possible "phthalate syndrome" in humans came from a study led by University of Rochester professor Shanna Swan. In 2005, Swan published results of a study of 85 mother-and-son pairs, showing that, as in rats, women with higher phthalate levels were more likely to give birth to boys with a shortened distance between the anus and the genitals. Boys whose mothers had the highest levels of mono-n-butyl phthalate were 10 times more likely to have a shortened ano-genital distance than boys whose mothers had the lowest levels of the chemicals. The boys were also more likely to have undescended testes, smaller scrota and smaller penises.

In a follow-up study, Swan and colleagues found that the phthalate levels associated with the reproductive effect were lower than the doses considered safe by the Environmental Protection Agency.

The same year that Swan's study was published, an expert panel convened by the National Toxicology Program expressed "some concern" that DEHP can affect the reproductive development of infants younger than 1 and baby boys older than 1, "concern" that the chemical could affect the male fetuses of women undergoing intensive medical care using DEHP-containing products, and "serious concern" that critically ill male infants exposed to the plasticizer could suffer damage to their developing reproductive systems.

Many scientists consider the findings on phthalates to be preliminary, but evidence of its potential effects in baby boys has been enough for lawmakers in the European Union, Mexico, Japan, Fiji and Argentina to ban the chemicals in plastic toys for young children.

"It's enough evidence to give us pause," said Richard Hellman, president of the American Assn. of Clinical Endocrinologists and a clinical professor of medicine at the University of Missouri, Kansas City, City School of Medicine.

Chemical widely found

If the science on human exposure to phthalates is in its infancy, however, the science on bisphenol A is still in the womb.

The chemical is manufactured in massive amounts: More than 6 billion pounds of bisphenol A are produced each year to make dental sealants, eyeglass lenses, toys, consumer electronics, CDs, DVDs, medical equipment, cans, and reusable water bottles, like Celina Lyons' Nalgene bottle. (Bisphenol A is found in polycarbonate plastics, which are coded with a No. 7. Not all No. 7 plastics, however, contain the chemical.)

Lately, the chemical has also been making headlines. This summer, two scientific panels announced somewhat conflicting conclusions about bisphenol A's toxicity. A government panel convened by the National Toxicology Program reviewed more than 500 published studies on the chemical and expressed "some concern" that it could cause neurological and behavioral effects in developing fetuses, infants and young children.

A group of 38 bisphenol A experts convened by the National Institutes of Health and the Environmental Protection Agency — including environmental health scientists, epidemiologists, molecular biologists, toxicologists, wildlife scientists and other researchers — reviewed 700 published studies on the chemical. Bisphenol A's ability to cause adverse health effects at low doses in lab animals, they wrote in a consensus statement published in the journal Reproductive Toxicology, "is a great cause for concern with regard to the potential for adverse effects in humans." More important, they pointed out, the levels that cause adverse effects in animals are lower than levels commonly seen in humans.

The vast majority of the studies on bisphenol A have not looked at its effects in humans; two dozen studies have measured levels of the chemical in people, and three have examined the health effects of everyday exposure to the chemical.

But in lab animals — on whom hundreds of studies have been done — bisphenol A damages the reproductive system by interfering with the effects of reproductive hormones. Male rats have reduced sperm counts and enlarged reproductive glands; female rodents have altered mammary glands, hit puberty faster than normal and have trouble getting pregnant.

Bisphenol A's capacity to cause such a range of health effects stems from its ability to mimic the human hormone estrogen. Its estrogenic activity was discovered accidentally by Stanford University researchers studying natural estrogens in 1993. A mysterious estrogen-mimicking chemical kept fouling their results: Bisphenol A, they realized, was leaching out of their polycarbonate laboratory flasks.

The chemical was originally thought to be a fairly weak estrogen-mimicker. But more recently, studies have shown that even at extremely low doses, it can exert an estrogenic effect on cells. In the more than 150 studies on the effects of very low doses of bisphenol A in animals, the chemical has been linked to prostate and mammary gland cancers, early onset of puberty and reproductive-organ defects.

The authors of the Reproductive Toxicology paper, led by University of Missouri-Columbia biological sciences professor Frederick vom Saal, suggested that human health trends — including increases in reproductive cancers, diabetes and obesity, declining semen quality in men and early puberty in girls — could be related to the health effects seen in lab animals exposed to low levels of bisphenol A.

"The effects in animals are occurring at blood levels that are below the average levels found in humans," Vom Saal said. Combine that with the fact that scientists understand the molecular mechanism through which the chemical causes health effects in animals — that is, by mimicking reproductive hormones — and it seems plausible that the chemical could be responsible for the same in humans.

But while studies show that bisphenol A can be found in the majority of Americans (it leaches out of medical equipment, dental sealants, baby bottles and the linings of food cans), epidemiological studies have yet to prove or disprove a link between the chemical and any health effects — largely because few such studies have been done.

Japanese researchers have conducted three studies on the chemical's effects in women. Scientists at the University of Tokyo in 2004 reported perplexing variation in serum levels of the chemical in women with and without endometrial hyperplasia, a potentially cancerous and estrogen-related thickening of the uterine lining in women. Levels were highest in women with a benign form of the condition and lowest in women with the worst form of the disease.

But a separate group of Japanese researchers published results that same year showing that women with polycystic ovarian syndrome had bisphenol A levels 50% higher than healthy women. And the University of Tokyo group in 2005 published results showing that levels of the chemical in women with a history of miscarriages were more than three times as high as levels in a comparable group of healthy women with no such history.

"They're small studies," Vom Saal said, "but they replicate what was seen in animals."

Studies are few

That paltry number of studies — on both bisphenol A and phthalates — has most scientists involved in the debate calling for more research.

"The bottom line is, we need more studies," said Hellman of the American Assn. of Clinical Endocrinologists. "We really don't have a handle on this."

Hellman and others agree that of the existing evidence, those studies pointing to a possible link between phthalate levels and reproductive harm in baby boys is most convincing.

Newborns and developing fetuses are, in general, highly vulnerable to toxic exposures. Pound for pound, Mount Sinai's Landrigan explained, kids breathe more air, consume more food and drink more water than adults; they also tend to put just about anything — edible or not — into their mouths, which translates into much bigger doses of environmental chemicals than adults take in.

Children and fetuses are also works in progress; their organ systems are still developing, their hormonal communication pathways are still being established, and their ability to metabolize food and chemicals is still being honed.

So while studies are beginning to suggest health effects in infants, the same chemicals may pose no risk to adults.

Regulations sought

That open question, however, has environmental and health advocates calling for tighter regulation of potentially toxic chemicals until the balance of epidemiological evidence comes in.

At present, said Jane Houlihan, vice president of research at the Environmental Working Group, a Washington, D.C.-based advocacy organization, "it's impossible for consumers to navigate store shelves to know what is safe."

Advocacy groups are calling for better labeling of consumer products, so shoppers can avoid products containing phthalates and bisphenol A as they choose. Companies are also taking steps, absent government regulation, to stop using potentially toxic chemicals.

Hospitals across the country are taking phthalate-containing PVC out of neonatal intensive care units. Kaiser Permanente and Catholic Healthcare West are phasing the chemical out of their operations altogether. A sizable list of toy makers, food conglomerates and pharmaceutical companies — including Lego, Playmobil, Dean Foods, Nestlé, Bayer and Bristol Myers — have pledged to phase out PVC too. Smaller and newer companies, like Boca Raton-based Born Free, are marketing baby bottles and cups free of bisphenol A.

Still other advocates argue that change is needed at a higher level, on par with the European Union's outright ban on phthalates used in children's toys, which was passed in 2005. "You really can't shop your way out of this," Houlihan said. "We're going to need to see change at a much broader level before you really have products that are safe on store shelves."

But many researchers — including those studying the chemicals in plastics — are taking a more measured approach. The CDC's Calafat pointed out that far more research is needed before scientists can say with certainty whether traces of plastic found in people are harmful or safe. Swan, at the University of Rochester, concurs. "I definitely don't think it's time for the government to say we all have to stop exposing pregnant women to PVC," Swan said. "But we are at a place where people should be given the choice to avoid it if they want to."