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Benign Study, Toxic Spin

Get ready for another round of the supposed horrors done to hormonal systems by so-called "endocrine disrupters." 

These manmade chemicals found in food, consumer products and the environment are alleged to cause everything from cancer to reproductive and developmental problems to attention deficit disorder. Though the news essentially is benign, its spin will be toxic. 

The scare's new round comes from Dr. John Brock, a researcher at the Centers for Disease Control and Prevention. Brock's report states higher-than-expected levels of a metabolite of an alleged ED — "di-n-butyl phthalate" or "DBP" — were detected in human urine samples. 

News of the study was leaked to The Hartford Courant last week. The study, which according to the CDC will be available on the Web September 1, won't officially be published until October in the U.S. government journal Environmental Health Perspectives

Foreshadowing the coming hype, the Courant quoted Brock saying DBP was detected at "[levels] higher than we anticipated" and at "levels we are concerned about." Brock added, "I can tell you that we're going to be working on phthalates for a long time here at the CDC." 

EDs grabbed the media spotlight with the March 1996 book Our Stolen Future, an alarmist's compendium of wild anecdotes. Without a scientific basis, for example, the authors blamed EDs for the phenomenon of "gay gulls" — female herring gulls that nested together because male gulls, supposedly feminized by chemicals, weren't interested in mating. Much to the chagrin of its supporters, however, the hoopla over the book faded in the face of unusually balanced media reports by respected scientists who criticized the book and its theories. 

The scare returned with a vengeance in June 1996, when researchers from Tulane University reported in the journal Science that combinations of pesticides and PCBs were 1,500 times more potent as EDs than the individual chemicals. In that study's wake, a federal law was hastily enacted requiring the Environmental Protection Agency to test chemicals for their ED potential. 

Within six months, though, scientists from around the world reported the Tulane results couldn't be duplicated — unusual for a laboratory study. The Tulane researchers subsequently retracted their study from publication. Incredibly, though the study was gone, the requirement for testing stayed. 

From 1997-1999, the ED scare emerged in different forms. Alarmists targeted soft plastic toys, vinyl intravenous bags, baby bottles and plastic food wrap as potential sources of exposure to EDs. Toy makers reformulated products even though no scientific data showed any cause for alarm. 

During the controversy, the National Academy of Sciences' research arm, the National Research Council, reviewed the science on EDs. In August 1999 the NRC issued a report that should have ended the ED scare, saying no persuasive evidence supported the ED theory. The NRC acknowledged that high-level exposures to some chemicals may pose a risk to humans and wildlife, but it concluded the evidence was inadequate to suggest that low-level exposures from the environment pose any risk. 

What are Brock's results? Should you be concerned? Brock didn't return any of several phone calls requesting an interview. But Brock presented his results several months ago at a closed-door meeting in Europe. First, though, here's some background on DBP. 

DBP is used in the manufacture of cellulose plastics, dyes, food packaging, perfumes, skin emollients, hair spray, nail polish and insect repellents. 

Chemical Industry Institute of Toxicology researchers reported in a recent issue of Toxicological Sciences no effects observed in rats given a DBP dose of 50 milligrams per kilogram of bodyweight per day during a key part of the gestational period. At twice this dose, about one-third of the rat pups showed a mild effect (retaining circles around their nipples for a longer period). At a dose 10 times the no-effect level, hypospadia (a birth defect of the urinary tract) was observed in fewer than 10 percent of the animals. 

"Acceptable" levels of human exposure to chemicals are typically set 100 times below the no-effects level in animals. There's no scientific basis for using 100; it's a convention believed to provide a large safety margin. When animal data involves birth defects, like for DBP, the acceptable level of exposure is set 1,000 times below the no-effects level to be even "safer." 

While Brock did not examine any health effects potentially associated with exposure to DBP and did not directly measure human exposure to DBP, he used his results to estimate human exposure to DBP — estimates presented privately, according to sources. 

Brock's estimate for an average exposure to DBP among his sample was about 30 times below the "acceptable" level in humans, based on the no-effect level observed in the CIIT study. His estimate at the 95th percentile level of exposure is almost 5 times below the "acceptable" level. Brock's worst-case estimated exposure is about 3.5 times greater than the "acceptable" exposure level. For unknown reasons, the subgroup in Brock's population with the highest estimated exposure are women of childbearing age. So birth defects are the outcome of concern. 

The "big deal" — if Brock's data is sound and his guesstimates of exposure are reliable — is that, in the worst case, a pregnant woman might be exposed to DBP at a level "only" about 278 times less than the no-effect level in rats and about 2,780 times less than the level at which 10 percent of rat pups are reported with hypospadia. Where's the danger? 

Brock's dubious result is no doubt why he resorted to publication with Environmental Health Perspectives. The less-than-rigorous journal once published a study featuring a weak statistical link between low-levels of air pollution and sudden infant death syndrome. Publication was timed to help the EPA battle for stricter air pollution standards. 

Despite employment with the CDC, Brock is a well-known activist-scientist. He signed "consensus statements" with other notorious advocates of the endocrine disrupter theory. These statements say, among other things, "We are certain ... endocrine-disrupting chemicals can undermine neurological and behavioral development and subsequent potential of individuals in the womb." 

But it's difficult to square this "certainty" with the National Research Council's conclusion there was no persuasive evidence supporting the ED theory. 

Coincidentally, the Courant article featured extensive quotes from Brock's fellow consensus statement signatories — the University of Florida's Louis Guillette Jr. and the EPA's Earl Gray. Guillette said "[Brock's study is] going to rewrite how we look at phthalates." Gray expressed "concern" that more chemical testing was needed. Brock and Guillette co-authored a study failing to link small penises among alligators from Florida's highly polluted Lake Apopka with chemicals. 

Adding to the ho-hum of Brock's study and the undeniable agendas of Brock and EHP is DBP's track record. DBP has been used in industrial process since 1900. Scientific study of DBP dates back to at least 1953. There is not a single study that links exposure to DBP with any human health effects — including Brock's. 

The good news is the DBP scare doesn't have a leg to stand on. When this round of the endocrine disrupter scare fades, the bell will soon sound for another. 

— Steven Milloy is a biostatistician, lawyer, adjunct scholar at the Cato Institute and publisher of Junkscience.com.