Last modified 6 November 2006
About phthalates Listen to an international teleconference What
are phthalates and how are they used?
While high doses of phthalates do constitute risks in the sense of traditional toxicology, these low doses change the stakes dramatically. Gray's work reveals that male reproductive development is acutely sensitive to some phthalates. For example, the phthalates dibutyl phthalate (DBP) and diethylhexyl phthalate (DEHP) produced dramatic changes in male sexual characteristics when exposure took place in utero, at levels far beneath those of previous toxicological concern. These changes included increases in the rates of hypospadias and other indications of demasculinization. Enough questions about phthalates have been raised during the last few years for the National Toxicology Program, under the auspices of its recently established "Center for the Evaluation of Risks to Human Reproduction" (CERHR), to convene a panel of independent experts in 1999 to review scientific evidence addressing developmental threats of phthalates. The panel issued a draft report in August 2000. Its conclusions are severely restricted by the fact that few of studies necessary to address fetal impacts of phthalates have been done. For a least one of the phthalates they addressed, DEHP, the panel had serious concern about health impacts. Not surprisingly, given the state of research the report's conclusions are tentative, establishing plausible but uncertain risk. One of the key points is DEHP's impact on developing Sertoli cells, cells in the male reproductive tract that are central to sperm formation. Damaged Sertoli cells during development lead to sperm maladies in adulthood, including low sperm count. DEHP does not cause Sertoli damage directly; damage instead is caused by a metabolite of DEHP, monoethylhexyl phthalate (MEHP). In summer 2006, two papers upped the ante considerably on possible low-level effects of phthalates. The ranges at which Gray et al. have conducted their experiments are close to the range of common human exposure, but still somewhat above. These new papers reveal biological impacts in animals well within the range of common human exposure, and show show non-monotonic action of DEHP at environmentally-relevant levels. One examined impacts on the activity of the enzyme aromatase, which is essential for masculinizing male brains. The second experimented with DEHP's ability to exacerbate allergic reactions to an allergen, providing a possible clue as to why allergy rates have gone up so much in the developed world. Non-monotonic dose response curves are important because they invalidate current approaches to developing health standards. In May 2005: For the first time, researchers have identified an association between pregnant women’s exposure to phthalates and adverse effects on genital development in their male children. The pattern of genital changes seen in these baby boys is consistent with the "phthalate syndrome" previously observed in rodents prenatally exposed to phthalates. It is also suggestive of "testicular dysgenesis syndrome," a human health condition proposed to be linked to exposure to endocrine-disrupting compounds. The adverse effects are seen at phthalate levels below those found in one-quarter of women in the United States, based on a nation-wide survey by the Centers for Disease Control. More... In August 2000, Puerto Rican scientists reported on an association between exposure to DEHP and premature breast development in young girls, possibly linking phthalates to trends in puberty. In September 2000, the US Centers for Disease Control released the first substantial assessment of phthalate exposure in the American public. Their study analyzed urine metabolite residues of seven phthalates. Levels were high for several of the compounds studied, particularly the metabolite of DBP. Of greatest concern was the discovery that in their sample, an disproportionate number of women of child-bearing age bore high levels of this metabolite. Given Gray's data on fetal vulnerability, this is precisely the population that should minimize exposure to this anti-androgen. In winter/spring 2002-2003, three studies linked phthalate exposure to reductions in semen quality. All were of men exposed to background, environmental levels of phthalates, not higher occupational levels. One showed DNA damage in sperm. Two others (one from the US, the other from India) found reductions in sperm quality in men with slightly elevated phthalate levels. Phthalate levels associated with the damage were well within the range experienced by many Americans. The
debate about regulation and public health protection European regulators kicked off this debate when they began to explore the possibility of bans on toys intended for infants that contained DEHP. This set in motion fierce industry lobbying from the United States to head off the ban, an effort that not only proved unsuccessful ultimately in Europe, but one that was matched in the US by a call by the Consumer Products Safety Commission for a voluntary phase-out by US manufacturers, not only from pacifiers and toys but also from certain medical devices. Several large US toy manufacturers, including Disney and Mattel, made public commitments supporting the phase-out. The debate heated up further in the US when an industry PR firm that masquerades as a public health organization, the American Council on Science and Health, put together a panel to review the safety of phthalates. Headed by retired Surgeon General C. Everett Koop, the panel ultimately issued a flawed report that concluded phthalates were safe. Their report failed to consider several key recent publications and misrepresented another, citing the latter as stating that no kidney damage was caused when in fact the research did not assess kidney damage. They committed an even more basic error, moreover, by accepting the absence of data as proof of safety. Absence of data proves only ignorance. A devastating critique of this report was published by Health Care Without Harm (a PDF file; long download on slow modems). The American Academy of Pediatrics entered the debate in June 2003, issuing a report in Pediatrics that recommends research on phthalates effects on the fetus and infants. Their review of the literature found that no studies had directly addressed this issue, yet animal research clearly documents harm and data from the US Centers for Disease Control shows widespread exposure.
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