BY OUR PHARMA CORRESPONDENT
11 August, 2005: Recent scientific evidences suggests that certain chemicals like phthalates and Bisphenol A (BPA) designed to soften plastics could cause potential harm.
Increasing number of research data indicate that these bioactive chemicals are dangerous and should be banned.
Nevertheless, the chemical industry insists that phthalates and BPA are harmless. American Plastics Council sources maintain that the potential human exposure to BPA is extremely low and poses no known risk to human health, citing safety assessments from European and US regulatory agencies.
While some others argue that European and US assessments are based on scientific literature published in the 1980s and 1990s. There are now over a hundred [recent] studies showing adverse affects of BPA in different animal models, they say. The tests performed on rodents cannot be extrapolated to indicate potential human health effects.
Regulatory agencies attempt to apply a substantial safety factor when extrapolating from animal models to the human situation. For example, the US Environmental Protection Agency (EPA) calculated the acceptable daily intake level (known as the Reference Dose, or RfD) for BPA by dividing the rodent "lowest effect" level of 50,000 µg/kg/day by 1000 to obtain an RfD of 50 µg/kg/day. The European Commission adopted a more conservative acceptable daily intake level of 10 µg/kg/day.
However, many recent studies have highlighted potential harmful effects of very low doses of phthalates and estrogenic compounds. These studies raise questions as to the actual human exposure levels. In the case of pregnant women, as BPA may be concentrated in the human placenta and amniotic fluid as fetal development represents the most sensitive period of life in terms of exposure to chemicals like phthalates and BPA.
Earlier, reproductive biologists from the University of South Dakota investigated the effects of estrogenic compounds on pregnant mice. They had found that fluctuations in the levels of the natural endogenous hormone estradiol induced changes in prostate development in utero.
In their study, they fed low levels of BPA (10 µg/kg/day) to pregnant mice for four days.1They then removed fetuses by cesarean section and removed the prostates from male embryos. Using sophisticated 3-D image reconstruction, they made precise measurements of the developing prostate. As a positive control, they group used diethylstilbestrol (DES), an estrogenic compound similar in structure to BPA and associated with reproductive organ defects and cancer in humans.
They noted that low-level exposure to the compounds caused an increase (up to 40%) in the size and the number of the prostate ducts, and increases in proliferation of the basal epithelial cells of the primary ducts. They also observed a narrowing of the bladder neck and urethra. The researchers suggest that the observed deformities could predispose animals to prostate cancer and bladder disease in later life, and that the virtually identical effects of BPA and DES make a strong case for the relevance of the rodent model and the potential human hazards.
Recently, the Tufts University Medical School in Boston researchers showed that environmentally relevant doses of BPA affect mammary gland development in mice and the University of Rochester School of Medicine and Dentistry, New York, reported an association between male genital defects and phthalate exposure in pregnant women. Also, in collaboration with researchers at Yale University they found evidence for BPA effects on brain development in rodents.
Still, researchers are divided over the study's relevance to human health.
BY OUR PHARMA CORRESPONDENT