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September 7, 1999
ALKYLPHENOLS BULLETIN
OCTYLPHENOL STUDY FINDS NO REPRODUCTIVE
OR ESTROGENIC EFFECTS
A new study has found no adverse effects on the reproductive system of laboratory rats from exposure to octylphenol (OP).
The study, "Two-Generation Reproduction Study with p-tert-Octylphenol (OP) in Rats," also did not show endocrine-related effects from OP. The study design is considered the definitive evaluation for effects on mammalian reproduction by government agencies and scientists throughout the world.
The researchers, led by Dr. R.W. Tyl of Research Triangle Institute, conclude that "no estrogenic or reproductive effects occurred from dietary exposure to rats for two generations over a 10,000 fold dose range." The researchers further conclude that the study did not support previous preliminary reports of effects on sperm count and testes weights from low doses of OP.
OP is used primarily to make octylphenol ethoxylate (OPE) surfactants, a class of alkylphenol ethoxylate (APE) compounds. OPEs are used in cleaning products and in pulp and paper, textiles, coatings and other industrial processes.
The researchers note that OP has been "implicated as an environmental estrogen due to its weak binding to the estrogen receptor" and that they conducted the study to "determine if OP presents a risk to [human] reproductive health."
The results of the study also indicate that OP would not be considered an "endocrine disrupter" in mammalian systems, using the internationally accepted definition of the term (Weybridge Conference).
The two-generation reproduction study in CD rats, which followed U.S. EPA OPPTS Guidelines, evaluated possible reproductive organ effects and measured sperm parameters. In addition to the requirements of the Guidelines, the study monitored female rats from the second generation up to vaginal opening, male rats from the second generation up to adulthood (to allow for sperm measurements) and measured dorsal prostate weights in adult rats. Doses for the study were selected in cooperation with the U.S. EPA to provide typical high-dose toxicity effects and to attempt to replicate effects on sperm counts and testes weights at lower doses, as previously reported by other researchers (Dr. Richard Sharpe and colleagues).
The researchers found no effects on any reproductive parameters and no effects on sperm measurements, estrous cycling or reproductive organs at dietary concentrations of 0, 0.2, 20, 200 and 2000 ppm (parts per million) of OP. Consistent with the study design, reduced parental and offspring body weights were observed at the highest dose.
Based on their findings, researchers established the No Observed Adverse Effect Level (NOAEL) for reproductive toxicity at greater than 150 milligrams of OP per kilogram of body weight per day and for general toxicity at approximately 15 mg/kg/day. Because potential human exposure to OP is generally estimated to be less than 0.001 mg/kg/day, many times lower than these NOAELs, it does not appear that the use of OP poses a significant risk to humans.
In addition to its contribution to the issue of reproductive toxicity of weakly estrogenic materials, this study demonstrates that positive results from in vitro and short-term in vivo assays must be confirmed in definitive studies before making assumptions regarding the potential hazard and risk of these types of chemicals. Further, it adds to the increasing evidence that weakly estrogenic materials do not exhibit unusual or a non-linear dose response and that low-dose effects are not expected.
The study results will be published in an upcoming edition of Regulatory Toxicology and Pharmacology. The results also were reported at a recent Society of Toxicologists (SOT) meeting in Washington, DC.
The study was sponsored by Union Carbide Corporation and Schenectady International, Inc.
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