May 13, 1997

A 90-day feeding study to evaluate the subchronic toxicity of nonylphenol in laboratory rats has been completed. At dietary doses of up to 2000 parts per million (ppm), no changes were noted in reproductive organs, in the estrus cycle of female rats or in sperm counts of male rats.

In this study, nonylphenol (para-nonylphenol) was administered in the diet to four groups of 15 male and 15 female Sprague-Dawley rats over a 90-day period, starting at six weeks of age. The doses tested were 0 (control), 200, 650 and 2000 ppm nonylphenol. An additional 10 male and 10 female rats were included in the control and high dose groups to allow observation of any recovery from nonylphenol-induced effects observed during the four-week period following 90 days of exposure in which both groups received the control diet. In addition to the standard toxicology endpoints measured in subchronic tests, estrus cycling was evaluated during the eighth week of the study and sperm counts, motility and morphology were evaluated at the end of the 90-day exposure period.

The study showed a decrease in food consumption and body weight in the rats fed the highest dose tested (2000 ppm). A microscopic kidney finding of decreased renal tubular hyaline droplets (considered related to alpha-2F-globulin) was seen in male rats receiving the top dose. The biological significance of this finding is unclear. No other biologically significant changes were noted in the study.

The no-observed-adverse-effect-level (NOAEL) for nonylphenol from this study was 650 ppm administered in the diet. This corresponds to a daily intake of approximately 45-50 milligrams nonylphenol per kilogram body weight in rats.

Nonylphenol is a key intermediate in the manufacture of nonylphenol ethoxylates (NPEs), used in many industrial processes. Nonylphenol is also used to make other end products with applications such as lubricant additives, polymer heat stabilizers and antioxidants, and curing agents.

The study was conducted by COVANCE Laboratories (formerly CORNING-Hazleton Laboratories) of Vienna, Virginia. Copies of the study report are available from the Alkylphenols and Ethoxylates Panel of the Chemical Manufacturers Association, sponsors of the study.