January 7, 2003
Review of a recent study1 raises many questions about its suggestion that there is a statistical correlation between diethyl phthalate (DEP) and DNA damage in sperm, according to Marian Stanley, Manager of the Phthalate Esters Panel.
"We take all such reports seriously, but we emphatically agree with the authors that many questions remain to be answered about the scientific validity of this study," said Ms. Stanley. "It is, as the authors say, a very preliminary study of a small, non-random sample of men, with no control group of fertile men. Furthermore, the study is at variance with the large body of other data on DEP, which show it to have very little biological activity in laboratory animals." DEP is a material used in cosmetics, perfumes and other personal care products.
The objective of the study was to determine whether there is any relationship between measures of sperm quality and phthalate exposure; however, the impact of other genetic, environmental, or behavioral factors on sperm quality was not investigated. One urine sample from each of several patients at an infertility clinic was analyzed for the presence of phthalate metabolites as evidence of phthalate exposure. The presence of MEP, a by-product of the metabolism of DEP, was correlated to one of the measures that the authors claim to indicate sperm quality, in an experimental procedure known as the comet assay. MEP exhibited no significant relationship to other comet assay measures, or to more traditional measures of sperm quality, such as sperm number and movement.
The study authors themselves caution against leaping to conclusions. They state in their paper that the data "must be interpreted cautiously since the phthalate levels are based on a single urine sample from a limited number of subjects."
Other questions raised by initial reviews of the report:
- It is well known that a statistical association between two observations does not indicate cause and effect. One would expect sperm samples taken from patients at an infertility clinic to show some abnormalities. It is unclear why the subjects were not compared to a control group drawn from the general population.
- The comet assay is an experimental test measure in the determination of fertility. The authors provide only limited evidence of the reliability of the comet assay to predict infertility; they do not claim that there is a correlation between the results of the comet assay and infertility.
- The levels of DEP found in the samples from the men tested are not unusually high. They are similar to those found in the general population by the Centers for Disease Control and Prevention in its biomonitoring study, which presumably included men with and without fertility problems consistent with the general population.
- The data on DEP was recently evaluated by an independent review panel and was given a clean bill of health for use in cosmetics. Activist groups that challenged the review panel on other conclusions did not question its conclusions about the safety of DEP.
The Panel supports all credible scientific research on phthalates and looks forward to a full-scale study conducted in accordance with standard scientific protocols.
Contact:
Marian K. Stanley
Manager, Phthalate Esters Panel
marian_stanley@americanchemistry.com
(703) 741-5623
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1 Duty, S, Singh, N, Manori S, et al. Environmental Health Perspectives, The relationship between environmental exposures to phthalates and DNA damage in human sperm using the neutral comet assay. 6 December 2002. http://ehpnet1.niehs.nih.gov/docs/2003/5756/abstract.pdf
