Boys exposed in the womb to high levels of a chemical found in vinyl products are born with slightly altered genital development, according to research published today.

The study of nearly 200 Swedish babies is the first to link the chemical di-isononyl phthalate (DiNP) to changes in the development of the human male reproductive tract.

Previous studies of baby boys in three countries found that a similar plastics chemical, DEHP, was associated with the same type of changes in their genitalia.

Less is known about the reproductive risks of DiNP, a chemical which scientists say may be replacing DEHP in many products such as vinyl toys, flooring and packaging. In mice, high levels block testosterone and alter testicular development.

“Our data suggest that this substitute phthalate may not be safer than the chemical it is replacing,” wrote the researchers, led by Carl-Gustaf Bornehag at Sweden’s Karlstad University, in the journal Environmental Health Perspectives.

Levels of DiNP in U.S. adults and children more than doubled in the past decade.

“This study raises concern about DiNP, which is being used in increased amounts in products that contain vinyl plastics, and the impact on the developing fetus,” said Dr. Russ Hauser, a professor of environmental and occupational epidemiology at Harvard School of Public Health who is not involved in the new study.

The researchers measured metabolites of five phthalates in the urine of pregnant women during the first trimester. Development of male reproductive organs begins during that period, said senior study author Shanna Swan, a professor of reproductive science at Mount Sinai Hospital in New York.

The researchers then measured the anogenital distance – the length between the anus and the genitals – when the boys were on average 21 months old. Boys who had been exposed to the highest levels of DiNP in the womb averaged a distance that was slightly shorter – about seven-hundredths of an inch – than the boys with the lowest exposures.

“These were really subtle changes,” Swan said.

Considered a sign of incomplete masculinization, shortened anogenital distance in men has been associated with abnormal testicular development and reduced semen quality and fertility. In men, this measurement is typically 50 to 100 percent longer than in women.

But it’s unknown whether a slightly shorter distance in infants corresponds with any fertility problems later in life.

“More research is needed to understand the extent to which shorter anogenital distance at birth is associated with impaired reproductive function later in life in humans,” said Emily Barrett, a reproductive health scientist at the University of Rochester Medical Center in New York.

For other phthalates, the study found shorter anogenital distance with higher concentrations, but the findings were not statistically significant, meaning they may have been due to chance. The Swedish women in the new study had phthalate levels similar to U.S. women in Swan's previous studies. Those studies, published in 2005 and 2008, linked several phthalates to shorter anogenital distance.

A spokesperson for the American Chemistry Council, a group representing chemical manufacturers, said the study "reports small changes that are associated with exposure to DiNP" but does not prove that the chemical caused the changes.

The spokesperson said the new findings "seem to contradict" the authors' earlier findings as well as two other studies that found no association between DiNP and men's anogenital distance. In addition, the study is based on a single urine sample from the mothers. As a result, the "plausibility is low," the industry group said. "To demonstrate causal associations in the field of epidemiology, there are criteria that should be evaluated and considered...We found that this study scores low for many important considerations."

The industry group did not answer questions about what types of products DiNP is used in. The scientists said exposures to the chemical can come from food or through skin contact with home furnishings or child-care articles.

In 2008, the United States temporarily banned use of DiNP and two other phthalate plasticizers in toys and other children's products. “This ban does nothing to protect the developing fetus,” Swan said.

The Consumer Product Safety Commission recommended in July to make the ban permanent and urged that “U.S. agencies responsible for dealing with DiNP exposures from food and other products conduct the necessary risk assessments.”

While it’s nearly impossible to eliminate exposure to phthalates, Swan suggested that pregnant women may be able to reduce their exposures by incorporating unprocessed, unpackaged foods into the diet and by avoiding heating or storing foods in plastic containers.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.