20 October 2010
Chemicals called phthalates that are present in most plastics maybe responsible for the global decline in male fertility according to several international studies
A technician takes a sample from a rubber band to measure how much of phthalates it contains during a demonstration at a laboratory in Berlin
A recent study conducted by the European Environmental Bureau found that all sorts of products – including pencils, shoes, erasers, paint and clothing – contain phthalates.
Phthalates are regularly used to make plastics more flexible. There are about 25 of them, and in recent decades they have permeated the very fabric of our society, right down to the shoes on our feet. They are in the air we breathe and the paint on our office walls and they put the flex in our electric cables. They are in our food, some scientists think, after leaching out of the pipes and plastics used in food processing machinery. They are in our bodies.
The global chemicals industry produces nearly six million tonnes of phthalates every year. Some scientists, and an increasing number of governments, have begun to suspect that phthalates might be connected to a massive drop in male fertility globally over the past few decades as well as the problems with sexual development of boys in the womb.
In pregnant rats, studies have proven that exposure to some phthalates reduces testosterone levels in the male foetus, interfering with development of the penis and descent of their testicles. But it was not until 2005 that scientists linked the chemicals to changes in humans.
It was by researchers at Rochester University, New York, studied the masculinity of newborn boys. "We found that in human male infants, as predicted by animal studies, when the mother was exposed to some phthalates, the boys had changes in their reproductive development, which was not fully masculinised," says Shanna Swan, who led the study. The study was not perfect – at just 134 infants, the sample size was small – but Swan is working on a new, bigger study.
Other scientists are also trying to pin down the link between phthalates and changes in humans. In an Edinburgh laboratory, a mouse wanders through its cage to sip at some water tainted with plastic softeners. Under the skin on its back are grafted tiny pieces of tissue from the testicles of a human foetus. The objective is to directly ascertain if those softeners could be confusing our hormones and mutating the genitalia of unborn infants.
"We have solid evidence testicular cancer has increased progressively in the past 50 to 70 years," said Richard Sharpe, who led the study, "and it has happened in a space of time that coincides with lifestyle and environmental changes"
Scientists are also beginning to better understand how phthalates enter our bodies. One of the main channels may be the food we eat. In one study, three volunteers abstained from eating for 48 hours, drinking only mineral water, while the levels of phthalates were measured in their urine.
Within the first 18 hours, levels of DEHP (Bis(2–ethylhexyl)phthalate) plummeted and remained low for the remaining 30 hours, suggesting that food was the main source. "I am certain that food is the main exposure route for DEHP, but spikes in phthalate levels seen in the study show there are other exposure routes too," said Holger Koch, who led the study. "We suspect phthalates are getting into food via the plastics used in the various steps of food processing."
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