Sperm production is directly disrupted by the effects of both a plastics component and a hormone used in the contraceptive Pill, scientists have found.
The discovery could account for declining human sperm counts seen in several studies, say the researchers.
It also adds to concerns over the effects of “hormone disrupter” chemicals in the environment.
The US team gave newborn male mice doses of the plastics chemical, bisphenol A, in their food. They also exposed the animals to estradiol, a synthetic form of oestrogen used in contraceptives.
Developing sperm from the treated mice did a poorer job of meiosis, the process by which cells combine genetic information from two parents.
As a result, more sperm died.
“We have a window of just a few days and we permanently change the way that the testis makes sperm in the adult,” said lead researcher Pat Hunt, from Washington State University.
Falling sperm counts have worried experts since the early 1990s, when Danish scientists reported “a genuine decline in semen quality over the past 50 years,” with possible implications for male fertility.
In another 2013 study, French researchers looked at the partners of more than 26,000 childless women and saw their semen concentration drop nearly two per cent for 17 years.
Hunt’s team investigated three mouse populations, one ‘outbred’ like humans and two others that were ‘inbred’.
The researchers saw a “very strong effect” on outbred mice and one of the inbred strains. The other inbred strain was not affected, possibly accounting for unconvincing results from previous similar studies.
“This mouse model would suggest that here’s actually a reason why these sperm counts would be falling,” said Hunt. “We’re actually doing something to this process that’s going to cause the death of more cells as they’re trying to make sperm. They’re going to get culled out by this quality-control mechanism and the upshot of that will be that if you do enough of this, you’ll drop sperm counts.”
BPA is widely used in the lining of food and drink cans, while oestradiol passes untreated through sewage plants.
Hunt, whose research is reported in the online journal Public Library of Science Genetics, fears that sperm counts will continue to fall with each exposed generation.
“We’ve seen effects over the course of several decades,” she said. “What about several generations? Infertility is becoming more common. Are we creating the perfect storm?”