Concerns that the environment may be affecting fertility seem to be confirmed by a recent study of sperm which discovered that quality has dropped significantly over the last 50 years.
While the researchers were not looking for a direct correlation between sperm levels and the environment, they did uncover a major increase in diseases of the testicles, almost in inverse proportion to the fall in sperm quality. The most notable disease was testicular cancer, which has increased fourfold in some countries.
They believe there could be a link to the environment, but they also suggest that some common prenatal influences could also be responsible.
The study team, based at the University of Copenhagen in Denmark, concluded: "As male fertility is to some extent correlated with sperm count the results may reflect an overall reduction in male fertility."
Their analysis was based on 61 papers, published between 1938 and 1990 which included data on 14,947 men from around the world.
They pointed out that previous warnings of infertility were disregarded because they were based on data from selected groups from clinics, vasectomy centres and semen donors. Other research has also not been systematic.
While noting the increase in testicular cancer, they also point out that other abnormalities such as cryptorchidism (undescended testicles) and hypospadias (where the urinary opening is on the underside of the penis), which also account for lower sperm counts have also increased recently.
Sperm density has also declined over the study period, implying a decrease in fertile men