The UK's Daily Telegraph reports that sperm counts are falling in Scotland:
The largest British study into sperm counts has found that they have fallen by almost 30 per cent in 14 years, researchers announce today.
The survey, based on almost 16,000 semen samples taken between 1989 and 2002, lends weight to concerns that sperm counts are falling.
But it is a controversial area because an accurate number for “normal” sperm counts is not precisely known and some studies have failed to find evidence of a reduction.
Dr Bhattacharya said the results were significant. The level of 62 million did not affect a man's fertility, “but we need to know if the counts are going to continue to fall.
Dr Bhattacharya said there were two broad reasons for the reduction: environment and genetic factors.
Other research has pointed to increased oestrogen in water supplies, the result of women's use of the Pill and hormone replacement therapy.
Industrial processes have also been blamed, including the use of solvents and high concentrations of lead.
A recent paper suggested that plastic-lined nappies might play a part because they raised the temperature of baby boys' scrotums.
The evidence is a little hard to parse. There's evidence suggesting this is a world-wide problem, at least in industrialized countries, but there are are also national and regional variations, probably due to environmental factors.
From having lived both places, I get the impression that industrial pollution and exposure to chemicals and to radiation (think Sellafield) are greater on average in the UK than the US, so the environmental explanation seems plausible to me.
Not that things are rosy in the US….
Although in the US there's evidence of dropping counts nationwide, there's also some evidence to suggest that the in the US the problem may be more serious in rural areas than in cities (or at least, in the one Missippi rural are studied). This dovetails with the suggestion that pesticides may be to blame. (Another surprising suggestion, which doesn't explain the city/rural result, is that the worldwide decline is due to putting iodine in table salt !)
A more comprehensive study reviewing US research on this subject is awaiting publication, but the web site describing it gives no hint of its conclusions.