Here is, probably, possibly, the Reuters story that set all this off last year, which btw comes up top on the google search:

Sperm count falling sharply in developed world, researchers say

[…]

Working with a team of researchers in the United States, Brazil, Denmark, Israel and Spain, Levine screened and brought together the findings of 185 sperm count studies from 1973 to 2011 and then conducted a so-called meta-regression analysis.

The results, published in the journal Human Reproduction Update, showed a 52.4 percent decline in sperm concentration and a 59.3 percent decline in total sperm count among North American, European, Australian and New Zealand men.

The former measures the concentration of semen in a man’s ejaculation, while the latter is semen concentration multiplied by volume.

In contrast, no significant decline was seen in South America, Asia and Africa. The researches noted, however, that far fewer studies have been conducted in these regions.

[…]