Chapter 34, Problem 3DAA

Sperm Counts Down on the Farm Contamination of water by agricultural chemicals affects reproductive function in some animals. Are there effects on humans? Epidemiologist Shanna Swan and her colleagues studied sperm from men in four cities in the United States (FIGURE 34. 22). The men were partners of women who had become pregnant and were visiting a prenatal clinic, so all were fertile. Of the four cities, Columbia, Missouri, is located in the county with the most farmlands. New York City in New York is in an area with no agriculture.

		Location of Clinic
	Columbia, Missouri	Los Angeles, California	Minneapolis, Minnesota	New York, New York
Average age	30.7	29.8	32.2	36.1
Percent nonsmokers	79.5	70.5	85.8	81.6
Percent with history of STD	11.4	12.9	13.6	15.8
Sperm count (million/ml)	58.7	80.8	98.6	102.9
Percent motile sperm	48.2	54.5	52.1	56.4

FIGURE 34.22 Characteristics men h four cities. All men were partners of woman who visited prenatal health clinics, and so were presumably fertile. STD stands for sexually transmitted disease.

Aging, smoking, and sexually transmitted diseases adversely affect sperm. Could differences in any of these variables explain the regional differences in sperm count?