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Gillian Bentley asks where is the evidence that environmental pollutants are causing human infertility? (É«ºÐÖ±²¥S, June 14). The comparisons she herself supplies constitute such evidence.

If xeno-oestrogens in pesticides affect fertility one would expect male sperm counts to be lower in Iowa and Texas than in New York. This is because there is substantial production of crops in Iowa and Texas for which pesticides are used. For example, corn in Iowa, cotton in Texas, and intensive livestock production (hogs in Iowa, grain-fed beef in Texas) can lead to pesticide residues being concentrated in livestock wastes.

As well as having an effect on those directly involved in agriculture, the excess pesticides leach down into the water table and affect wells and rural water supplies. By contrast, there is much less crop and intensive livestock production in New York, and a greater reliance on town water supplies.

There is also circumstantial evidence on fertility in certain sectors of agriculture. In Belgium, men working in hothouses are considered to be particularly at risk from a loss of fertility from pesticide use, and men working on fruit farms where spraying has been taking place have also been found to be affected. In the United States, a chemical used in banana production was withdrawn because of a decline in the fertility of plantation workers there.

Heather Field Griffith University Brisbane