An American study has shown that men who live in agricultural areas have poorer quality and sperm than their urban counterparts. The research, published in Environmental Health Perspectives, suggests that exposure to water containing chemicals drained from farmland may be the reason.

The team, led by professor Shanna Swan of the University of Missouri-Columbia, studied semen samples from 512 men living in Columbia, Minneapolis, Los Angeles and New York City. According to the research team, approximately 57 per cent of the Columbia area is agricultural, compared with 19 per cent in Minneapolis, five per cent in Los Angeles and no rural areas in New York City. All of the men had pregnant partners and so were considered to be fertile.

The results showed that semen of the men from Columbia had an average concentration of 58.7 million sperm per millilitre, which was far lower than the concentration in the semen of men from the less rural areas. The men from Los Angeles had an average concentration of 80.8 million per millilitre; Minneapolis men averaged 98.6 million; and New York 102.9 million. The quality of the sperm from the men from Columbia was also poorer, containing fewer motile sperm than men from the more urban areas.

Professor Swan said the results had been 'a total surprise' as the team had expected that poorer air quality in urban areas would lead to lower sperm concentrations and poorer sperm quality. A follow-up study will be conducted to see if any specific chemicals used on farms can be linked to sperm quality.