Sir

In the News Feature “Fertilized to death” (Nature 425, 894–895; 2003), your reporter repeats a claim sometimes made in the medical literature that blue-baby syndrome (methaemoglobinaemia) is caused by excess nitrate in the tap water used to make up infant formula. However, it is nitrite, synthesized from nitrate by bacteria, that is the ultimate culprit in methaemoglobinaemia.

As humans cannot convert nitrate present in food or water to nitrite by themselves, the most likely source of bacterial contamination in cases of blue-baby syndrome is poor hygiene in making up infant formula. Fortunately, infants acquire an enzyme by the age of six months that protects them against nitrite poisoning.

It is true, of course, that excess nitrate levels in tap water are caused by fertilizer run-off and leaching into rivers, but it is surprising that there are far fewer cases of blue-baby syndrome in Europe (which has much higher levels of nitrate in tap water) than in the United States.

It is also worth noting that, despite hopes that organic farming would reduce nitrate in tap water, recent studies show that nitrate leaching from well-managed organic and conventional farms is effectively identical1,2.

A less-advertised, and cheaper, way of reducing nitrate levels in drinking water is 'no-till' agriculture. The plough has been used as a means of controlling weeds since the advent of agriculture itself. However, methods whereby crop material is mulched and left on the surface, and weeds controlled by herbicides, have been found to produce after several years a soil structure that is highly resistant to erosion, run-off and leaching.

Nitrate loss from a fertilized no-till field is approximately 12–20% of that from the equivalent ploughed field. Greater use of no-till, which is increasingly common in the United States but receives little encouragement from governments in Europe, would probably see nitrate levels in tap water return to those found before 1950 — about a quarter of current levels.