Researchers from the University of East Anglia in Norwich, England are using the nitrogen content of fruits and vegetables to detect falsely labeled organic produce.
The demand for organic produce has been increasing. This Discovery News article explains that "the higher prices obtained by [organic food] producers provides an economic incentive for a few unscrupulous traders to pass off conventionally grown produce as organic."
Several industry-accepted organic food tests exist (organic certification and inspection) but this new test is the first to assess whether produce has been grown with synthetic or natural nitrogen fertilizers. According to the United States Department of Agriculture organic farmers cannot use any fertilizers containing synthetic ingredients.
This Scientific American article delineates the science behind the test.
Nitrogen makes up over 75 percent of the atmosphere, though the isotope nitrogen 15 (a stable, but heavier form of the element with an extra neutron in its nucleus) accounts for less than 0.5 percent of that amount. The heavy nitrogen, however, is enriched in crops grown with natural fertilizer, like manure. Ammonia in the manure is a source of nitrogen--both the lighter nitrogen 14 and the isotope. Ammonia that is composed of molecular nitrogen 14 is more volatile and typically escapes the manure over time, leaving easily detectable amounts of nitrogen 15 present in the fertilizer as well as in the crops grown in it. Conventional crops are typically grown with synthetic fertilizers, which do not lead to this isotopic enrichment.
The test is not perfect yet. For example it can only reliably characterize tomatoes about 60% of the time, lettuce 30% of the time and carrots 10% of the time. Experts believe, however, that it may be useful as a supplement to current methods.
"A test for synthetic nitrogen would be a useful extra test option where there is suspicion but the test on its own per se cannot be thought of as a replacement for organic certification and inspection."
The findings are reported in the Journal of Agricultural and Food Chemistry.
AP Photo/Richard Drew
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