CHEMISTRY 1000 Topics of Interest #3: “Organic” Chemistry

“Organic” Produce Chemists use the term “organic” to describe carbon-containing compounds. Technically, that makes all produce “organic”. This presentation relates to the layperson’s definition of “organic produce” – not the chemist’s definition. Interest in organic produce – food grown without the application of synthetic pesticides, fertilizers or hormones – is growing. Some claim that there are health benefits to eating organic produce. Others feel that it is a more environmentally friendly way to farm. Certainly, it is a more expensive way to farm and, as such, organic produce tends to cost more than conventionally grown produce. J. Chem. Ed. (2007) 84, A.S. Bateman, S.D. Kelly, M. Woolfe J. Agric. Food Chem. (2007) 55,

“Organic” Produce So, how can we tell that the grocery store’s organic produce was, in fact, grown organically? It might carry a sticker saying that it is “certified organic”. This certification involves inspection of the farm where the produce is grown and the farming practices used. This certification costs money. A test to determine whether produce really was grown organically is being developed in the United Kingdom. This test uses the ratio of two nitrogen isotopes ( 14 N and 15 N) in produce to determine whether natural or synthetic fertilizers were used. How does the test work? All living matter contains nitrogen. As produce is grown, it acquires much of its nitrogen from fertilizers. Natural fertilizers such as manure and compost tend to contain more 15 N than air. Synthetic fertilizers tend to contain about the same amount of 15 N as air does. J. Chem. Ed. (2007) 84, A.S. Bateman, S.D. Kelly, M. Woolfe J. Agric. Food Chem. (2007) 55,

“Organic” Produce The graphs below compare 15 N/ 14 N ratios of organic and conventionally grown produce. The x-axis shows a value,  15 N, calculated by taking the difference between the 15 N/ 14 N ratio of the produce and the 15 N/ 14 N ratio of air, dividing by the 15 N/ 14 N ratio of air then multiplying by 1000‰.  15 N = 0 indicates that the 15 N/ 14 N ratio is the same as for air.  15 N > 0 indicates that the 15 N/ 14 N ratio is greater than for air.  15 N < 0 indicates that the 15 N/ 14 N ratio is less than for air.