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CHEMISTRY 1000
Topics of Interest #1:
“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.
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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, 1244-1246
A.S. Bateman, S.D. Kelly, M. Woolfe J. Agric. Food Chem. (2007) 55, 2664-2270
“Organic” Produce
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So, how can we tell that the grocery store’s organic produce was, in
fact, grown organically?
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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 (14N and 15N) in produce to determine whether
natural or synthetic fertilizers were used.
How does the test work?
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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 15N than air. Synthetic fertilizers
tend to contain about the same amount of 15N as air does.
J. Chem. Ed. (2007) 84, 1244-1246
A.S. Bateman, S.D. Kelly, M. Woolfe J. Agric. Food Chem. (2007) 55, 2664-2270
“Organic” Produce

The graphs below compare 15N/14N ratios of organic and conventionally
grown produce. The x-axis shows a value, d15N, calculated by taking the
difference between the 15N/14N ratio of the produce and the 15N/14N ratio
of air, dividing by the 15N/14N ratio of air then multiplying by 1000‰.
15
15N/14N ratio is the same as for air.
 d N = 0 indicates that the
15
15N/14N ratio is greater than for air.
 d N > 0 indicates that the
15
15N/14N ratio is less than for air.
 d N < 0 indicates that the