Vegetables give up dirty secrets

HOW GREEN ARE MY VEGETABLES?: Researcher Karyne Rogers has developed a test to show whether vegetables have been grown organically.

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Animal poo or industrial fertiliser? A Kiwi scientist has developed a test to detect foul play in the organic food industry.

An isotope test looks at base elements in vegetables, and shows whether they were raised with organic manure or industrial fertiliser.

All organic materials contain isotopes such as carbon and nitrogen. If these can be studied using mass spectrometers, all sorts of things can be learnt. And unlike tests for pesticide residue, the results cannot be fudged with a bit of soap and water.

"It should stop people being fobbed off by someone else's half-baked organic vegetables," says the scientist who developed the test, senior researcher Karyne Rogers from GNS Science.

As vegetables grow, they take on nitrogen from fertiliser. A criterion for organic vegetables is that only organic fertiliser, usually manure, can be used. The signatures from manure and industrial fertiliser are different. The test is expected to be used by organic vegetable suppliers. Dr Rogers says it is cheap, shows results within 10 days and can be done at any stage of growth.

The test could also determine whether vegetables were grown hydroponically or in soil. A similar test could detect whether they were raised in a greenhouse heated by fossil fuels.

The test works best on fast-growing plants such as vegetables, and not so well on slow-growing ones, such as fruits.

Commonsense Organics managing director Jim Kebbell said growers already went through a certification process, but the new test looked "quite useful".

The Commerce Commission has twice brought prosecutions over false claims about organic food. However, both cases involved butchers.

The director of the commission's fair trading branch, Adrian Sparrow, said: "Any information that verifies claims businesses make about their products and services, helps consumers make informed choices."

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