Testing for contaminants as part of the process of achieving Organic Certification for fruit and vegetable growers.
About this Testing
Public concern over the presence of heavy metals and pesticides in fruit, vegetables and animal products has resulted in rapidly increasing demand for foods certified as "organic". To produce food that is able to be sold as organic, a producer must be certified by a certification body, such as BioGro NZ Inc.
Organic certification encompasses the whole of the production process, therefore any ingredient used in the production of the food needs to be tested to ensure it has no chemical residues above the standard levels acceptable. Organic Compost is often in demand for Organic growers, but even if Organic certification is not being sought, the standards above will provide useful guidelines for testing.
Maximum chemical residues accepted by Biogro in soil and compost are shown in the table below. Where soil residue levels fail to meet Biogro standards products from that property may still be able to be certified where the products meet Biogro’s standards for food.
BioGro Standard for Soil (mg/kg dry weight)
BioGro Standard for Compost (mg/kg dry weight)
Arsenic sprays were used to control sheep parasites, but can be found naturally at high levels.
Used largely in batteries and pigments
Used widely in industry, e.g. in the electroplating industry
Used as pigments in dyes, paints, inks, and plastics. Also as anticorrosive agents to paints, primers, and other surface coatings.
Used in horticultural sprays.
Lead based paints, was also used as an anti-knock additive in petrol.
Used in thermometers and dental amalgam
Used widely in industry
Used widely in industry.
Previously used as an insecticide to control lice on cattle.
Previously used as an insecticide to control grass grub.
Other Chemical residues of concern
Organochlorine, Organonitrogen and Organophosphorus Pesticides
The Multiresidue Pesticides screen contains more than 150 pesticides including DDT, Lindane, Dieldrin, Atrazine, etc
Includes pesticides such as 2,4-D and 2,4,5-T. Of particular interest is Clopyralid which is often used as a herbicide, but can be detrimental to plants at levels below 0.01mg/kg
Sulfonyl Urea Herbicides (SU)
Relatively harmless to humans, SU's are extremely toxic to plants and can be detrimental to plants at low-ppb levels.
Taking a Sample
A representative sample of the soil or compost (approximately 500g weight) should be taken. This is best achieved by taking about 10 small sub-samples from different areas, combining into one in a plastic bag, removing any large stones, plant material etc and mixing well.