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.
Contaminant
Chemical Class
Bio-Gro Standard for Soil (mg/kg dry weight)
Bio-Gro Standard for Compost (mg/kg dry weight)
Comment
Arsenic
Heavy Metal
< 20
< 20
Arsenic sprays were used to control sheep parasites, but can be found naturally at high levels.
Cadmium
Heavy Metal
< 2
< 1
Used largely in batteries and pigments
Chromium (total)
Heavy Metal
< 150
< 150
Used widely in industry, e.g. in the electroplating industry
Chromium (VI)
Heavy Metal
< 1
< 1
Used as pigments in dyes, paints, inks, and plastics. Also as anticorrosive agents to paints, primers, and other surface coatings.
Copper
Heavy Metal
< 60
< 60
Used in horticultural sprays.
Lead
Heavy Metal
< 100
< 250
Lead based paints, was also used as an anti-knock additive in petrol.
Mercury
Heavy Metal
< 1
< 1
Used in thermometers and dental amalgam
Nickel
Heavy Metal
< 35
< 60
Used widely in industry
Zinc
Heavy Metal
<300
< 300
Used widely in industry.
Lindane
Organo-chlorine Pesticide
< 2.0
-
Previously used as an insecticide to control lice on cattle.
DDT
Organo-chlorine Pesticide
< 0.2
-
Previously used as an insecticide to control grass grub.
Other Chemical residues of concern
Contaminant
Comment
Price ($NZ)
Organochlorine, Organonitrogen and Organophosphorus Pesticides
The Multiresidue Pesticides screen contains more than 150 pesticide including DDT, Lindane, Dieldrin, Atrazine, etc
$260
Acidic Herbicides
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
$250
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.
$250 + $250 set up charge
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.
Unsure about the correct container to use to submit a sample? Consult our container guide
