Organic soil care - Potentially Toxic Elements (PTEs)

Potentially Toxic Elements (PTEs) include heavy metals and other elements, many of which are naturally present in the soil. Some are essential to plants and animals in trace amounts but can be toxic at higher levels. There are many different standards setting maximum permissible levels in soil and materials added to the soil. The variation in these standards shows that no one really knows the answer.

For these Guidelines we have chosen the Soil Association figures for permitted levels in the soil. For levels in materials added to the soil, and the quantity of such materials that can be applied, we have taken those set by the EU Ecolabelling board. These are stricter than those set by the EU Organic standards, but as these Guidelines are for gardeners, who come into closer contact with the soil than many farmers, and where materials are likely to be applied to the top few inches of soil, we felt these were more appropriate.

Maximum permitted levels of heavy metals in topsoil mg/kg*
Arsenic	Cadmium	Chromium	Copper	Lead	Mercury	Nickel	Zinc
50	2	150	50	100	1	50	150
*Soil Association Organic Standards April 2005

Maximum permitted levels in soil improvers (mg/kg dry matter)**
Arsenic	Cadmium	Chromium	Copper	Lead	Mercury	Nickel	Zinc
10	1	100	100	100	1	50	300
**COMMISSION DECISION of 3 November 2006 establishing revised ecological criteria and the related assessment and verification requirements for the award of the Community eco-label to soil improvers (notified under document number C(2006) 5369) (2006/799/EC).

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