Copper and zinc pollution of agricultural soil
Copper and zinc are essential nutrients for plants. They are also essential trace elements for humans, and a lack or excess of these elements can have negative health impacts. The pollution of soil with zinc and copper is basically due to direct agricultural inputs: the two heavy metals are found in farm animal waste and plant protection products. Farm animal waste, for example cattle and pig slurry, can contain significant quantities of zinc and copper which originates from animal feed, to which the heavy metals have been added for health reasons or to improve the productivity of farm animals. Arable soils and intensive grasslands are most severely affected by this pollution. In addition, copper is a component of fungicides, and market-garden, orchard and vineyard soils often present high levels of copper pollution that may even exceed the legal guide value.
On average, the level of copper and zinc pollution is low in soils used for agricultural purposes (guide value in accordance with Annex 1, SoilPO: Cu -> 40 mg/kg dry matter; Zn -> 150 mg/kg dry matter). Nonetheless, the current state can only be described as moderately satisfactory as the level of pollution in some soils far exceeds the guide value. This mainly concerns soils used for special crops, e.g. vines, fruit, and for intensive vegetable cultivation.
Over the entire measurement period, the average copper content in agriculturally used soil only increased minimally. However, clear increases in the copper content of the soil from some of the sites were observed. The sites in question included areas on which a lot of farm animal waste is spread (slurry and manure), intensively used grassland, some of the arable sites and some areas used for the cultivation of special crops in which copper was used as a fungicide.
In the case of zinc, there was an obvious increase in the average content, hence the trend can clearly be assessed as negative. These increases were most obvious in soils on which a lot of farm animal waste (slurry and manure) is spread.
Possibilities exist today for reducing zinc and copper inputs in certain soils: studies have shown that the quantities of zinc and copper contained in animal feed could be reduced considerably without any negative impact on the animals.
Every five years since 1985, a composite sample has been taken from the top 20 centimetres of the soil in each of the 103 permanent plots operated by the Swiss Soil Monitoring Network (NABO).
The indicator was calculated on the basis of data from around 50 monitoring sites used mainly for field crops, intensive grassland and special crops (market gardening, orchards, vineyards)
Testing for zinc and copper levels is carried out on the topsoil, as this is where the pollutants, which originate from agricultural spraying, accumulate.
The zinc and copper content is analysed in accordance with the method specified in the Soil Pollution Ordinance (nitric acid extraction 2M HNO3). The results (in mg per kg of dry soil) are presented in terms of the average pollutant content per measurement cycle.