Behavior of copper (Cu) and zinc (Zn) in soils amended with agricultural effluents, isotopic approach

Soil is one of the most important non-renewable natural resources on Earth. It provides support for food production and habitat for humans and living organisms. Soil pollution caused by heavy metals can negatively affect the sustainability of this resource. In the world, pig slurry (PS) application on agricultural soils is a frequently used strategy which helps improving the physico-chemical properties of soils and increases the agricultural yield. However, pig manure contains high levels of Copper (Cu) and Zinc (Zn) concentrations and consequently the massive pig slurry applications cause an increase of the Cu and Zn concentrations in PS-amended soils. The aim of this work was to discriminate between anthropogenic and natural Cu contributions in PS-amended soils, using the isotopic approach. Soil samples of natural and PS-amended soils were sampled in Santa Maria, Brazil and analyzed for their Cu isotopic compositions. The highest Cu and Zn concentrations were observed in the surface horizons of amended soil. The isotopic signatures of δ65Cu analyzed in amended soils are different from those observed in natural soils, but close to the isotopic signatures of the pig manure used. Mixing calculations showed that the proportion of Cu coming from the pig slurry can reach up to 30 % of the total Cu accumulated in the surface horizons of the amended soils.