Stable isotopes analysis combined with X-ray absorption spectroscopy reveal the fate of organic waste-borne copper and zinc in amended soils

Abstract

Copper (Cu) and zinc (Zn), two potentially toxic trace elements, are commonly abundant in organic wastes (OWs) recycled in soils as fertilizer. Yet current knowledge on the long-term behavior and fate of Cu and Zn in soil following OW spreading is scant. We addressed this issue by studying the fate of OW-borne Cu and Zn in amended soils from four different long-term field experiments. By combining the stable isotope analysis and X-ray absorption spectroscopy, we identified changes in Cu and Zn concentrations, speciation and isotopic compositions in the amended soils only when OW had been applied at high rates over long periods. Under these conditions, we highlighted that: (i) all OW-derived Cu and Zn had accumulated in the topsoil layer regardless of the soil and OW type; (ii) the amended soil isotopic signatures were the result of the mixing of OW-borne and natural Cu and Zn; and (iii) Cu and Zn exhibited distinct speciation patterns in amended soils. Indeed, the unprecedented persistence of OW-borne crystallized Cu(I)-sulfide in the amended soils contrasted with the complete transformation of pig slurry-borne nanosized Zn-sulfide or household compost-derived amorphous Zn phosphate and Zn complexed by organic matter.

This study was part of the DECoDE project, funded by the Continental and Coastal Ecosphere Structuring Initiative (EC2CO). The authors are grateful to the French National Research Institute for Agriculture, Food and Environment (INRAE) and the French Agricultural Research Centre for International Development (CIRAD) for funding the Ph.D. scholarship of Abraham Pappoe. We acknowledge the European Synchrotron Radiation Facility (ESRF) for providing access to synchrotron radiation facilities.The two French field experiments are part of the SOERE PRO (network of long-term experiments dedicated to the study of impacts of organic waste product recycling), certified and funded in 2013 by ALLENVI (Alliance Nationale de Recherche pour l′Environnement) and integrated as a service of the infrastructure “Investment for the future” AnaEE-France, overseen by the French National Research Agency (ANR 11-INBS-0001). We thank all those who participated in the field experiments and management of the SOERE-PRO sites, as well as the partners, notably Veolia Research and Innovation (VERI) and Runéo.