Experimental Evaluation of Zinc and Copper Terrestrial Ecotoxicity Prediction by Life Cycle Assessment in Agricultural Recycling of Livestock Effluent

The agronomic benefits of organic waste application on farmland can be overshadowed by the potential health and environmental impacts associated with trace element emissions, especially copper (Cu) and zinc (Zn). This has prompted a need for life cycle assessment (LCA) models to predict their terrestrial comparative toxicity potential (<i>CTP</i>) and impact score. We compared the LCA (reference method) prediction ability with that obtained with an experimental data set obtained from a month-long incubation experiment (experimental method) on a soil amended or not with 31 livestock effluents mimicking agronomically relevant scenarios. The impact scores for Cu and Zn differed between the reference and experimental methods due to <i>CTP</i> discrepancies between the two methods. The application of 31 livestock effluents on the soil resulted in variability in the experimentally determined <i>CTP</i> for Zn and Cu (0.6 and 1.9 log₁₀ units) comparable to the <i>CTP</i> variability estimated by the reference method for several hundred worldwide soils. These results could be explained by the inadequate prediction of the dissolved organic carbon concentration and Cu and Zn concentration and speciation in soil solution. We propose refinements to the multilinear regressions used for the <i>CTP</i> computation that take the soil property patterns following livestock effluent application on soils into account.