Application of Cu Isotopes to Identify Cu Sources in Soils Impacted by Multiple Anthropogenic Activities

Abstract

Copper (Cu) is an important micronutrient for animals and plants, but it is toxic at high concentrations in soil. Soils adjacent to industrial areas would be subjected to severe Cu pollution. Identifying heavy metal sources in the surface environment is crucial for understanding their pollution level and fate. This study investigated Cu content, isotope composition of topsoils, and two soil profiles with varying levels of Cu contamination and related potential Cu sources in southwest China. The difference in Cu isotope compositions of tailing (1.29 ± 0.08 ‰), smelting fly ash (0.04 ± 0.03 ‰), coal (2.44 ± 0.09 ‰), coal-burning fly ash (0.34 ± 0.03 ‰), and geogenic soil (0.10 ± 0.03 ‰) enabled us to distinguish anthropogenic Cu from geogenic Cu. The plot of δ65Cu value and 1/Cu demonstrates that Cu of the polluted soils is at least from three endmembers: the smelting fly ash, the fly ash from coal combustion, and the background soils. Based on the mass balance model, we calculate that the fly ash from smelting is the major contributor, contributing approximately 41% of Cu contamination, and the contributions from coal-combustion fly ash and background soils are 31% and 28%, respectively. Additionally, soil profile results suggest that anthropogenic Cu could transport through soil profiles and influence Cu content and isotope signatures of deep soils, at least to a depth of ~90cm. Finally, our research indicates that Cu isotopes could be a powerful tool for tracing pollution sources if the isotope ratios of the potential sources are distinct and different from those of soil samples. Thus, a systematic analysis of all the endmember Cu isotope signatures for each case is a prerequisite for tracing pollution via Cu isotopes.

Keywords: Cu isotopes, Heavy metals, Source tracing, Soils, Anthropogenic inputs