Leaching dynamics of Zn2+, Pb2+ and Cu2+ in urban soils of a semi-arid region: A quantitative analysis

In this study, we evaluate the leaching process and movement of PTEs once they reach the soil profile in urban soils in a semiarid city in northwest Mexico. Concentrations of Zn²⁺, Pb²⁺ and Cu²⁺ were quantified in an urban area using ion-exchange resin (IER) samplers. The IER is a passive method based on ion-exchange resins which allows sampling the transport of elements in macropores under unsaturated flow conditions. Samples were taken during three monitoring periods in a city influenced by the North American Monsoon (NAM). In the first monitoring period, the IER samplers showed leaching rates of 323.40 g Zn²⁺ ha⁻¹ 15 wk⁻¹, 361.90 g Pb²⁺ ha^-115 wk⁻¹, and 31.9 g Cu²⁺ ha^-115 wk⁻¹. The second period estimated 101.50 g Zn²⁺ ha⁻¹ 37 wk⁻¹, 58.20 g Pb²⁺ ha⁻¹ 37 wk⁻¹, and 20.00 g Cu²⁺ ha⁻¹ 37 wk⁻¹. Finally, in the third monitoring period concentrations of 141.90 g Zn²⁺ ha^-117 wk⁻¹, 32.10 g Pb²⁺ ha⁻¹ 17 wk⁻¹ and 20.70 g Cu²⁺ ha⁻¹ 17 wk⁻¹ were found. The highest leaching rate of PTEs was identified in the central area of the city and its surroundings, influenced mainly by flood areas and high surface runoff. The results of this study demonstrate the role that monsoon rains and runoff plays in the movement and distribution of PTEs in urban areas.