Abstract
The mobility of selected heavy metals in trace concentrations was investigated in a standard OECD soil irrigated with the effluent of a real municipal wastewater treatment plant. While Cd, Cu and Ni accumulation-migration patterns were mainly influenced by the mobility of colloids generated from soil organic and inorganic matter, Zn mobility was more influenced by the wastewater content of dissolved organic matter and by its salinity. Metal accumulation caused by interaction with colloids resulted in contamination peaks both in different zones of the soil column and in the leaching solution. The release of metals in the leachate was correlated to the contemporary release of silicates from kaolinite and dissolved organic matter, identified through UV absorbance and chemical oxygen demand monitoring. The hypothesized colloidal mobilization was confirmed by spectroscopic studies. The highly heterogeneous complexes of organic and inorganic molecules responsible for metal transport through soil appeared to be structured in highly stable micellar aggregates.
Highlights
The recovery and reuse of wastewater in agriculture is a promising strategy to face water scarcity issues [1]
Trace heavy metals (HMs) mobilization in soil is controlled by colloidal mobilization
Colloids, which might be organic, inorganic or mineral organic associations (MOAs), are released from the soil matrix over time and act as a metal carrier, moving through the soil column with a lower velocity than the water flow, selectively interacting with contaminants contained in the irrigation water
Summary
The recovery and reuse of wastewater in agriculture is a promising strategy to face water scarcity issues [1]. The presence of trace level concentrations of potentially harmful pollutants is permitted in irrigation water by existing regulations all over the world, since it does not represent a short-term hazard for environmental quality. Some compounds, such as heavy metals (HMs), can accumulate in the soil through the years [5], reaching the crops and eventually entering the food chain [6]
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