How Historical Copper Contamination Affects Soil Structure and Mobilization and Transport of Colloids.

Copper is accumulated in soils due to human activities such as mining industry, agriculture practises, or waste deposals. High concentrations of copper can affect plants and soil organisms, and subsequently the soil structure and its inner space architecture. In this work we investigated the effect of copper concentration on the movement of an inert tracer, tritium, and the mobilization and transport of colloid particles in undisturbed soil cores (10 cm diameter and 8 cm height). The cores were sampled along a copper gradient of 21 to 3837 mg Cu kg^-1 soil on an abandoned arable soil polluted by copper 90 years ago. Leaching experiments were carried out for 48 hrs at an irrigation rate of 10 mm hr^-1.

The accumulated amount of colloids released from the columns increased with the copper concentration. A sharp increase was observed when the copper concentration increased from 466 to 2228 mg kg^-1_. All columns showed similar behaviour with a high particle concentration associated with the first flush followed by a lower, more constant particle concentration.

The tritium breakthrough curves suggested preferential flow through larger pores. Arrival time of the first 5% of the tritium mass was ranged between 0.01 to 0.43 pore volumes, with longer times for the most contaminated point, likely related with its higher soil density and lower air permeability.

The copper pollution affected colloid and tracer transport in the soil columns. The release of colloids especially in the most contaminated points and the occurrence of preferential flow can lead to colloid facilitated transport of copper deeper into the soil profile.