How physical alteration of technic materials affects mobility and phytoavailabilty of metals in urban soils?

- Wastes/technic materials are present in the coarse fraction of urban topsoils.
- Technic materials contribute to metal contamination of urban Technosols.
- Forced physical alteration of artefacts enhances phytoavailability of metals.
- In long term, the risk of metal transfer from urban soils to plants could increase.

One fundamental characteristic distinguishing urban soils from natural soils is the presence of technic materials or artefacts underlining the influence of human activity. These technic materials have different nature (organic or inorganic) and origins. They contribute to the enrichment of the soil solution by metallic trace elements. The present study aims to determine the effect of physical alteration of the technic coarse fraction on the bioavailability of metallic trace elements in urban Technosols. In general, results show that physical alteration increases the metallic trace elements water extractible concentrations of technic materials. The ability of lettuce to accumulate metallic trace elements, even at low concentrations, underlines the capacity of technic materials to contaminate the anthropised soil solution by bioavailable metals. The highest metal levels, accumulated by the various organs of the lettuce (leaves and roots), were measured in plants grown in presence of metallic particles mixtures. This indicates that the majority of metallic trace elements released by this technic constituent is bioavailable and explains the low plant biomass obtained. The abundant part of metallic trace elements released by the other technic constituents (building materials, bones, wood, plastic and fabric-paper) remains less bioavailable. Under anthropised soil conditions, technic materials have a significant effect on the metallic trace elements behavior. They impact the flow of these metallic elements in Technosols, which can increase their bioavailability and, therefore, the contamination of the food chain.