Effect of soil copper content and pH on copper uptake of selected vegetables grown under controlled conditions

A one-year greenhouse experiment was conducted to study the transfer of copper from contaminated agricultural soils to edible and nonedible structures of lettuce, tomato, and onion plants. Study soils were selected from two basins of central Chile (Santiago and Cachapoal) to represent two similar total soil copper gradients with different pH values. Results showed that free ionic Cu and Cu in saturation extracts were very low in comparison to total Cu contents of study soils (<0.002% and <0.04%, respectively). The concentrations of free ionic copper and of copper in saturation extracts were correlated to total Cu levels and to soil pH. Mean copper concentrations were higher in lettuce than in tomato and onion plants and in vegetables grown on acidic soils of the Cachapoal basin. However, copper levels in edible tissues of tomato and lettuce plants were similar to copper levels described for plants grown on unpolluted soils except for onion bulbs, which had higher values. This indicates that copper translocation to edible, above-ground structures seemed to be well regulated, as their concentrations were fairly constant. The study shows that Cu concentration in study vegetables depends on various factors, including plant species and tissue; site-specific soil factors, such as pH, organic matter, dissolved organic carbon, and conductivity; and several Cu pools, such as total, extractable, and free ionic Cu. Thus, our results support the intensity/capacity concept in that Cu concentration in plants or plant tissues depends not only on the availability of free copper ions in soil solution but also on other soil copper pools that supply the element to the soil solution.