No abstract

No abstract

No abstract

Cadmium (Cd) is one of the most toxic heavy metals, polluting the general environment. The application of sewage sludge, wastewaters and Cd-containing fertilizers causes an increase in Cd content in agricultural soils. Cd is easily taken up by plants and then enters the food chain, resulting in a serious health issue for humans. There is increasing concern regarding the occurrence of cadmium in rice, not only in the rice-growing areas of the Far East, but also in Europe. In this work we highlighted that, even when the agricultural soil is unpolluted and the concentration of Cd is low, e.g. 0.96 mg kg −1 , the Cd content of rice may still exceed the regulatory limit of 0.2 mg kg −1. To reduce the uptake of Cd by rice, paddy-field flooding and soil amendment with lime and compost were tested in a field trial during 2003 and 2004 in Rosate, near Milan, Italy. We found that submersion was the main factor decreasing the Cd concentration in rice grain, producing maximum concentrations of 0.14 mg kg −1 in 2003 and 0.06 mg kg −1 in 2004. By comparison, Cd concentrations was at least two times higher for rice cultivated by irrigation only. Moreover, the addition of lime decreased the Cd concentration of rice by about 25% versus control under dry conditions. Lime addition thus appears to be a promising technique to reduce the bioavailability of soil Cd and minimize Cd concentrations in the produced rice. In contrast, the application of compost alone does not produced a significant effect. Differences in uptake over the years, with concentrations up to 40% lower in 2004, can be explained by differences in transpiration. These results shows that the influence of climatic conditions on Cd uptake in plants should not be underestimated. Such agronomic information represents a very helpful tool for rice growers, in particular in the case of cultivation of Cd-polluted soils and production of Cd-contaminated rice grain. paddy field / rice / water management / fertilizers

A laboratory study was conducted to evaluate the availability of arsenic (As) to roots in nine soils from five fields in Tuscany (Italy). Concentrations of As in soils range from 200 to 1200 mg kg À1 as a result of human activities and natural deposition. In a first stage, potentially root-available As and the risk of crop uptake were estimated using the diffusion gradient in thin films (DGT) technique. In a second stage, a glasshouse experiment was performed to compare As depletion in the rhizosphere by the hyperaccumulator Pteris vittata (ladder brake), and by the test plant Agrostis capillaris (colonial bentgrass). In this stage, DGT results were supported by a sequential extraction procedure. The main objectives were to study the root availability of As in old, contaminated soils and the modification of the available pool size over time. The phytoextraction efficiency of Pteris vittata as applied to this case study was also investigated. In all samples, concentrations of total and potentially root-available As in soil solution were small compared with total As in soil (approximately 0.0003-0.03%, corresponding to 3.5-350 mg l À1 , respectively). There was also little re-supply of As from the solid phase to the soil solution. In the rhizosphere, despite uptake by Pteris and Agrostis, total and root available As in solution were sustained over time. It appeared that plants induced a re-supply of As from the solid phase. Despite the uptake and translocation of As by Pteris (50.7 mg kg À1 and 6.6 mg As kg À1 in fronds and roots, respectively) together with plant biomass (17.2 g per plant), the success of phytoextraction appears unlikely. The results obtained demonstrated the sensitivity of DGT to root-induced changes in soil and the suitability of the technique as an easy-to-use tool to predict assimilation by plants.