Soluble metal pool as affected by soil addition with organic inputs.

The potential impact of diverse inputs of organic matter (hay, maize straw, and peat) on the mobility and bioavailability of Cd, Cu, Pb, and Zn was examined at laboratory scale for three soils with contrasting properties and for two moisture regimes: field capacity and saturated conditions. Soil solution was characterized for total soluble metals, dissolved soil organic carbon, and ultraviolet absorbance at 254 nm. Speciation analyses were performed with WHAM VI. For field capacity conditions, metal mobility increased (Pb>Cu>Zn>Cd) for all soils and treatments compared with controls and was significantly correlated (p<0.05) with dissolved organic matter (r=0.540). Solubilization of organic matter was mostly driven by Al mobilization (r=0.580, p<0.05) and variations in solution pH. The bioavailable pool of metals, estimated as free ion activities, decreased with the increasing occurrence of metal-organic matter complexes, which was accompanied by an increase in solution of highly aromatic organic matter. Soil saturation generally decreased metal mobility and the ratio of metal-organo matter complexes in solution. Consistently, such effects were accompanied by a decrease in the solubilization of organic matter and lower mobilization of Al, Fe, and Mn.

Effects of silicon on copper toxicity in Erica andevalensis Cabezudo and Rivera: a potential species to remediate contaminated soils.

The influence of silicon on responses to copper excess was studied in plants of Erica andevalensis. Plantlets were grown in nutrient solutions containing two Cu (1 and 500 µM) and three Si concentrations (0, 0.5 and 1 mM). Plant growth, water content, and mineral nutrient concentration were determined. Plants grown with 500 µM Cu showed differences in growth and shoot water content depending on Si supply. The addition of 1 mM Si in high-Cu nutrient solutions significantly improved plant growth and reduced water loss preventing plant death related to Cu-excess. Silicon supply reduced significantly leaf Cu concentration (up to 32%) and increased Cu concentration in roots. Phytoliths isolated from leaves were analysed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Such phytoliths consisted in silica deposits associated with Cu and other elements (K, Ca, P). Improvement by Si of Cu tolerance in E. andevalensis was clearly related to the inhibition of Cu upward transport. The leaf phytoliths formed in Si-treated plants might have some contribution to tolerance by Cu immobilisation and inactivation.

Evaluation of some pollutant levels in bitter orange trees: implications for human health.

Samples of bitter orange (Citrus aurantium L.) fruits (epicarp and mesocarp), leaves and its fruit marmalade from sites in Seville (Andalucia, Spain) with different levels of traffic were analysed for Ba, Cd, Cu, Fe, Mn, Ni, Pb and Zn concentrations by ICP/AES. Comparative values are given from a background area. The effect of washing on metal content in epicarp and leaves was investigated. Results revealed that Ba, Fe and Mn accumulated in leaves > epicarp > mesocarp, Cu and Ni in leaves > epicarp congruent withmesocarp and Zn leaves > mesocarp > epicarp. Washing had no significant effect on epicarp metal content while it removes part of Cu, Fe and Zn deposited on leaves. Bitter orange fruits are used mainly to make marmalade; artificial contamination effects on fruit composition were investigated and the dietary intake of the elements was determined. The citrus fruits sprayed with metal solution showed a significant increase in the studied elements compared to untreated fruits. The levels of all elements studied were lower than provisional tolerable daily intake values indicating that bitter orange marmalade consumption is safe for alimentary use. CAPSULE: Bitter orange tree exhibit differences in metal content between fruits and leaves and fruits are safe for consumption.

Indicators of change in the organic matter in arid soils.

Soil organic matter is a key component in ecosystems, as it is the essential part of a set of relevant processes and constitutes an important carbon pool contributing to Global Change. The design of environmental monitoring programmes should include indicators of the current status of ecosystems, alerting to incipient changes in them. In this context, a sampling scheme has been designed taking into account the main processes and soil uses affecting the dynamics of soil organic matter. Well-tested parameters were determined in order to assess which of them are most useful as indicators of soil organic matter evolution in arid soil, such as that in the "Cabo de Gata-Níjar" Natural Park (SE Spain). The parameters characterising the lability of the different fractions indicate changes in soil organic matter triggered by changes in soil use and soil dynamics. Changes in soil use, when drastic, are best reflected by those fractions comprising a high percentage of the total soil carbon, while the processes having slower dynamics are best demonstrated by the labile fractions. As a result of the sensitivity analysis of parameters versus changes, and taking into account the operational difficulties for determining them, the following indicators are proposed for a monitoring programme: total organic carbon, active fraction of the organic carbon and ratios of this fraction versus total organic carbon (%) (as given by the lability index proposed).