Isabel Martínez-Alcalá

Impact of fresh and composted solid olive husk and their water-soluble fractions on soil heavy metal fractionation; microbial biomass and plant uptake

The use of waste materials as organic amendments in soil remediation can affect metal solubility; this interaction will vary with the characteristics of the organic matter that is added to the soil. A pot experiment was carried out in a calcareous, metal-polluted soil, using Beta maritima L. as an indicator species for the treatment effects on metal solubility. The treatments were: fresh solid olive husk, a mature compost, their respective water extracts (as the most reactive and biodegradable fraction) and an unamended, control soil. The compost reduced metal availability and plant uptake, while fresh olive husk favoured Mn bioavailability and produced phytotoxicity. The water-soluble extract from fresh solid olive husk also provoked elevated Mn solubility in soil, but did not increase Mn uptake by plants. The application of water-soluble organic matter obtained from compost did not affect heavy metal solubility significantly. Therefore, composted olive husk seems to be the most-appropriate material for the development of bioremediation strategies.

Chemical and biological properties in the rhizosphere of Lupinus albus alter soil heavy metal fractionation.

To understand better the suitability of white lupin (Lupinus albus L.) for phytoremediation of heavy metal-contaminated soils, the effect of its roots on chemical and biological properties of the rhizosphere affecting soil metal fractionation was studied. Plants were cultivated in two similar soils, with high levels of Zn, Cd, Cu and Pb but differing pH values (4.2 and 6.8). In the rhizosphere of both soils, its roots induced increases in water-soluble carbon, which influenced the fractionation of heavy metals and ultimately their uptake by plant roots. In the rhizosphere of the acid soil, the concentrations of 0.1M CaCl(2)-extractable Mn, Zn and Cu were lower than in the bulk soil, possibly due to their increased retention on Fe (III) hydroxides/oxyhydroxides, while in the neutral soil only the Zn concentration was lower. Higher concentrations of heavy metals were found in plants growing on the acid soil, reflecting their greater availability in this soil. The restricted transfer of heavy metals to the shoot confirms the potential role of this species in the initial phytoimmobilisation of heavy metals, particularly in neutral-alkaline soils.

Responses of Noccaea caerulescens and Lupinus albus in trace elements-contaminated soils.

Plants exposed to trace elements can suffer from oxidative stress, which is characterised by the accumulation of reactive oxygen species, alteration in the cellular antioxidant defence system and ultimately lipid peroxidation. We assessed the most-appropriate stress indexes to describe the response of two plant species, with different strategies for coping with trace elements (TEs), to particular contaminants. Noccaea caerulescens, a hyperaccumulator, and Lupinus albus, an excluder, were grown in three soils of differing pH: an acidic soil, a neutral soil (both contaminated mainly by Cu, Zn and As) and a control soil. Then, plant stress indicators were measured. As expected, N. caerulescens accumulated higher levels of Zn and Cd in shoots than L. albus, this effect being stronger in the acid soil, reflecting greater TE solubility in this soil. However, the shoot concentrations of Mn were higher in L. albus than in N. caerulescens, while the As concentration was similar in the two species. In L. albus, the phenolic content and lipid peroxidation were related with the Cu concentration, whereas the Zn and Cd concentrations in N. caerulescens were more closely related to glutathione content and lipid peroxidation. Interestingly, phytochelatins were only found in L. albus grown in polluted soils. Hence, the two species differed with respect to the TEs which provoked stress and the biochemical indicators of the stress, there being a close relationship between the accumulation of TEs and their associated stress indicators in the different plant organs.