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This study addresses the growing problem of soil salinity. In Mediterranean regions, disused solid waste landfills have given rise to disturbed ecosystems. At such sites, both mobile soil anions and cations have toxic effects on plants. Thus, detailed knowledge of these effects is needed for the phytoremediation of soils facing the problem of salinization. In this study, high chloride levels were detected in soil samples from several sealed waste landfill sites showing metal pollution. We also examined the nutrition behaviour of six native and five cultivated herbaceous species (two forage species and three for human consumption) grown in soils containing zinc chloride. Based on the tolerance shown by Lolium rigidum to this salt in a first bioassay, we assessed its behaviour in the presence of other chlorides and other Zn salts (sulphates and nitrites). Besides providing plant anion concentrations (which are particulary novel results), our study identified Lolium rigidum as a species able to well-tolerate soil salinity and accumulate high levels of zinc chloride indicating its possible use for the phytostabilization of soils polluted with this salt.

Sewage sludges from urban wastewater treatment plants are often used to remediate degraded soils. However, the benefits of their use in metal-polluted soils remain unclear and need to be assessed in terms of factors besides soil fertility. This study examines the use of thermal-dried sewage sludge (TDS) as an amendment for heavy metal-polluted soil in terms of its effects on soil chemical properties, leachate composition, and the growth of native plant communities. To assess the response of the soil and its plant community to an increase in metal mobilization, the effects of TDS amendment were compared with those of the addition of a chelating agent (ethylenediaminetetraacetic acid [EDTA]). The experimental design was based on a real-case scenario in which soils from of an abandoned mine site were used in a greenhouse bioassay. Two doses of TDS and EDTA were applied to a soil containing high Pb, Zn, Cu, and Cd levels (4925, 5675, 404, and 25 mg kg, respectively). Soil pH was 6.4, and its organic matter content was 5.53%. The factors examined after soil amendment were soil fertility and heavy metal contents, leachate element losses, the plant community arising from the seed bank (plant cover, species richness and biodiversity, above/below ground biomass), and phytotoxic effects (chemical contents of abundant species). Thermal-dried sewage sludge emerged as a good phytostabilizer of Pb, Zn, Cu, and Cd given its capacity to reduce the plant uptake of metals and achieve rapid plant cover. This amendment also enhanced the retention of other elements in the plant root system and overall showed a better capacity to remediate soils polluted with several heavy metals. The addition of EDTA led to plant productivity losses and nutritional imbalances because it increased the mobility of several elements in the soil and its leachates.

The soils of many abandoned mine sites in the central region of Spain are heavily polluted with a number of different metals. Having frequently found Agrostis castellana growing at these old mine sites, this study was designed to assess its remediation capacity for this type of setting. In an initial field study, plant specimens were collected from 4 abandoned mine sites to determine pollutant concentrations in their roots and shoots. This was followed by a 4-year bioassay in a controlled environment in which soils collected from the mines were used to set up microcosms. Maximum root concentrations of the most polluting elements present in the bioassay were 3625 mg kg−1 Zn, 2793 mg kg−1 Cu, 13042 mg kg−1 Pb, 49 mg kg−1 Cd and 957 mg kg−1 As. These concentrations represent root bioaccumulation indices of over 1 and usually >2. In contrast, indices of transfer to above-ground phytomass were always < 1, indicating this species is a good candidate for use as a phytostabilizer. However, the high metal concentrations that could reach the above-ground mass of this plant determines a need for close monitoring and avoiding the use of areas under restoration for hunting or grazing.