Chiara Ferronato

Heavy metal risk assessment after oxidation of dredged sediments through speciation and availability studies in the Reno river basin, Northern Italy

PurposeThe distribution of heavy metals was investigated in sediments of both natural and artificial watercourses of the Reno river basin (Northern Italy) with the aim of assessing their pollution risk before and after dredging operations. The different solubility and availability of metals in wet and dry sediments were investigated in order to identify the main critical variables controlling metal adsorption into sediments, their speciation and, therefore, their potential environmental hazard.Materials and methodsTwenty-four sampling stations were selected in the Reno basin network, and sediment sampling was seasonally carried out in 2012–2013. Pseudo-total metal content was determined through acid digestion with aqua regia, and the geoaccumulation index (Igeo) of metals was estimated using regional mean background values. Leaching tests were carried out through partial dissolution techniques (deionized water and diethylenetriaminepentaacetic acid (DTPA) extraction) on wet and dry samples, while the speciation of metals was investigated by a five-step sequential extraction. All analyses were performed by inductively coupled plasma optical emission spectrometry (ICP-OES).Results and discussionArtificial watercourses presented higher contamination levels than natural ones, and a different pollution level was found when Igeo was applied. The sequential extraction showed that metals in river sediments are mostly immobilized in the residual phase (e.g. Cr), while in canals, weak bonds were found (e.g. Cd). The dredging of sediments, and their consequent oxidation, enhances the availability of metals according to their affinity with organic matter (e.g. Cu and Pb) or carbonates (e.g. Zn). The different remobilization rate obtained by changing the oxidation status of sediments highlighted the importance of metal availability studies for assessing and predicting their environmental hazard.ConclusionsThe effect of oxidation processes on the availability of heavy metals depends on the geogenic or anthropogenic nature of the element, on the redox status of the sediment and on the affinity of the metal with the different mineralogical phases of the sediment. In redox changing environments, the prediction of the environmental risk from metals before and after sediment land disposal gives more useful information than the knowledge of total metal concentration. The use of leaching techniques, combined with the calculation of background values, is strongly recommended for the assessment of metal hazard in sediments.

Adsorption of pathogenic microorganisms, NH4 + and heavy metals from wastewater by clinoptilolite using bed laminar flow

Abstract The contamination of water bodies in urban areas is a serious problem, which may increase when wastewater is discharged without complete remediation. Due to their high adsorption capacity and ion-exchange properties, zeolites, such as clinoptilolite, can be used successfully to detoxify the wastewater before discharging it into the water body. In this study, experimental use of clinoptilolite is presented for water remediation. A static flow (A) and a laminar flow (B) method were applied in order to evaluate the efficiency of clinoptilolite for reducing different contaminants in the outflow wastewater of an old municipal treatment plant in Bologna District (Northern Italy). Mesocosm experiments were performed in order to achieve reduction of the microbial faecal indicators and of the excess nutrients and heavy metals in the effluent. During the experiments, pathogenic microorganisms, ammonium and heavy metals were reduced by as much as between 78 and 95% within 24 h, highlighting the great efficiency of this low-cost material for water remediation.

Soil properties and plant community relationship in a saltmarsh of the Grado and Marano lagoon (northern Italy)

PurposeThe relationship between soil properties and plant communities was investigated in a saltmarsh of the Grado and Marano lagoon (northern Italy), where hydrology and micromorphology strongly influence the features of the ecosystem. A multidisciplinary approach was used to assess the change of soil properties and plant communities in relation to the submergence of soil.Materials and methodsThe plant community and soil profile surveys were both carried out along a transect in six sampling sites of the Gran Chiusa saltmarsh (Grado and Marano lagoon). The morphological and physicochemical parameters of soil profiles were investigated, and soils were classified according to Soil Taxonomy. The concentration of macronutrients in both soils and plants was analysed by inductively coupled plasma-optical emission spectrometry. Cluster and linear discriminant analysis were used to assist the interpretation of the data of plant communities and soil properties, respectively. The bioconcentration factor explored the macronutrient relationship between plant community and soil.Results and discussionA high, middle and low zone were identified by clustering the different plant communities along the studied transect. Discriminant analysis showed how the increase in soil submergence supported the accumulation of S and Ca content and depletion of Fe and Na. The development of different plant communities was linked to both soil water saturation and to the capacity of halophytes to tolerate anoxic conditions or salinity, by extrusion or bioconcentration strategies.ConclusionsThis study demonstrates that tide level plays an important role in the pedological development and chemical transformations along a soil hydrosequence. The micromosaic vegetation pattern may therefore represent a useful index of the hydrological and nutritional status of the underlying soils and could be used to predict changes in coastal ecosystems.

Thallium Toxicity in Mediterranean Horticultural Crops (Fragaria vesca L., Mentha pulegium L., Ocimum basilicum L.)

Thallium is a non-essential, toxic element that concerns mining areas and their acid drainage effluents. Minerals containing thallium can be eroded, and Tl can be leached into soil, thus being spread into the environment and adsorbed by plants and living organisms, entering the food chain, and inducing serious toxicity problems. In this study, the Tl cycle was observed and analyzed on basil, mint, and strawberry cultivated in a greenhouse and irrigated with Tl-contaminated water. The Tl content in both bulk and rhizosphere soils as well as thallium present in different plant organs were analyzed during the experiment, with the aim of revealing both physiological symptoms and metabolic disorders linked to the Tl toxicity. The mechanism of plants to exclude, uptake, translocate, and tolerate Tl varied among the different species, and both the bioconcentration factor (BCF) and the translocation index (TI) were calculated to highlight a different response to Tl toxicity of strawberry, mint, and basil. Basil is the less tolerant species, while mint and strawberry showed different self-defense mechanism against Tl adsorption and translocation.