Thallium uptake and risk in vegetables grown in pyrite past-mining contaminated soil amended with organic fertilizer (compost): A potential method for Tl contamination remediation

Thallium (Tl) is a highly toxic trace metal that can cause severe pollution and damage to the ecological system. In this study, a field trial was conducted in a Tl-rich pyrite-barite past-mining area to unveil the fate of Tl in agricultural practice. Tuscany kale and red chicory cultivated in soil impacted by the dismissed mine of Valdicastello Carducci (Northern Tuscany, Italy) displayed significantly different uptake behaviors of Tl. Hyper-accumulation of Tl was observed in kale leaves and its content reached up to 17.1 mg kg-1 whereas only <0.70 mg kg-1 of Tl was found in leaves of red chicory. Due to the regionally polymetallic pollution, Tuscany kale grown in this area possessed a great Tl intake risk for the residents. As for the fertilization treatment, Tl in Tuscany kale leaves fertilized with mineral fertilizer (NPK) and compost were 21.4 and 12.8 mg kg-1. The results suggested a potential remediation ability of compost in diminishing Tl in the vegetable leaves and thus may reduce its risk in the soil-crop system. Since Tl poisoning emergency may occur in agricultural fields near past-mining zones, it is critical to establish possible remediation measures to ensure food safety surrounding former mining areas likewise.

Hexavalent chromium release over time from a pyrolyzed Cr-bearing tannery sludge

Pyrolysis in an inert atmosphere is a widely applied route to convert tannery wastes into reusable materials. In the present study, the Cr(III) conversion into the toxic hexavalent form in the pyrolyzed tannery waste referred to as KEU was investigated. Ageing experiments and leaching tests demonstrated that the Cr(III)-Cr(VI) inter-conversion occurs in the presence of air at ambient temperature, enhanced by wet environmental conditions. Microstructural analysis revealed that the Cr-primary mineral assemblage formed during pyrolysis (Cr-bearing srebrodolskite and Cr-magnetite spinel) destabilized upon spray water cooling in the last stage of the process. In the evolution from the higher to the lower temperature mineralogy, Cr is incorporated into newly formed CrOOH flakes which likely react in air forming extractable Cr(VI) species. This property transforms KEU from an inert waste to a hazardous material when exposed to ordinary ambient conditions.

Trace Elements in Soil and Urban Groundwater in an Area Impacted by Metallurgical Activity: Health Risk Assessment in the Historical Barga Municipality (Tuscany, Italy)

Trace elements were measured in soil and groundwater collected within the Fornaci di Barga urban area (Serchio River Valley, Tuscany, Italy), a territory that integrates natural assets with touristic vocation, impacted by long-lasting metallurgical activity. Epidemiological studies highlighted that the area surrounding the industrial plants is characterized by a persistent excess of diseases, attributed to heavy metal pollution. Soils were taken in school gardens, public parks, sport grounds and roadsides. The results indicate that Cu, Zn and Cd represent the main contaminants in surface soil, likely originated by deposition of airborne particulate matter from metallurgical activity. Risk assessment considering soil ingestion and dermal contact exposure routes revealed that the cadmium Hazard Quotient approaches unity for children, and the cadmium risk-based concentration obtained by combining exposure information with toxicity data is only slightly lower compared with the cadmium maximum concentration actually measured in soil. Groundwater does not show evidence of trace metal contamination, suggesting that the migration of contaminants from soil to subsurface is a slow process. However, assessment of the possible interconnections between shallow and deep-seated aquifers requires monitoring to be continued. The obtained results highlight the possible link between space clusters of diseases and metal concentration in soil.

Toxicity of Thallium at Low Doses: A Review

A mini review of the toxicity of Thallium (Tl) at low doses is herein presented. Thallium has severe toxicity. Although its acute biological effects have been widely investigated and are well known, its biological effects on human health and in cell cultures at low doses (<100 μg/L) due, for example, to Tl chronic exposure via consumption of contaminated water or foods, have often been overlooked or underestimated. Relatively few papers have been published on this topic and are herein reviewed to provide a focused scientific opinion in the light of current worldwide regulatory issues.

Water quality and solute sources in the Marsyangdi River system of Higher Himalayan range (West-Central Nepal)

Surface waters, cold and hot springs were collected in different catchments along the Marsyangdi basin, in the Himalayan Range of West-Central Nepal, during the post-monsoon season in 2017 and analyzed for major ions and trace elements, with the aim of assessing the sources of dissolved species and to contribute in watershed planning. The major element data indicate that surface waters coming from the Tethyan Himalayan Sequence (THS) range from the Ca-Mg-HCO₃ to the Ca-Mg-HCO₃-SO₄ water-types and reflect a two-component mixing of waters from carbonate- and sulfate-bearing sources. The latter component is attributable to sulfide oxidation with minor silicate weathering. In the Greater Himalaya Sequence (GHS), alteration of pedogenetic carbonates formed in response to silicate weathering under a variable CO₂ gas pressure dominates, yielding a Ca-HCO₃ signature. The stability diagram in the K₂O-Al₂O₃-SiO₂-H₂O system and the paired increases in Ca²⁺, Na⁺, K⁺ and silica indicate that degradation of silicate minerals through kaolinization and possibly plagioclase albitization reactions is the main process for hot groundwater. Cold and hot springs define a trend of increasing Li, SiO₂ and Cl^-, suggesting that lithium was leached from silica-rich sources, such as pegmatite dykes and sills occurring in host rocks, and concentrated into halite-bearing salt aquifers. In hot waters Sb, As and Tl exceed the EU and USEPA thresholds. Tl is usually incorporated into pyrite and correlates with Li indicating the occurrence of an ore-bearing zone possibly related to hydrothermal activity at the transition zone between THS and GHS, as suggested by the relatively high Ba, Ni, Cu, Sb, As and Mn contents. The obtained data on water quality have significant implications for people living along the Upper Marsyangdi River in the management of water resources, especially in terms of the enhancement of cold water aquaculture and hot water uses for recreation purposes and tourism.

Chromium isotopes tracking the resurgence of hexavalent chromium contamination in a past-contaminated area in the Friuli Venezia Giulia Region, northern Italy

The origin of a resurgent hexavalent chromium contamination in groundwater from a phreatic aquifer in the Friuli Venezia Giulia Region plain was investigated by chromium isotopic systematics. The area underwent a severe Cr(VI) contamination by industrial effluents in 1997, when Cr(VI) concentration in groundwater reached 4500 µg/L. In subsequent years the contamination naturally attenuated, totally disappearing in 2003. A renewal of water contamination was observed in 2008, Cr(VI) reaching 1560 µg/L. The δ⁵³Cr value in groundwater and extracts from sediments was measured in 2009-2011, and it ranges between -3.21 and +0.21‰ and between -4.71 and +1.26‰, respectively. Due to the lack of geogenic Cr-sources, these data are interpreted as evidence of the subsequent oxidation through Mn-oxides of the Cr(III) hosted in the aquifer and originated by the reduction of the original industrial chromates. Cr(III) is characterized by negative δ⁵³Cr, starting from the δ⁵³Cr value around zero of Cr(VI) in industrial effluents. Oxidation liberates soluble Cr(VI) which is transported by groundwater and permeated soils. The complex Cr-isotopic vs. concentration distribution reflects both the new Cr(VI) reduction and dilution processes in the aquifer system. From an environmental point of view, the data raise concerns regarding the potential impact of past Cr(VI)-contamination.

Influence of environmental and anthropogenic parameters on thallium oxidation state in natural waters

The abandoned mining area of Valdicastello Carducci (Tuscany, Italy) is characterized by the massive presence of thallium in the acid mine drainages and in the valley stream crossing the region. We previously found that Tl(III), generally considered the less stable oxidation state of thallium, is present both in the stream and in tap water distributed in the area, whereas acid mine drainages only contain Tl(I). These findings posed some concern related to the reactivity and dispersion of this toxic element in the environment. Since the valence state of thallium determines its toxicity, distribution and mobility, the study of thallium redox speciation appears crucial to understand its environmental behaviour. In this work, water samples collected from the mine drainages and the contaminated stream were adopted as model to study the distribution of aqueous Tl(I)/Tl(III) as a function of light exposure and solution properties and composition. The influence of three light sources and organic acids was evaluated. Thallium speciation was also assessed in tap water after treatment with common oxidizing agents, and in the rust crust collected from the public waterworks.

Human exposure to thallium through tap water: A study from Valdicastello Carducci and Pietrasanta (northern Tuscany, Italy)

A geological study evidenced the presence of thallium (Tl) at concentrations of concern in groundwaters near Valdicastello Carducci (Tuscany, Italy). The source of contamination has been identified in the Tl-bearing pyrite ores occurring in the abandoned mining sites of the area. The strongly acidic internal waters flowing in the mining tunnels can reach exceptional Tl concentrations, up to 9000μg/L. In September 2014 Tl contamination was also found in the tap water distributed in the same area (from 2 to 10μg/L). On October 3, 2014 the local authorities imposed a Do Not Drink order to the population. Here we report the results of the exposure study carried out from October 2014 to October 2015, and aimed at quantifying Tl levels in 150 urine and 318 hair samples from the population of Valdicastello Carducci and Pietrasanta. Thallium was quantified by inductively coupled plasma - mass spectrometry (ICP-MS). Urine and hair were chosen as model matrices indicative of different time periods of exposure (short-term and long-term, respectively). Thallium values found in biological samples were correlated with Tl concentrations found in tap water in the living area of each citizen, and with his/her habits. Thallium concentration range found in hair and urine was 1-498ng/g (values in unexposed subjects 0.1-6ng/g) and 0.046-5.44μg/L (reference value for the European population 0.006μg/L), respectively. Results show that Tl levels in biological samples were significantly associated with residency in zones containing elevated water Tl levels. The kinetics of decay of Tl concentration in urine samples was also investigated. At the best of our knowledge, this is the first study on human contamination by Tl through water involving such a high number of samples.