Bioaccessibility of Cd and Pb in tailings from a zinc smelting in Brazil: implications for human health

Nanosized titanium dioxide elevates toxicity of cationic metals species for Daphnia - have aging and natural organic matter an unexpected impact?

In aquatic ecosystems, nanosized titanium dioxide particles (nTiO₂) likely interact with natural organic matter (NOM) and may alter the ecotoxicity of co-occurring metals. The magnitude of changes in toxicity may be modulated by the duration of interactions (i.e. aging) between these factors. As those interactions are hardly addressed in literature, the present study aimed at assessing the impact of aging durations (0, 1, 3 and 6 days) on metals with mainly cationic (silver (Ag), cadmium (Cd)) or anionic (arsenic (As)) toxic ions in combination with three nTiO₂ levels (0.0, 0.6 and 3.0 mg/L) and two NOM levels (0 versus 8 mg TOC/L). The interaction of these factors was additionally investigated for two aging scenarios: in one scenario nTiO₂ were aged together with one of the metals, while in other scenario metals were added to aged nTiO₂. Subsequently, their combined acute effects on Daphnia magna were assessed. The results uncovered that nTiO₂ elevate the toxicity of metals with mainly cationic species (i.e. Ag⁺ and Cd²⁺) with the effect size depending on their valence electron. Contrary, nTiO₂ have no impact on the metal with mainly anionic species (i.e. HAsO₄^2-). Furthermore, NOM reduced metal toxicity only for Ag and aging duration had a limited impact on the test outcome suggesting that relevant interactions between metal and nTiO₂ occur rather quick (below 24 h). These findings suggest that the charge of metals' most toxic species is the determining factor for its interaction with nanoparticles and the resulting ecotoxicological effect assessment.

Interactions of cadmium and zinc in high zinc tolerant native species Andropogon gayanus cultivated in hydroponics: growth endpoints, metal bioaccumulation, and ultrastructural analysis

Cadmium (Cd) and zinc (Zn) toxicity causes physiological disorders and harms plants, interfering with the rehabilitation of areas affected by mining activities. This study evaluated how the exposure to Zn and/or Cd affects the growth of native andropogon grass (Andropogon gayanus Kunth) plants originally found in areas contaminated with Cd and/or Zn due to zinc mining activities. Plants were cultivated for 7 weeks in a nutrient solution treated with Zn (142.3-854.0 μM) or Cd (0.9-13.3 μM) separately or combined with a molar ratio of 64:1 (Zn:Cd). A control treatment was grown in a complete Hoagland and Arnon solution (without Cd). Plant height, stem diameter, internode length, dry weight, Cd and Zn concentration, and accumulation in shoots/roots, as well as ultrastructure of roots and leaves were analyzed at the end of the experiment. The root dry weight was not significantly affected by the addition of the metals. Moreover, Zn provided higher shoot dry weight (up to 160%) relative to control. Andropogon grass tolerated both metals better separately than when applied together. Transmission electron microscopy analyses showed modifications such as vesiculation and vacuolation in the ultrastructure of andropogon tissues by Cd and/or Zn. The andropogon grass was tolerant to the doses tested, evidencing that it has potential for recovering areas contaminated with Zn and/or Cd.

Investigating the relationship between speciation and oral/lung bioaccessibility of a highly contaminated tailing: contribution in health risk assessment

Anthropogenic activities such as industrial, mining, or agricultural are the main sources of environmental contamination. One of the most problematic contaminations concerns metals and metalloids from mining activities. This contamination raises the question of the environmental risk induced and the spread of this pollution (geographical and trophic) and the associated health risk. The integrated, multi-analytical approach of this study conducted on the mining district of Cartagena-La Union (Murcia, Spain) as part of the Interreg SUDOE European project "Soil Take Care" aims to (i) precisely define the speciation of contaminants of interest (Zn, Pb, Cd, As), (ii) predict the environmental risk related to storage stability, and (iii) establish the link between the speciation of the bearing phases and the associated health risk. To do this, a representative zone in the Cartagena-La Union mining district close to the populations was chosen. A physic-chemical characterization of the samples was performed (pH, electrical conductivity, CEC, and total metal(loid) concentrations), and the mineralogy was determined using XRD and SEM-EDS. The environmental risk was highlighted from sequential BCR-type extractions and EN-12457 leaching tests. Finally, the health risk was defined using the PSF inhalation bioaccessibility test and UBM bioaccessibility protocol (based on an operational chemical methodology mimicking soil ingestion and its residence in the gastrointestinal tract of the human body). These analyses revealed 2 groups of samples with distinct behavior. The first group of samples presents relatively stable bearing phases, mainly found in the residual fraction (As and Pb), presenting only a low health risk (very low bioaccessible). The second group consists of Cd and/or Zn-bearing phases, mainly labile (resulting from dissolution/precipitation phenomena), while gastric bioaccessibility reaches more than 85%. Note that Pb, Cd, and Zn have the potential to cause non-carcinogenic risks to children and As and Pb present a carcinogenic risk for children and adults even if only the bioaccessible fraction is considered. It has therefore been shown that the meteoric alteration of the tailing induces a change in speciation leads to an increase in environmental and health risks. These results are essential because they highlight the need for an integrated approach in order to clearly highlight the presence of risks but also that this approach will allow a better understanding of the potential rehabilitation path of this site.

Linking oral bioaccessibility and solid phase distribution of potentially toxic elements in extractive waste and soil from an abandoned mine site: Case study in Campello Monti, NW Italy

Oral bioaccessibility and solid phase distribution of potentially toxic elements (PTE) from extractive waste streams were investigated to assess the potential human health risk posed by abandoned mines. The solid phase distribution along with micro-X-ray fluorescence (micro-XRF) and scanning electron microscopy (SEM) analysis were also performed. The results showed that the total concentrations of PTE were higher in <250 μm size fractions of waste rock and soil samples in comparison to the <2 mm size fractions. Mean value of total concentrations of chromium(Cr), copper (Cu), and nickel (Ni) in waste rocks (size fractions <250 μm) were found to be 1299, 1570, and 4010 mg/kg respectively due to the parent material. However, only 11% of Ni in this sample was orally bioaccessible. Detailed analysis of the oral bioaccessible fraction (BAF, reported as the ratio of highest bioaccessible concentration compared with the total concentration from the 250 μm fraction) across all samples showed that Cr, Cu, and Ni varied from 1 to 6%, 14 to 47%, and 5 to 21%, respectively. The variation can be attributed to the difference in pH, organic matter content and mineralogical composition of the samples. Non-specific sequential extraction showed that the non-mobile forms of PTE were associated with the clay and Fe oxide components of the environmental matrices. The present study demonstrates how oral bioaccessibility, solid phase distribution and mineralogical analysis can provide insights into the distribution, fate and behaviour of PTE in waste streams from abandoned mine sites and inform human health risk posed by such sites .