Bruno Henriques

Evaluation of an approach for the characterization of reactive and available pools of twenty potentially toxic elements in soils: Part I – The role of key soil properties in the variation of contaminants’ reactivity

Harmful effects of potentially toxic elements (PTEs) in soils relate to their geochemically reactive fraction. To assess the degree of the reactivity, specific extractions or models are needed. Here we applied a 0.43 M HNO(3) chemical extraction to assess reactive pools of a broad range of PTEs in 136 contaminated and non-contaminated soils. Furthermore we derived Freundlich-type models based on commonly available soil properties (pH, organic carbon and clay) as well as extended models that used other properties such as amorphous Al and Fe oxides and evaluated their possible use in risk assessment. The approach allowed to predict the reactivity of As, Hg, Co, U, Ba, Se, Sb, Mo, Li, Be (r(2): 0.55-0.90) elements not previously included in such studies, as well as that of Cd, Zn, Cu, Pb, Ni and Cr (r(2): 0.73-0.90). The inclusion of pH, organic carbon and clay improved the performance of all models except for Be and Mo, although the role of clay is not completely clear and requires further investigation. The ability of amorphous metal oxides to affect the reactivity of As, Hg, Cu, Ni, Cr, Sb, Mo and Li was expressed by the models in agreement with known geochemical processes leading to the retention of PTEs by the solid matrix. Hence, such approach can be a useful tool to account for regional differences in soil properties during the identification of risk areas and constitute a significantly more powerful tool than the analysis of total pools of PTEs in soils.

Water-soluble fraction of mercury, arsenic and other potentially toxic elements in highly contaminated sediments and soils.

The water-soluble contents of mercury, arsenic and other potentially toxic elements in highly contaminated sediment and soil samples from Portugal were determined. Mercury and arsenic concentrations were detectable and reproducible among replicate experiments. Despite the acidic pH, the low organic carbon content and the exceptionally high levels of contamination of certain samples (total mercury contents varied between 0.15 and 3180 mg kg(-1) while total arsenic concentrations ranged from 11 to 6365 mg kg(-1)), the water-soluble percentages of both mercury (<1.2%) and arsenic (<4.6%) were generally low. The variability of the water-soluble fractions of these two elements among these samples and at the occurring pH conditions seems not to be associated with the release of other potentially toxic elements. The highest water-soluble concentrations of the remaining potentially toxic elements were generally observed in the 15-25 cm depth layer of sediments from areas colonised with plants (Halimione portulacoides) and in mining soil samples. Zinc, cobalt, copper and cadmium showed the highest water-soluble percentages of elements in relation to total metal contents. Given the high contamination levels, the availability of potentially toxic elements in these areas as well as possible risks to the environment and humans should be further investigated. The presence of plants (H. portulacoides) appears to cause significant changes in the sediment matrix that increase the mobility of several potentially toxic elements, particularly in the 15-25 cm depth layer. The effects of vegetation on the fractionation of potentially toxic elements on these sediments should be further studied.

Evaluation of an approach for the characterization of reactive and available pools of 20 potentially toxic elements in soils: Part II – Solid-solution partition relationships and ion activity in soil solutions

To assess environmental risks related to contaminants in soil it is essential to predict the available pool of inorganic contaminants at regional scales, accounting for differences between soils from variable geologic and climatic origins. An approach composed of a well-accepted soil extraction procedure (0.01 M CaCl(2)) and empirical Freundlich-type models in combination with mechanistically based models which to date have been used only in temperate regions was applied to 136 soils from a South European area and evaluated for its possible general use in risk assessment. Empirical models based on reactive element pools and soil properties (pH, organic carbon, clay, total Al, Fe and Mn) provided good estimations of available concentrations for a broad range of contaminants including As, Ba, Cd, Co, Cu, Hg, Mo, Ni, Pb, Sb, Se and Zn (r(2): 0.46-0.89). The variation of the pools of total Al in soils expressed the sorptive capacity of aluminosilicates and Al oxides at the surfaces and edges of clay minerals better than the actual variability of clay contents. The approach has led to recommendations for further research with particular emphasis on the impact of clay on the solubility of As and Sb, on the mechanisms controlling Cr and U availability and on differences in binding properties of soil organic matter from different climatic regions. This study showed that such approach may be included with a good degree of certainty for first step risk assessment procedures to identify potential risk areas for leaching and uptake of inorganic contaminants in different environmental settings.

Optimized graphene oxide foam with enhanced performance and high selectivity for mercury removal from water

This work explores the preparation of three-dimensional graphene oxide macroscopic structures, shaped by self-assembling single graphene oxide (3DGO) sheets with control of its surface chemistry by combining with nitrogen functional groups (3DGON), or with nitrogen and sulphur functional groups (3DGOSN), and their application in the removal of mercury (Hg(II)) from aqueous solutions. The chemical structure of the materials was assessed by using different characterization techniques: SEM, XPS and BET. Adsorption studies conducted in Hg(II) contaminated ultra-pure water reveal the enhanced ability of 3DGON for the adsorption of this metal, when compared to the other GO foams. A small dose of 3DGON (10 mg L(-1)) allows to remove up to 96% of Hg(II) after 24 h of contact time, leading to a residual concentration in solution close to the guideline value for drinking water (1 μg L(-1)). The ability of this material to adsorb Hg (II) was evaluated relatively to different experimental parameters such as pH, sorbent dose, time and effect on different competing metal ions. Real application was also evaluated by testing its performance in two different natural matrices, river and sea water, with very promising results.

Risks associated with the transfer of toxic organo-metallic mercury from soils into the terrestrial feed chain.

Although the transfer of organo-metallic mercury (OrgHg) in aquatic food webs has long been studied, it has only been recently recognized that there is also accumulation in terrestrial systems. There is still however little information about the exposure of grazing animals to OrgHg from soils and feed as well as on risks of exposure to animal and humans. In this study we collected 78 soil samples and 40 plant samples (Lolium perenne and Brassica juncea) from agricultural fields near a contaminated industrial area and evaluated the soil-to-plant transfer of Hg as well as subsequent trophic transfer. Inorganic Hg (IHg) concentrations ranged from 0.080 to 210mgkg(-1) d.w. in soils, from 0.010 to 84mgkg(-1) d.w. in roots and from 0.020 to 6.9mgkg(-1) d.w. in shoots. OrgHg concentrations in soils varied between 0.20 and 130μgkg(-1) d.w. representing on average 0.13% of the total Hg (THg). In root and shoot samples OrgHg comprised on average 0.58% (roots) and 0.66% (shoots) of THg. Average bioaccumulation factors (BAFs) for OrgHg in relation to soil concentrations were 3.3 (for roots) and 1.5 (for shoots). The daily intake (DI) of THg in 33 sampling sites exceeded the acceptable daily intake (ADI) of THg of both cows (ADI=1.4mgd(-1)) and sheep (ADI=0.28mgd(-1)), in view of food safety associated with THg in animal kidneys. Estimated DI of OrgHg for grazing animals were up to 220μgd(-1) (for cows) and up to 33μgd(-1) (for sheep). This study suggested that solely monitoring the levels of THg in soils and feed may not allow to adequately taking into account accumulation of OrgHg in feed crops and properly address risks associated with OrgHg exposure for animals and humans. Hence, the inclusion of limits for OrgHg in feed quality and food safety legislation is advised.

Competitive effects on mercury removal by an agricultural waste: application to synthetic and natural spiked waters

In this work, the efficiency of a local and highly available agricultural waste, the raw rice husk, was used to remove mercury (Hg) from synthetic and natural waters, spiked with concentrations that reflect the contamination problems found in the environment. Different operating conditions were tested, including initial pH, ionic strength, the presence of co-ions (cadmium) and organic matter. The sorption efficiency of rice husk was slightly affected by the presence H+ ions (pH range between 3 and 9), but in the presence of NaNO3 and NaCl electrolytes and in binary solutions containing Cd2+ and Hg2+, the sorption efficiency was dependent on the nature and levels of the interfering ion and on the initial concentration of Hg2+ used. Nevertheless, in a situation of equilibrium the effect of those ions was negligible and the removal efficiency ranged between 82% and 94% and between 90% and 96% for an initial Hg2+ concentration of 0.05 mg L−1 and 0.50 mg L−1, respectively. In more complex matrices, i.e. in the presence of humic substances and in natural river waters, the speciation and dynamics of Hg was changed and a fraction of the metal becomes unavailable in solution. Even then, the values obtained for Hg removal were satisfactory, i.e. between 59% and 76% and 81% and 85% for an initial concentration of Hg2+ of 0.05 and 0.50 mg L−1, respectively.

Oral bioaccessibility and human exposure to anthropogenic and geogenic mercury in urban, industrial and mining areas

The objective of this study was to characterize the link between bioaccessibility and fractionation of mercury (Hg) in soils and to provide insight into human exposure to Hg due to inhalation of airborne soil particles and hand-to-mouth ingestion of Hg-bearing soil. Mercury in soils from mining, urban and industrial areas was fractionated in organometallic forms; mobile; semi-mobile; and non-mobile forms as well as HCl-extractable Hg. The in vitro bioaccessibility of Hg was obtained by extracting soils with (1) a simulated human gastric fluid (pH1.5), and (2) a simulated human lung fluid (pH7.4). Total soil Hg concentrations ranged from 0.72 to 1.8 mg kg(-1) (urban areas), 0.28 to 94 mg kg(-1) (industrial area) and 0.92 to 37 mg kg(-1) (mining areas). Both organometallic Hg as well as 0.1M HCl extractable Hg were lower (<0.5% of total Hg) than Hg extracted by gastric fluid (up to 1.8% of total Hg) and lung fluid (up to 12% of total Hg). In addition, Hg extracted by lung fluid was significantly higher in urban and industrial soils (average 5.0-6.6% of total Hg) compared to mining soils. Such differences were related to levels of mobile Hg species in urban and industrial soils compared to mining soils. These results strengthen the need to measure site-specific Hg fractionation when determining Hg bioaccessibility. Results also show that ingestion and/or inhalation of Hg from soil particles can contribute up to 8% of adult total Hg intake when compared to total Hg intake via consumption of contaminated fish and animal products from contaminated areas.

Biochemical impacts of Hg in Mytilus galloprovincialis under present and predicted warming scenarios

The interest in the consequences of climate change on the physiological and biochemical functioning of marine organisms is increasing, but the indirect and interactive effects resulting from warming on bioconcentration and responsiveness to pollutants are still poorly explored, particularly in terms of cellular responses. The present study investigated the impacts of Hg in Mytilus galloprovincialis under control (17°C) and warming (21°C) conditions, assessing mussels Hg bioconcentration capacity, metabolic and oxidative status after 14 and 28days of exposure. Results obtained showed greater impacts in mussels exposed for 28days in comparison to 14days of exposure. Furthermore, our findings revealed that the increase in temperature from 17 to 21°C reduced the bioconcentration of Hg by M. galloprovincialis, which may explain higher mortality rates at 17°C in comparison to 21°C. Lower Hg concentration at 21°C in mussels tissue may result from valves closure for longer periods, identified by reduced energy reserves consumption at higher temperature, which in turn might also contributed to higher oxidative stress in organisms exposed to this condition. The highest LPO levels observed in mussels exposed to higher temperatures alone indicate that warming conditions will greatly affect M. galloprovincialis. Furthermore, the present study showed that the impacts induced by the combination of Hg and warming were similar to the ones caused by increased temperature acting alone, mainly due to increased antioxidant defenses in organisms under combined effects of Hg and warming, suggesting that warming was the factor that mostly contributed to oxidative stress in mussels. Although higher mortality was observed in individuals exposed to 17°C and Hg compared to organisms exposed to Hg at 21°C, the oxidative stress induced at higher temperature may generate negative consequences on mussels reproductive and feeding capacity, growth and, consequently, on population maintenance and dynamics.

Biochemical responses and accumulation patterns of Mytilus galloprovincialis exposed to thermal stress and Arsenic contamination

Organisms in marine systems are exposed to multiple stressors that create a range of associated environmental and ecotoxicological risks. Examples of stressors include alterations related to climate change, such as temperature increase, and the exposure to pollutants arising from human activities. The present study evaluated the impacts of Arsenic exposure (1mg/L) and warming (21°C) in Mytilus galloprovincialis, acting alone and in combination. Our results demonstrated that both Arsenic exposure and warming induced oxidative stress and reduced mussels metabolism, with changes becoming more prominent with the exposure time and when mussels were exposed to both stressors in combination. Furthermore, results obtained showed higher As accumulation in organisms exposed to warming treatments. The present study showed that under warming scenarios, the negative impacts induced by As may be enhanced in ecologically and economically relevant bivalves, with potential impacts on population stocks due to increased sensitivity to pollutants, which may eventually result in biodiversity loss and socio-economic impacts.

Removal and recovery of Critical Rare Elements from contaminated waters by living Gracilaria gracilis

The experiments performed in this work proved the ability of Gracilaria gracilis to concentrate and recover Critical Rare Elements (CRE) from contaminated waters. The importance of recycling these elements is related to their very limited sources in Nature and progressive use in technologies. Moreover, their mining exploitation has negative environmental impact, and recent studies point them as new emerging pollutants. To the best of our knowledge, this is the first report on the application of living macroalgae for the removal and recovery of CRE. G. gracilis (2.5gL-1, fresh weight) was exposed to mono- and multi-element saline solutions of 500μgL-1 of Y, Ce, Nd, Eu and La. Removal was up to 70% in 48h, with bioaccumulation following Elovich kinetic model. In multi-element solutions, selectivity was not observed although removal of lanthanides improved comparatively to single-element solutions. No mortality or adverse effect on growth was registered. The subsequent macroalgae digestion allowed collecting virtually 100% of all elements in a 300-fold more concentrated solution. The overall results suggest the application of living macroalgae as a simple and effective alternative technology for removing and recovering CRE from wastewaters, contributing to an improvement of water quality and CRE recycling.