Nuno Cruz

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.

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.

Soil-pore water distribution of silver and gold engineered nanoparticles in undisturbed soils under unsaturated conditions

Release of engineered nanoparticles (ENPs) to soil is well documented but little is known on the subsequent soil-pore water distribution of ENPs once present in soil. In this study, the availability and mobility of silver (Ag) and gold (Au) ENPs added to agricultural soils were assessed in two separate pot experiments. Pore water samples collected from pots from day 1 to 45 using porous (<0.17 μm) membrane samplers suggest that both Ag and Au are retained almost completely within 24 h with less than 13% of the total added amount present in pore water on day 1. UV-Vis and TEM results showed that AuENPs in pore water were present as both homoaggregates and heteroaggregates until day 3 after which the concentration in pore water was too low to detect the presence of aggregates. A close relation between the concentration of Au and Fe in pore water suggests that the short term solubility of Au is partly controlled by natural soil colloids. Results suggest that under normal aerated soil conditions the actual availability of Ag and AuENPs is low which is relevant in view of risk assessment even though the impact of environmental conditions and soil properties on the reactivity of ENPs (and/or large ENPs aggregates) retained in the solid matrix need to be addressed further.

Mechanical and durability properties of a soil stabilised with an alkali-activated cement

Alkali-activated cements (AAC) have been extensively studied for different applications as an alternative to Portland cement (which has a high carbon footprint) and due to the possibility of including waste materials such fly ash or slags. However, few works have addressed the topic of stabilised soils with AAC for unpaved roads, with curing at ambient temperature, where the resistance to wetting and drying (WD) as well as the mechanical properties evolution over time is particularly relevant. In this paper, silty sand was stabilised with an AAC synthesised from low calcium fly ash and an alkaline solution made from sodium silicate and sodium hydroxide. The evolution of stiffness and strength up to 360 days, the tensile strength, and the performance during WD cycles were some of the characteristics analysed. Strength and stiffness results show a significant evolution far beyond the 28th curing day, but still with a reasonable short-term strength. Strength parameters deduced from triaxial tests were found to be very high with stress–strain behaviour typical of cemented soils. Durability properties related to resistance to immersion and WD cycles were found to comply with existing specifications for soil–cement, giving validity for its use as soil–cement replacement.

Using neural networks and support vector regression to relate marchetti dilatometer test parameters and maximum shear modulus

In the last two decades, small strain shear modulus became one of the most important geotechnical parameters to characterize soil stiffness. Finite element analysis have shown that in-situ stiffness of soils and rocks is much higher than what was previously thought and that stress-strain behaviour of these materials is non-linear in most cases with small strain levels, especially in the ground around retaining walls, foundations and tunnels, typically in the order of 10−2 to 10−4 of strain. Although the best approach to estimate shear modulus seems to be based in measuring seismic wave velocities, deriving the parameter through correlations with in-situ tests is usually considered very useful for design practice.The use of Neural Networks for modeling systems has been widespread, in particular within areas where the great amount of available data and the complexity of the systems keeps the problem very unfriendly to treat following traditional data analysis methodologies. In this work, the use of Neural Networks and Support Vector Regression is proposed to estimate small strain shear modulus for sedimentary soils from the basic or intermediate parameters derived from Marchetti Dilatometer Test. The results are discussed and compared with some of the most common available methodologies for this evaluation.

Maximum Shear Modulus Prediction by Marchetti Dilatometer Test Using Neural Networks

The use of Neural Networks for modeling systems has been widespread, in particular within areas where the great amount of available data and the complexity of the systems keeps the problem very unfriendly to treat following traditional data analysis methodologies. In the last two decades, small strain shear modulus became one of the most important geotechnical parameters to characterize soil stiffness. Finite element analysis have shown that in-situ stiffness of soils and rocks is much higher than was previously thought, and that stress-strain behaviour of these materials is non-linear in most cases with small strain levels, especially in the ground around retaining walls, foundations and tunnels typically in the order of 10− 2 to 10− 4 of strain. Although the best approach seems to be based in measuring seismic wave velocities, deriving the parameter through correlations with in-situ tests is usually considered very useful for design practice. In this work, a new approach using Neural Networks is proposed for sedimentary soils and the results are discussed and compared with some of the most common available methodologies for this evaluation.

Seepage water quality of a soil treated with alkali-activated cement at room temperature

Modern societies are great producers of waste because of their energy and natural resource needs. Many of these wastes are disposed of in landfills, which require a significantly sized area of soil...

Characterization of Soil Treated With Alkali-Activated Cement in Large-Scale Specimens

Soil improvement with hydraulic binders is currently used in practice because of the advantages of using the local soil enhancing its geotechnical properties. However, environmental issues related to quicklime applications and carbon-dioxide emissions associated to Portland cement production encouraged the development of new binders. In this work, alkaline-activated cement (AAC) synthetized by fly ash and an alkaline solution was used to stabilize silty sand. The behavior of the treated soil was evaluated performing tests on a physical model and the results were compared to laboratory data to define its compaction, strength, and stiffness properties. Those tests include nuclear density gauge measurements, light falling weight deflectometer tests, and plate load tests, whereas unconfined compression tests with unload–reload cycles and seismic wave measurements were performed at the laboratory. These tests, very common in current geotechnical practice, have proved to be also adequate to quality control and to evaluate the geomechanical properties of this material. The results at 28 days show a significant improvement given by the AAC, but still show some sensitivity to water when flooded. The comparison of results from different tests provided the evolution of stiffness with strain level.

Estimating the maximum shear modulus with neural networks

Small strain shear modulus is one of the most important geotechnical parameters to characterize soil stiffness. In-situ stiffness of soils and rocks is much higher than was previously thought as finite element analysis have shown. Also, the stress-strain behaviour of those materials is non-linear in most cases with small strain levels. The commun approach for getting the small strain shear modulus is usually based on measure of seismic wave velocities. Nevertheless, for design purposes is very useful to derive that modulus from correlations with in-situ tests output parameters. In this view, the use of Neural Networks seems very appropriate as the complexity of the system keeps the problem very unfriendly to treat following traditional data analysis methodologies. In this work, the use of Neural Networks is proposed to estimate small strain shear modulus for sedimentary soils from the basic or intermediate parameters derived from Marchetti Dilatometer Test.

Characterization of Stiff Residual Soils with Dynamically Push-in DMT

DMT (Marcheti Flat Dilatometer Test) has been increasingly used with success in the evaluation of geomechanical properties of soft to medium soils, with moderate compacity or consistency (N SPT less than 30). The insertion of the Flat Blade has been traditionally made by static pushing, which is an operational limitation in hard to stiff soils, in particular in heterogeneous saprolitic residual soils. This has been limiting the practitioners, when, as in Portugal, pressuremeter test is not common practice, leading to rely exclusively in dynamic penetration test (such as SPT or DPSH — super-heavy dynamic probing), which are very limited in, among other levels, deriving stiffness properties. In this context, the dynamic penetration of the DMT blade has been explored as an alternative to static push-in, assuming that the characteristics of the test — by inducing a solicitation that is eminently horizontal, may, in some way, preserve the intrinsic characteristics of the natural soil. This is being explored as a possible potential of this device for these natural ambient. The present paper will be presenting a comparative analysis of the results obtained in both static and dynamically push-in DMT tests in weathered profiles of granitic masses and reference earthfills.