Slurry wall containment performance: monitoring and modeling of unsaturated and saturated flow

A specific 2-year program to monitor and test both the vadose zone and the saturated zone, coupled with a numerical analysis, was performed to evaluate the overall performance of slurry wall systems for containment of contaminated areas. Despite local physical confinement (slurry walls keyed into an average 2-m-thick aquitard), for at least two decades, high concentrations of chlorinated solvents (up to 110 mg l^− 1) have been observed in aquifers that supply drinking water close to the city of Milan (Italy). Results of monitoring and in situ tests have been used to perform an unsaturated-saturated numerical model. These results yielded the necessary quantitative information to be used both for the determination of the hydraulic properties of the different media in the area and for the calibration and validation of the numerical model. Backfill material in the shallower part of the investigated aquifer dramatically affects the natural recharge of the encapsulated area. A transient simulation from wet to drought periods highlights a change in the ratio between leakages from lateral barriers that support a specific scenario of water loss through the containment system. The combination of monitoring and modelling allows a reliable estimate of the overall performance of the physical confinement to be made without using any invasive techniques on slurry wall.     

Bioaccumulation and biotransformation of arsenic compounds in Hediste diversicolor (Muller 1776) after exposure to spiked sediments

This study focused on the exposure of the common ragworm Hediste diversicolor (Müller 1776) to sediments enriched with different arsenic compounds, namely arsenate, dimethyl-arsinate, and arsenobetaine. Speciation analysis was carried out on both the spiked sediments and the exposed polychaetes in order to investigate H. diversicolor capability of arsenic bioaccumulation and biotransformation. Two levels of contamination (acute and moderate dose) were chosen for enriched sediments to investigate possible differences in the arsenic bioaccumulation patterns. The highest value of arsenic in tissues was reached after 15 days of exposure to dimethyl-arsinate (acute dose) spiked sediment (1,172?±?176 μg/g). A significant increase was also obtained in worms exposed both to arsenate and arsenobetaine. Speciation analysis showed that trimethyl-arsine oxide was the predominant chemical form in tissues of H. diversicolor exposed to all the spiked sediments, confirming the importance of this intermediate in biological transformation of arsenic.     

A multidisciplinary weight of evidence approach for classifying polluted sediments: Integrating sediment chemistry, bioavailability, biomarkers responses and bioassays

Evaluation of chemical bioavailability and onset of biological alterations is fundamental to assess the hazard of environmental pollutants, particularly when associated to sediments which need to be removed. In the present work, five sediment samples were collected from the Venice Lagoon and data from sediment chemistry were integrated with those of bioaccumulation of chemicals in European eel (Anguilla anguilla) exposed under laboratory conditions, responses of a wide battery of biomarkers, and standardized ecotoxicological bioassays. The overall results were elaborated within a recently developed, software-assisted weight of evidence (WOE) model which provides synthetic indices for each of considered line of evidence (LOE), before a general evaluation of sediment hazard. Levels of chemicals in sediments were not particularly elevated when compared to sediment quality guidelines of Venice Protocol. On the other hand, bioavailability was evident in some samples for Cd, Cu, Zn and, especially, polycyclic aromatic hydrocarbons. The ecotoxicological approach provided further evidence on the biological and potentially harmful effects due to released contaminants, and oxidative-mediated responses appeared of primary importance in modulating sublethal responses and the onset of cellular alterations. Biomarkers variations were sensitive, and more evident variations included significant changes of cytochrome P450 biotransformation pathway, antioxidant responses, onset of oxidative damages, lysosomal membrane stability and genotoxic effects. The results obtained from the battery of bioassays indicated that responses measured at organism level were in general accordance but less marked compared to the onset of sublethal changes measured through biomarkers. Overall this study revealed differences when comparing evaluations obtained from different LOEs, confirming the importance of considering synergistic effects between chemicals in complex mixtures. Compared to a qualitative pass-fail approach toward normative values, the proposed WOE model allowed a quantitative characterization of sediment hazard and a better discrimination of on the basis of various types of chemical and biological data.     

Ecotoxicological effects of sediments from Mar Piccolo,South Italy: toxicity testing with organisms from different trophic levels

The Mar Piccolo of Taranto (Ionian Sea, Southern Italy) is a semi-enclosed and strongly polluted basin. For decades, it has been subjected to different anthropogenic impacts. These stressors caused severe sediments contamination with high concentration of different pollutants (PAHs, PCB, heavy metals). In order to assess the current status of sediments contamination, an ecotoxicological investigation combined with chemical analysis (heavy metals, PAH, and PCB) has been performed. In order to derive ecologically relevant conclusions, a multiorganisms and multiend-points approach has been applied, exposing organisms from different trophic levels to elutriate and whole sediment. The battery of bioassays consists of a microalgal growth inhibition test (Dunaliella tertiolecta), acute and sublethal assays (end-points: mortality, immobilization and swimming speed alteration) on crustaceans larvae and juveniles, and rotifers (Amphibalanus amphitrite, Artemia salina, Corophium insidiosum and Brachionus plicatilis), and embryotoxicity test on echinoderms (Paracentrotus lividus). Considering the high levels of sediment contamination highlighted from chemical analysis, an unexpected very low toxic effect was observed, even considering the sublethal end-point (larval swimming speed alteration). The results of this study suggest a very complex contaminants dynamic in the Mar Piccolo sediments that, despite a strong level of contamination, seems to not affect in a proportional manner the biological compartment.     

Assessing sediment hazard through a weight of evidence approach with bioindicator organisms: a practical model to elaborate data from sediment chemistry, bioavailability, biomarkers and ecotoxicological bioassays

Quality assessments are crucial to all activities related to removal and management of sediments. Following a multidisciplinary, weight of evidence approach, a new model is presented here for comprehensive assessment of hazards associated to polluted sediments. The lines of evidence considered were sediment chemistry, assessment of bioavailability, sub-lethal effects on biomarkers, and ecotoxicological bioassays. A conceptual and software-assisted model was developed with logical flow-charts elaborating results from each line of evidence on the basis of several chemical and biological parameters, normative guidelines or scientific evidence; the data are thus summarized into four specific synthetic indices, before their integration into an overall sediment hazard evaluation. This model was validated using European eels (Anguilla anguilla) as the bioindicator species, exposed under laboratory conditions to sediments from an industrial site, and caged under field conditions in two harbour areas. The concentrations of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons and trace metals were much higher in the industrial compared to harbour sediments, and accordingly the bioaccumulation in liver and gills of exposed eels showed marked differences between conditions seen. Among biomarkers, significant variations were observed for cytochrome P450-related responses, oxidative stress biomarkers, lysosomal stability and genotoxic effects; the overall elaboration of these data, as those of standard ecotoxicological bioassays with bacteria, algae and copepods, confirmed a higher level of biological hazard for industrial sediments. Based on comparisons with expert judgment, the model presented efficiently discriminates between the various conditions, both as individual modules and as an integrated final evaluation, and it appears to be a powerful tool to support more complex processes of environmental risk assessment.     

Agricultural and green infrastructures: the role of non-urbanised areas for eco-sustainable planning in a metropolitan region

Non-Urbanised Areas (NUAs) are part of agricultural and green infrastructures that provide ecosystem services. Their role is fundamental for the minimization of urban pollution and adaptation to climate change. Like all natural ecosystems, NUAs are endangered by urban sprawl. The regulation of sprawl is a key issue for land-use planning. We propose a land use suitability strategy model to orient Land Uses of NUAs, based on integration of Land Cover Analysis (LCA) and Fragmentation Analysis (FA). With LCA the percentage of evapotranspiring surface is defined for each land use. Dimensions and densities of NUAs patches are assessed in FA. The model has been developed with Geographical Information Systems, using an extensive set of geodatabases, including orthophotos, vectorial cartographies and field surveys. The case of the municipality of Mascalucia in Catania metropolitan area (Italy), characterized by a considerable urban sprawl, is presented.     

Sowing simulation tests of a pneumatic drill equipped with systems aimed at reducing the emission of abrasion dust from maize dressed seed

The utilization of dressed seed for spring sowing is a widespread practice to control some pests with reduced doses of chemical products. However some insecticides employed in maize seed dressing, namely belonging to the neonicotinoid family and fipronil, have been claimed to play a role in the decline of honeybees (Apis mellifera L.). Pneumatic drills used in maize sowing are charged with contributing to the dispersion of the abrasion dust produced by dressed seeds, favoring the contamination of the honeybee habitat. Different devices similar to air deflectors have been introduced on pneumatic drills in order to reduce dust drift. During previous field tests carried out by the authors during recent years reduction of dust concentration both in the air and at soil surface has been shown as a consequence of their application. As field tests are affected by the variability of environmental parameters (namely wind speed and direction) the results are not always reliable, comparable and of a general validity. This paper refers to a sowing simulation test system in which pneumatic drills can be tested at a fixed point under controlled conditions of the main environmental parameters. In the test area, protected by external influences, artificial wind conditions are created by means of a fan. The drill, suitably placed in the test area, operates the seed distribution "sur place" by means of an electric engine connected to the drill's driving wheel. A 22.5 m long sampling area, leeward with respect to the drill position, has been identified. Along the sampling area a series of Petri dishes has been placed, with the aim of capturing the depositing dust and providing the concentration of the active ingredients (a.i.) at ground level. At the same time, three air samplers with PTFE diskette filters have been used for the detection of the a.i. The test system has been used for the test of a pneumatic drill, equipped with and without air deflectors, using maize seed dressed with four a. i. (imidacloprid, clothianidin, thiametoxam, fipronil). The results showed regularly decreasing of the concentrations as distance increased, both in the air and at ground level. Moreover, the difference determined by the adoption of the drift reducing device (air deflectors) resulted clear and it can be quantified at around 50 % of the a.i. amounts observed without deflectors. Finally, the paper proposes a data processing method that, from the values observed at fixed point, provides the theoretical a.i. concentration behavior that would occur in field, under the same conditions of wind speed and direction and working speed. The obtained results are coherent with previous field test.     

Hydrogen sulphide removal from landfill gas

Control of odours should be considered to be a fundamental issue in order to site, design and manage sanitary landfills. With regard to construction and demolition (C&;D) debris, landfilling was the mainly adopted solution in many European Countries; in particular, gypsum drywalls can produce high concentrations of hydrogen sulphide (H₂S) in landfill gas ranging from 7 ppm to 100 ppm. In some cases also dangerous concentrations until to 12,000 ppm were detected. In this paper H₂S removal efficiency in a lab-scale vertical packed scrubber was investigated. Hydrogen sulphide abatement was evaluated for inlet H₂S concentrations of 1000–100–10 ppm, adjusting scrubbing liquid pH in the range 9–12.5 by means of caustic soda (NaOH 2N solution). Moreover, best operating conditions for the system were defined as well as H₂S abatement along the tower and liquid recirculation effectiveness in case of inlet H₂S concentration of 10 ppm (typical odour concentration). Results showed that pH of 11.5 in scrubbing liquid could be considered the best value for removal of different inlet H₂S concentrations, also taking into account parasitical consumption of NaOH due to CO₂ absorption. Moreover, in case of continuous working of the system at H₂S concentration of 10 ppm, strong removal efficiency was already obtained with a packed bed height of about 70 cm. Significant performances were ensured after 1 h of constant activity, consuming about 3 ml of soda per cubic meter of polluted air. Subsequently liquid blowdown was necessary.     

Uncontrolled methane emissions from a MSW landfill surface: Influence of landfill features and side slopes

Sanitary landfills for Municipal Solid Waste (MSW) disposal have been identified as one of the most important anthropogenic sources of methane (CH₄) emissions; in order to minimize its negative effects on the environment, landfill gas (LFG) recovery is a suitable tool to control CH₄ emissions from a landfill site; further, the measurement of CH₄ emissions can represent a good way to evaluate the effectiveness of LFG recovering systems. In general, LFG will escape through any faults in the landfill capping or in the LFG collection system. Indeed, some areas of the capping can be more permeable than others (e.g. portions of a side slope), especially when considering a temporarily capped zone (covered area that is not expected to receive any further waste for a period of at least 3 months, but for engineering reasons does not have a permanent cap yet). These areas, which are characterized by abnormal emissions, are usually defined as “features”: in particular, a feature is a small, discrete area or an installation where CH₄ emissions significantly differ from the surrounding zones. In the present study, the influence that specific features have on CH₄ emissions has been investigated, based on direct measurements carried out in different seasons by means of a flux chamber to the case study of Palermo (IT) landfill (Bellolampo). The results showed that the flux chamber method is reliable and easy to perform, and the contoured flux maps, obtained by processing the measured data were found to be a suitable tool for identifying areas with abnormal (high) emissions. Further, it was found that a relationship between methane emission rates and landfill side slope can be established. Concerning the influence of the temporary HDPE cover system on CH₄ recovery efficiency, it contributed to a significant decrease of the free surface area available for uncontrolled emissions; this aspect, coupled to the increase of the CH₄ volumes collected by the LFG recovery system, led to a significant increase of the recovery efficiency.     

Regional assessment of climate change impacts on maize productivity and associated production risk in Switzerland

A simple model of yield was used along with climate scenarios to assess the impact of climate change on grain maize productivity and associated economic risk in Switzerland. In a first application, changes in the precipitation regime alone were shown to affect the distribution of yield considerably, with shifts not only in the mean but also in the standard deviation and the skewness. Production risk was found to respond more markedly to changes in the long-term mean than in the inter-annual variability of seasonal precipitation amounts. In a further application, yield projections were generated with respect to a full climate scenario, with the emission pathway as specified in the IPCC A2 scenario. Anticipation of the sowing date was found to reduce the negative impact of climate change on yield stability, but was not sufficient to ensure average productivity levels comparable to those observed at present. We argued that this was caused by the reduction in the duration of the growing season, which had a stronger impact than suggested by previous studies. Assuming no change in price relations, the results also revealed a strong increase in production risk with climate change, with more than a doubling in the probability of yield falling short of a critical threshold as compared to today’s situation.