Bio-induced reduction of Cr(VI) in aquifers by organic substrates injection

Hexavalent chromium is a primary toxic element used in galvanic processes, in metallurgical industry and for the production of dyes and pigments. Conventional methods for Cr(VI) remediation, pump&treat and excavation, are expensive and require a large amount of energy and time. Innovative technologies include bio-induced reduction, that is Cr(VI) reduction to Cr(III) by injection of organic substrates that are readily biodegraded by autochthonous microorganisms in the aquifer, resulting in reducing conditions. Lab scale batch tests were carried out, with two different soil (A and B) and solid/liquid ratios (25% and 50% on weight basis). Initial Cr(VI) concentrations were 5000 or 10000 µg/L. Ultrafiltration permeates of cheese whey and beer distillation residues were used as the organic substrates. In all microcosms, dissolved oxygen decreased from about 6 mg/L to values <1 mg/L after 1-2 d incubation, and the redox potential from approximately +250 mV to -400 mV by 11 d. After about 40 days, the highest Cr(VI) abatements were obtained in soil A microcosms fed with beer distillation residues, as soil A had an initial total heterotrophic bacteria concentration three orders of magnitude higher than soil B. Fe(II) availability was also a key factor in Cr(III) co-precipitation

Bioremediation of Hexavalent Chromium—A Few Significant Site Histories in Italy

In Lombardy (Italy), about 25% of the sites ranked in the Regional Plan of Contaminated Sites are affected by Cr(VI) in groundwater and/or soil. Therefore innovative sustainable remediation techniques are under investigation, with pilot- or full-scale applications. In situ bioremediation has a significant role in the remediation techniques for its general sustainability in terms of environmental impact and costs. However, while organics can be mineralized, inorganics can only change their oxidation state, hopefully reducing their toxicity and mobility in the environment. Various patented products were used at five polluted sites in order to reduce Cr(VI) to Cr(III) via bio-induced reduction, bio-reduction and bioimmobilization. The experience pointed out that Cr(VI) concentration in groundwater can be significantly reduced (up to three order of magnitudes), but the unsaturated zone should be treated as well in order to solve the problem definitely. Soil heterogeneity is a critical issue and mixtures usually have to be injected at different depths. Iron, manganese and sulphate side-contamination can result in groundwater after injections

An integrated human health risk assessment framework for alkylphenols due to drinking water and edible crop consumption

INTRODUCTION The scarcity of clean freshwater is becoming a major issue for present and future generations, especially in densely urbanised areas. This situation promotes the potential cross-contamination of different environmental compartments by contaminants of emerging concern (CECs) which, in fact, have already been detected worldwide in surface water, groundwater and soils. In particular, the CECs released by wastewater treatment plants (WWTPs) can end up both in the recipient surface water and groundwater, both of which are used as drinking water (DW) sources. Furthermore, if those water sources and reclaimed wastewater are used for irrigation, CECs can be directly absorbed by crops intended for human consumption or accumulate in soil and translocate to crops over time. Hence, both DW and edible crops are critical CEC exposure pathways for humans, the combined effect of which requires further investigation. This work is aimed at developing an integrated framework for a quantitative chemical risk assessment due to CECs in complex multiple-use scenarios, combining DW and edible crop consumption, as a decision-making support tool for optimising solutions to minimise risks and social costs. METHODOLOGY The developed procedure includes several steps. Firstly, the analysed system boundaries are defined, to evaluate all the phenomena affecting the fate of CECs from source to end user. Then, CEC migration (e.g. diffusion in surface water, infiltration in soil, uptake by food crops) and human exposure (via water and edible crop consumption) are modelled in an integrated framework as a function of boundary conditions, CECs and by-products characteristics, and proposed interventions. Exposure models are calibrated through literature data, field monitoring and lab tests where, for instance, the CECs’ fate and uptake by vegetables from contaminated soils have been investigated. In the hazard assessment step, a toxicological characterisation was performed to obtain single CEC adverse effect potencies, aimed at applying the Relative Potency Factors methodology for combining CECs that affect the same endpoint. Lastly, exposure and hazard assessment steps are combined to quantitatively estimate the risk to human health from a mixture of CECs, which includes uncertainty analyses to account for knowledge gaps and to provide decision-makers with the confidence level of the risk estimation. RESULTS The developed quantitative risk assessment procedure has been applied to a case study on the mixture of two alkylphenols, i.e. bisphenol-A (BPA) and nonylphenol (NP), used as reference CECs. Literature and field-monitoring data were used to feed the model, with an estimate of BPA and NP concentration in DW up to 0.1 and 0.35 μg/L, respectively, as a function of different system boundary conditions. As for their uptake in edible crops, lab tests with contaminated soil (BPA=75 μg/kg and NP=10 mg/kg, according to the range reported in literature for soil irrigated with reclaimed wastewater or amended with biosolids) demonstrated a significant transfer of NP from soil to vegetables, with concentrations of up to 230 μg/kg fresh weight (f.w.) in the edible parts. No BPA (&lt;8 μg/kg f.w.) was found in vegetables, unlike its metabolite para-hydroxybenzoic acid (up to 56 μg/kg f.w). Those results highlight that both DW and edible crop consumption exposure pathways are critical for the risk to human health due to BPA, NP and their by-products. Several interventions in WWTPs or in DW treatment plants and distribution networks were simulated, demonstrating promising cumulative risk reduction. DISCUSSION Integrated modelling of the fate of CEC mixtures in complex multiple-use water systems, combined with quantitative risk assessment, has proven to be an effective tool to identify the main causes of risk for humans and to assign the various CEC source contributions. Lab tests proved to be useful to investigate the fate of CECs, including metabolites, in the soil system and potential transfer to food crops, corroborating the information from literature and monitoring data for model calibration. Integrated modelling also made it possible to explore several intervention strategies to be adopted at different points of the water system, identifying those that achieve the minimum overall mixture risk. Moreover, in addition to CEC toxicological characterisation, this procedure allows decision-makers to prioritise CECs to be regulated not only based on their exposure levels but looking at their contribution to the overall mixture risk. Lastly, uncertainty analysis made it possible to properly consider the availability and quality of CEC data, especially as regards their physical-chemical behaviour and toxicity, thereby providing the degree of confidence for the estimated risk, which is a key factor for taking informed decisions concerning CEC

Five-Year Vapor Monitoring for Risk Management at a Hydrocarbon-Polluted Site

Soil remediation (excavation and off site disposal) was partially carried out in 2005 at a site in Milan (Italy), leaving a residual volume of soil polluted with petroleum-derived hydrocarbons. Indoor air, outdoor air, crawl-space air and soil gas samplings have been carried out since January 2009. In March 2011 the monitoring network was upgraded to its final configuration (18 indoor, 7 outdoor and 4 crawl-space sampling locations, 60 soil gas probes at four different depths from ground surface); after that, one monitoring campaign a season was performed till November 2013, fractionating hydrocarbons according to a modified version of the Massachusetts Department of Environmental Protection approach. In order to permanently keep risk below acceptable levels, a mitigation system of the contaminated source was installed in December 2013 and it is still working. Three monitoring campaigns of ambient air have been performed since then. Although not strictly necessary in terms of time-averaged health risk, the mitigation system allowed to extract significant amounts of mono- and light poly-cyclic aromatic hydrocarbons. This has helped manage worries about future uncontrolled exposure of people working at the site

In Situ Aerobic Biostimulation of Groundwater at a National Priority Site in Italy

Sarroch plant (CA, Italy) is an industrial area listed in the Italian Priority List of polluted sites. Pollution in groundwater has been addressed thanks to the design of a remediation action based on the aerobic biodegradation of petroleum hydrocarbons (predominantly mono-aromatic and short-chain aliphatic hydrocarbons) promoted by the injection of oxygen-releasing compounds. The feasibility of biostimulation at the site was preliminary assessed by means of laboratory tests. The direct push injection of the product has been foreseen at 2800 points, distributed along multiple lines perpendicular to the groundwater flow direction, over a total length of approximately 8 km and a total area of 90 hectares. According to the pollutant concentration measured in the different zones of the site, a different number of injection campaigns and injection frequency has been scheduled (3 to 10 campaigns, every 5 to 12 months). The estimated cost for the bioremediation action is 23 million Euros. Compared to the previous project approved in 2010, including a seafront physical barrier and groundwater circulation wells – in situ well stripping, the in situ injection of the oxygen-releasing compounds is an improvement toward a quicker, more effective and sustainable remediation of groundwater at the site. In view of all this, in 2017 the public authorities approved the variant of the project

Emerging contaminants in sediments: a review

Emerging Contaminants (ECs) are chemicals for which new concerns have recently raised in terms of occurrence, fate, adverse effects on human health and the environment. ECs include pharmaceuticals, nanomaterials, compounds used in personal care products, plastics, pesticides and flame retardants, and compounds with a large variety of uses (e.g., phenolic and perfluorinated compounds, chlorinated paraffins, etc.). The EU Water Framework Directive 2013/39/EU deals with the status of water bodies and reports an updated list of priority substances. Some of these (e.g., nonylphenols, di(2-ethylhexyl)phthalate DEHP, perfluorooctane sulfonate PFOS, hexabromocyclododecanes, polybrominated diphenyl ethers, etc.) are emerging contaminants with high affinity towards suspended solids and sediments, due to their physicochemical properties (e.g., Koc value, etc.). The review focuses on this group of pollutants, reporting about the occurrence and distribution in sediments and biota, bioaccumulation and ecotoxicity, and the target or limit values that have been set in order to protect the aquatic environment and the human health