Does groundwater protection in Europe require new EU-wide environmental quality standards?

Contamination of the Soil–Groundwater–Crop System: Environmental Risk and Opportunities

The increasing development of industries, resulting in a large volume of mining, smelting, and combustion wastes, and intense agricultural activities, due to demand for food and energy, have caused environmental hazards for food quality and ecosystems. This is a review on the contamination of the soil–groundwater–crop system and a potential reduction of the contamination by a gradual shift towards green economy within the European Union and on a worldwide scale. Available mineralogical and geochemical features from contaminated Neogene basins have shown a diversity in the contamination sources for soil and groundwater, and highlighted the need to define the contamination sources, hot spots, degree/extent of contamination, and provide ways to restrict the transfer of heavy metals/metalloids into the food chain, without the reduction of the agricultural and industrial production. Among harmful elements for human health and ecosystems, the contamination of groundwater (thousands of μg/L Cr(VI)) by industrial activities in many European countries is of particular attention. Although Cr(VI) can be reduced to Cr(III) and be completely attenuated in nature under appropriate pH and Eh conditions, the contamination by Cr(VI) of coastal groundwater affected by the intrusion of seawater often remains at the hundreds μg/L level. A positive trend between B and Cr(VI) may provide insights on the role of the borate [B(OH)4]− ions, a potential buffer, on the stability of Cr(VI) in coastal groundwater. Efforts are needed towards reducing toxic metal(loids) from the industrial wastewaters prior to their discharge into receptors, as well as the transformation of hazardous mining/industrial wastes to new products and applications to the optimization of agricultural management strategies.

Molecular characterization of microbial communities in a peat-rich aquifer system contaminated with chlorinated aliphatic compounds

In an aquifer-aquitard system in the subsoil of the city of Ferrara (Emilia-Romagna region, northern Italy) highly contaminated with chlorinated aliphatic toxic organics such as trichloroethylene (TCE) and tetrachloroethylene (PCE), a strong microbial-dependent dechlorination activity takes place during migration of contaminants through shallow organic-rich layers with peat intercalations. The in situ microbial degradation of chlorinated ethenes, formerly inferred by the utilization of contaminant concentration profiles and Compound-Specific Isotope Analysis (CSIA), was here assessed using Illumina sequencing of V4 hypervariable region of 16S rRNA gene and by clone library analysis of dehalogenase metabolic genes. Taxon-specific investigation of the microbial communities catalyzing the chlorination process revealed the presence of not only dehalogenating genera such as Dehalococcoides and Dehalobacter but also of numerous other groups of non-dehalogenating bacteria and archaea thriving on diverse metabolisms such as hydrolysis and fermentation of complex organic matter, acidogenesis, acetogenesis, and methanogenesis, which can indirectly support the reductive dechlorination process. Besides, the diversity of genes encoding some reductive dehalogenases was also analyzed. Geochemical and 16S rRNA and RDH gene analyses, as a whole, provided insights into the microbial community complexity and the distribution of potential dechlorinators. Based on the data obtained, a possible network of metabolic interactions has been hypothesized to obtain an effective reductive dechlorination process.

Emerging organic compounds in European groundwater

In Europe, emerging organic compounds (EOCs) in groundwater is a growing research area. Prioritisation for monitoring EOCs in Europe was formalised in 2019 through the development of the first voluntary groundwater watch list (GWWL). Despite this, groundwater occurrence data in the peer reviewed literature for Europe has not been reviewed to date. Questions surrounding the effect, toxicity, movement in the subsurface and unsaturated zone make the process of regulating EOC use difficult. The aim in Europe is to develop a unified strategy for the classification, and prioritisation of EOCs to be monitored in groundwater. This paper compiles evidence from the recent published studies from across Europe, since 2012, when the last major literature global review of EOCs in groundwater took place. A total of 39 studies were identified for review based on specific selection criteria (geography, publication date, sample size>10, inclusion of EOCs data). Data on specific compounds, and associated meta-data, are compiled and reviewed. The two most frequently detected EOCs, carbamazepine and caffeine, occurred in groundwater at concentrations of up to 2.3 and 14.8 μg/L, respectively. The most frequently reported category of compounds were 'Pharmaceuticals'; a highly studied group with 135 compounds identified within 31 of the 39 studies. In Europe, the majority of reviewed studies (23) were at a regional scale, looking specifically at EOCs in a specific city or aquifer. The use of analytical methods is not uniform across Europe, and this inevitably influences the current assessment of EOCs in groundwater. A correlation between the number of compounds analysed for, and the number detected in groundwater highlights the need for further studies, especially larger-scale studies throughout Europe. For the development of EU and national regulation, further work is required to understand the occurrence and impacts of EOCs in groundwater throughout Europe and elsewhere.

Horizontal permeable reactive barriers with zero-valent iron for preventing upward diffusion of chlorinated solvent vapors in the unsaturated zone

Chlorinated solvents are extensively used in many activities and hence in the past decades impacted a large number of sites. The presence of these contaminants in groundwater is challenging particularly for the management of the vapor intrusion pathway. In this work we examine the potential feasibility of using horizontal permeable reactive barriers (HPRBs) placed in the unsaturated zone to treat chlorinated solvent vapors emitted from groundwater. Zero-valent iron (ZVI) powders, partially saturated with water and characterized by different specific surface areas (SSA), were tested, alone or mixed with sand, in lab-scale batch reactors using TCE as model compound. Depending on the type of iron powder used, a reduction of TCE concentration in the vapor phase from approximately 35% up to 99% was observed after 3 weeks of treatment. The best performance in terms of TCE reduction was obtained using the ZVI characterized by the intermediated values of the specific surface area (SSA). This finding, which is in contrast with the results generally observed in in aqueous solutions, was tentatively attributed to a non-selective higher reactivity of the fine-grained iron samples with water and dissolved oxygen (with a consequent iron passivation) or to the occurrence of a diffusion-limited reaction kinetics. Based on the first-order kinetic degradation rate constants estimated from the experimental data, a horizontal barrier of 1 m containing ZVI or a mixture of ZVI and sand can potentially lead to an attenuation of TCE vapors over 99%.

Pollution characteristics of aromatic hydrocarbons in the groundwater of China

Much of the world's groundwater supply has been contaminated by aromatic hydrocarbons originating from anthropogenic sources. To study the occurrence and distribution characteristics of aromatic hydrocarbons in groundwater, 24 aromatic hydrocarbon compounds were selected: Five BTEX compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene), 10 alkyl-substituted benzene, and 9 halogenated aromatics. These aromatic hydrocarbons were then analyzed from 355 samples collected from across China. Results indicated that aromatic hydrocarbons were detected in 59 out of 355 samples. Of the selected aromatic hydrocarbons, BTEX compounds were detected with high frequency and at low concentrations; comparatively, halogenated aromatics were detected with low frequency and at high concentrations. The aromatic hydrocarbon characteristics found in both karst and pore groundwater samples were then determined using their respective hydrogeological conditions and corresponding human activities. In karst groundwater, BTEX compounds were the most frequently detected aromatic hydrocarbon. The high detection frequencies of aromatic hydrocarbons were caused by their rapid migration, owing to the developed conduit system in the sampled karst area. The low concentrations of aromatic hydrocarbons in karst groundwater samples were caused by low-intensity human activity along with special hydrogeological conditions with higher redox potential and the unique compositions of aromatic hydrocarbons. Alkyl-substituted aromatics and halogenated aromatics were detected at higher concentrations in pore groundwater, owing to high-intensity human activity. Aromatic hydrocarbon pollution was gradually decreased along piedmont-alluvial plain-coast line, owing to a decrease in aquifer vulnerability. These were positively correlated with the size of the aquifer's particles. Samples with a high accumulative concentration of these aromatic hydrocarbons tended to occur in pore groundwater with a high concentration of either SO₄^2- or Cl^-.

Groundwater diffuse pollution in functional urban areas: The need to define anthropogenic diffuse pollution background levels

Groundwater status in highly urbanized areas is particularly affected by anthropogenic influence due to diffuse pollution deriving from many sources. This makes very often challenging to determine whether the observed groundwater conditions are the result of localized pollutant sources (PS-Point Sources). In the EU legislative framework it is accepted that, when Natural Background Levels (NBLs) of undesirable elements are proven to be higher than specific Groundwater Quality Standards (GQSs), NBLs should be assumed as GQSs. No procedure is instead defined when anthropogenic Diffuse Pollution Background levels (DBPLs) are higher than GQSs and make unfeasible any remediation strategy. Among the many contaminants affecting groundwater, the chlorinated solvents, tetrachloroethylene (PCE), trichloroethylene (TCE) and trichloromethane (TCM) among the organics and hexavalent chromium, among the inorganics, having been widely used in several industries all over Europe, are very often the most prevalent contaminants in soil and groundwater. Aim of this paper is to discuss a multivariate statistical approach to address the issue of identification of anthropogenic Diffuse Pollution Background Levels. With such aim, an area of about 1600 km², including the Functional Urban Area of Milan, was considered and 10 independent geochemical datasets, provided by local and regional agencies, and covering the period 2003-2014 were merged into a single database after homogenization and multiple quality checks. A total of 618,258 chemical analyses from 3477 sampling wells were considered, being all samples collected and analyzed through internally consistent protocols. The analysis enabled to identify five main clusters, having specific hydrogeological characteristics, different temporal profiles and pollutant background concentration levels, which were also found to respond differently to meteo-climatic changes. This study offers a robust knowledge basis for drafting a diffuse pollution management plan of the area.

Multi-element compound specific stable isotope analysis of chlorinated aliphatic contaminants derived from chlorinated pitches

Tetrachloroethene and trichloroethene are typical by-products of the industrial production of chloromethanes. These by-products are known as "chlorinated pitches" and were often dumped in un-contained waste disposal sites causing groundwater contaminations. Previous research showed that a strongly depleted stable carbon isotope signature characterizes chlorinated compounds associated with chlorinated pitches whereas manufactured commercial compounds have more enriched carbon isotope ratios. The findings were restricted to a single case study and one element (i.e. carbon). This paper presents a multi-element Compound-Specific Stable Isotope Analysis (CSIA, including carbon, chlorine and hydrogen) of chlorinated aliphatic contaminants originated from chlorinated pitches at two sites with different hydrogeology and different producers of chloromethanes. The results show strongly depleted carbon signatures at both sites whereas the chlorine and the hydrogen signatures are comparable to those presented in the literature for manufactured commercial compounds. Multi-element CSIA allowed the identification of sources and site-specific processes affecting chloroethene transformation in groundwater as a result of emergency remediation measures. CSIA turned out to be an effective forensic tool to address the liability for the contamination, leading to a conviction for the crimes of unintentional aggravated public water supply poisoning and environmental disaster.

Pesticides Curbing Soil Fertility: Effect of Complexation of Free Metal Ions

Researchers have suggested that the reason behind infertility is pernicious effect of broad spectrum pesticides on non target, beneficial microorganism of soil. Here, studying the chelating effect of selective organophosphate and carbamate pesticides with essential metal ions, at all possible combinations of three different pH (4 ± 0.05, 7 ± 0.05 and 9 ± 0.05) and three different temperatures (15 ± 0.5°C, 30 ± 0.5°C and 45 ± 0.5°C), shows very fast rate of reaction which further increases with increase of pH and temperature. Carbonyl oxygen of carbamate and phosphate oxygen of organophosphate were found to be common ligating sites among all the complexes. Formed metal complexes were found to be highly stable and water insoluble on interaction with essential metal ions in solvent medium as well as over silica. Density functional theory (DFT) calculations not only reinforced the experimental observations, but, after a wide computational conformational analysis, unraveled the nature of the high stable undesired species that consist of pesticides complexed by metal ions from the soil. All in all, apart from the direct toxicity of pesticides, the indirect effect by means of complexation of free metal ions impoverishes the soil.

Inclusion of emerging organic contaminants in groundwater monitoring plans

Groundwater is essential for human life and its protection is a goal for the European policies. All the anthropogenic activities could impact on water quality. •Conventional pollutants and more than 700 emerging pollutants, resulting from point and diffuse source contamination, threat the aquatic ecosystem.•Policy-makers and scientists will have to cooperate to create an initial groundwater emerging pollutant priority list, to answer at consumer demands for safety and to the lack of conceptual models for emerging pollutants in groundwater.•Among the emerging contaminants and pollutants this paper focuses on organic wastewater contaminants (OWCs) mainly released into the environment by domestic households, industry, hospitals and agriculture. This paper starts from the current regulatory framework and from the literature overview to explain how the missing conceptual model for OWCs could be developed.•A full understanding of the mechanisms leading to the contamination and the evidence of the contamination must be the foundation of the conceptual model. In this paper carbamazepine, galaxolide and sulfamethozale, between the OWCs, are proposed as "environmental tracers" to identify sources and pathways ofcontamination/pollution.

Natural background groundwater composition in the Azores archipelago (Portugal): a hydrogeochemical study and threshold value determination

Groundwater discharges were sampled in selected springs from São Miguel (Furnas and Fogo trachytic central volcanoes) and Santa Maria islands (Azores, Portugal), in order to characterize natural background levels (NBLs) and proceed to the determination of threshold values (TVs). Besides being a key issue in order to fully assess the anthropogenic pressures, NBLs are also instrumental to derive TVs, therefore complying with requirements from the European Union Groundwater Directive. The composition of groundwater corresponds mainly to low mineralized Na-HCO3 to Na-Cl water types, the latter dominant in Santa Maria island, with a decreasing order of Na>Ca>Mg>K and Cl>HCO3>SO4>NO3 for cations and anion respectively. The majority of the samples are slightly acid to slightly alkaline (pH range of 5.45-7.43), and the electrical conductivity range between 180 and 1458 μS/cm. Groundwater composition is controlled by two major drivers, addition of sea salts and dissolution of silicate minerals. Results shown that TVs established along the present study are in general in the lower rank when compared to the range of values proposed by the several EU member states, with the main exception of NO3, reflecting the impact of agriculture activities over water quality in the Azores, and lower than the national ones. The comparison between the estimated NBL and TV with values derived with another dataset from the Azores, usually higher, depicts the effect of a larger and diverse number of groundwater sources over calculations. On the other hand, all samples which show a contribution from volcanic/hydrothermal systems were excluded from the dataset, which explains why the derived NBLs and TVs are lower comparing to other active volcanic areas, which is also a conservative approach on a subject that has regulatory implications.