Natural Background Levels Research Articles

Ecological Risk Assessment of Heavy Metals at Township Scale in the High Background of Heavy Metals, Southwestern, China

Heavy metals (HMs) are naturally occurring elements that have high natural background levels in the environment. Therefore, it is important to conduct ecological risk assessment and identify potential sources of HMs. In the past, studies were conducted at the regional scale. The accuracy of those studies could not meet the needs of spatial planning and natural resource management. Therefore, it is necessary to conduct ecological risk assessment at the township scale. In this study, 1092 soil samples (from 0-20 cm depth) were collected in the town of Reshui, an area with high background levels of soil HMs with the parent material of carbonatite, which is commonly found in Southwest China. The town of Reshui is a multi-ecological risk superimposed area where the ecological risk is high. In this study, concentrations of HMs (Cd, Cr, As, Hg, Pb, Cu, Zn, and Ni) in the topsoil were analyzed, and statistical analysis (SA), geographic information system (GIS) modeling, and positive matrix factorization (PMF) analysis were performed. The geoaccumulation index (Igeo) and potential ecological risk index (PERI) were applied for the ecological risk assessment and quantification of the sources of the soil HMs. The mean values of HM concentrations in the topsoil were 18.1, 1.18, 174.1, 202.2, 0.09, 71.1, 34.9, and 167.2 mg ·kg-1for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were considerably higher than the average background value (ABV) in soils in Yunnan Province except for As and Pb. The average concentrations of Cd, Cr, Cu, and Ni exceeded the screening values specified in the soil contamination risk in agricultural land (GB 15618-2018) by 5.82, 1.16, 4.04, and 1.02 times, respectively. The Igeo value shows that the major pollutant is Cu in the surface soil of the study area, followed by Cr, and Cd. Speciation analysis of HMs indicates that HMs (Cr, As, Pb, Cu, Zn, and Ni) mainly exist in the residual form, mostly from the geological background with low bioavailability. The potential effective components of Hg have higher levels, but the total amount of Hg and its pollution risk are lower. Cd has a high bioavailability ratio, is easy to enter the soil solution and be absorbed by crops, and is the HM with the highest pollution risk in the study area. The PERI shows that the proportions of low ecological risk, moderate risk, and high risk soil samples are 44.23%, 54.40%, and 1.37% of the total number of samples, respectively. Hg and Cd were the major sources of risk because of their high toxicity coefficient. The PMF analysis indicates that there are four major sources of HMs in the study area: human activity, natural sources, coal mining and traffic emissions, and agricultural sources with the risk contribution ratios of 9.29%, 53.67%, 11.23%, and 25.81%, respectively. The PMF analysis effectively quantified the ecological risk from these sources, providing a reference for further pollution control and prevention measures.

Comparison of soil properties in urban and non‐urban grasslands in Budapest area

AbstractThis study focused on the physical, chemical and microbiological characteristics of soils from different grasslands in the Budapest area. Our aim was to assess the influence of anthropogenic activities on these soils by comparing three types of site: urban, green‐urban and non‐urban. From these sites, a total of 72 topsoil samples were collected and analysed. The results indicated that many properties of soils varied greatly between the different types of site. Urban soils had significantly higher pH, carbonate and salt content, but smaller organic carbon content than the other soils. These differences could be explained in part by the greater artefact content, as the latter was significantly correlated with most of the main soil properties. Concentrations of the heavy metals measured (Co, Cu, Cr, Fe, Mn, Ni, Pb, Zn) were generally smaller in non‐urban soils. In urban and green‐urban soils, Cu, Cr, Ni and Pb levels were above the natural background levels, due to anthropogenic inputs in the city. Results of microbiological analyses were controversial. According to most probable number (MPN), there was no significant difference between types of site for bacterial and fungal numbers in soil. However, dehydrogenase activity and the number of bacterial cells were larger in non‐urban than in urban soils. It was also found that microbial parameters were influenced by many soil properties, for example organic matter and macronutrient (N, P, K) content of soils, the presence and amount of artefacts and metal concentrations in soil.

Trajectories of technogenic tritium in the Rhône River (France)

Tritium is a radioisotope of hydrogen with a half-life of 12.32 years and was used for its luminescent properties by the watchmaking industry from 1962 to the 2008. Tritiated luminescent salts were integrated in the paints applied on the index and dial of watches and clocks. French and Swiss watchmaking workshops used more than 28 000 TBq of tritium over this period of time and produced almost 350 million watches. Despite the end of tritiated salts use in watchmaking workshops in 1992 in France and 2008 in Switzerland, high level of organically bound tritium (OBT) are still observed in sediments of the Rhône River downstream the Lake Geneva. Contamination of the Rhône River by tritiated hot particles since 1962 up to nowadays remains poorly documented. In order to assess the long term behavior and fate of technogenic tritium in this river and its trajectories in the river system, two sediment cores were collected at the upstream (UC) and downstream (DC) part of the Rhône River in France and OBT contents were determined. For both sedimentary cores, maximum OBT contents were registered over the 1980s when tritium was intensively used by watchmaking industries. These residual OBT contents are 1 000 to 10 000 fold higher than current natural background levels in riverine sediments. The OBT contents progressively decreased since 1989 with close effective half-life in upstream and downstream area (5 ± 2 years). The OBT contents were lower in DC than in UC due to the dilution by uncontaminated sediments delivered by tributaries not affected by the watchmaking industries. Trajectories analysis indicates that the resiliency of the Rhône River system in regards to this contamination would be reached in 14–70 years and in 14–28 years respectively for the upstream and downstream part of the river.

Hydrogeochemical characterization and determination of natural background levels (NBL) in groundwater within the main lithological units in Slovenia

Groundwater represents a vast and highly important source of drinking water. As a part of the hydrological cycle, it can only be managed by understanding the components that make up its vulnerability profile. These are referenced with anthropogenic influences related to pressures connected with land use and the ever-increasing conversion of land surface for urban use. The quality of groundwater can be assessed and expressed using a number of different chemical parameters. In this paper, we focus on the analysis of groundwater’s physico-chemical field parameters and the major ions present in Slovenian aquifers. Several statistical methods were applied to outline the relevant criteria involved in determining the groundwater’s natural background. Additionally, a graphical method was applied to evaluate the source of major ions distribution in the groundwater. The most common BRIDGE methodology used to determine background values is based on upper percentile values. It turns out that this methodology might be relevant for chemical parameters mainly affected by geogenic sources, while the “anthropogenic” parameters have to be treated with a different approach e.g., probability plot method.

Assessment of hydrochemical backgrounds and threshold values of groundwater in a part of desert area, Rajasthan, India

Natural background levels (NBLs) and threshold values (TVs) are crucial parameters for identification and the quantification of groundwater pollution, and the evaluation of pollution control measures. The cumulative probability distribution technique was used for the evaluation of NBLs for 36 samples collected during two climate conditions in the part of the desert area from Rajasthan, India. The NBLs for Na+, Cl−, SO42−, HCO3−, NO3− and F− ions were assessed and compared with the natural and anthropogenic processes. The TVs were also calculated for Na+, Cl−, SO42−, HCO3−, NO3− and F− ions, and compared with the drinking limits of the Bureau of Indian Standards. Additionally, the pollution percentage (%) at the individual well was estimated and identified the polluted zones. Results indicate that most of the polluted areas were situated in the southern part, which was influenced by the natural and anthropogenic factors. The sodium concentrations above the TVs, in indicating the saline nature of water. Chloride threshold value above the drinking water limit was mainly observed in the dry season, related to intensive evaporation and industrial waste, which leads to groundwater quality degradation. The NO3− concentration (∼56% samples) above the TVs indicates extensive use of nitrate fertilizers and sewage effluent. The values of total dissolved solids (TDS) shows the suspicious scenario as about 84% of the samples in the dry period and about 89% in the wet season exceeding the drinking limit. Assessment of background concentrations and threshold values on regional and local scale assigns the basis for the identification of groundwater pollution, and helpful for better water quality guidelines to protecting of water resources.

Modification of the existing maximum residue levels for copper compounds in fresh herbs and edible flowers.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant LLG Sachsen‐Anhalt, Dez. Pflanzenschutz submitted a request to the competent national authority in Germany to modify the existing maximum residue levels (MRLs) for copper compounds in herbs and edible flowers. The data submitted in support of the request were found sufficient to derive an MRL proposal of 150 mg/kg, confirming the MRL proposal of the MRL review, for copper compounds in herbs and edible flowers in support of the intended indoor use. Based on the risk assessment results, EFSA concluded that the long‐term intake of copper residues resulting from the intended and existing uses, natural background levels and monitoring levels might present a risk to consumer health. Although residues in herbs and edible flowers are minor contributors to the overall consumer exposure, a risk management decision has to be taken whether it is appropriate to increase the existing MRLs for these crops, given that a potential consumer intake concern could not be excluded.

Sub-millimeter distribution of labile trace element fluxes in the rhizosphere explains differential effects of soil liming on cadmium and zinc uptake in maize

Trace element concentrations in the rhizosphere were quantified to better understand why soil liming often fails to reduce cadmium (Cd) uptake by plants. Maize seedlings were grown on a soil with natural background levels of Cd and zinc (Zn). Soil liming increased soil pH from 4.9 to 6.5 and lowered the soil solution free ion activities by factor 7 (Cd) and 9 (Zn). In contrast, shoot Cd concentrations were unaffected by liming while shoot Zn concentrations were lowered by factor 1.9. Mapping of labile soil trace elements using diffusive gradients in thin films (DGT) in combination with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) revealed an almost complete depletion of Cd in the rhizosphere in all soil treatments, showing that Cd uptake is controlled by diffusion. The flux of Cd from soil to the DGT, with direct contact between the soil and the binding gel, was unaffected by liming whereas it decreased by factor 3 for Zn, closely mimicking the contrasting effects of liming on Cd and Zn bioavailability. This evidence, combined with additional flux data of freshly spiked Cd and Zn isotopes in soil and with modelling, suggests that the diffusive transport of Cd in unsaturated soil is more strongly controlled by the labile adsorbed metal concentration than by its concentration in solution. This is less the case for Zn because of its inherently slower desorption compared to Cd.

Probabilistic assessment of spatial heterogeneity of natural background concentrations in large-scale groundwater bodies through Functional Geostatistics

We propose and exemplify a framework to assess Natural Background Levels (NBLs) of target chemical species in large-scale groundwater bodies based on the context of Object Oriented Spatial Statistics. The approach enables one to fully exploit the richness of the information content embedded in the probability density function (PDF) of the variables of interest, as estimated from historical records of chemical observations. As such, the population of the entire distribution functions of NBL concentrations monitored across a network of monitoring boreholes across a given aquifer is considered as the object of the spatial analysis. Our approach starkly differs from previous studies which are mainly focused on the estimation of NBLs on the basis of the median or selected quantiles of chemical concentrations, thus resulting in information loss and limitations related to the need to invoke parametric assumptions to obtain further summary statistics in addition to those considered for the spatial analysis. Our work enables one to (i) assess spatial dependencies among observed PDFs of natural background concentrations, (ii) provide spatially distributed kriging predictions of NBLs, as well as (iii) yield a robust quantification of the ensuing uncertainty and probability of exceeding given threshold concentration values via stochastic simulation. We illustrate the approach by considering the (probabilistic) characterization of spatially variable NBLs of ammonium and arsenic detected at a monitoring network across a large scale confined groundwater body in Northern Italy.

Transfer of Some Toxic Metals from Soil to Honey Depending on Bee Habitat Conditions

Abstract The transfer of toxic metals from soil to honey was studied based on two different areas of the Podkarpackie region located in the south-east part of Poland: U-urbanized and E-ecologically pure. The metal content was determined using the ICP-OES method with prior microwave mineralization of the soil, plant (goldenrod, dandelion, rapeseed, tilia and fir), bee bodies and honey samples collected from 10 sampling points (U-5 and E-5). The impact of soil pH on heavy metal mobility was also evaluated. It was found that Podkarpackie soils are less contaminated with heavy metals as compared to other regions of Poland and only in the case of cadmium an enhancement of the natural background level was observed. The migration of heavy metals, especially cadmium, in the soil-plant-bee-honey food chain was accelerated by soil acidity (p<0.05). The influence of human activity (region development) on heavy metals concentrations was not significant (p>0.05). Based on bioaccumulation factors, goldenrod and dandelion plants were confirmed as cadmium accumulators. It was also confirmed that the bodies of bees act as an effective barrier to the migration of heavy metals from the environment to honey, due to this, honey is free from these metals and safe for human consumption.

Application of the Karst Disturbance Index (KDI) to Kobokwe Cave and Gorge, SE Botswana: Implications for the Management of a Nationally Important Geoheritage Site

Geoheritage sites can provide an excellent resource for sustainable development that represents a growing movement in Africa. Kobokwe Cave is formed within the Middle Proterozoic–aged sandstone of Kobokwe Gorge and is nationally important; the cave is the site where British missionary David Livingstone spent a night in 1847 and subsequently converted Kgosi (Chief) Kgari Sechele I, the first and only Christian “conversion” at that time by Livingstone. However, the site currently appears undervalued as there are little stewardship and minimal organized tourism and is affected by litter, graffiti, fires, illegal dumping and sand mining, and noise pollution from a nearby road; the building of the road itself destroyed a boulder of cultural significance. To test the level of environmental disturbance, the Karst Disturbance Index (KDI) was employed and this is the first known application to a non-carbonate karst environment and the first such application in Africa. Field observations were coupled with laboratory analyses of physico-chemical, nitrate, and heavy metal parameters in soil and water from the site. The final KDI score for Kobokwe of 0.29 is classed as showing “minor disturbance” and likely due to low visitor numbers although the sub-category of cultural disturbance scored 12 and is relatively high, as also found in previously published KDI studies from the USA, Italy, and Mexico. The analytical results are mostly at natural background levels, except for Pb in the cave floor soil (5.13 mg/L) and Pb in all water samples (0.3–0.63 mg/L) likely due to nearby vehicular traffic; also, Fe in all water samples (0.79–1.13 mg/L) that has possibly leached from the gorge sandstone and the spring water was slightly above standard background levels and possibly leached from nearby soil/rock. Future recommendations to avoid further disturbance and to promote environmental management of the site include community involvement, litter bin installation, graffiti removal, tour guides, information panels, entrance gate, tarred road, footpath installation, and enforcing of stronger site stewardship.

Corrigendum for “Skyglow extends into the world’s Key Biodiversity Areas”

Corrigendum for “Skyglow extends into the world’s Key Biodiversity Areas”

Trace Elements in the Spring Waters of Moscow

Data on the levels of major ions (Na+, K+, Mg2+, Ca2+, $${\text{C}}{{{\text{l}}}^{ - }}{\text{,}}$$$${\text{SO}}_{{\text{4}}}^{{{\text{2}} - }}{\text{,}}$$$${\text{HCO}}_{{\text{3}}}^{ - }$$) and dissolved trace elements (Rb, Cs, Be, Sr, Ba, B, Si, Pmin, V, Cr, Ge, As, Mo, W, Sb, Te, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ag, Sn, Pb, Al, Ga, Ti, Zr, and U) in the waters of 30 springs in Moscow during the winter low water period are presented. The geometric mean values and ranges of concentration of the studied components, as well as correlations between them were established. The presence of hydrochemical anomalies of dissolved iron and manganese in the northeast of Moscow with an excess of the maximum permissible concentration (MPC) for these elements was revealed, whereas in the rest of the city their concentrations corresponds to the natural background levels almost everywhere.

Urban soil contamination in Salerno (Italy): Concentrations and patterns of major, minor, trace and ultra-trace elements in soils

This work discusses the results of a geochemical survey conducted in the Salerno urban area to determine the sources patterns of major, minor, trace and ultra-trace elements in soils. In particular, the study focused on elements that are potentially toxic and listed in the environmental Italian legislation (D.L. 152/06), in order to effectively monitoring an important aspect of environment health. A total of 151 topsoil samples were collected, air-dried and sieved (<2 mm). After aqua regia digestion the samples were analyzed for 42 elements by ICP-MS and ICP-AES. Geostatistical analyses were carried out in order to show the single element spatial distribution and the distribution of factor scores elemental associations from R-mode factor analysis. In performing factor analysis, the additive logratio (alr) transformation was applied to the whole dataset in order to deal with the closure effects of the investigated geochemical data, avoiding artefacts and spurious correlation. The use of alr-transformed data instead of the normal data in the factor analysis allowed for a better interpretation of the distribution patterns, since this produced four factor models which, once mapped, were easier to interpret.The study revealed that major and minor elements (Al, Ca, Fe, K, Mg, Na, P, S and Ti) have a perfectly natural distribution with no discernible association to any human activity or presence. In contrast, many trace and ultra-trace elements (Ag, As, Au, Ba, Be, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Pd, Pt, Rh, Sb, Sn, Tl, V and Zn) show anomalous concentration values located almost exclusively in highly inhabited areas, industrial sites and along high traffic roads. Other trace and ultra-trace elements (B, Bi, Ga, La, Sc, Se, Sr, Te, Th, Tl, U and W) show concentrations compatible with the natural background levels. Some potentially toxic elements (e.g. Pb and Zn) reach concentration levels tens of times higher than the legal limits in the busiest areas of the city. Exposure to high concentrations of these contaminants may cause health problems to people living in these zones.

Cadmium behavior in a karst environment hydrological cycle

Karst regions are important water providers, supplying approximately 25% of the world population. These areas present higher vulnerability to contamination due to hydrodynamics, which hampers the natural depuration of these waters until reaching the underground environment. High concentrations of cadmium (Cd) are observed in the São Miguel watershed, state of Minas Gerais, Brazil. This toxic element is generally and predominantly released into the atmosphere by burning materials that have Cd in their composition, potentially contaminating surface and groundwater. Therefore, the objective of the study is to map Cd concentrations in the hydrological cycle of the São Miguel karst watershed and, through natural background level values (NBL 90%) of rainwater, surface water and groundwater, to understand the seasonal behavior of this element, and to identify the most vulnerable areas to contamination. To achieve this goal, rainwater, surface, and groundwater seasonal monitoring were conducted in 87 sampling stations. A total of 335 samples were collected, distributed over a watershed area of 520km2. Concentrations of cadmium above 1μg/L were found in 21.49% of samples during the rainy season. The origin and distribution of Cd were related to rainfall. For rainwater samples, 90% presented Cd concentration of 3.06μg/L. When these waters precipitate, they contaminate surface waters (NBL 90% = 1.50μg/L) and groundwater (NBL 90% = 2.81μg/L). This study presented a hydrochemical cycle map and proposed NBL values of Cd for surface water and groundwater, helping to understand how the environment is contaminated by this element.

Assessing natural background levels in shallow groundwater in a large semiarid drainage Basin

Natural background level (NBL) is a prerequisite for identifying groundwater pollution and for the evaluation of pollution control effectiveness. However, due to regional differences of natural geogenic, hydrogeological, biological and atmospheric processes, together with long-term intense anthropogenic activities, it is no longer reasonable to assess NBL as a single value without including human impact. This paper shows the importance of regional division based on the knowledge of geology, hydrogeology and anthropogenic activities on the assessment of NBLs. In the study, the Guanzhong Basin, situated in central China with an area of 20,035 km2 was divided into ten groundwater environmental units (GEUs) based on hydrogeological structures and groundwater flow systems. A total of 509 shallow groundwater samples were collected throughout the basin. Based on samples from each GEU, NBLs of Na+, Ca2+, Mg2+, HCO3−, SO42−, Cl−, F−, Cr6+, TH and TDS were evaluated by using iterative 2-δ technique (2-δ), calculated distribution function (CDF) and Grubbs’ test. The results indicate the distinct characteristics of NBLs for the various GEUs: NBLs of Na+, SO42−, Cl−, HCO3−, F− and TDS north of the Wei River obviously exceeded those in the south; NBLs of most ions for GEU-V and GEU-X were highest north and south of the Wei River, respectively. Through detailed analyses of the natural and anthropogenic influences on NBLs, we found that the outcrops of Tertiary rocks in the Li mountains determine the highest NBLs of chemical components for GEU-X south of the Wei River; long-term irrigation is responsible for the highest NBLs of TDS, Na+, Mg2+, HCO3−, SO42− and Cl− for GEU-V; rapid urbanization in Xi’an (GEU-VIII) slows down the accumulation of chemical components (e.g. TDS) in shallow groundwater by reducing evaporation and mixing of shallow water with deep water through ground fissures. Assessment of NBLs on a regional scale lays the basis for identification of groundwater pollution and is helpful for the reasonable management and effective protection of groundwater resources.

Determination of groundwater threshold values: A methodological approach

This article is concerned with the establishment of natural background levels and threshold values for naturally-occurring parameters in groundwaters in the absence of relevant and accurate long-term spatial data. A new approach was developed and exemplified, adopting the groundwaters of the Gediz River Basin, Turkey, as a case study. The available groundwater monitoring data was from a one-year seasonal water quality monitoring campaign. The approach used combines pre-selection, selection and statistical evaluation of the selected data to eliminate outliers to determine natural background levels. The application of three different statistical tools, namely, probability plot, 2-σ iteration, and distribution function methods, resulted in different natural background level estimates. The 2-σ iteration method provided the most conservative values for almost all the parameters. The use of this three-step approach, which adopts different statistical methods, appeared to solve the limited data availability challenges specific to groundwater contamination and improve natural background level assessment and threshold value setting. Lessons learned from this study can help policymakers to promote similar initiatives in other countries where groundwater quality data is limited.

Natural background levels and validation of the assessment of intrinsic vulnerability to the contamination in the Carste Lagoa Santa Protection Unit, Minas Gerais, Brazil

The contamination of karst aquifers by anthropogenic activities causes a major issue regarding environmental policies, since they present high sensitivity, influenced by unique features such as dolines, swallow holes, and conduits. This paper is focused on the Carste Lagoa Santa Protection Unit, MG, Brazil, and presents three main objectives: to determine the natural background levels of chloride, nitrate, sulfate, and phosphate; to indicate the locations where the concentrations of those parameters exceed the natural background levels in the existing vulnerability map and, finally, to determine the proportion of the areas (in percentage) where this surpassing occurs, according to the vulnerability classes (high, moderate and low). Results have shown values (90th percentile) of 2.4 mg/L, 1.0 mg/L, 5.3 mg/L, and 0.1 mg/L, for Cl−, NO3−, SO4−2, and PO4−3, respectively, indicating that for all four parameters, there were areas (mainly distributed within moderate vulnerability portions) where the values were surpassed, which suggests anthropogenic activity due to the presence of urban settlements and agricultural activities. Therefore, the proposal of natural background levels was essential to understand the hydrochemistry of the studied region.

Snow pollution by nitrogen-containing substances as a consequence of rocket launches from the Baikonur Cosmodrome

In this paper, we assessed snow pollution by nitrogen-containing substances including rocket propellants – UDMH (unsymmetrical dimethylhydrazine, (СН3)2NNH2) and NT (nitrogen tetroxide, N2O4) – and their transformation products (NDMA (nitrosodimethylamine, (CH3)2NNO), NO3−, NO2− and NH4+) within the falling regions (FRs) of the first and second stages of Proton-M rockets launched from the Baikonur Cosmodrome. At the first stage FR in Central Kazakhstan, snow with a pH range from 1.7 to 9.0 was contaminated by N-containing substances (maximal value in g/L): UDMH – 0.27, NDMA – 0.04, NO3− – 19, NH4+ – 0.04 and NO2− – 0.13. The first stage landing resulted in snow contamination by soil dust particles and N-containing substances at a rate of 13 g/m2 and 82 mg/m2/day, respectively. The maximal permissible addition (MPA) for UDMH, NDMA and NO3− to the 0–5 cm layer of soil was estimated at 0.06, 0.006 and 70.2 mg/m2, respectively. At the second stage FR in the NE Altai, substances released by space transportation were absent and the concentration of NO3− and NH4+ corresponded to the natural background level. The index of contamination (IC) was used for characterizing the degree of snow contamination by N-containing substances. A simulation model was developed for analysing the dependence of snow contamination by rocket propellant components on the weather parameters.

Groundwater pollution assessment in landfill areas: Is it only about the leachate?

Groundwater is the environmental compartment very often involved in the broader issues related to contaminated sites characterization and reclamation. It is not uncommon to find areas in which some substances directly linked to the petrographic composition of the aquifer reach high values exceeding the limits set by the regulations. These concentrations are defined as Natural Background Levels (NBL) and the need to quantify their real contribution, in areas subject to strong anthropogenic pressures, represents an emerging problem. Global statistical analyses and laboratory testing are proposed here to distinguish between the impacts of different forcing influencing water quality in hydrogeological systems. The study focus on the application of a methodology based on the Component Separation analysis for the NBL estimation of selected chemical species in potentially contaminated aquifers flowing in the proximity of landfill areas, and on the subsequent validation of the results through experimental studies of field samples. A site located in Calabria, Italy, and constituting a typical example of an aquifer which has been subjected to possible contact with the leachate produced by waste degradation is considered. The work is keyed to NBLs characterization of aluminum, iron and manganese and to the identification of their natural component for a proper environmental assessment of the site. Estimated NBLs are consistent with the geochemical composition of site samples. The adopted methodology can represent a useful instrument to distinguish effective anthropogenic contamination from natural conditions and to define realistic environmental clean-up goals.

Assessment of background levels and pollution sources for arsenic and fluoride in the phreatic and confined groundwater of Xi'an city, Shaanxi, China.

The presence of arsenic and fluoride in groundwater and their impacts on human health have been reported in many countries worldwide, but little information is available on As or F- contamination in Xi'an city. This study highlights the distribution and sources of As and F- anomalies in different aquifers of Xi'an city, based on the assessment of natural background levels (NBLs) and threshold values (TVs). Groundwater samples collected from phreatic and confined aquifers were analyzed to evaluate NBLs and TVs, usingmedian + 2MAD, Tukey inner fence (TIF), and percentile-based methods. Results showed that NBLs and TVs of As and F- in the phreatic aquifer were lower than those in the confined aquifer, indicating importance of the geological effects on the enrichment of arsenic and fluoride in the confined aquifer. Combined with hydrogeochemical methods, the distributions of As and F- anomalies show that high concentrations of As in both aquifers and F- in the confined aquifer can be attributed to the upward flow of geothermal water through faults and ground fissures, while high concentrations of F- in the phreatic aquifer may be greatly influenced by contaminated rivers. Although geological structures such as faults and ground fissures contribute to the high concentrations of potentially toxic elements, anthropogenic activities cannot be ignored because over exploitation of groundwater accelerates the development of ground fissures and results in the upward flow and mixing of geothermal water with groundwater in the upper aquifers.