Explore the vast range of titles available.

In this study, we attempted to calculate the Natural Background Level (NBL) for 12 selected chemical compounds in the Urmia aquifer, northwestern Iran. In this study, combined methods including pre-selection and statistical methods for determining NBLs have been used. In the pre-selection method, the concentration of nitrate (NO3 ≥ 19.97 ppm) and chloride (Cl ≥ 200 ppm) were used as the main criteria to identify and eliminate samples affected by human activities. The selected concentration of nitrate is determined using the comparison of the results of various statistical and graphical evaluations including Quantile-Quantile plot (Q-Q plot), Box & Whisker plot (BW), Box & Whisker plot Iterative (BWI), Grubbs test, Mean and standard deviation (mean ± 2σ) (MSD), and median absolute deviation (MAD). After identifying the final data set, the NBL of the selected chemical compounds was calculated by two techniques including the Iterative 2σ technique (2σ) and calculated distribution function (CDF). Due to higher concentration relative to the reference values (REF), this study has focused on the calculation of NBL values of SO4, F, As, and Mn. The results showed that the upper limit of NBLs calculated for these variables is about 125 ppm, 1 ppm, 8.5 ppb, 80 ppb, respectively. Given that no study has been conducted to determine the NBLs of chemical compounds in groundwater in Iran, the results of this study can be a roadmap for decision-makers and researchers to better manage this aquifer and other water resources in this country with limited freshwater resources.

In this study, site-specific natural background levels (NBLs) were determined for 18 elements (Al, As, Be, Cd, Co, Cu, Cr, Fe, Hg, K, Mn, Mo, Ni, Pb, Tl, U, V, and Zn) in two sediment cores collected offshore the Bagnoli-Coroglio brownfield site (Gulf of Pozzuoli, southern Italy) to accurately assess the degree of contamination and the historical trends in Heavy Metals (HMs) enrichment. This objective was pursued taking in account the high temporal and spatial variability of the geochemical properties of the area due to the local geothermal activity. Moreover, the temporal variation of Polycyclic Aromatic Hydrocarbons (PAHs) was investigated. 226 Ra was used as an extraordinary marker to confirm 210 Pb dating. It especially allowed defining the geochronological framework of the sediment core closer the brownfield up to around 1500, providing compelling support to correlate the investigated elements’ occurrences with natural geogenic dynamic. Sediment samples were accurately dated and analyzed for chemical and particle size composition. The contamination factor (Cf) and the pollution load index (PLI) showed very high enrichment of Cd, Cu, Hg, Pb, and Zn. The contamination profiles of HMs and PAHs follow the same pattern in both sediment cores, increasing from deep to upper layers. The highest contamination levels for HMs and PAHs were observed between 10 and 30 cm, corresponding to the periods of most intense industrial activity. Decreasing trends of pollutants were observed in the surface layers (0–10 cm), probably affected by a natural attenuation process due to the cessation of industrial activities.

The determination of groundwater background levels is a prerequisite for assessing and analyzing groundwater characteristics. Shanghai is among the most economically developed regions in China and is located in the estuary of the Yangtze River, where frequent hydrogeochemical processes occur. Moreover, the frequency of anthropogenic activities in Shanghai is very high. Consequently, assessing groundwater background levels in Shanghai is inherently limited if only statistical methods are adopted or anthropogenic impacts are ignored. In this study, hydrochemical and statistical methods were coupled to identify groundwater anomalies and background levels. The results revealed distinct differences in hydrochemical characteristics between the two selected independent units (Chongming and Qingpu units), highlighting the necessity of reasonably delineating hydrogeological units for obtaining background values. Furthermore, for these two independent units, different optimal methods for identifying and eliminating anthropogenic groundwater anomalies were determined. The use of coupled methods was demonstrated to be substantially superior to the use of purely statistical approaches. Hydro-HCA was identified as the optimal identification method for the Chongming unit, whereas Hydro-Grubbs was determined as the most suitable method for the Qingpu unit. This could be attributed mainly to the coupled methods accounting for not only the dispersion of the data itself but also the intrinsic relationships and evolutionary processes of hydrochemical components. These findings could provide reliable information for subsequent groundwater background surveys and studies on groundwater pollution characteristics in Shanghai and to guide future endeavors aimed at protecting groundwater resources.

Understanding the groundwater natural background levels (NBLs) is important in distinguishing groundwater contamination and guiding the groundwater management. Groundwater environment in suburb areas around the large city may suffer from strong impact of human activity during rapid urbanization which will have significant effect on the groundwater natural background levels. Although many previous studies have proposed different methods to understand the spatial distribution of NBLs, its temporal evolution and the relationship with groundwater quality is not well understood. In this study, we investigated the long-term evolution of NBLs and groundwater hydrochemical anomalies in the 59 wells of the Pinggu basin by combining the comprehensive groundwater hydrochemical anomalies identification and groundwater quality assessment. NO 3 − , Cl − , and SO 4 2− were found to be as the major chemical constitutions demonstrating the strong anomaly degree, which decreased over time. The zoning and evolution of groundwater quality also aligned with the variation of anomaly areas. Regions with a higher degree of abnormality were consistent with those with poorer groundwater quality. The impact of human activities on the groundwater environment decreased in the Pinggu basin compared to the initial years due to the efforts of environment protection and governance by the local government. Investigating the temporal and spatial variation, hydrochemical properties by combination of NBLs and groundwater quality assessment provided a useful approach to understand groundwater environment in rapidly urbanizing areas.

Determining the controlling factors of the quality of groundwater can help decision-makers in preparing optimal management plans and a sustainable supply of water for drinking and agriculture. The results of factor analysis and hierarchical cluster analysis show that the chemical composition of groundwater in the Fereidan region (Iran) is controlled by both geogenic and anthropogenic factors. The natural background level of major variables and heavy metals including Cu, Zn, Hg, Cd, Pb, and As have been estimated using probabilistic and deterministic methods including the iterative 2 σ outlier test, calculated distribution function (CDF), 95th percentile, and iterative Grubbs test (IGT). The results show that the pre-selection process and removal of outliers play a significant role in calculating NBLs and threshold values (TVs). Although heavy metals had different datasets and it was impossible to perform the pre-selection process for them, nevertheless, CDF, iterative 2 σ , and 95th percentile methods were also used to calculate their NBLs. As the results show, Δ% between NBLs calculated by CDF, iterative 2 σ , 95th percentile methods, and IGT is greater than that for complete datasets. This is because contaminated samples were not removed by the pre-selection process and some of these data remained in the final dataset. This shows itself as a skewed dataset of some heavy elements including Cu, Zn, and Cd. Therefore, if the goal is strict planning to take away the freedom of farmers and local planners to pollute the aquifer by providing smaller NBLs and TVs, it is better to use the smaller NBLs and TV determined by the IGT method after the pre-selection process. Graphical abstract

A multi-tracer approach has been implemented in the southwestern part of the Lake Chad Basin to depict the functioning of aquifers in terms of recharge, relationship with surface water bodies, flow paths and contamination. The results are of interest for sustainable water management in the region. The multi-layered structure of the regional aquifer was highlighted with shallower and intermediate to deep flow paths. The shallower aquifer is recharged with rainwater and interconnected with surface water. The groundwater chemistry indicates geogenic influences in addition to a strong anthropogenic fingerprint. The intermediate to deep aquifer shows a longer residence time of groundwater, less connection with the surface and no to only a little anthropogenic influence. Ambient Background Levels (ABLs) and Threshold Values (TVs) show the qualitative status of the groundwater bodies and provide helpful information for water resources protection and the implementation of new directives for efficient and more sustainable groundwater exploitation.

Assessment of natural background levels (NBLs) of compositional groundwater parameters helps to identify the potential threats to groundwater resources. This study is the first attempt to apply the pre-selection-based BRIDGE (Background cRiteria for the IDentification of Groundwater thrEshold) methodology to calculate the NBLs and threshold values (TVs) of major groundwater constituents in the southwest Bengal Basin, Bangladesh. A database consisting of 78 groundwater samples was used to assess the NBLs and associated TVs of the major groundwater parameters (EC, Ca 2+ , Mg 2+ , Na + , K + , Cl − , NO 3 − , SO 4 2− , PO 4 3− , Mn 2+ , and Fe 2+ ). NBLs were derived based on 90th and 97.7th percentiles. The status of regional groundwater resources was assessed by applying 90th percentile NBL on a regional dataset ( n  = 196). Results revealed the “poor” chemical status of shallow aquifers denoting heavy deterioration of the groundwater quality due to anthropogenic interventions. Nitrate contamination and salinization were identified as the major threats to the deep groundwater of the southwest Bengal Basin. Finally, to verify the chemical status of groundwater in a heavily urbanized area, derived TVs were applied throughout the experimental site Khulna. Twenty-five deep groundwater samples were collected for this purpose. Though most of the parameters exhibited “good” chemical status, nitrate demonstrated anthropogenic groundwater contamination in Khulna City. Thus, the developed TVs would provide an early warning system of pollution. On a national scale, it is expected to facilitate the sustainable groundwater management of the country and contribute to achieving the Sustainable Development Goals (SDG) of the United Nations (UN) in Bangladesh.

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.

Perfluorinated compounds (PFCs), such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), are a family of commonly used industrial chemicals whose persistence and ubiquity in blood samples of humans and wildlife have become a growing concern. Despite PFOS and PFOA having been found in human blood and tissue samples from occupationally exposed workers and the general worldwide population, little systematic knowledge has accrued with respect to exposure levels in Uyghurs in the Sinkiang-Uighur Autonomous Region of China, which is predominantly agricultural and pastoral. Our goal was to provide background data for biological monitoring in the general population of this region. In this study, 110 self-reported healthy human serum samples were collected from nonoccupationally exposed Uyghurs volunteers and analyzed by microbore HPLC-electrospray tandem mass spectrometry. Among the 110 blood specimens, PFOS was detected in 102 samples (93 %) and ranged from the lower limit of quantification of 0.01 to 22.63 μg/L with a median of 1.93 μg/L (interquartile range 1.00–3.43 μg/L). The median was higher among males (2.39 μg/L; interquartile range 1.23–4.40 μg/L) than that among females (1.20 μg/L; interquartile range 0.83–2.77 μg/L). No significant difference was observed with respect to age. The concentration of PFOA was lower than that of PFOS and was found only in seven samples (6 %) at concentrations above the limit of quantification. This study is the first investigation to reveal serum PFOS and PFOA levels in the general population of Uyghurs. PFOS and PFOA concentrations found in the present investigation were lower than those found in recent studies consisting of subjects from different geographic locations (PFOS 5.0–44.7 μg/L, PFOA 1.5–10 μg/L).

Information about natural background levels (NBLs) of chemicals in source waters allows water utilities to identify trends in drinking water contamination. We estimate NBLs for chemicals in source waters for Icelandic water utilities at both national levels with all data pooled, and according to geological regime. NBLs were derived by collecting samples from 79 aquifers considered largely unimpacted by human activities. The aquifers were categorized into four geological settings that are representative of the geology of Iceland. NBLs were calculated as 90%iles of all aquifers in each setting and in all pooled. There was a statistical difference between the geological settings in 11 parameters of 37 tested. The 90%ile for nitrate for all aquifers pooled was 1.36 mg/l, indicating little anthropogenic influence on water used for public water supply in Iceland. The results were compared to the chemical status of 60 European aquifers, collected for the European Union's Sixth Framework Program Background Criteria for the Identification of Groundwater Thresholds project, revealing lower dissolved solids concentration for Icelandic groundwater than that from other parts of Europe. The explanation is likely due to high permeability of young geology settings and low population density in Iceland whereas there is a long history of agriculture and industry in most European countries.