Unraveling Health Risk and Speciation of Arsenic from Groundwater in Rural Areas of Punjab, Pakistan

Exploring the arsenic removal potential of various biosorbents from water

Globally, contamination of groundwater with toxic arsenic (As) is an environmental and public health issue given to its carcinogenic properties, thereby threatening millions of people relying on drinking As-contaminated well water. Here, we explored the efficiency of various biosorbents (egg shell, java plum seed, water chestnut shell, corn cob, tea waste and pomegranate peel) for arsenate (As(V)) and arsenite (As(III)) removal from As-contaminated water. Significantly, egg shell and java plum seed displayed the greatest As(III) elimination (78-87%) at 7 pH followed by water chestnut shell (75%), corn cob (67%), tea waste (74%) and pomegranate peel (65%). In contrast, 71% and 67% of As(V) was removed at pH 4.1 and 5.3 by egg shell and java plum seed, respectively. The maximum As(V) and As(III) sorption by all the biosorbents was obtained, notably for egg shell and java plum seed, after 2 h contact time. Langmuir isotherm and pseudo-second order models best fitted the sorption data for both forms of As. The -OH, -COOH, -NH₂ and sulfur-bearing surface functional groups were possibly involved for As(III) and As(V) removal by biosorbents. The scanning electron microscopy combined with the energy dispersive X-ray spectroscopy (SEM-EDX) analysis showed that the heterogeneous surface of biosorbents, possessing rough and irregular areas, could have led to As sorption. Both As(V) and As(III) were successfully desorbed (up to 97%) from the biosorbents in four sorption/desorption (regeneration) cycles. This pilot-scale study highlights that egg shell and java plum seed have the greatest ability to remove both As species from As-contaminated drinking water. Importantly, these findings provide insights to develop an inexpensive, effective and sustainable filtration technology for the treatment of As in drinking water, particularly in developing countries like Pakistan.

Arsenic accumulation in lettuce (Lactuca sativa L.) and broad bean (Vicia faba L.) crops and its potential risk for human consumption

Exposure to arsenic (As) is considered one of the primary health risks humans face worldwide. This study was conducted to determine As absorption by broad beans and lettuce crops grown in soil with As contents and irrigated with water contaminated with this toxic element, in Pastos Chicos, Jujuy (Argentina). Total dry biomass (TDB) and total As were determined in soils, roots, leaves, pods and seeds. These data were used to determine several parameters, such as translocation (TF) and bioconcentration (BCF) factors, target hazard quotient (THQ), and carcinogenic risk (CR). Broad bean plants had the lowest biomass production when exposed to As in irrigation water and soil. Lettuce plants presented TDB reductions of 33.3 and 42.8% when grown in soil polluted with As, and in control soil under irrigation with contaminated water, respectively. The presence of this toxicant in broad bean seeds and lettuce leaves (edible parts) exceeded the limits established by Código Alimentario Argentino, i.e. 0.10 and 0.30 mg/kg, respectively. THQ values for lettuce leaves were higher than 1, the same as those for broad bean seeds when grown in soil with As contents and irrigated with arsenic-contaminated water, thus suggesting that consumers would run significant risks when consuming these vegetables. Furthermore, this type of exposure to As implied a CR that exceeded the acceptable 1 × 10^-4 risk level. Hence, we may conclude that consuming lettuce and broad beans grown at the evaluated site brings about considerable health risks for local residents.

Health risk assessment of arsenic and other potentially toxic elements in drinking water from an industrial zone of Gujrat, Pakistan: a case study

Present study aimed to provide a baseline data on arsenic (As) and other potentially toxic element (PTEs; Cd, Cr, Cu, Ni, and Pb) contamination in groundwater and soils (surface and sub-surface) from an industrial area of district Gujrat, Pakistan. Statistical parameters, principal component analysis-multiple linear regression (PCA-MLR), and health risk assessment model were used to elaborate the interrelations, source contributor, and associated health risks. This study revealed that the concentrations of Cd, Cr, Cu, and Pb in drinking water were within the permissible limits of the World Health Organization (WHO). However, As and Ni concentrations exceeded the WHO limits of 10 μg/L for As and 0.07 mg/L for Ni. In soils, the concentration of Cr was within permissible limits, whereas As, Cd, Cu, Ni, and Pb exceeded the prescribed values. Solid waste and industrial effluents from the area also contained high levels of As, Cd, Cr, Cu, Ni, and Pb. Calculated health index of As and other PTEs for industrial site and control area was less than 1 which indicated that the groundwater was assumed to be safe for drinking. High contamination of As (15 mg/kg) and other PTEs (Pb was 978, Cr 51, Cu 111, Cd 68, and Ni was 90 mg/kg, respectively) in upper soil could be due to the discharge of industrial effluent prior to the treatment, which signifies the industrial contribution towards As and heavy metal contamination. It can be concluded that critical examination of soil profile affinity to the respective, industrial waste pollutants can reduce the health risks to the local community. This trend not only reveals the geochemistry of the area but also useful for developing a link to access health risk and associated remediation processes.

Biosorption of Pb(II) from contaminated water onto Moringa oleifera biomass: kinetics and equilibrium studies

The present study aims at evaluating a batch scale biosorption potential of Moringa oleifera leaves (MOL) for the removal of Pb(II) from aqueous solutions. The MOL biomass was characterized by FTIR, SEM, EDX, and BET. The impact of initial concentrations of Pb (II), adsorbent dosage, pH, contact time, coexisting inorganic ions (Ca²⁺, Na⁺, K⁺, Mg²⁺, CO₃^2-, HCO₃^-, Cl^-), electrical conductivity (EC) and total dissolved salts (TDS) in water was investigated. The results revealed that maximum biosorption (45.83 mg/g) was achieved with adsorbent dosage 0.15 g/100 mL while highest removal (98.6%) was obtained at adsorbent biomass 1.0 g/100 mL and pH 6. The presence of coexisting inorganic ions in water showed a decline in Pb(II) removal (8.5% and 5%) depending on the concentrations of ions. The removal of Pb(II) by MOL decreased from 97% to 89% after five biosorption/desorption cycles with 0.3 M HCl solution. Freundlich model yielded a better fit for equilibrium data and the pseudo-second-order well described the kinetics of Pb(II) biosorption. FTIR spectra showed that -OH, C-H, -C-O, -C = O, and -O-C functional groups were involved in the biosorption of Pb(II). The change in Gibbs free energy (ΔG = -28.10 kJ/mol) revealed that the biosorption process was favorable and thermodynamically driven. The results suggest MOL as a low cost, environment-friendly alternative biosorbent for the remediation of Pb(II) contaminated water.

Arsenic removal from aqueous solutions and groundwater using agricultural biowastes-derived biosorbents and biochar: a column-scale investigation

In this study, column-scale laboratory experiments were performed to evaluate the arsenic (As) removal efficiency of different agricultural biowastes-derived biosorbents (orange peel, banana peel, rice husk) and biochar, using As-containing solutions and As-contaminated groundwater. All the biosorbents and biochar efficiently removed (50-100%) As from groundwater (drinking well water). Arsenic removal potential of biosorbents varied with their type, As concentration, contact time, and As solution type. After 1 h, the As removal efficiency of all the biosorbents was 100%, 100% and 90% for 5, 10, and 50 µg/L As-contaminated groundwater samples, respectively; and it was 50%, 90%, and 90% for 10, 50, and 100 µg/L As solutions, respectively. After 2 h, all the biosorbents and biochar removed 100% As from aqueous solutions except for 100 µg/L As solution. This showed that the biosorbents and biochar could be used to reduce As contents below the WHO safe limit of As in drinking water (10 µg/L). Fourier transform infrared (FTIR) spectroscopy indicated possible role of various surface functional moieties on biosorbents/biochar surface to remove As from solution and groundwater. This pilot-scale column study highlights that the biosorbents and biochar can be effectively used in remediation of As-contaminated groundwater, although the soluble salts in groundwater increased after treatment with biochar.

Arsenic removal by natural and chemically modified water melon rind in aqueous solutions and groundwater

Contamination of groundwater with toxic arsenic (As) has become an emerging health and environmental problem around the world, which has seen significant attention amongst the scientists for development of new sorbents to remediate As-contaminated water. Here, we explored the arsenate (As(V)) and arsenite (As(III)) sorption to natural water melon rind (WMR), xanthated WMR and citric acid-modified WMR in aqueous solutions, and determined potential of the most potent sorbent for As removal in groundwater. Xanthated WMR (X-WMR) showed relatively higher As(V) and As(III) removal than the citric acid modified WMR (CA-WMR) and natural WMR. The maximum As(III) (99%) and As(V) (98%) removal was obtained at pH 8.2 and 4.6, respectively, by X-WMR at 4 mg L^-1 initial As(V) and As(III) concentrations and sorbent dose of 1 g L^-1. Langmuir isotherm model best fitted (R² of up to 0.96) the data both for As(III) and As(V) sorption to X-WMR. Sorption kinetics of As(V) and As(III) was well described (R² of up to 0.99) by the pseudo second-order model on surface of the X-WMR. Thermodynamic investigations revealed that As(V) and As(III) sorption was endothermic and spontaneous. The FTIR spectroscopy depicted the presence of different surface function groups (OH, COOH, S-bearing (C=S, S=O and S-S)) which were involved in As(V) and As(III) sequestration on the sorbents examined here. Significantly, X-WMR showed (up to 49%) greater As(III) and As(V) sorption than that of natural WMR. Our results demonstrated that X-WMR efficiently removed 94%-100% (n = 16) of As from As-contaminated drinking well water which possessed detectable concentrations of some anions (e.g., SO₄, CO₃, HCO₃). This study highlights that the X-WMR has potential to remove As, notably As(III), from solutions and drinking water, and might be utilized as a reactive medium for the treatment of As-contaminated water.

A meta-analysis of the distribution, sources and health risks of arsenic-contaminated groundwater in Pakistan

Globally, millions of people who rely on groundwater for potable purposes and agriculture have been inadvertently exposed to toxic arsenic (As) because of its natural occurrence in groundwater in several countries of Asia, Europe and America. While the presence of As in groundwater and its impacts on human health have been documented in many countries, there is little information on As contamination in Pakistan. This review highlights, for the first time, the extent and severity of As-induced problems in Pakistan based on relevant published papers; discusses possible sources of As contamination of aquifers; and estimates As-induced potential health hazards in the country in relation to global data. Data from 43 studies (>9882 groundwater samples) were used to describe As variability in groundwater of Pakistan and for comparison with global data. The mean groundwater As content reported in these studies was 120 μg/L (range: 0.1-2090 μg/L; SD: ±307). About 73% of the values for mean As contents in the 43 studies were higher than the World Health Organization (WHO) permissible limit (10 μg/L) for drinking water, while 41% were higher than the permissible limit of As in Pakistan (50 μg/L). It was observed that groundwater samples in some areas of Punjab and Sindh provinces contained high As concentrations which were almost equal to concentrations reported in the most contaminated areas of the world. We predicted that the mean values of ADD, HQ and CR were 4.4 μg kg^-1day^-1 (range: 0-77 μg kg^-1day^-1), 14.7 (range: 0-256) and 0.0029 (range: 0-0.0512), respectively, based on mean As concentrations reported in Pakistan. In addition, this article proposes some integrated sustainable solutions and future perspectives keeping in view the regional and global context, as well as the on-ground reality of the population drinking As-contaminated water, planning issues, awareness among civil society and role of the government bodies. Based on available data, it is predicted that almost 47 million people in Pakistan are residing in areas where more than 50% of groundwater wells contain As concentrations above the WHO recommended limit of As in drinking water.

Absorption of arsenic from soil and water by two chard (Beta vulgaris L.) varieties: A potential risk to human health

The accumulation of arsenic (As) in vegetables poses a risk of contamination to humans via the food chain. Two chard (var. cicla and var. d'ampuis) crops were grown for 60 days in greenhouses on Aridisol soil, and irrigated with water from Pastos Chicos, Jujuy (Argentina). The soil and water used in the trial presented 49 and 1.44 mg/L As concentration levels, respectively. Total dry biomass (TDB) and total As were determined in soils, roots and leaves. The latter was quantified by atomic absorption spectrometry with hydride generation, and bioconcentration and translocation factors were determined. TDB in var. cicla showed statistically significant differences when the plant was cultivated in control soil and watered with the toxicant (2.04 g), as compared with the treatment without exposure (2.8 g). TDB in var. d'ampuis presented statistically significant differences with respect to that of the control when the plants were grown in soils with As and watered with the toxicant (3.3 g). This variety increased its biomass in the presence of As. In the two Swiss chard varieties evaluated, the largest As accumulation in root and leaves was found when they were cultivated in contaminated soil and watered with distilled water. The presence of the toxicant in the leaves exceeded the limits established by Código Alimentario Argentino, i.e. 0.30 mg/kg. Total target hazard quotient (THQ) values for As were higher than 1, suggesting that consumers would run significant risks when consuming these chard varieties. Furthermore, it was determined that the carcinogenic risk (CR) posed by this type of exposure to As exceeded the acceptable risk level of 1 × 10^-6. Based on this evidence, we may conclude that consuming chard cultivated on the evaluated site brings about considerable risks to local residents' health.

Effects of Fe-S-As coupled redox processes on arsenic mobilization in shallow aquifers of Datong Basin, northern China

High arsenic groundwater generally coexists with elevated Fe²⁺ concentrations (mg L^-1 levels) under reducing conditions, but an explanation for the extremely high arsenic (up to ∼2690) concentrations at very low Fe²⁺ (i.e., μg L^-1 levels) in groundwater of Datong Basin remains elusive. Field groundwater investigation and laboratory microcosm experiments were implemented in this study. The field groundwater was characterized by weakly alkaline (pH 7.69 to 8.34) and reducing conditions (Eh -221.7 to -31.9 mV) and arsenic concentration averages at 697 μg L^-1. Acinetobacter (5.9-51.3%), Desulfosporosinus (4.6-30.2%), Brevundimonas (3.9-19%) and Pseudomonas (3.2-14.6%) were identified as the dominant genera in the bacterial communities. Bacterially mediated arsenate reduction, Fe(III) reduction, and sulfate reduction are processes occurring (or having previously occurred) in the groundwater. Results from incubation experiment (27 d) revealed that nitrate, arsenate, and Fe(III)/sulfate reduced sequentially with time under anoxic conditions, while Fe(III) and sulfate reduction processes had no obvious differences, occurring almost simultaneously. Moreover, low Fe²⁺ concentrations were attributed to initially high pH conditions, which relatively retarded Fe(III) reduction. In addition, arsenic behavior in relation to groundwater redox conditions, matrices, and solution chemistry were elaborated. Bacterial arsenate reduction process proceeded before Fe(III) and sulfate reduction in the incubation experiment, and the total arsenic concentration (dominated by arsenite) gradually increased from ∼7 to 115 μg L^-1 as arsenate was reduced. Accordingly, bacterially mediated reductive desorption of arsenate is identified as the main process controlling arsenic mobility, while Fe(III) reduction coupled with sulfate reduction are secondary processes that have also contributed to arsenic enrichment in the study site. Overall, this study provide important insights into the mechanism controlling arsenic mobility under weakly alkaline and reducing conditions, and furnishes that arsenate reduction by bacteria play a major role leading to high accumulation of desorbed arsenite in groundwater.

The evaluation of arsenic contamination potential, speciation and hydrogeochemical behaviour in aquifers of Punjab, Pakistan

In this study, we tested 123 groundwater wells from five different areas of Punjab, Pakistan for arsenic (As) contamination level and species, as well as delineated hydrogeochemical behaviour of As in aquifers. Results revealed that 75% and 41% of the groundwater wells exceeded the safe As limit of World Health Organisation (WHO, 10 μg L^-1) and Pakistan-EPA (50 μg L^-1), respectively. Arsenite (As(III)) and arsenate (As(V)) spanned 0-80% and 20-100% of total As (1.2-206 μg L^-1), respectively. The mean As content (5.2 μg L^-1) of shallow wells at 9-40 m depth did not exceed the WHO safe limit, representing a safe aquifer zone for pumping of groundwater compared to deeper wells at 41-90 m (51 μg L^-1) and >90 m (23 μg L^-1) depths. Piper-plot elucidated that the aqueous chemistry was dominated with Na-SO₄, Na-Ca-SO₄, Na-Mg-SO₄ type saline water. Principal component analysis grouped As concentration with well depth, pH, salinity, Fe and CO₃, exhibiting that these hydrogeochemical factors could have potential role in controlling As release/sequestration into the aquifers of study area. Geochemical modeling showed positive saturation indices only for iron (Fe) oxide-phases, indicating Fe oxides as the major carriers of As. Overall, this study provides insights to tackle emerging As threat to the communities in Punjab, Pakistan, as well as help develop suitable management/mitigation strategies - based on the baseline knowledge of As levels/species and factors governing As contamination in the study area.

A Review of Environmental Contamination and Health Risk Assessment of Wastewater Use for Crop Irrigation with a Focus on Low and High-Income Countries

Population densities and freshwater resources are not evenly distributed worldwide. This has forced farmers to use wastewater for the irrigation of food crops. This practice presents both positive and negative effects with respect to agricultural use, as well as in the context of environmental contamination and toxicology. Although wastewater is an important source of essential nutrients for plants, many environmental, sanitary, and health risks are also associated with the use of wastewater for crop irrigation due to the presence of toxic contaminants and microbes. This review highlights the harmful and beneficial impacts of wastewater irrigation on the physical, biological, and chemical properties of soil (pH, cations and anions, organic matter, microbial activity). We delineate the potentially toxic element (PTEs) build up in the soil and, as such, their transfer into plants and humans. The possible human health risks associated with the use of untreated wastewater for crop irrigation are also predicted and discussed. We compare the current condition of wastewater reuse in agriculture and the associated environmental and health issues between developing and developed countries. In addition, some integrated sustainable solutions and future perspectives are also proposed, keeping in view the regional and global context, as well as the grounded reality of wastewater use for crop production, sanitary and planning issues, remedial techniques, awareness among civil society, and the role of the government and the relevant stakeholders.

Arsenic removal by Japanese oak wood biochar in aqueous solutions and well water: Investigating arsenic fate using integrated spectroscopic and microscopic techniques

In this study, we examined the sorption of arsenite (As(III)) and arsenate (As(V)) to Japanese oak wood-derived biochar (OW-BC) in aqueous solutions, and determined its efficiency to remove As from As-contaminated well water. Results revealed that, among the four sorption isotherm models, Langmuir model showed the best fit to describe As(III) and As(V) sorption on OW-BC, with slightly greater sorption affinity for As(V) compared to As(III) (Q_L=3.89 and 3.16mgg^-1; R²=0.91 and 0.85, respectively). Sorption edge experiments indicated that the maximum As removal was 81% and 84% for As(III)- and As(V)-OW-BC systems at pH7 and 6, respectively, which decreased above these pH values (76-69% and 80-58%). Surface functional groups, notably OH, COOH, CO, CH₃, were involved in As sequestration by OW-BC, suggesting the surface complexation/precipitation and/or electrostatic interaction of As on OW-BC surface. Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that 36% of the added As(III) was partially oxidized to As(V) in the As(III) sorption experiment, and in As(V) sorption experiment, 48% of As(V) was, albeit incompletely, reduced to As(III) on OW-BC surface. Application of OW-BC to As-contaminated well water (As: 27-144μgL^-1; n=10) displayed that 92 to 100% of As was depleted despite in the presence of co-occurring competing anions (e.g., SO₄^2-, CO₃^2-, PO₄^3-). This study shows that OW-BC has a great potential to remove As from solution and drinking (well) water. Overall, the combination of macroscopic sorption data and integrated spectroscopic and microscopic techniques highlight that the fate of As on biochar involves complex redox transformation and association with surface functional moieties in aquatic systems, thereby providing crucial information required for implication of biochar in environmental remediation programs.

Arsenic Uptake, Toxicity, Detoxification, and Speciation in Plants: Physiological, Biochemical, and Molecular Aspects

Environmental contamination with arsenic (As) is a global environmental, agricultural and health issue due to the highly toxic and carcinogenic nature of As. Exposure of plants to As, even at very low concentration, can cause many morphological, physiological, and biochemical changes. The recent research on As in the soil-plant system indicates that As toxicity to plants varies with its speciation in plants (e.g., arsenite, As(III); arsenate, As(V)), with the type of plant species, and with other soil factors controlling As accumulation in plants. Various plant species have different mechanisms of As(III) or As(V) uptake, toxicity, and detoxification. This review briefly describes the sources and global extent of As contamination and As speciation in soil. We discuss different mechanisms responsible for As(III) and As(V) uptake, toxicity, and detoxification in plants, at physiological, biochemical, and molecular levels. This review highlights the importance of the As-induced generation of reactive oxygen species (ROS), as well as their damaging impacts on plants at biochemical, genetic, and molecular levels. The role of different enzymatic (superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase) and non-enzymatic (salicylic acid, proline, phytochelatins, glutathione, nitric oxide, and phosphorous) substances under As(III/V) stress have been delineated via conceptual models showing As translocation and toxicity pathways in plant species. Significantly, this review addresses the current, albeit partially understood, emerging aspects on (i) As-induced physiological, biochemical, and genotoxic mechanisms and responses in plants and (ii) the roles of different molecules in modulation of As-induced toxicities in plants. We also provide insight on some important research gaps that need to be filled to advance our scientific understanding in this area of research on As in soil-plant systems.

Arsenic removal by perilla leaf biochar in aqueous solutions and groundwater: An integrated spectroscopic and microscopic examination

In this study, we examined the removal of arsenite (As(III)) and arsenate (As(V)) by perilla leaf-derived biochars produced at 300 and 700 °C (referred as BC300 and BC700) in aqueous environments. Results revealed that the Langmuir isotherm model provided the best fit for As(III) and As(V) sorption, with the sorption affinity following the order: BC700-As(III) > BC700-As(V) > BC300-As(III) > BC300-As(V) (Q_L = 3.85-11.01 mg g^-1). In general, As removal decreased (76-60%) with increasing pH from 7 to 10 except for the BC700-As(III) system, where notably higher As removal (88-90%) occurred at pH from 7 to 9. Surface functional moieties contributed to As sequestration by the biochars examined here. However, significantly higher surface area and aromaticity of BC700 favored a greater As removal compared to BC300, suggesting that surface complexation/precipitation dominated As removal by BC700. Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy demonstrated that up to 64% of the added As(V) was reduced to As(III) in BC700- and BC300-As(V) sorption experiments, and in As(III) sorption experiments, partial oxidation of As(III) to As(V) occurred (37-39%). However, XANES spectroscopy was limited to precisely quantify As binding with sulfur species as As₂S₃-like phase. Both biochars efficiently removed As from natural As-contaminated groundwater (As: 23-190 μg L^-1; n = 12) despite in the presence of co-occurring anions (e.g., CO₃^2-, PO₄^3-, SO₄^2-) with the highest levels of As removal observed for BC700 (97-100%). Overall, this study highlights that perilla leaf biochars, notably BC700, possessed the greatest ability to remove As from solution and groundwater (drinking water). Significantly, the integrated spectroscopic techniques advanced our understanding to examine complex redox transformation of As(III)/As(V) with biochar, which are crucial to determine fate of As on biochar in aquatic environments.

Biosorption of chromium(VI) in aqueous solutions by chemically modified Strychnine tree fruit shell

Chromium(VI) was removed from aqueous solution using sulfuric- and phosphoric-acid-activated Strychnine tree fruit shells (SSTFS and PSTFS) as biosorbents. Effects of various parameters such as adsorbent dose (0.02-0.1 g/L), temperature (303-333 K), agitation speed, solution pH (2-9), contact time, and initial Cr(VI) concentration (50-250 mg/L) were studied for a batch adsorption system. The optimum pH range for Cr(VI) adsorption was determined as 2. Equilibrium adsorption data were analyzed with isotherm models and the Langmuir and Freundlich models got best fitted values for SSTFS (R² value - 0.994) and PSTFS (R² value - 0.996), respectively. The maximum adsorption capacities of SSTFS and PSTFS were 100 and 142.85 mg/g, respectively. The biosorption process was well explained by pseudo-second-order kinetic model with higher R² value (SSTFS - 0.996, PSTFS - 0.990) for both biosorbents. Characterization of biosorbents was done using Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analysis, energy-dispersive X-ray analysis, and thermogravimetric analysis. Thermodynamic studies revealed the spontaneous, endothermic, and randomness in nature of the Cr(VI) adsorption process. Different concentrations of NaOH solutions were used to perform the desorption studies. The results demonstrated that both SSTFS and PSTFS can be used as an effective and low-cost biosorbent for removal of Cr(VI) from aqueous solutions.

Human health implications, risk assessment and remediation of As-contaminated water: A critical review

Arsenic (As) is a naturally occurring metalloid and Class-A human carcinogen. Exposure to As via direct intake of As-contaminated water or ingestion of As-contaminated edible crops is considered a life threatening problem around the globe. Arsenic-laced drinking water has affected the lives of over 200 million people in 105 countries worldwide. Limited data are available on various health risk assessment models/frameworks used to predict carcinogenic and non-carcinogenic health effects caused by As-contaminated water. Therefore, this discussion highlights the need for future research focusing on human health risk assessment of individual As species (both organic and inorganic) present in As-contaminated water. Various conventional and latest technologies for remediation of As-contaminated water are also reviewed along with a discussion of the fate of As-loaded waste and sludge.

Influence of groundwater and wastewater irrigation on lead accumulation in soil and vegetables: Implications for health risk assessment and phytoremediation

The current study evaluated the effect of groundwater and wastewater irrigation on lead (Pb) accumulation in soil and vegetables, and its associated health implications. A pot experiment was conducted in which spinach (Spinacia oleracea), radish (Raphanus sativus), and cauliflower (Brassica oleracea) were irrigated with groundwater and wastewaters containing varying concentrations of Pb. Lead contents were measured in wastewaters, soils and root and shoot of vegetables. We also measured health risk index (HRI) associated with the use of vegetables irrigated by wastewaters. Results revealed that Pb contents in groundwater and wastewater samples (range: 0.18-0.31 mg/L) were below the permissible limits (0.5 mg/L) set by the Food and Agriculture Organization (FAO). Application of Pb-containing groundwater and wastewater increased Pb concentration in soil and vegetables. Lead concentrations in all soils ranged from 10 to 31 mg/kg and were below the permissible limits of 300 mg/kg set by the European Union. Significant Pb enrichment was observed in the soils whereby all types of vegetables were grown and assessed for Pb risk. Our data showed that Pb contents, in all three vegetables (21-28 mg/kg DW), were higher than the permissible Pb limit of FAO (5 mg/kg Dry Weight (DW)). The HRI values were > 1.0 for radish and cauliflower. It is proposed that Vehari city wastewater/groundwater must be treated prior to its use for irrigation to avoid vegetable contamination by Pb, and as such for reducing Pb-induced human health risk.

Arsenic and fluoride removal by potato peel and rice husk (PPRH) ash in aqueous environments

Finding appropriate adsorbent may improve the quality of drinking water in those regions where arsenic (As) and fluoride (F^-) are present in geological formations. In this study, we evaluated the efficiency of potato peel and rice husk ash (PPRH-ash)-derived adsorbent for the removal of As and F from contaminated water. Evaluation was done in batch adsorption experiments, and the effect of pH, initial adsorbate concentration, contact time, and adsorbent dose were studied. Characteristics of adsorbents were analyzed using scanning electron micropcope (SEM) and Fourier transform infrared (FTIR) spectroscopy. Both the Langmuir and Freundlich isotherm models fitted well for F^- and As sorption process. The maximum adsorption capacity of adsorbent for As and F^- was 2.17 μg g^-1 and 2.91 mg g^-1, respectively. The As and Fi removal was observed between pH 7 and 9. The sorption process was well explained with pseudo-second order kinetic model. Arsenic adsorption was not decreased in the presence of carbonate and sulfate. Results from this study demonstrated potential utility of this agricultural biowaste, which could be developed into a viable filtration technology for As and F^- removal in As- and F-contaminated water streams.

Heavy metals in contaminated environment: Destiny of secondary metabolite biosynthesis, oxidative status and phytoextraction in medicinal plants

Contamination of soils, water and air with toxic heavy metals by various human activities is a crucial environmental problem in both developing and developed countries. Heavy metals could be introduced into medicinal plant products through contaminated environment (soil, water and air resources) and/or poor production practices. Growing of medicinal plants in heavy metal polluted environments may eventually affect the biosynthesis of secondary metabolites, causing significant changes in the quantity and quality of these compounds. Certain medicinal and aromatic plants can absorb and accumulate metal contaminants in the harvestable foliage and, therefore, considered to be a feasible alternative for remediation of polluted sites without any contamination of essential oils. Plants use different strategies and complex arrays of enzymatic and non-enzymatic anti-oxidative defense systems to cope with overproduction of ROS causes from the heavy metals entered their cells through foliar and/or root systems. This review summarizes the reports of recent investigations involving heavy metal accumulation by medicinal plants and its effects on elicitation of secondary metabolites, toxicity and detoxification pathways, international standards regarding in plants and plant-based products, and human health risk assessment of heavy metals in soil-medicinal plants systems.

Drinking Water Quality Status and Contamination in Pakistan

Due to alarming increase in population and rapid industrialization, drinking water quality is being deteriorated day by day in Pakistan. This review sums up the outcomes of various research studies conducted for drinking water quality status of different areas of Pakistan by taking into account the physicochemical properties of drinking water as well as the presence of various pathogenic microorganisms. About 20% of the whole population of Pakistan has access to safe drinking water. The remaining 80% of population is forced to use unsafe drinking water due to the scarcity of safe and healthy drinking water sources. The primary source of contamination is sewerage (fecal) which is extensively discharged into drinking water system supplies. Secondary source of pollution is the disposal of toxic chemicals from industrial effluents, pesticides, and fertilizers from agriculture sources into the water bodies. Anthropogenic activities cause waterborne diseases that constitute about 80% of all diseases and are responsible for 33% of deaths. This review highlights the drinking water quality, contamination sources, sanitation situation, and effects of unsafe drinking water on humans. There is immediate need to take protective measures and treatment technologies to overcome unhygienic condition of drinking water supplies in different areas of Pakistan.

Arsenic in groundwater of the Kolkata Municipal Corporation (KMC), India: Critical review and modes of mitigation

This study represents the first comprehensive report of groundwater arsenic contamination status in the Kolkata Municipal Corporation (KMC). During the past 23 years, 4210 groundwater samples were analysed from all 141 wards in the KMC: 14.2% and 5.2% samples had arsenic >10 μg/l and >50 μg/l, respectively, representing 77 and 37 wards. The study shows that the number of arsenic contaminated samples (and wards) in the southern part of the KMC exceeds that of other parts of the city. The daily intake of arsenic from drinking water was estimated as 0.95 μg per kg bw and the cancer risk was estimated as 1425/10⁶. Analyses of biological samples (hair, nail and urine) showed elevated concentrations of arsenic indicating the presence of subclinical arsenic poisoning, predicting an enhanced lifetime cancer risk for the population in southern part of the KMC. In the KMC, groundwater is not a sustainable source of freshwater due to arsenic, high iron, hardness and total dissolved solids. Its continued use is impelled by the lack of an adequate infrastructure to treat and supply surface water and in some wards the unaccounted for water (UFW) is even >45% incurred during distribution. The rare imposition of a water tax makes the water supply systems unsustainable and fosters indifference to water conservation. To mitigate the arsenic problem, continuous groundwater monitoring for pollutants, a treated surface water supply with strict policy implications, rainwater harvesting in the urban areas and introduction of water taxes seem to be long-term visible solutions.

Comparative effect of calcium and EDTA on arsenic uptake and physiological attributes of Pisum sativum

In this study, we determined the effect of ethylenediaminetetraacetic acid (EDTA) and calcium (Ca) on arsenic (As) uptake and toxicity to Pisum sativum. Plants were treated with three levels of As (25, 125, and 250 µM) in the presence and absence of three levels of Ca (1, 5, and 10 mM) and EDTA (25, 125, and 250 µM). Exposure to As caused an overproduction of hydrogen peroxide (H2O2) in roots and leaves, which induced lipid peroxidation and decreased pigment contents. Application of both Ca and EDTA significantly reduced As accumulation by pea, Ca being more effective in reducing As accumulation. Both Ca and EDTA enhanced As-induced H2O2 production, but reduced lipid peroxidation. In the case of pigment contents, EDTA significantly reduced pigment contents, whereas Ca significantly enhanced pigment contents compared to As alone. The effect of As treatment in the presence and absence of EDTA and Ca was more pronounced in younger leaves compared to older leaves. The effect of amendments varied greatly with their applied levels, as well as type and age of plant organs. Importantly, due to possible precipitation of Ca-As compounds, the soils with higher levels of Ca ions are likely to be less prone to food chain contamination.

Phosphate-assisted phytoremediation of arsenic by Brassica napus and Brassica juncea: Morphological and physiological response

In this study, we examined the potential role of phosphate (P; 0, 50, 100 mg kg^-1) on growth, gas exchange attributes, and photosynthetic pigments of Brassica napus and Brassica juncea under arsenic (As) stress (0, 25, 50, 75 mg kg^-1) in a pot experiment. Results revealed that phosphate supplementation (P100) to As-stressed plants significantly increased shoot As concentration, dry biomass yield, and As uptake, in addition to the improved morphological and gas exchange attributes and photosynthetic pigments over P0. However, phosphate-assisted increase in As uptake was substantially (up to two times) greater for B. napus, notably due to higher shoot As concentration and dry biomass yield, compared to B. juncea at the P100 level. While phosphate addition in soil (P100) led to enhanced shoot As concentration in B. juncea, it reduced shoot dry biomass, primarily after 50 and 75 mg kg^-1 As treatments. The translocation factor and bioconcentration factor values of B. napus were higher than B. juncea for all As levels in the presence of phosphate. This study demonstrates that phosphate supplementation has a potential to improve As phytoextraction efficiency, predominantly for B. napus, by minimizing As-induced damage to plant growth, as well as by improving the physiological and photosynthetic attributes.

Chromium(VI) sorption efficiency of acid-activated banana peel over organo-montmorillonite in aqueous solutions

In the present study, we examined sorption of chromate (Cr(VI)) to acid-activated banana peel (AABP) and organo-montmorillonite (O-mont) as a function of pH, initial Cr(VI) concentration at a sorbent dose of 4 g L^-1 and at 20 ± 1°C in aqueous solutions. In sorption edge experiments, maximum Cr(VI) removal was obtained at pH 3 after 2 hours by AABP and O-mont (88% and 69%). Sorption isotherm data showed that the sorption capacity of AABP was higher than O-mont (15.1 vs. 6.67 mg g^-1, respectively, at pH 4). Freundlich and Langmuir models provided the best fits to describe Cr(VI) sorption onto AABP (R² = 0.97) and O-mont (R² = 0.96). Fourier transform infrared spectroscopy elucidated that for AABP mainly the -OH, -COOH, -NH₂, and for O-mont intercalated amines and -OH surface functional groups were involved in Cr(VI) sorption. The scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) analyses, although partly, indicate that the (wt. %) proportion of cations (e.g., Ca, Mg) in AABP decreased after Cr(VI) sorption. This may be due to ion exchange of chromite (Cr(III)) (produced from Cr(VI) reduction) with cationic elements in AABP. Also, Cr(VI) desorption (using phosphate solution) from AABP was lower (29%) than that from O-mont (51%) up to the third regeneration cycle. This bench scale comparative study highlights that the utilization of widely available and low-cost acid-activated biomaterials has a greater potential than organo-clays for Cr(VI) removal in aqueous media. However, future studies are warranted to precisely delineate different mechanisms of Cr(VI) sorption/reduction by acid-activated biomaterials and organo-clays.

Arsenic accumulation and physiological attributes of spinach in the presence of amendments: an implication to reduce health risk

The current study examined the effect of calcium (Ca) and ethylenediaminetetraacetic acid (EDTA) on arsenic (As) uptake and toxicity to spinach (Spinacia oleracea) as well as assessed the potential human health risks. Spinach seedlings were exposed to three levels of As (25, 125, and 250 μM) alone or together with three levels of EDTA (25, 125, and 250 μM) and Ca (1, 5, and 10 mM). The effect of EDTA and Ca was assessed in terms of As contents in roots and shoots, hydrogen peroxide production, chlorophyll contents, and lipid peroxidation. The accumulation and toxicity of As to spinach plants increased with increasing As levels in nutrient solution. Exposure to As resulted in lipid peroxidation and reduced chlorophyll contents. The highest level of As alone (250 μM) showed highest human health risk (hazard quotient of 7.09 at As-250). Addition of EDTA enhanced As accumulation by spinach, while reduced As toxicity to spinach, as well as human health risk (hazard quotient of 4.01 at As-250). Similarly, Ca significantly reduced As toxicity to spinach and the human health risks (hazard quotient of 3.79 at As-250) by reducing its accumulation in spinach. Higher levels of Ca were more effective in reducing As uptake and toxicity as well as enhancing chlorophyll contents.

Chromium speciation, bioavailability, uptake, toxicity and detoxification in soil-plant system: A review

Chromium (Cr) is a potentially toxic heavy metal which does not have any essential metabolic function in plants. Various past and recent studies highlight the biogeochemistry of Cr in the soil-plant system. This review traces a plausible link among Cr speciation, bioavailability, phytouptake, phytotoxicity and detoxification based on available data, especially published from 2010 to 2016. Chromium occurs in different chemical forms (primarily as chromite (Cr(III)) and chromate (Cr(VI)) in soil which vary markedly in term of their biogeochemical behavior. Chromium behavior in soil, its soil-plant transfer and accumulation in different plant parts vary with its chemical form, plant type and soil physico-chemical properties. Soil microbial community plays a key role in governing Cr speciation and behavior in soil. Chromium does not have any specific transporter for its uptake by plants and it primarily enters the plants through specific and non-specific channels of essential ions. Chromium accumulates predominantly in plant root tissues with very limited translocation to shoots. Inside plants, Cr provokes numerous deleterious effects to several physiological, morphological, and biochemical processes. Chromium induces phytotoxicity by interfering plant growth, nutrient uptake and photosynthesis, inducing enhanced generation of reactive oxygen species, causing lipid peroxidation and altering the antioxidant activities. Plants tolerate Cr toxicity via various defense mechanisms such as complexation by organic ligands, compartmentation into the vacuole, and scavenging ROS via antioxidative enzymes. Consumption of Cr-contaminated-food can cause human health risks by inducing severe clinical conditions. Therefore, there is a dire need to monitor biogeochemical behavior of Cr in soil-plant system.

Arsenic toxicity and epimutagenecity: the new LINEage

Global methylation pattern regulates the normal functioning of a cell. Research have shown arsenic alter these methylation landscapes within the genome leading to aberrant gene expression and inducts various pathophysiological outcomes. Long interspersed nuclear elements (LINE-1) normally remains inert due to heavy methylation of it's promoters, time and various environmental insults, they lose these methylation signatures and begin retro-transposition that has been associated with genomic instability and cancerous outcomes. Of the various high throughput technologies available to detect global methylation profile, development of LINE-1 methylation index shall provide a cost effect-screening tool to detect epimutagenic events in the wake of toxic exposure in a large number of individuals. In the present review, we tried to discuss the state of research and whether LINE-1 methylation can be considered as a potent epigenetic signature for arsenic toxicity.

Human exposure assessment of different arsenic species in household water sources in a high risk arsenic area

Understanding arsenic speciation in water is important for managing the potential health risks associated with chronic arsenic exposure. Most arsenic monitoring studies to date have only measured total arsenic, with few looking at arsenic species. This study assessed 228 ground water sources in six unstudied villages in Pakistan for total, inorganic and organic arsenic species using ion chromatography inductively coupled plasma collision reaction cell mass spectrometry. The concentration levels approached 3090μgL^-1 (95% CI, 130.31, 253.06) for total arsenic with a median of 57.55μgL^-1, 3430μgL^-1 (median=52) for arsenate (As⁺⁵) and 100μgL^-1 (median=0.37) for arsenite (As⁺³). Exceedance of the WHO provisional guideline value for arsenic in drinking water (10μgL^-1) occurred in 89% of water sources. Arsenic was present mainly as arsenate (As⁺⁵). Average daily intake of total arsenic for 398 residents living in the sampled houses was found up to 236.51μgkg^-1day^-1. This exposure estimate has indicated that 63% of rural residents exceeded the World Health Organization's provisional tolerable daily intake (PTDI) of 2.1μgkg^-1day^-1 body weight. Average daily intake of As⁺⁵ was found to be 15.63μgkg^-1day^-1 (95% CI, 5.53, 25.73) for children ≤16 and 15.07μgkg^-1day^-1 (95% CI, 10.33, 18.02) for adults. A mean daily intake of 0.09μgkg^-1day^-1 was determined for As⁺³ for children and 0.26μgkg^-1day^-1 for adults. Organic arsenic species such as monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and Arsenobetaine (AsB) were found to be below their method detection limits (MDLs).

Foliar heavy metal uptake, toxicity and detoxification in plants: A comparison of foliar and root metal uptake

Anthropologic activities have transformed global biogeochemical cycling of heavy metals by emitting considerable quantities of these metals into the atmosphere from diverse sources. In spite of substantial and progressive developments in industrial processes and techniques to reduce environmental emissions, atmospheric contamination by toxic heavy metals and associated ecological and health risks are still newsworthy. Atmospheric heavy metals may be absorbed via foliar organs of plants after wet or dry deposition of atmospheric fallouts on plant canopy. Unlike root metal transfer, which has been largely studied, little is known about heavy metal uptake by plant leaves from the atmosphere. To the best of our understanding, significant research gaps exist regarding foliar heavy metal uptake. This is the first review regarding biogeochemical behaviour of heavy metals in atmosphere-plant system. The review summarizes the mechanisms involved in foliar heavy metal uptake, transfer, compartmentation, toxicity and in plant detoxification. We have described the biological and environmental factors that affect foliar uptake of heavy metals and compared the biogeochemical behaviour (uptake, translocation, compartmentation, toxicity and detoxification) of heavy metals for root and foliar uptake. The possible health risks associated with the consumption of heavy metal-laced food are also discussed.

Refinement of arsenic attributable health risks in rural Pakistan using population specific dietary intake values

BACKGROUND

Previous risk assessment studies have often utilised generic consumption or intake values when evaluating ingestion exposure pathways. If these values do not accurately reflect the country or scenario in question, the resulting risk assessment will not provide a meaningful representation of cancer risks in that particular country/scenario.

OBJECTIVES

This study sought to determine water and food intake parameters for one region in South Asia, rural Pakistan, and assess the role population specific intake parameters play in cancer risk assessment.

METHODS

A questionnaire was developed to collect data on sociodemographic features and 24-h water and food consumption patterns from a rural community. The impact of dietary differences on cancer susceptibility linked to arsenic exposure was evaluated by calculating cancer risks using the data collected in the current study against standard water and food intake levels for the USA, Europe and Asia. A probabilistic cancer risk was performed for each set of intake values of this study.

RESULTS

Average daily total water intake based on drinking direct plain water and indirect water from food and beverages was found to be 3.5Lday^-1 (95% CI: 3.38, 3.57) exceeding the US Environmental Protection Agency's default (2.5Lday^-1) and World Health Organization's recommended intake value (2Lday^-1). Average daily rice intake (469gday^-1) was found to be lower than in India and Bangladesh whereas wheat intake (402gday^-1) was higher than intake reported for USA, Europe and Asian sub-regions. Consequently, arsenic-associated cumulative cancer risks determined for daily water intake was found to be 17 chances in children of 3-6years (95% CI: 0.0014, 0.0017), 14 in children of age 6-16years (95% CI: 0.001, 0.0011) and 6 in adults of 16-67years (95% CI: 0.0006, 0.0006) in a population size of 10,000. This is higher than the risks estimated using the US Environmental Protection Agency and World Health Organization's default recommended water intake levels. Rice intake data showed early life cumulative cancer risks of 15 chances in 10,000 for children of 3-6years (95% CI: 0.0012, 0.0015), 14 in children of 6-16years (95% CI: 0.0011, 0.0014) and later life risk of 8 adults (95% CI: 0.0008, 0.0008) in a population of 10,000. This is lower than the cancer risks in countries with higher rice intake and elevated arsenic levels (Bangladesh and India). Cumulative cancer risk from arsenic exposure showed the relative risk contribution from total water to be 51%, from rice to be 44% and 5% from wheat intake.

CONCLUSIONS

The study demonstrates the need to use population specific dietary information for risk assessment and risk management studies. Probabilistic risk assessment concluded the importance of dietary intake in estimating cancer risk, along with arsenic concentrations in water or food and age of exposed rural population.

Arsenic sorption to nanoparticulate mackinawite (FeS): An examination of phosphate competition

Nanoparticulate mackinawite (FeS) can be an important host-phase for arsenic (As) in sulfidic, subsurface environments. Although not previously investigated, phosphate (PO₄^3-) may compete with As for available sorption sites on FeS, thereby enhancing As mobility in FeS-bearing soils, sediments and groundwater systems. In this study, we examine the effect of PO₄^3- on sorption of arsenate (As(V)) and arsenite (As(III)) to nanoparticulate FeS at pH 6, 7 and 9. Results show that PO₄^3- (at 0.01-1.0 mM P) did not significantly affect sorption of either As(V) or As(III) to nanoparticulate FeS at initial aqueous As concentrations ranging from 0.01 to 1.0 mM. At pH 9 and 7, sorption of both As(III) and As(V) to nanoparticulate FeS was similar, with distribution coefficient (K_d) values spanning 0.76-15 L g^-1 (which corresponds to removal of 87-98% of initial aqueous As(III) and As(V) concentrations). Conversely, at pH 6, the sorption of As(III) was characterized by substantially higher K_d values (6.3-93.4 L g^-1) than those for As(V) (K_d = 0.21-0.96 L g^-1). Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that up to 52% of the added As(V) was reduced to As(III) in As(V) sorption experiments, as well as the formation of minor amounts of an As₂S₃-like species. In As(III) sorption experiments, XANES spectroscopy also demonstrated the formation of an As₂S₃-like species and the partial oxidation of As(III) to As(V) (despite the strictly O₂-free experimental conditions). Overall, the XANES data indicate that As sorption to nanoparticulate FeS involves several redox transformations and various sorbed species, which display a complex dependency on pH and As loading but that are not influenced by the co-occurrence of PO₄^3-. This study shows that nanoparticulate FeS can help to immobilize As(III) and As(V) in sulfidic subsurface environments where As co-exists with PO₄^3-.

Bioaccessibility and arsenic speciation in carrots, beets and quinoa from a contaminated area of Chile

Consumption of vegetables grown in arsenic (As)-contaminated soils is an important exposure route to the element for humans. The present study is focused on locally-grown, frequently-consumed vegetables, such as carrots (Daucus carota), beets (Beta vulgaris) and quinoa (Chenopodium) from the As-polluted Chiu Chiu area in Northern Chile. The latter region is affected both by As discharge from copper mining activity and natural As contamination, leading to a high As content in local food and water. For the selected vegetables, the following aspects were investigated: i) Their total As, Cu, Pb, Cr, Cd and Mn content; ii) Arsenic speciation in the edible part of the vegetables by liquid chromatography inductively-coupled plasma mass spectrometry (LC-ICPMS) analysis; iii) Arsenic bioaccessibility in the vegetables during in vitro gastrointestinal digestion; iv) Arsenic species present in the extracts obtained from in vitro gastrointestinal digestion; and v) Arsenic dietary exposure estimates for the assessment of the risk posed by the vegetables consumption. A significant degree of As contamination was found in the vegetables under study, their metal content having been compared with that of similar Spanish uncontaminated products. In vitro gastrointestinal digestion of the studied vegetables led to quantitative extraction of As from carrots and beets, whereas efficiency was about 40% for quinoa. For carrots, only As(III) and As(V) species were found, being their concentration levels similar. In the case of quinoa, around 85% of the element was present as As(V). For beets, inorganic As(V) and unknown overlapped As species (probably arsenosugars) were found. No significant transformation of the original As species was observed during in vitro gastrointestinal digestion. Arsenic dietary exposure values obtained for the three vegetables (0.017-0.021μg As person(-1)day(-1)) were much lower than the JFCFA's safety limit of 50μg As person(-1)day(-1). Therefore, no toxicological risk would be expected from the intake of these vegetables.

Determination of total arsenic and arsenic species in drinking water, surface water, wastewater, and snow from Wielkopolska, Kujawy-Pomerania, and Lower Silesia provinces, Poland

Arsenic is a ubiquitous element which may be found in surface water, groundwater, and drinking water. In higher concentrations, this element is considered genotoxic and carcinogenic; thus, its level must be strictly controlled. We investigated the concentration of total arsenic and arsenic species: As(III), As(V), MMA, DMA, and AsB in drinking water, surface water, wastewater, and snow collected from the provinces of Wielkopolska, Kujawy-Pomerania, and Lower Silesia (Poland). The total arsenic was analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and arsenic species were analyzed with use of high-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC/ICP-MS). Obtained results revealed that maximum total arsenic concentration determined in drinking water samples was equal to 1.01 μg L(-1). The highest concentration of total arsenic in surface water, equal to 3778 μg L(-1) was determined in Trująca Stream situated in the area affected by geogenic arsenic contamination. Total arsenic concentration in wastewater samples was comparable to those determined in drinking water samples. However, significantly higher arsenic concentration, equal to 83.1 ± 5.9 μg L(-1), was found in a snow sample collected in Legnica. As(V) was present in all of the investigated samples, and in most of them, it was the sole species observed. However, in snow sample collected in Legnica, more than 97 % of the determined concentration, amounting to 81 ± 11 μg L(-1), was in the form of As(III), the most toxic arsenic species.

Arsenic(V) biosorption by charred orange peel in aqueous environments

Biosorption efficiency of natural orange peel (NOP) and charred orange peel (COP) was examined for the immobilization of arsenate (As(V)) in aqueous environments using batch sorption experiments. Sorption experiments were carried out as a function of pH, time, initial As(V) concentration and biosorbent dose, using NOP and COP (pretreated with sulfuric acid). Arsenate sorption was found to be maximum at pH 6.5, with higher As(V) removal percentage (98%) by COP than NOP (68%) at 4 g L(-1) optimum biosorbent dose. Sorption isotherm data exhibited a higher As(V) sorption (60.9 mg g(-1)) for COP than NOP (32.7 mg g(-1)). Langmuir model provided the best fit to describe As(V) sorption. Fourier transform infrared spectroscopy and scanning electron microscopy combined with energy dispersive X-ray spectroscopy analyses revealed that the -OH, -COOH, and -N-H surface functional groups were involved in As(V) biosorption and the meso- to micro-porous structure of COP sequestered significantly (2-times) higher As(V) than NOP, respectively. Arsenate desorption from COP was found to be lower (10%) than NOP (26%) up to the third regeneration cycle. The results highlight that this method has a great potential to produce unique 'charred' materials from the widely available biowastes, with enhanced As(V) sorption properties.