Potential phosphorus and arsenic mobilization from Bangladesh soils by particle dispersion

Time since faecal deposition influences mobilisation of culturable E. coli and intestinal enterococci from deer, goose and dairy cow faeces

Mobilisation is a term used to describe the supply of a pollutant from its environmental source, e.g., soil or faeces, into a hydrological transfer pathway. The overarching aim of this study was to determine, using a laboratory-based approach, whether faecal indicator bacteria (FIB) are hydrologically mobilised in different quantities from a typical agricultural, wildlife and wildfowl source, namely dairy cattle, red deer and greylag goose faeces. The mobilisation of FIB from fresh and ageing faeces under two contrasting temperatures was determined, with significant differences in the concentrations of both E. coli and intestinal enterococci lost from all faecal sources. FIB mobilisation from these faecal matrices followed the order of dairy cow > goose > deer (greatest to least, expressed as a proportion of the total FIB present). Significant changes in mobilisation rates from faecal sources over time were also recorded and this was influenced by the temperature at which the faecal material had aged over the course of the 12-day study. Characterising how indicators of waterborne pathogens are mobilised in the environment is of fundamental importance to inform models and risk assessments and develop effective strategies for reducing microbial pollution in catchment drainage waters and associated downstream impacts. Our findings add quantitative evidence to support the understanding of FIB mobilisation potential from three important faecal sources in the environment.

Contradictory tendency of As(V) releasing from Fe-As complexes: Influence of organic and inorganic anions

The strong ability of ferrihydrite and its aged minerals for fixing arsenate is a key factor in remediating arsenate-polluted environments. It is therefore crucial to clarify the stability of Fe-As complexes and the release conditions for As(V). The As(V) release amount was evaluated and compared in the presence of six representative anions, namely, phosphate, silicate, sulfate, inositol hexaphosphate, citrate, and oxalate. It was found that the As(V) release amount changed with the aging time of ferrihydrite and that this tendency generally followed two rules. These are, longer aging time leads to lower As(V) release (Rule 1), and longer aging time leads to higher As(V) release (Rule 2). Whether Rule 1 or Rule 2 dominated As release depended on the number of surface groups, size of competing anions, and contribution of As(V) re-adsorption. Characterization results using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) provided evidence for the predicted mechanisms of As(V) release under various circumstances. In this work, it was demonstrated that when inorganic anions such as sulfate and silicate are present, ferrihydrite with longer aging time led to decreased As(V) release. When organic anions are present, ferrihydrite with less aging time results in reduced As(V) leaching. For anions such as phosphate, the As(V) release amount in relation to the ferrihydrite aging time depends on the concentration of phosphate ions. Nevertheless, the ligand concentration and As(V) loading rate on ferrihydrite should be simultaneously considered for the rule governing As(V) releasing.

Inhibition of arsenic transport from soil to rice grain with a sustained field-scale aerobic rice cultural practice

A field-scale investigation has been carried out to assess the uptake of Arsenic (As) in rice under aerobic practice. Two consecutive field experiments have been designed considering the rice cultivation system's variation in the comparison between aerobic and flooded practices during monsoon and post-monsoon seasons using the cultivars of Swarna masuri and Satabdi, respectively. Notwithstanding the impact of the rice cultivation systems, the implications of amendments like iron, silicon, and organic matter were also taken into account on As uptake by rice. We hypothesized that the application of amendments in combination with sustained aerobic practice would reduce the subsequent accumulation of As in rice as compared to flooded practice (control). However, regardless of the cultivation systems, the grain productivity of rice delivered a non-significant impact. Results revealed that the plant available As content in soil under aerobic practice was averaged 22% and 26% lower than flooded, during monsoon and post-monsoon seasons, respectively. Aerobic treatment significantly reduced accumulation of As in root and straw as compared to flooded (p < 0.05), which in accordance corresponded to lower translocation efficiency of As from root to straw. For Swarna masuri, the bioaccumulation of As in polished rice, husk and bran was reduced by 33%, 48% and 47%, respectively, under aerobic practice. On the contrary, Satabdi exhibited a reduction in As accumulation with 54% in polished rice, followed by 31% and 38% in husk and bran, respectively. The inhibition of As uptake in rice was notably impacted by iron, silicon, and organic matter. Following the treatments of rice cultivation system and amendment, the bioaccumulation of As in rice plant parts was arranged in the order of root > straw > grain > husk > bran > polished rice in both the cultivars. The health risk assessment was also considered to estimate the potential human health risk measuring the estimated dietary intake and the health hazard quotient. The results highlighted that the consumption of rice grown in aerobic practice was ensured to provide non-carcinogenic health risk as compared to rice grown in flooded practice. In the overall attempt, the present investigation corroborates the insinuation of specific management practices in quantifying the reduction of As bioavailability in rice with subject to the concern of reducing human health risk.

Geochemical variability in the soils of Bangladesh as affected by sources of irrigation water and inundation land types

Paddy soils in Bangladesh experience extensive irrigation with groundwater and surface water, both having variable geochemical constituents. The soils also have topological variations across the landscape. To understand the geochemical variability in the soils as affected by the different sources of irrigation water and the topographical variability, cultivation zones of paddy soils irrigated with both groundwater (n = 904) and surface water (n = 281) across Bangladesh were sampled and analyzed for a suit of seventeen geochemical elements. This study also assessed the extent and distribution of arsenic and the other geochemical elements in the paddy soils (n = 1209) as well as in a set of neighboring non-paddy soils (n = 235) within the different inundation land types (highland, medium highland-1, medium highland-2, medium lowland, lowland and very lowland) of Bangladesh. The mean concentrations of aluminum (26,000 mg/kg), cobalt (13 mg/kg), copper (32 mg/kg), iron (28,250 mg/kg), lead (18 mg/kg), magnesium (8050 mg/kg), molybdenum (1.02 mg/kg), nickel (41 mg/kg), potassium (4870 mg/kg), sodium (750 mg/kg) and zinc (70 mg/kg) in the surface water-irrigated paddy soils were found to be significantly (0.001 ≥ p ≤ 0.05) higher compared to the concentrations in the soils irrigated with groundwater (23,400; 12; 28; 25,650; 17; 7000; 0.96; 36; 4350; 600; and 62 mg/kg, respectively). Therefore, surface water used for paddy irrigation could increase the inputs of a number of toxic elements in the paddy soils having potential risk of crop contamination. Arsenic in the paddy and non-paddy soils varied significantly (F = 24.74, p < 0.001 and F = 3.42, p < 0.01, respectively) within the inundation land types, the very lowland (9.95 and 6.72 mg/kg, respectively) and lowland (8.33 and 5.20 mg/kg, respectively) having the highest mean arsenic concentrations and the medium highland-1 (5.27 and 5.17 mg/kg, respectively) having the lowest. The concentrations of the other geochemical elements analyzed were also observed to be higher, in general, in the soils of very lowland and lowland. Since the low-level lands are predominantly used for paddy cultivation, higher concentrations of various toxic elements, particularly arsenic, in such soils pose an increased risk of rice toxicity in Bangladesh. The results of this study present an inimitable geochemical database for the surface soils across Bangladesh which can be used in any future studies on the geomorphologically variable agricultural and non-agricultural Bangladeshi soils, providing a basis for environmental pollution assessment and sustainable mitigation approaches.

Arsenic in a groundwater environment in Bangladesh: Occurrence and mobilization

Groundwater with an excessive level of Arsenic (As) is a threat to human health. In Bangladesh, out of 64 districts, the groundwater of 50 and 59 districts contains As exceeding the Bangladesh (50 μg/L) and WHO (10 μg/L) standards for potable water. This review focuses on the occurrence, origin, plausible sources, and mobilization mechanisms of As in the groundwater of Bangladesh to better understand its environmental as well as public health consequences. High As concentrations mainly was mainly occur from the natural origin of the Himalayan orogenic tract. Consequently, sedimentary processes transport the As-loaded sediments from the orogenic tract to the marginal foreland of Bangladesh, and under the favorable biogeochemical circumstances, As is discharged from the sediment to the groundwater. Rock weathering, regular floods, volcanic movement, deposition of hydrochemical ore, and leaching of geological formations in the Himalayan range cause As occurrence in the groundwater of Bangladesh. Redox and desorption processes along with microbe-related reduction are the key geochemical processes for As enrichment. Under reducing conditions, both reductive dissolution of Fe-oxides and desorption of As are the root causes of As mobilization. A medium alkaline and reductive environment, resulting from biochemical reactions, is the major factor mobilizing As in groundwater. An elevated pH value along with decoupling of As and HCO₃^- plays a vital role in mobilizing As. The As mobilization process is related to the reductive solution of metal oxides as well as hydroxides that exists in sporadic sediments in Bangladesh. Other mechanisms, such as pyrite oxidation, redox cycling, and competitive ion exchange processes, are also postulated as probable mechanisms of As mobilization. The reductive dissolution of MnOOH adds dissolved As and redox-sensitive components such as SO₄^2- and oxidized pyrite, which act as the major mechanisms to mobilize As. The reductive suspension of Mn(IV)-oxyhydroxides has also accelerated the As mobilization process in the groundwater of Bangladesh. Infiltration from the irrigation return flow and surface-wash water are also potential factors to remobilize As. Over-exploitation of groundwater and the competitive ion exchange process are also responsible for releasing As into the aquifers of Bangladesh.

Arsenic contamination, subsequent water toxicity, and associated public health risks in the lower Indus plain, Sindh province, Pakistan

Arsenic (As) contamination in drinking water is a global public health risk. The present study highlighted the geological and anthropogenic causes of As contamination in groundwater (GW) and surface water (SW) and assessment of their potential health risks in Sindh province of Pakistan. Upon analyzing 720 GW and SW samples from 18 different sites, the estimates of As in groundwater and surface water was observed in the range of 0 to 125 and 0 to 35 μg/L with mean values of 46.8 and 15.43 μg/L respectively. Majority of the samples exceeded WHO permissible limit of As (10 μg/L) with higher concentration detected in groundwater samples compared to surface water. Moreover, both of these sample sources were found not potable based on physicochemical characteristics. The results of statistical analysis (correlation analysis, principal component analysis (PCA), and hierarchy cluster analysis (HCA)) indicate that natural mobilization of As in groundwater is believed to be enhanced by the pH-based reductive dissolution of iron hydroxide (FeOH) and competitive sorption of bicarbonate minerals in the presence of microorganisms along with evaporative enrichment while water logging, coal mining, and excessive use of pesticides are believed to be the anthropogenic causes of As enrichment. Furthermore, enormous health risk was associated with As in terms of chronic daily intake (CRI), hazard quotient (HQ), and cancer risk probability (CR) in GW and SW. Mean HQ values in GW were 4.47 mg/kg/day in adults and 3.89 mg/kg/day in children (standard HQ ≤ 1) and was 1.43 and 1.28 mg/kg/day in SW. Mean CR value in both GW and SW was found higher than the safe limit (10^-6) having a mean of 2 × 10^-3 in GW and 7 × 10^-4 (mg/kg/day) in SW. These findings suggest that majority of the sampling sites carry serious public health risk due to high As values and hence demands exigent remedial and management measures.

High arsenic contamination and presence of other trace metals in drinking water of Kushtia district, Bangladesh

Drinking water with excessive concentration levels of arsenic (As) is a great threat to human health. A hydrochemical approach was employed in 50 drinking water samples (collected from Kushtia district, Bangladesh) to examine the occurrence of geogenic As and the presence of trace metals (TMs), as well as the factors controlling As release in aquifers. The results reveal that the drinking water of shallow aquifers is highly contaminated by As (6.05-590.7 μg/L); 82% of samples were found to exceed the WHO recommended limit (10 μg/L) for potable water, but the concentrations of Si, B, Mn, Sr, Se, Ba, Fe, Cd, Pb, F, U, Ni, Li, and Cr were within safe limits. The Ca-HCO₃-type drinking water was identified as having high contents of As, pH and HCO₃^-, a medium-high content EC, and low concentrations of NO₃^-, SO₄^2-, K⁺, and Cl^-. The significant correlation between As and NO₃^- indicates that NO₃^- might be attributed to the use of phosphate fertilizers and a factor responsible for enhancing As in aquifers. The study also reports that the occurrence of high As and the presence of TMs in drinking water may be a result of local anthropogenic activities, such as irrigation, intensive land use and the application of agrochemicals. The insignificant correlation between As and SO₄^2- demonstrated that As is released from SO₄^2- minerals under reducing conditions. An elevated pH value along with decoupling of As and HCO₃^- plays a vital role in mobilizing As to aquifer systems. Moreover, the positive relationship between As and Si indicated that As is transported in the biogeochemical environment. The reductive suspension of Mn(IV)-oxyhydroxides also accelerated the As mobilization process. Over exploitation of tube-well water and the competitive ion exchange process are also responsible for the release of As in aquifers.

An insight into fractionation, toxicity, mobility and source apportionment of metals in sediments from El Temsah Lake, Suez Canal

El Temsah Lake is one of the most important wetlands in the Suez Canal area and the major source of fish for the area. In this study, the relative role of sediments' geochemical properties and metals geochemical fractionation in determining Cd, Cr, Fe, Mn, Ni, and Pb mobility and toxicity was especially concerned. The results reflected that the increasing order of contamination for the investigated metals according to individual contamination factor (ICF) was: Cr > Mn > Ni > Pb > Cd > Fe. Risk assessment code (RAC) classification showed that the relative amounts of easily dissolved phases of metals in the sediments followed the order of Ni > Cr > Cd > Pb > Fe > Mn. The toxicity as indicated by toxic unit (TU) due to an individual metal followed a descending order of Ni > Cr > Pb > Cd, indicating that Ni and Cr accounted for the majority of the overall sediment toxicity while, Cd contributed the least to the ΣTU. This work constitutes a good basis for further studies about metal fractionation in El Temsah Lake which might help policy makers to take effective decisions for proper management of the lake.

Geographical variation of arsenic distribution in paddy soil, rice and rice-based products: A meta-analytic approach and implications to human health

Arsenic is considered as ubiquitous toxic element belonging to the highest health hazard category. Wide ranges of natural as well as anthropogenic activities are subject to create global arsenic distribution in the broad sense. Rice is the major staple food consumed by world's population on the maximum scale. Growing environment of rice typically attributed by geographical origin may influence on arsenic bioavailability in rice grain. Over exploitation of arsenic contaminated, groundwater resources have recognised as major concern in agricultural perspective for rice production. On the other hand, biogeochemical weathering of arsenic bearing rocks as the geogenic origin, mining activities and application arsenical pesticides are recognised to be well known factors responsible to increase the soil arsenic level. Transfer of arsenic into rice is rightly acquainted from these possible sources of contamination in different regions around the world. Consequently, such substantial geographical variation reflects bioavailability as well as speciation of arsenic in rice. In this manuscript, we discuss the contribution of different arsenic entering pathways in soil-rice systems from regional variability. Furthermore, we attempted to apply the meta-analysis in order to predict the comparative risk assessment on distribution pattern of total and inorganic arsenic in rice commercialised from various rice producing regions of Asia, Europe and US by considering a selected number of data set an extensive range of market basket and field survey. In addition, we finally focus on health risk assessment associated by the consumption of rice and rice-based infant products as the dietary intake from the different of origin. Furthermore, we must detect and categorize the possible source of contamination, which may critically enhance the bioavailability of arsenic in rice in order to minimize the risk. These are the major aspects reviewed here.

Prospect of phytoaccumulation of arsenic by Brassica juncea (L.) in Bangladesh

The phytoaccummulation of arsenic by Brassica juncea (L.) was investigated for varying concentrations selected within the range that is evident in Bangladeshi soil. B. juncea (Rai and BARI-11) was grown in the hydroponic media under greenhouse condition with different concentrations (0.5, 1.0, 15, 30, 50 and 100 ppm) of sodium arsenite. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to analyze the data. Mapping of potential area of phytoaccumulation of arsenic by B. juncea was done using Geographic information system (GIS). Arsenic was detected at lower concentrations (0.5 and 1.0 ppm) only at root system of the plant. For higher concentrations (15, 30, and 50 ppm) arsenic was detected both in the root and shoot systems. The results suggested that at 15 and 50 ppm uptake was higher compared to 30 ppm. For 100 ppm of arsenic no plant growth was observed. In Bangladesh, where concentration of arsenic is at lower level and present only at rooting zone, B. juncea may be used for phytoaccumulation of arsenic keeping usual agronomic practices. However, for higher concentrations, B. juncea can be regarded as a good accumulator of arsenic where uptake of arsenic was up to 1% of total biomass of the plant.

Arsenic in Bangladeshi soils related to physiographic region, paddy management, and mirco- and macro-elemental status

While the impact of arsenic in irrigated agriculture has become a major environmental concern in Bangladesh, to date there is still a limited understanding of arsenic in Bangladeshi paddy soils at a landscape level. A soil survey was conducted across ten different physiographic regions of Bangladesh, which encompassed six types of geomorphology (Bil, Brahmaputra floodplain, Ganges floodplain, Meghna floodplain, Karatoya-Bangali floodplain and Pleistocene terrace). A total of 1209 paddy soils and 235 matched non-paddy soils were collected. The source of irrigation water (groundwater and surface water) was also recorded. The concentrations of arsenic and sixteen other elements were determined in the soil samples. The concentration of arsenic was higher in paddy soils compared to non-paddy soils, with soils irrigated with groundwater being higher in arsenic than those irrigated with surface water. There was a clear difference between the Holocene floodplains and the Pleistocene terraces, with Holocene floodplain soils being higher in arsenic and other elements. The results suggest that arsenic is most likely associated with less well weathered/leached soils, suggesting it is either due to the geological newness of Holocene sediments or differences between the sources of sediments, which gives rise to the arsenic problems in Bangladeshi soils.

Total As and As Speciation in Italian Rice as Related to Producing Areas and Paddy Soils Properties

Rice and rice-based foodstuffs are important pathways for inorganic As dietary intake. This work shows a detailed picture of As content and speciation in Italian rice, which contributes to more than one-half of the European production, and addresses the role of soil chemistry and agronomic management on As concentration in rice grain, in view of ameliorative strategies. The mean total As content in Italian white rice was 155 ± 65 μg kg^-1 with significant differences among producing areas, while the mean inorganic As was 102 ± 26 μg kg^-1, largely below the E.U. limit of 200 μg kg^-1 for white rice, although part of the production would not be suitable for baby food production, which requires less than 100 μg kg^-1 of inorganic As. The differences in As content and speciation in rice among the studied areas resulted from the complex interactions of soil, plant, and anthropic factors. Among others, Si nutrition seemed to play a key role in regulating As transfer from soil to plant.

Relation between various soil phosphorus extraction methods and sorption parameters in calcareous soils with different texture

The aim of this study was to investigate the influence of soil texture on phosphorus (P) extractability and sorption from a wide range of calcareous soils across Hamedan, western Iran. Fifty seven soil samples were selected and partitioned into five types on the basis of soil texture (clay, sandy, sandy clay loam, sandy loam and mixed loam) and the P extracted with calcium chloride (PCaCl2), citrate (Pcitrate), HCl (PHCl), Olsen (POls), and Mehlich-3 (PM3) solutions. On the average, the P extracted was in the order PHCl>PM3>Pcitrate>POls>PCaCl2. The P extracted by Pcitrate, PHCl, POls, and PM3 methods were significantly higher in sandy, sandy clay loam and sandy loam textures than clay and mixed loam textures, while soil phosphorus buffer capacity (PBC) was significantly higher in clay and mixed loam soil textures. The correlation analysis revealed a significant positive relationship between silt content Freundlich sorption coefficient (KF), maximum P sorption (Qmax), linear distribution coefficient (Kd), and PBC. All extractions were highly correlated with each other and among soil components with silt content. The principal component analysis (PCA) performed on data identified five principal components describing 74.5% of total variation. The results point to soil texture as an important factor and that silt was the crucial soil property associated with P sorption and its extractability in these calcareous soils. DPSM3-2 (PM3PM3+Qmax×100) and DPScitrate (PcitratePcitrate+Qmax×100) proved to be good indicators of soil's potential P release in these calcareous soils. Among the DPS, 21% of soils reported DPSM3-2, values higher than the environmental threshold, indicating build-up of P and P release. Most of the studied sandy clay loam soils had exceeded the environmentally unacceptable P concentration. Various management practices should be taken into account to reduce P losses from these soils. Further inorganic and organic P fertilizer inputs should be reduced in some parts of studied area.