Neutron activation analysis of wheat samples.

The deficiency of essential micronutrients and excess of toxic metals in cereals, an important food items for human nutrition, can cause public health risk. Therefore, before their consumption and adoption of soil supplementation, concentrations of essential micronutrients and metals in cereals should be monitored. This study collected soil and two varieties of wheat samples-Triticum aestivum L. (Jordão/bread wheat), and Triticum durum L. (Marialva/durum wheat) from Elvas area, Portugal and analyzed concentrations of As, Cr, Co, Fe, K, Na, Rb and Zn using Instrumental Neutron Activation Analysis (INAA) to focus on the risk of adverse public health issues. The low variability and moderate concentrations of metals in soils indicated a lower significant effect of environmental input on metal concentrations in agricultural soils. The Cr and Fe concentrations in soils that ranged from 93-117 and 26,400-31,300mg/kg, respectively, were relatively high, but Zn concentration was very low (below detection limit <22mg/kg) indicating that soils should be supplemented with Zn during cultivation. The concentrations of metals in roots and straw of both varieties of wheat decreased in the order of K>Fe>Na>Zn>Cr>Rb>As>Co. Concentrations of As, Co and Cr in root, straw and spike of both varieties were higher than the permissible limits with exception of a few samples. The concentrations of Zn in root, straw and spike were relatively low (4-30mg/kg) indicating the deficiency of an essential micronutrient Zn in wheat cultivated in Portugal. The elemental transfer from soil to plant decreases with increasing growth of the plant. The concentrations of various metals in different parts of wheat followed the order: Root>Straw>Spike. A few root, straw and spike samples showed enrichment of metals, but the majority of the samples showed no enrichment. Potassium is enriched in all samples of root, straw and spike for both varieties of wheat. Relatively to the seed used for cultivation, Jordão presented higher transfer coefficients than Marialva, in particular for Co, Fe, and Na. The Jordão and Marialva cultivars accumulated not statistically significant different concentrations of different metals. The advantages of using INAA are the multielementality, low detection limits and use of solid samples (no need of digestion).

Impact of irrigation with arsenic-rich groundwater on soils and crops.

The study was carried out in an intensively cultivated agricultural area of central Spain where high arsenic (As) concentrations in groundwater were previously reported. The concentrations and distribution of As in soils and crops (wheat, potato, sugar beet and carrot) were determined to know the effect of irrigation with As-rich groundwater in the agricultural fields, and to estimate its impact on the food chain contamination. Irrigation water shows high As concentrations ranging between 38 and 136 microg/l. Total As contents in the studied agricultural soils are higher than 10 mg/kg exceeding the As content in two control areas and the results of this study reflect that irrigation with As-rich groundwater led to the elevated As levels in the agricultural soils. Total As concentration in soils of a sugar beet plot (36 mg/kg) is higher than that found in soils of the less intensively watered field (11 mg/kg), and more than 3.5 times higher than that in the soils of the control area irrigated with uncontaminated water (<10 mg/kg). Water soluble As in soils ranges between 0.03 and 0.9 mg/kg exceeding the limit of 0.04 mg/kg for agricultural use and shows a significant correlation with total As and organic matter (OM) content in soils. Arsenic contents in potato tuber samples are 35 times higher than that measured in potato tuber of uncontaminated control sites (0.03 mg/kg). Elevated As contents (3.9-5.4 mg/kg DW) were also found in root samples of sugar beet. The As contents in vegetable samples are higher than As content (0.1 mg/kg DW) in plants of uncontaminated control areas, and the limits for foodstuffs (0.5-1 mg/kg DW) set by legislation of many countries reflecting the risk of food chain contamination by As in this study area.

Evaluation of various chemical extraction methods to estimate plant-available arsenic in mine soils.

Elevated levels of bioavailable As in mining soils, agricultural areas and human habitats may cause potential toxicity to human health, plants and microbe. Therefore, it is essential to determine proper soil chemical extraction method in order to estimate plant-available As in mining soils and protect agricultural and environmental ecosystems by evaluation of environmental risk and implementation of remediation measures. In this study, six single soil chemical extraction processes and four-step sequential chemical extraction protocol were used to determine the relative distribution of As in different chemical forms of soils and their correlations with total As in plants grown in mining areas and greenhouse experiments. The strongest relationship between As determined by single soil chemical extraction and As in plant biomass was found for sodium acetate and mixed acid extractant. The mean percent of total As extracted was: ammonium oxalate (41%)>hydroxylamine hydrochloride (32%)>mixed acid (16%)>phosphate (6%)>sodium acetate (1.2%)>water (0.13%). This trend suggests that most of the As in these soils is inside the soil mineral matrix and can only be released when iron oxides and other minerals are dissolved by the stronger chemical extractant. Single soil chemical extraction methods using sodium acetate and mixed acids, that extract As fractions complexed to soil particles or on the surface of mineral matrix of hydrous oxides of Fe, Mn and Al (exchangeable+sorbed forms) can be employed to estimate and predict the bioavailable As fraction for plant uptake in mining affected soils. In sequential chemical extraction methods, ammonium nitrate and hydroxylamine hydrochloride may be used to provide closer estimates of plant-available As in mining soils.

Mobilization of arsenic in groundwater of Bangladesh: evidence from an incubation study.

The extensive extraction of arsenic (As)-contaminated groundwaters for drinking, household and agricultural purposes represents a serious health concern in many districts of Bangladesh. This laboratory-based incubation study investigated the sources and mechanisms of As mobilization in these groundwaters. Several incubation studies were carried out using sediments collected from the Bangladesh aquifer that were supplemented, or not, with different nutrients, followed by an analysis of the sediment suspensions for pH, ORP (oxidation-reduction potential), EC (electrical conductivity) and As and Fe(II) concentrations. In the substrate-amended sediment suspensions incubated under anaerobic environment, there was a mobilization of As (maximum: 50-67 microg/l) and Fe(II) (maximum: 182 microg/l), while the ORP value decreased immediately and drastically (as much as -468 mV to -560 mV) within 5-6 days. In the sediment suspensions incubated under control and aerobic conditions, no significant As mobilization occurred. The simultaneous mobilization of As and Fe(II) from sediments is a strong indication that their mobilization resulted from the reduction of Fe oxyhydroxide by the enhanced activity of indigenous bacteria present in the sediments; this phenomenon also provides insights on the mobilization mechanism of As in groundwater. The concentrations of As in the sediments used in the incubation studies were strongly linked to the gradients of redox potential development that was stimulated by the quantity of organic nutrient (glucose) used. The penetration of surface-derived organic matter into the shallow aquifer may stimulate the activity of microbial communities, thereby leading to a reduction of iron oxyhydroxide and As release.

Arsenic pollution in groundwater: a self-organizing complex geochemical process in the deltaic sedimentary environment, Bangladesh.

The presence of considerable concentrations of As (Sonargon: below detection limit (bdl)-1.46 mg/l; Faridpur: bdl-1.66 mg/l) and some other elements (like B, F, U) in groundwater of the Ganges-Meghna-Brahmaputra (G-M-B) rivers flood plain indicate that several millions of people are consuming contaminated water. Conditions regulating the mobilization and diagenetic behavior of arsenic in sediments are not well characterized, although understanding these conditions is essential in order to predict the modes of transfer of this contaminant from sediments to groundwater. Analyses of vertical profiles of total arsenic and iron as well as easily soluble As and reducible (reactive) iron concentrations in sediments of the Ganges and Meghna flood plains show no arsenic-enriched layer up to 36-m depth. However, arsenic content in sediments is relatively higher than mean crustal concentration, showing some peaks (Sonargaon: 27.9 mg/kg; 3 m, 31.5 mg/kg; 9 m, 27.30 mg/kg; 16 m, 37.70 mg/kg; 29.5 m, Faridpur: 19.80 mg/kg; 6 m, 26.60 mg/kg; 14.5 m, 29.40 mg/kg; 25 m) depending on the periodical differences in sedimentary cycling of arsenic, metal (hydr)oxides and organic matter. Seasonal changes have no clear or consistent effect on the groundwater arsenic concentrations; with the exception of a small-scale localized irregular change (10-16%). However, easily reducible metal oxides and hydroxides were significant factors affecting the retention of arsenic by sediments during leaching. The biogeochemical cycling of arsenic and iron is closely coupled in deltaic systems where iron oxy-hydroxides provide a carrier phase for the deposition of arsenic in sediments. Analytical results of mimic leaching experiments strongly supported the reduction (Fe oxy-hydroxides) mechanism for arsenic mobilization in alluvial aquifer of deltaic sedimentary environment of G-M-B rivers flood plain.

Arsenic poisoning in groundwater: health risk and geochemical sources in Bangladesh.

Of the 2508 water samples analyzed in 10 districts of Bangladesh, 51%, on an average, contained arsenic levels of 0.05 to 2.50 mg/l. 95% of nail, 96% of hair, and 94% of urine samples contained arsenic above the normal level. Approximately 3.58 million people out of a total of 17.92 million who are drinking water containing arsenic levels >0.20 mg/l are potentially exposed to high risk of health hazard. Eight thousand and five hundred arsenic patients are identified; they are suffering from various skin lesions, gangrene in leg, skin, lung, bladder, liver, and renal cancer. A big portion of the total population is highly vulnerable to various internal cancers. Lowest arsenic concentration in drinking water producing dermatological disease is found to be 0.103 mg/l. However, the exposure time to develop arsenicosis varies from case to case reflecting its dependence on arsenic level in drinking water and food, nutritional status, genetic variant of human being, and compounding factors. This study has determined the high intensity of fluorescent humic substances in drinking water containing elevated concentrations of arsenic and very low concentrations of heavy metals. The synergistic/antagonistic effect of fluorescent compounds present in drinking water may aggravate the toxicity of arsenic. Geochemical study suggests that arsenic may be released from both reductive dissolution of Fe and Mn (oxy)hydroxide and microbial oxidation of organic matter.