Considered the king of poisons, arsenic occurs naturally in the environment being present in air, soil, water and food. Its presence in drinking water is of global concern. Initial chronic exposure is manifested by skin lesions. Additionally, arsenic consumption impairs certain visceral organs: bladder, liver, prostate, etc. More over, arsenic is a recognized carcinogenic substance.When in Bangladesh started the program to lead safe drinking water in the 60’s, they never imagined the catastrophic consequences. Water wells were drilled in the whole country. The arsenic problem was recognized recently in the 90’s.  In order to understand the nature of arsenic  in the environment and how it could possibly reach groundwater in Bangladesh, this work explains some chemical characteristics of arsenic, the geological formation of the basin, and its mobility.The origin of arsenic contamination in the Bangladesh Delta is due to the geologic nature of the basin rather than the possibility of an arsenic rich mineral. The profile of sediments shows that the Delta is not homogeneous, but rather heterogeneous even in closer areas. The driving process for arsenic mobility is mainly the reduction by iron oxyhydroxides coupled with organic matter, including other factors such as particle size, depth, morphology, metal content, as well

Arsenic (As) concentrations in groundwater that exceed the Maximum Contaminant Level (MCL) (10 μg/L) for drinking water have been reported throughout the United States, with higher occurrences in the Southwestern basin-fill aquifers. Levels of As above the MCL were measured in wells throughout the Cache Valley Basin, Utah. The As is naturally occurring in geologic material from the soil surface to depths of groundwater. This study reports on the mechanisms of retention and solubilization of As through these zones using geochemical modeling and microcosm studies. Two cores (NP 9 and NP 13) were collected from the soil surface to the depth of groundwater and sectioned based on observed redoximorphic features. Pore water was analyzed for As and iron( Fe) redox species, general water quality parameters and solid phase As, Fe and Mn using sequential extractions. These data were used in PHREEQC and MINTEQ geochemical models to predict mechanisms of As retention. Microcosm studies were performed using sediments from the water table zone. The sediments were exposed to oxidized, reduced, and poisoned conditions over time to evaluate the effect of the seasonal fluctuating water table on As release. Modeling results indicated As(V) was dominantly sorbed to hydrous ferric oxides (HFO) throughout both profiles. Although much less As(V) was sorbed to CaCO3, the percentage associated with calcite was 1.7 to 3.3% and 6 to 59% in the surface and water table zones for NP 9 and NP 13, respectively. As(III) solubility was controlled by the formation of an As-S mineral, orpiment. Microcosm findings, over 113-day incubation, concluded that regardless of treatment condition, As is released. For reduced samples As in solution was primarily As(III), while oxidized and poisoned samples only released As(V). The release of As under every condition, and the lack of reduced As and Fe in the poisoned samples, indicates that As release is abiotically controlled, while reduction is microbially driven. Carbonate minerals were the source of As(V) under treatment conditions as determined using an acetate extraction. Desorption of As(V) from carbonate minerals and the reduction of As(V) to As(III) played a significant role in explaining solution phase As(III) concentrations.

Arsenik är en naturligt förekommande halvmetall som orsakar stora hälsoproblem genom exponering t.ex. via dricksvatten. På grund av arseniks negativa effekter på människors hälsa sänktes den tillåtna gränsen i dricksvatten från 50 μg/l till 10 μg/l 2003 av WHO. Arsenik förekommer i huvudsak i två oorganiska former, arsenat (AsO43-) och arsenit (AsO33-), där arsenit är en betydligt mer mobil och toxisk form. Vilken form som dominerar påverkas i första hand av redoxförhållanden men även av pH. Reduktion från arsenat till arsenit är gynnsamma vid lägre pH och vid syrefria (reducerade) förhållanden. I Sverige har tidigare användning av arsenik, t.ex. vid impregneringsanläggningar, orsakat föroreningar som än idag ligger kvar. I Hjältevad i Eksjö kommun drev Televerket under 1940- till 1980-talet en impregneringsanläggning för telefonstolpar. Impregneringsvätska, innehållande bland annat arsenik, kunde spridas inom området till största del på grund av en tank som började läcka under 1960-talet. En omfattande sanering med jordtvätt genomfördes 1997. Senare kontroller har dock påvisat stadigt ökade halter. Med anledning av de ökade halterna har ett arbete inletts för att kartlägga föroreningssituationen. Syftet med examensarbetet är att utvärdera grundvattenkemin i Hjältevad genom att visualisera föroreningsföroreningsplymen, undersöka mobiliteten genom att undersöka samband mellan halten arsenik och kemiska parametrar samt göra en fördjupad analys av spridningsrisken med hjälp av Kd-värden. Data från jord- och grundvattenprovtagningar genomförda under augusti och september 2017 bearbetades med hjälp av ArcMap och Excel. Resultatet visade att låga redoxförhållanden sannolikt har bidragit till ökad spridning av arsenik vilket till stor del förekom i den reducerade formen arsenit. De högsta halterna var koncentrerade till området kring den f.d. läckande tanken, där halter så höga som 2200 μg/l kunde uppmätas i grundvattnet. Vidare visade provtagningsresultaten att mängden förorenad jord missbedömdes vid saneringen 1997 (halter på 238 mg/kg kunde uppmätas i jorden). Slutsatsen drogs att redoxförhållanden inom området är gynnsamma för att arsenik ska förekomma i den reducerade formen arsenit, att arseniks mobilitet med stor sannolikhet är betydligt högre än vad som tidigare bedömdes samt att risker föreligger om inga åtgärder vidtas. / Arsenic is a naturally occurring metalloid that causes major health problems for people affected by exposure, e.g. through their drinking water. Due to the negative effects on human health, the permissible concentration in drinking water was lowered in 2003, from 50 μg/l to 10 μg/l. Arsenic predominantly exists in two inorganic forms, arsenate (AsO43-) and arsenite (AsO33-), where arsenite is a more mobile and toxic. Which forms that dominates is controlled by pH and redox potential. Reduction from arsenate to arsenite is favorable at lower pH and at anoxic (reduced) conditions. In Sweden previous use of arsenic, e.g. at impregnation plants, caused pollution still affecting soils and groundwater. In Hjältevad, Eksjö municipality, an impregnation plant for telephone poles was run by Televerket during the 1940s to 1980s. Impregnating fluid, including arsenic, was spread in the area, mainly due a leaky storage tank during the 1960s. The site was remediated in 1997 using soil washing. However, monitoring program demonstrated steadily increased levels in a well situated downstream the contaminated area. Due to the increased contamination levels of arsenic in the ground water, a detailed investigation was initiated to identify the pollution situation. The main objective was to investigate about the chemical and physical processes affecting the mobilization of arsenic. Groundwater and soil materials were sampled from the area and evaluated using ArcMap and Excel. In support of this evaluation, distribution coefficients (Kd) for soil materials from the aqvifer were obtained by leaching tests performed at oxidized conditions. The result showed that reducing conditions in the aquifer appeared to have caused increased mobilization of arsenic in the area and that large amounts of pollution was not removed at the remediation in 1997 (levels of 238 mg/kg arsenic could be detected in the soil). In the collected samples, arsenic mainly occurred in the reduced form arsenite. The highest levels in the groundwater were found in the area around the former leaky tank, where concentrations up to 2200 μg/l was measured. The conclusion was that large amounts of pollution was not removed at the remediation in 1997, and that arsenic mobility seems to be significantly higher than previously assessed and that action needs to be taken to stop the spread.