Inorganic arsenic in cooked rice and vegetables from Bangladeshi households

Many Bangladeshi suffer from arsenic-related health concerns. Most mitigation activities focus on identifying contaminated wells and reducing the amount of arsenic ingested from well water. Food as a source of arsenic exposure has been recently documented. The objectives of this study were to measure the main types of arsenic in commonly consumed foods in Bangladesh and estimate the average daily intake (ADI) of arsenic from food and water. Total, organic and inorganic, arsenic were measured in drinking water and in cooked rice and vegetables from Bangladeshi households. The mean total arsenic level in 46 rice samples was 358 microg/kg (range: 46 to 1,110 microg/kg dry weight) and 333 microg/kg (range: 19 to 2,334 microg/kg dry weight) in 39 vegetable samples. Inorganic arsenic calculated as arsenite and arsenate made up 87% of the total arsenic measured in rice, and 96% of the total arsenic in vegetables. Total arsenic in water ranged from 200 to 500 microg/L. Using individual, self-reported data on daily consumption of rice and drinking water the total arsenic ADI was 1,176 microg (range: 419 to 2,053 microg), 14% attributable to inorganic arsenic in cooked rice. The ADI is a conservative estimate; vegetable arsenic was not included due to limitations in self-reported daily consumption amounts. Given the arsenic levels measured in food and water and consumption of these items, cooked rice and vegetables are a substantial exposure pathway for inorganic arsenic. Intervention strategies must consider all sources of dietary arsenic intake.     

Role of Fe(II), phosphate, silicate, sulfate, and carbonate in arsenic uptake by coprecipitation in synthetic and natural groundwater

Competitive effects of phosphate, silicate, sulfate, and carbonate on As(III) and As(V) removal at pH approximately 7.2 have been investigated to test the feasibility of Fe(II)(aq) and hydroxylapatite crystals as inexpensive and potentially efficient agents for remediation of contaminated well-water, using Bangladesh as a type study. Arsenic(III) removal approximately 50-55% is achieved, when Fe(II)(aq) oxidizes to Fe(III) and precipitates as Fe(OH)3 at 25 degrees C and 3h reaction time, in the presence of all the oxyanion. Similar results were obtained for well-water samples from two sites in Bangladesh. Heating at 95 degrees C for 24h results in 70% As(III) uptake due to precipitation of magnesian calcite. A two-step process, Fe(II) oxidation and Fe(OH)3 precipitation at 25 degrees C for 2h, followed by magnesian calcite precipitation at 95 degrees C for 3h, yields approximately 65% arsenic removal while reducing the expensive heating period. In the absence of silicate, up to 70% As(III) uptake occurs at 25 degrees C. In all cases, As(III) was oxidized to As(V) in solution by dissolved oxygen and the reaction rate was probably promoted by intermediates formed during Fe(II) oxidation. Iron-catalyzed oxidation of As(III) by oxygen and hydrogen peroxide is pH-dependent with formation of oxidants in the Fenton reaction. Buffering pH at near-neutral values by dissolved carbonate and hydroxylapatite seeds is important for faster Fe(II) oxidation kinetics ensuring rapid coprecipitation of As as As(V) in the ferric phases.     

Bioremoval of arsenic species from contaminated waters by sulphate-reducing bacteria

A mixed culture of sulphate-reducing bacteria was used to study the bioremoval of arsenic species (As(III) or As(V)) from groundwater. During growth of a mixed SRB culture adapted to 0.1 mg/L arsenic species through repeated sub-culturing, 1 mg/L of either As(III) or As(V) was reduced to 0.3 and 0.13 mg/L respectively. Sorption experiments on the precipitate produced by batch cultured sulphate-reducing bacteria (SRB-PP) indicated a removal of about 77 and 55% of As(V) and As(III) respectively under the following conditions: pH 6.9; biomass (2 g/L); 24 h contact time; initial arsenic concentration, 1 mg/L of either species. These results were compared with synthetic iron sulphide as adsorbent. The adsorption data were fitted to Langmuir and Freundlich isotherms. Energy dispersive X-ray analysis showed the SRB-PP contained elements such as sulphur, iron, calcium and phosphorus. Biosorption studies indicated that SRB cell pellets removed about 6.6% of the As(III) and 10.5% of the As(V) from water containing an initial concentration of 1 mg/L of either arsenic species after 24 h contact.