https://doi.org/10.15255/KUI.2001.047
Published: Kem. Ind. 51 (7-8) (2002) KUI-47/2001
Paper reference number: KUI-47/2001
Paper type: Review
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Arsenic in Drinking Water

M. Habuda-Stanić and M. Kuleš+

Abstract

Toxicity and carcinogenicity of arsenic is well known in recent decades. The latest researches show connection between arsenic in drinking water and occurrence of skin cancer, cancer of lungs and other internal organs. Ground waters in eastern Croatia are enriched with iron, manganese, ammonia and organic matter andas consequence of soil contamination, arsenic is a usual contaminant of these waters. At the beginning of the year 2000 the samples taken from waterworks in twelve cities in eastern Croatia were examined regarding arsenic content and organic matter (COD value). The results shown increased concentrations of arsenic and organic matter (Fig. 1). Some values exceed the national standard for drinking water which is for arsenic 50 _g L?1 e. g. 10 _g L?1 recommended by The World Health Organization. Arsenic can occur in the environment in several oxidation states (-3; 0, +3 and +5). In natural waters arsenicusually appears in inorganic forms as oxyanions of trivalent arsenite (As(III)) and pentavalent arsenate(As(V)). Redox potential and pH value are most important factors in controlling arsenic speciation, and arsenic is mostly found as H2AsO4?, HAsO42?; H3AsO42? and H2AsO3? (Table 1). Arsenic toxicity depends on arsenic form. Specially toxic is arsenic (V) which is water soluble, and arsenic(III) which is hard to isolate. Water consumption with high arsenic concentrations leads to absorption of arsenic by human population which is manifested in increased concentration of arsenic in hair, nails and urine and in later phases it can cause inactivation of enzymes, hyperkeratosis, peripheral vascular disease, cancer of skin, lungs andother internal organs. Chronic arsenic poisoning can occur after long-term exposure through drinking-water. Most common methods for arsenic determination in drinking water are: Silver Diethylditiocarbamate Spectrophotometric Method with Sodium Borohydride (trivalent arsenic isreduced by aqueous sodium borohydride solution to arsine AsH3, which is absorbed in silver diethyldithiocarbamateand morpholine solution. Red color develops and the intensity is spectrophotometrically measured at 520 nm. The minimum detectable quantity is 1 _g arsenic L-1); Silver Diethylditiocarbamate Spectrophotometric Method with zinc (after reduction of pentavalent arsenicto the trivalent state and reduction by elementary zinc, arsenite is absorbed in silver diethyldithiocarbamateand chloroform solution. The red-violet complex is formed and spectrophotometrically measured at a wavelength of 510 nm. The minimum detectable quantity is 1 _g arsenic L-1); Atomic Absorption Spectrometric Method (this method is applicable to the determination of arsenic byconversion to its hydrides by sodium borohydride reagent and aspiration into an atomic absorption atomizer of an atomic absorption spectrometer and converted to the gas-phase atoms. Adsorption is measured at a wavelength of 193.7 nm. The minimum detectable quantity is 0.1 _g arsenic L-1). Effective removal of arsenic in drinking water demands oxidation of trivalent in pentavalent arsenicwhich can be provided by free chlorine, hypochlorite, ozone, permanganate and hydrogen peroxide/Fe2+ (Fenton?s reagent). The precipitation-coagulation methods are mostly provided by ferric andaluminum salts (FeCl3 and Al2(SO4)3 x 6H2O). Aluminum salts are less effective than ferric salts at thesame pH value. Typical flow for coagulation and direct filtration plant for arsenic removal is shown atFig. 2. Ferric hydroxide is effective for removal of arsenic (III) and arsenic (V) by optimal pH value without any chemicals. Activated carbon process can also remove a large amount of arsenic in appropriate conditions of pH value, species of active carbon, ferric(II) ions concentration and total concentration of arsenic in water. Ions exchange removes arsenic(V) effectively. With special version of an ion exchanger arsenic(III) can be also removed. Membrane treatment removes arsenic (V) in amount of 95% and arsenic (III) in87% by reverse osmosis, and 40 to 74% of total arsenic by nanofiltration. Typical design of membrane filtrationplant for arsenic removal is shown in Fig. 3. Home-system for water filtration based on reverse osmosis and granulated activated carbon was examined by water taken from the Osijek waterworks system. Results are shown in Fig. 4.

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Keywords

arsenic, toxicology, arsenic determination, arsenic removal, drinking water