Quality of groundwater in eastern Croatia. The problem of arsenic pollution

Groundwater in the area of eastern Croatia contains high concentrations of iron, manganese, ammonia, organic substances and arsenic. The appearance of inorganic arsenic in groundwater is mainly caused by arsenic from natural geological sources. Since the groundwater is the main source of drinking water for the population in this area, almost 200,000 people are daily drinking water with arsenic concentration ranging from 10 to 610 µg/L. The Croatian legislation recently revised the maximum concentration limit (MCL) for arsenic in drinking water to 10 µg/L. The population in the two towns (Osijek and Vinkovci) of this region is supplied with groundwater processed by coagulation-filtration method, but in the other towns and villages water treatment implies only rapid sand filtration. Both methods for water treatment have resulted with higher arsenic concentration than MCL, so the main goal of this study was determination of population exposure to arsenic via drinking water and possible improvement of drinking water quality. Population exposure to arsenic via drinking water is determined with hair analysis, since the hair arsenic concentration is one of three most commonly employed biomarkers used to identify or quantify overall arsenic exposure. During this study the preliminary analyses of hair arsenic concentrations in several towns and villages in eastern Croatia were provided. The positive correlation between heightened arsenic concentration in drinking water and hair arsenic concentration was determined. In order to improve drinking water quality e.g. arsenic removal from contaminated drinking water, different modified adsorbents were used and compared (zeolite–clinoptilolite, manganese greensand and cationic exchange resin). Adsorbents were chemically modified and saturated with Fe(III) ions, while the arsenic solutions were prepared by processed groundwater.

This study confirmed a strong relationship between the arsenic concentration in hair and heightened arsenic concentration in drinking water in the area of eastern Croatia. The existing conventional water treatment based on coagulation and filtration process or rapid sand filtration removes arsenic up to 40 µg/L, which still exceeds the Croatian maximum concentration limit of 10 µg/L. The arsenic concentration in drinking water from some water supply system exceeds 600 µg/L. The investigation of adsorptions characteristics of Fe3+-complexes with zeolite–clinoptilolite and cationic resin showed that the examined material can be used in order to increase the efficiency of arsenic removal from natural arsenic- Table 2 Adsorption of As(III) and As(V) onto different adsorbents saturated with Fe3+-ions: Freundlich and Langmuir isotherms (adsorbent dose: 2.5 g/L; pH: 7.4; temperature 25°C) Adsorbens Modified manganese greensand Modified cationic exchange resin Modified zeolite Freundlich isotherm As(III) K (µg/L) 0.619 n 1.272 R2 0.982 Langmuir isotherm As(III) Xm (µg/g) 228.830 k 0.001 Kxm 0.2745 R2 0.944 As(V) 0.325 1.956 0.817 As(III) 4.863 2.1368 0.841 As(V) 1.556 1.020 0.942 As(III) 5.379 2.5804 0.968 As(V) 4.183 2.843 0.734 As(V) 8.699 0.007 0.062 0.797 As(III) 77.580 0.014 1.096 0.844 As(V) 42.463 0.006 0.243 0.975 As(III) 55.309 0.017 0.927 0.931 As(V) 36.350 0.016 0.589 0.785 ć contaminated water. At the chosen pH value of 7.4, which represents the average pH value of groundwater, the modified zeolite showed the best adsorbent characteristics.