256
element is common and widely distributed in rocks and soil, and thus it is naturally present in groundwater (Hem 1985).
Arsenic is highly undesirable in groundwater. Stable forms in water solution are
arsenate (As
5+
) and arsenite (As
3+
) oxyanions. It may exist in the form of sulfides in
the sulfide ore deposits. Considering the mean values, higher concentrations of As
are present in deep groundwater with a maximum measured concentration of
177 μg/l (Table 8.3). Elevated concentrations of arsenic are frequently found in
groundwater worldwide (Ravenscroft et al. 2009), and the pollution of groundwater
with this toxic element has become a global concern problem. Most of the EU member states have established a threshold value (TV) of 10 μg/l for groundwater bodies. Polluted groundwater has been found in many parts of the world in different
hydrogeological and geochemical conditions. Literature data show that majority of
the arsenic polluted groundwater is mostly affected by natural contamination when
As is released from the natural bedrock of the aquifer (Rosas et al. 1999; Smedley
and Kinniburgh 2002; Smedley et al. 2005; Berg et al. 2001; Polya et al. 2005).
Other sources like mining activities, industry, and the use of arsenic pesticides are
also found as contributors for elevated As concentrations in groundwater (Twarakavi
and Kaluarachchi 2006; Bernard 1983; Grantham and Jones 1977; Smedeley et al.
2007; Komnitsas et al. 1995; Chakraborti et al. 1999; Pandey et al. 2002; Bednar
et al. 2002; Cai et al. 2002; Wiegand 1999). Arsenic-bearing rocks like calcite forms
of limestone, iron oxide minerals, and sodium feldspars are common for the investigated region (Rakicevik and Pendzerkoski 1973). In the Strumica region, almost
35% of investigated groundwater samples showed As concentration greater than
10 μg/l from which 16% have concentration greater than 50 μg/l. There are four
mobilization mechanisms of As in nature: reductive dissolution, alkali desorption,
sulfide oxidation, and geothermal (Ravenscroft et al. 2009). Reducing environment
present in the groundwater of the investigated area; high Fe, Mg, and HCO 3 ; and
low SO 4 and NO 3 content suggest that reductive dissolution is a major mechanism
by which arsenic is released into the groundwater. Arsenic-polluted samples from
the investigated region containing more than 50 mg/l of arsenic are characterized by
low concentrations of SO 4 (med 7.38 mg/l), PO 4 (med 1.08 mg/l), K (med 5.03 mg/l),
Ca (med 42.58 mg/l), Mg (med 9.63 mg/l), Cu (med 0.85 mg/l), Zn (med 21.57 mg/l),
and Pb (med 1.13 mg/l).
Boron concentration in investigated samples ranged from less than 0.5 to 136 μg/l
with a low median value of 6.25 μg/l. It is an essential element for plants but in
higher concentrations may be harmful. Therefore, boron concentrations in groundwater are very important if it is used for irrigation purposes. The most sensitive to
boron are lemon and orange trees and blackberry. The lowest toxic concentrations
cited in the literature data are 0.75 mg/l. Such concentrations were not observed in
the investigated groundwater.
The presence of barium in groundwater can suggest the presence of industrial
waste pollution, saltwater intrusion, mixing of natural saline and brine waters, and
dissolution of Ba-bearing minerals like barite (BaSO 4 ). Barium concentrations in
investigated groundwater ranged between 1.25 and 128 μg/l with a median value of
B. Kovacevik et al.
element is common and widely distributed in rocks and soil, and thus it is naturally present in groundwater (Hem 1985).
Arsenic is highly undesirable in groundwater. Stable forms in water solution are
arsenate (As
5+
) and arsenite (As
3+
) oxyanions. It may exist in the form of sulfides in
the sulfide ore deposits. Considering the mean values, higher concentrations of As
are present in deep groundwater with a maximum measured concentration of
177 μg/l (Table 8.3). Elevated concentrations of arsenic are frequently found in
groundwater worldwide (Ravenscroft et al. 2009), and the pollution of groundwater
with this toxic element has become a global concern problem. Most of the EU member states have established a threshold value (TV) of 10 μg/l for groundwater bodies. Polluted groundwater has been found in many parts of the world in different
hydrogeological and geochemical conditions. Literature data show that majority of
the arsenic polluted groundwater is mostly affected by natural contamination when
As is released from the natural bedrock of the aquifer (Rosas et al. 1999; Smedley
and Kinniburgh 2002; Smedley et al. 2005; Berg et al. 2001; Polya et al. 2005).
Other sources like mining activities, industry, and the use of arsenic pesticides are
also found as contributors for elevated As concentrations in groundwater (Twarakavi
and Kaluarachchi 2006; Bernard 1983; Grantham and Jones 1977; Smedeley et al.
2007; Komnitsas et al. 1995; Chakraborti et al. 1999; Pandey et al. 2002; Bednar
et al. 2002; Cai et al. 2002; Wiegand 1999). Arsenic-bearing rocks like calcite forms
of limestone, iron oxide minerals, and sodium feldspars are common for the investigated region (Rakicevik and Pendzerkoski 1973). In the Strumica region, almost
35% of investigated groundwater samples showed As concentration greater than
10 μg/l from which 16% have concentration greater than 50 μg/l. There are four
mobilization mechanisms of As in nature: reductive dissolution, alkali desorption,
sulfide oxidation, and geothermal (Ravenscroft et al. 2009). Reducing environment
present in the groundwater of the investigated area; high Fe, Mg, and HCO 3 ; and
low SO 4 and NO 3 content suggest that reductive dissolution is a major mechanism
by which arsenic is released into the groundwater. Arsenic-polluted samples from
the investigated region containing more than 50 mg/l of arsenic are characterized by
low concentrations of SO 4 (med 7.38 mg/l), PO 4 (med 1.08 mg/l), K (med 5.03 mg/l),
Ca (med 42.58 mg/l), Mg (med 9.63 mg/l), Cu (med 0.85 mg/l), Zn (med 21.57 mg/l),
and Pb (med 1.13 mg/l).
Boron concentration in investigated samples ranged from less than 0.5 to 136 μg/l
with a low median value of 6.25 μg/l. It is an essential element for plants but in
higher concentrations may be harmful. Therefore, boron concentrations in groundwater are very important if it is used for irrigation purposes. The most sensitive to
boron are lemon and orange trees and blackberry. The lowest toxic concentrations
cited in the literature data are 0.75 mg/l. Such concentrations were not observed in
the investigated groundwater.
The presence of barium in groundwater can suggest the presence of industrial
waste pollution, saltwater intrusion, mixing of natural saline and brine waters, and
dissolution of Ba-bearing minerals like barite (BaSO 4 ). Barium concentrations in
investigated groundwater ranged between 1.25 and 128 μg/l with a median value of
B. Kovacevik et al.