Drinking-water Quality (World Health Organization 2004), sets up the recommendation for a provisional
guideline value of 10 lg l-1. This value coincides with other standards such as that set up by EPA (Environmental
Protection Agency 2001) and several regulatory bodies throughout the world. However, values as
high as 20 lg l-1 (Instituto Uruguayo de Normas Te´cnicas 2008) can still be found in some countries.
For drinking water sources, such as river or groundwater, the maximum values set up are often lower (10 lg l-1).
Selenium on the other hand is now known as necessary for life. It occurs in all environments unevenly distributed throughout the planet; in some places, selenium concentrations in soil are so low that
consumption of vegetables by animals or humans cannot guarantee the recommended daily intake of
selenium. In other areas, it can be found at high levels, for example, in soils in very dry zones of USA where there
are plants with high concentrations of selenium (Fordyce 2005). In the 1950s, the essentiality of selenium in animals and humans was revealed with the discovery of its ability to prevent the Keshan disease, first described in
1935 in the Chinese province of that name. This population showed symptoms attributed to selenium deficiency: different degrees of heart disease or cardiac deficiencies; myocardial histology showed degeneration and necrosis of ultrastructure of muscle fibers. Selenium is an essential component of enzymes
such as glutathione peroxidase that is found in human tissues (Flynn and Cashman 1997).
Subsequently, its important role as part of the body’s antioxidant mechanisms and the role in
protecting the body against heavy metals as well as its importance in the immune system were discovered (Tiglea and Mello De Capitani 2003; Fordyce 2005). Related to the latter, the patients with AIDS show evidence of selenium deficiency, such as a marked decrease in the activity of glutathione peroxidase. RDA (Recommended Dietary Allowance) accepted value in the USA ranges from 20 lg/day for children under 3 years of age up to 55 lg/day for adults. These values can be increased to 60 lg/day for pregnant women and 70 lg/day during lactation (Flynn and Cashman 1997). These nutritional requirements should
be satisfied by food and water ingested by the individual. Selenium has one of the narrowest ranges between
dietary deficiency and toxic levels, so control in the intake of selenium by humans and other animals is
imperative (Fordyce 2005). The WHO guideline value for selenium in drinking water is 10 lg l-1 (World
Health Organization 2004).
In Uruguay, the government promotes the monitoring of some trace elements in waters through
different programs involving surface and groundwater as well as drinking water. The increasing interest in these trace elements has expanded the need for reliable data, which puts considerable pressure on environmental analytical laboratories. This has triggered research for new and
improved automated analytical methods for the determination of ultra-trace levels of arsenic and selenium
in water samples. These methods should not only be reliable but also fast and environmentally friendly.
Total arsenic and selenium at the trace and ultratrace levels are determined by atomic absorption
spectrometry (AAS) and atomic fluorescence spectrometry (AFS) (Standard Methods, APHA 1998;
Welz and Sperling 1999). For AAS determinations, electrothermal atomization can be used (Aleixo and
No´brega 2003; Paiva Oliveira et al. 2005; Hung et al. 2004; Michon et al. 2007). However, the use of
hydride generation (HG) (Dedina and Tsalev 1995) is preferable since it provides separation of the analyte
from the matrix which in turn reduces the effects of a number of interferences. Hydride generation can be
coupled to atomic absorption (HG-AAS) or to atomic fluorescence (HG-AFS) spectrometric detection. The
latter provides lower detection limits at the cost of more expensive instrumentation. Hydride generation can be automated employing different flow techniques such as flow injection
analysis (FIA) (Zhang and Adeloju 2008; Li et al. 2009) or sequential injection analysis (SIA) (Semenova et al. 2000). Multicommutated flow analysis (MCFA) is an emerging flow technique based on flow
networks built around solenoid valves which can becommutated independently under computer control in order to perform specific tasks (Reis et al. 1994; Rocha et al. 2002; Catala´ Icardo et al. 2002; Feres et al.
2008). This technique has proven to be very flexible since several modifications can be carried out simply
by changing parameters in the control software. For instance, the sample volume can be easily changed
by modifying the time a given solenoid valve is 274 Environ Geochem Health (2012) 34:273–278 123
Drinking-water Quality (World Health Organization 2004), sets up the recommendation for a provisional
guideline value of 10 lg l-1. This value coincides with other standards such as that set up by EPA (Environmental
Protection Agency 2001) and several regulatory bodies throughout the world. However, values as
high as 20 lg l-1 (Instituto Uruguayo de Normas Te´cnicas 2008) can still be found in some countries.
For drinking water sources, such as river or groundwater, the maximum values set up are often lower (10 lg l-1).
Selenium on the other hand is now known as necessary for life. It occurs in all environments unevenly distributed throughout the planet; in some places, selenium concentrations in soil are so low that
consumption of vegetables by animals or humans cannot guarantee the recommended daily intake of
selenium. In other areas, it can be found at high levels, for example, in soils in very dry zones of USA where there
are plants with high concentrations of selenium (Fordyce 2005). In the 1950s, the essentiality of selenium in animals and humans was revealed with the discovery of its ability to prevent the Keshan disease, first described in
1935 in the Chinese province of that name. This population showed symptoms attributed to selenium deficiency: different degrees of heart disease or cardiac deficiencies; myocardial histology showed degeneration and necrosis of ultrastructure of muscle fibers. Selenium is an essential component of enzymes
such as glutathione peroxidase that is found in human tissues (Flynn and Cashman 1997).
Subsequently, its important role as part of the body’s antioxidant mechanisms and the role in
protecting the body against heavy metals as well as its importance in the immune system were discovered (Tiglea and Mello De Capitani 2003; Fordyce 2005). Related to the latter, the patients with AIDS show evidence of selenium deficiency, such as a marked decrease in the activity of glutathione peroxidase. RDA (Recommended Dietary Allowance) accepted value in the USA ranges from 20 lg/day for children under 3 years of age up to 55 lg/day for adults. These values can be increased to 60 lg/day for pregnant women and 70 lg/day during lactation (Flynn and Cashman 1997). These nutritional requirements should
be satisfied by food and water ingested by the individual. Selenium has one of the narrowest ranges between
dietary deficiency and toxic levels, so control in the intake of selenium by humans and other animals is
imperative (Fordyce 2005). The WHO guideline value for selenium in drinking water is 10 lg l-1 (World
Health Organization 2004).
In Uruguay, the government promotes the monitoring of some trace elements in waters through
different programs involving surface and groundwater as well as drinking water. The increasing interest in these trace elements has expanded the need for reliable data, which puts considerable pressure on environmental analytical laboratories. This has triggered research for new and
improved automated analytical methods for the determination of ultra-trace levels of arsenic and selenium
in water samples. These methods should not only be reliable but also fast and environmentally friendly.
Total arsenic and selenium at the trace and ultratrace levels are determined by atomic absorption
spectrometry (AAS) and atomic fluorescence spectrometry (AFS) (Standard Methods, APHA 1998;
Welz and Sperling 1999). For AAS determinations, electrothermal atomization can be used (Aleixo and
No´brega 2003; Paiva Oliveira et al. 2005; Hung et al. 2004; Michon et al. 2007). However, the use of
hydride generation (HG) (Dedina and Tsalev 1995) is preferable since it provides separation of the analyte
from the matrix which in turn reduces the effects of a number of interferences. Hydride generation can be
coupled to atomic absorption (HG-AAS) or to atomic fluorescence (HG-AFS) spectrometric detection. The
latter provides lower detection limits at the cost of more expensive instrumentation. Hydride generation can be automated employing different flow techniques such as flow injection
analysis (FIA) (Zhang and Adeloju 2008; Li et al. 2009) or sequential injection analysis (SIA) (Semenova et al. 2000). Multicommutated flow analysis (MCFA) is an emerging flow technique based on flow
networks built around solenoid valves which can becommutated independently under computer control in order to perform specific tasks (Reis et al. 1994; Rocha et al. 2002; Catala´ Icardo et al. 2002; Feres et al.
2008). This technique has proven to be very flexible since several modifications can be carried out simply
by changing parameters in the control software. For instance, the sample volume can be easily changed
by modifying the time a given solenoid valve is 274 Environ Geochem Health (2012) 34:273–278 123
การแปล กรุณารอสักครู่..