**2. Arsenic in water**

environment and can originate from natural and anthropogenic sources [3]. Natural sources of arsenic are: rocks with incorporated arsenic compounds, activity of volcanoes and some biological processes. Anthropogenic sources are numerous, from mining to different types of production (pesticides, wood preservatives, and pigments). When the arsenic compounds reach groundwater, it is hard to distinguish the origin, both natural and anthropogenic arse-

**Figure 1.** The number of publications with keyword arsenic, according to Science Direct.

According to Science Direct, during the last decade, a significant number of scientific papers reporting the results from arsenic investigations are presented in **Figure 1**. The focus of these researches was the development and improvement of methods for arsenic detection, extrac-

The investigation of arsenic species and their behavior in various samples, especially in natural waters and environment is important for chemistry and environmental protection. The

Depending on the oxido-reduction conditions, microbiological environment, arsenic species can be present in water in solution or in a precipitated form, and they can also adsorb or desorb from the existing precipitates [1, 2]. When arsenic species are soluble in water, they can be present in both inorganic and organic forms. For iAs species both As(III), arsenite, and As(V), arsenate, can be present. For oAs species, MMA and DMA are soluble forms of organic arsenic species. From the value of the chemical equilibrium constants for each molecular or ionic form of arsenic in water, the present species can be recognized [3]. When choosing and

nic species are released [3].

10 Arsenic - Analytical and Toxicological Studies

tion, separation and removal.

most common arsenic species are presented in **Table 1**

Arsenic enters the water through the dissolution of minerals, ores soil, sediments, water, living organisms and rocks containing high concentrations of arsenic. Drinking water from surface water bodies usually does not contain high concentrations of arsenic. Higher concentrations have only been found in the groundwater. Human activities influence and change the content of arsenic in nature. When using arsenic compounds for different purposes, there is a direct influence. There is also indirect influence that affects the mobility of arsenic from different natural sources. Organic arsenic compounds such as AsB, AsC, TETRA, TMAO, arsenosugars and arsenic-containing lipids are mainly found in marine organisms although some of these compounds have also been found in terrestrial species.

Despite the fact that iAs species are predominant in natural waters, the presence of oAs has also been reported. Even though the main analytical interest is to determine total arsenic in water, it is also important to develop the procedures for As species determination, separation, and removal. The distribution of i As and oAs species is a function of pH value of water [2].

**3. Determination of arsenic and arsenic species in water**

that are used for determination of arsenic and arsenic species in water.

order to have an insight into ability and application of available techniques.

ICP-MS, are recommended, and they are mostly used [13].

**limit (μg L−1)**

ICP-AES Total arsenic ~30 Minimal sample volume;

**Methodology Detection Detection** 

and arsenic speciation

and arsenic speciation

speciation

speciation

HPLC-ICP-MS Total arsenic 0.01 No need for sample

HG-AAS Total arsenic

HPLC-HG-AAS Total arsenic

HPLC-HF-AAS Arsenic

IC-ICP-MS Arsenic

analysis.

There are a variety of chemical methods from classical to contemporary analytical techniques

There has been several review articles on the speciation of arsenic in a variety of samples [10–14]. These reviews focus on (1) determination of total content of arsenic and (2) speciation

A review of contemporary methods for arsenic and arsenic species in water is presented in **Table 2**. The parameters, as detection limit, advantages and disadvantages are pointed out in

The total concentration of arsenic in drinking water (mostly traces of arsenic, level of μg L−1 or less) can be detected only by sophisticated analytical techniques as ICP-MS, GF-AAS and HG-AAS [3, 14]. For As speciation analysis, well-established methods that involve the coupling of separation techniques, such as HPLC with a sensitive detection system, that is,

> no sample pretreatment and short measurement

time

GF-AAS Total arsenic ~0.025 Approved by US EPA — [3, 14]

1–47 No need for sample pretreatment

0.05–0.8 Rapid, inexpensive.

0.01 No need for sample pretreatment

**Table 2.** A review of contemporary methods for arsenic and arsenic species determination in water.

pretreatment

No need for sample pretreatment

ICP-MS Total arsenic ~0.1 Approved by US EPA Spectral and matrix

**Advantages Disadvantage Ref.**

Expensive; needs lot of knowledge for operating and interpretation of data

Arsenic in Water: Determination and Removal http://dx.doi.org/10.5772/intechopen.75531 13

— [3, 14]

— [3, 14]

— [19]

— [13]

interferences

0.6–6.0 Approved by US EPA — [14]

[14]

[11, 13, 19]

**Figure 2.** The distribution of iAs and oAs species as a function of pH values of water [2]. Copyright approved by publisher.

The distribution of arsenic species vs. pH values of water is presented in **Figure 2** [2].

As(III) species: H3 AsO3 , H2 AsO3 − , HAsO3 2− and AsO3 3−, are stable under slightly reducing aqueous conditions. As(V) species: H3 AsO4 , H2 AsO4 − , HAsO4 2− and AsO4 3−, are stable in oxygenated waters [6]. Two valences of the same element, molecular (ortho, H3 AsO3 , H3 AsO4 and meta forms, HAsO2 , HAsO3 ) and ionic forms with different charges make the research of arsenic removal from water more challenging and indivisible of arsenic chemistry knowledge. Any arsenic removal technology strongly depends on the water conditions and the stability of arsenic forms in the water.

Bearing in mind the fact that arsenic occurs in water in molecular and ionic form depending on water pH, the main goal of many investigations is to select the most efficient exchanger, not only in terms of efficiency, but also in terms of applicability in the wide range of water pH values in real and environmentally friendly water treatment systems. In neutral conditions, As(V) species are completely in ionic form (H2 AsO4 − and HAsO4 2−), while As(III) is in molecular (H3 AsO3 or HAsO2 ), as shown in **Figure 2** [2].
