Arsenic [As, 33]
15
from gold-mining areas and reported that most of As was in forms susceptible to
dissolution in acid medium; fractions coprecipitated with amorphous and crystalline
Fe oxides, and were fixed by MnO 2 and Al 2 O 3 . Recently, it has been concluded that
bacteria are responsible for most of the redox As transformation in the environment (Santini 2012).
3.3 WATERS
Range of As concentration in seawater is estimated at 1.2–3.7 μg/L (Table 3.1).
Low mean As content in the north Pacific Ocean is given by Nozaki (2005).
Global average of As content in river water is calculated as 0.62 μg/L, ranging
from 0.1 to 9.5  μg/L. However, contaminated water may contain much higher
amount of As, with Lake Erie (United States) and Tocone River (Chile) containing up to 300  μg/L and 800  μg/L, respectively (Kabata-Pendias and Pendias
1999). Gaillardet et al. (2003) calculated the global riverine flux of As to seawater at 25 kt/yr.
In water, As is present as trivalent (dominated in reducing conditions) and pentavalent (dominated in oxidizing conditions). Also, its methylated form, resulted
mainly from phytoplankton activities, constitutes about 10% of the total As concentration in most oceans. Arsenic in water is often in acid forms: H 3 AsO 3 and H 3 AsO 4
(Höll 2011). Also, organic compounds, often as products of microbial transformation, are present in water as monomethyl arsenic acid (MMAA) and dimethylarsenic
acid (DMAA). As Niedzielski et al. (2000b) reported that several other As-organic
compounds may occur in water. According to these authors, the range of As species contents in lake water includes (in μg/L): As 3+ : 0.85–1.0; As 5+ : 0.15–0.35; and
As-organic: <0.15.
Groundwater may contain very high levels of As, which resulted in its elevated
concentration in well water. As-enriched groundwater is present over large areas in
some countries. Reported by Battacharya et al. (2002) and Burges and Ahmed (2006),
high As concentrations in shallow well water are as follows (in μg/L): Argentina,
100–4800; Bangladesh,  <1–3000; China, <100–1860; Mexico, 330–1100; and
Thailand, 120–6700.
Arsenic content in bottom sediments is a good information on water pollution. Its
average content in bottom sediments of San River (Poland) varies between <0.5 and
10 mg/kg, and is a bit higher in mule sediments than the sandy ones (Bojakowska
et al. 2008). As content in stream-bottom sediments of National Park, Montgomery
(Pennsylvania State), in 1995 ranged from 2 to 5 mg/kg (USGS 1997). Assessment
limits for As in sediments are established as follows (in mg/kg): effects range low,
8.2; effects range median, 70; probable effect level (PEL), 17; 33; and 17 (EPA 2000,
2013). The Environment Canada Sediment Quality Guidelines (USGS 2001) gave
other values for As in lake-bottom sediments (in mg/kg): threshold effects level, 5.9;
PEL, 17; and probable effect concentration, 33. Sediment Quality Guidelines are also
based on the acid volatile sulfide/simultaneously extracted metal ratios (Griethuysen
et al. 2006).
According to a recent estimation, up to 200 million people in 70 countries are
at risk from As-contaminated drinking water (Santini 2012). Removal of arsenic