**3. Edaphology properties of soil related with mercury**

Soil is a collection of natural bodies on the Earth' surface, in places that most of them have been modified by man in its quality and containing living matter and supporting or capable of supporting plants. Soil grades at its lower margin to hard rock or to earthy materials virtually devoid of roots, animals or marks of other biologic activity.

formations and the impact of its various chemical forms are vital to preventing harmful effects on humans and the environment. Nevertheless, physicochemical characteristics of mercury are either useful or necessary for many industrial and agricultural applications, and mercury may be scattered over large area, depending on the source (Leopold et al, 2010; Nick, 2012).

of some types of alkaline batteries, fluorescent lamps, electrical contacts, and instruments such as pressure gauges and thermometers, among others. Hg salts are used in antiseptic ointments and creams and skin lightening. Among the activities that generate the most pollution by Hg, is the burning of coal and chlor-alkali plants: other important sources are mining and metal‐ lurgy and the burning of municipal solid waste, which may contain instruments such as pressure gauges, thermometers, alkaline batteries and fluorescent lamps. The mercury released into the air tends to settle and adhere to soil organic matter (Hinton and Veiga,

Natural and anthropogenic mercury emissions are mainly in the form of elemental mercury

soluble in small doses, and can be found in soil and sediments. In contrast, the presence of

[HgS]) depends on the local chemical environment. The life time of these compounds in air is very short (on the scale of minutes) and they are rapidly removed by deposition processes because of high water solubility and surface activity. Figure 2 shows the main mercury species in the atmosphere, hydrosphere and sediment (Leopold et al, 2010; Nik, 2012; Slowey et al,

Over 90 % of surface water mercury is from atmospheric deposition. Hg2+ usually undergoes

(DMeHg, (CH3)2Hg), though these reactions can be reversed using microorganisms and/or

Hg2+ (Hg2+and its complexes) and organic mercury (MeHg, MeHg complexes and DMeHg).

(Hg2+) and MeHg forms complexes with other dissolved compounds in fresh water, but for the most part, only forms complexes with chlorine in sea water. DMeHg is found in the deep sea.

Soil is a collection of natural bodies on the Earth' surface, in places that most of them have been modified by man in its quality and containing living matter and supporting or capable of supporting plants. Soil grades at its lower margin to hard rock or to earthy materials virtually

Three main forms of mercury are found in natural waters: elemental mercury (Hg0

inorganic forms of Hg2+ bonded to organic and/or inorganic species ([HgClx]

a biomethylation process that forms methylmercury (MeHg, CH3Hg+

**3. Edaphology properties of soil related with mercury**

devoid of roots, animals or marks of other biologic activity.

photolytic decomposition. All these species are highly mobile.

), which makes up about 99 % of total atmospheric mercury. However, biogeochemical

) is mainly used to produce chlorine gas and caustic soda, and is part

and Hg2+. Most inorganic Hg-

compounds are water

) and dimethyl mercury

can be found at all depths. Inorganic mercury

), inorganic

2-x; [HgII-DOC];

The metal mercury (Hg0

830 Environmental Risk Assessment of Soil Contamination

2001; Nick, 2012).

transformations can oxidize it, forming Hg+

2005; Wartel et al, 1999; Shi et al, 2005).

With solubility (at 25°C) of 0.08 mg L-1, Hg0

(Wartel et al, 1999, Shi et al, 2005, Slowey et al, 2005).

(Hg0

**Figure 2.** Distribution of mercury species in atmosphere, hydrosphere and sediment (Leopold et al, 2010).

In general, physical, chemical and biological soil characteristics are highly correlated param‐ eters that are necessary to understand. The specific elemental composition of each particular soil reflects, to a degree modified over time by weathering and the chemical composition of the parent material from which the soil is formed. For instance, the extractability of the different elements depends on the soil properties.

Soil as important part of the ecosystems which must be protected in the environment context, and it is necessary be studied the possible overall impact of measures for protection, with a very special attention from mining activities. The soil resource occupies a fundamental part of the ecosystems;whena soilisdegraded,theothers componentsofthe ecosystems aredegradedtoo.

The fate of the heavy metal in soils depends upon many soil processes that are governed by several soils properties of which soil pH and redox potential are known to be the most important parameters. Thus, the solubility of trace elements is often shown as a function of pH affected by amount and kind of organic matter. Trace elements are known to be accumu‐ lated in surface soils as a result of contamination from point sources as mining activities.

An appreciable amount of the soils has been made unusable because of pollution. Highly contaminated soils belong to a high healthy risk to human being and their environmentally harmful effects. That is why soil should be correctly understood and underestimated long range lethal effects that can have irreversible consequences. The improvement of soils damaged and contaminated by pollutants need of the particular soils, requires a full under‐ standing of soil properties and of the deteriorating factors.

Mercury is a microelement: its Clark value in the Earth's crust is 56 µg Kg-1 (Fügedi et al, 2011). It is characterized by a dual geochemical behavior: it is liable to extreme concentration and to dispersion, the latter resulting in an approximately entirely even concentration. It is found either as a native metal (near to 80 % in hydrothermal and vapors) or in cinnabar, corderoite, livingstonite and other minerals. Cinnabar (HgS) is the most common ore. Mercury ores usually occur in very young orogenic belts where rock of high density on upper mantle is forced to the crust of the Earth (Ozerova, 1996).

Given that mercury is enriched by an extremely wide variety of geological processes (Fergusson, 1990) from the formation of hydrocarbon to hydrothermal mineral occurrences, it can be regarded as an universal geochemical indicator of young geological effects; its disper‐ sion halos are more extensive than that of any other element (Fügedi et al, 2011).

Historically there were two main registered Mercury mines: Almaden (Spain) and Idrija (Slovenia) in Europe. Later new occurrences were found in California and worldwide. It was used in gold separation. In Mexico we know mercury mines from the Pre-Hispanic era (Scharek et al., 2010) and a usage in cultic fests (Figure 3). In 2005, China was the top producer of mercury with almost two-thirds global share followed by Kyrgyzstan. Several other countries are believed to have unrecorded production of mercury from copper electro winning processes and by recovery from effluents.

**Figure 3.** Typical cinnabar occurrences in a limestone system (Formation Las Trancas, San Joaquin, Querétaro, Mexico, photo by P. Scharek)
