**1. Introduction**

Quality of life is based on an intricate relationship of various factors that include having sufficient nutrition, adequate accommodation and environment, social and psychological fulfillment, and health. Not neglecting the importance of these factors, environment stands out as it plays a crucial role in people's physical, mental, and social well-being.

Given the link between environment and health, as environmental chemicals affect not only the surroundings but also the quality of food and water, there has been a growing concern in the scientific community in the last decades, and consequently an increase in studies characterizing the environmental availability of elements, particularly in the soil. These recent studies have added substantial knowledge regarding elemental availability in soils, particularly for the biogeochemistry of trace elements [1]. The assessment of the concentrations of trace elements in soil is very important not only for environmental purposes, such as

quantifying the contamination level, but also to help solve problems associated with elemental toxicity or deficiency in humans and plants.

Trace elements (TEs) are dietary minerals present in living tissues in small amounts; some of them are known to be nutritionally essential, playing a vital role in the normal metabolism and physiological functions of animals and humans [2]. The TEs' essentiality for the human body has been a matter of discussion throughout time and the term "trace elements" has never been clearly defined, being used both in geochemistry and biological sciences for chemical elements that occur in the Earth's crust in amounts less than 0.1% (1000 mg/kg) [1]. Despite their "low" content in the human body, TEs are components of a complex physiological system involved in the regulation of vital functions at all stages of development of the living organism [3].

Throughout time, limited attempts have been made for classifying trace elements. In 1973, WHO [4] classified 19 trace elements into three groups: (i) essential elements: zinc, copper, selenium, chromium, cobalt, iodine, manganese, and molybdenum; (ii) probably essential elements; and (iii) potentially toxic elements. Shortly after, Frieden [5] considered 29 types of elements present in the human body and classified them into five groups:


More recently, Frieden [6] proposed a biological classification of trace elements based on their amount in tissues: (i) essential trace elements: boron, cobalt, copper, iodine, iron, manganese, molybdenum, and zinc; (ii) probably essential trace elements: chromium, fluorine, nickel, selenium, and vanadium; and (iii) physically promoter trace elements: bromine, lithium, silicon, tin, and titanium.

As TEs play a significant role in the regulation of many important adaptive mechanisms, including the functioning of all vital systems of the organism, the balance of each element in an optimum range of concentrations is fundamental. The chronic deficiency of essential TEs can, therefore, result in metabolic disturbances and distinct clinical and morphological changes; on the other hand, we must

**103**

*Trace Elements in Volcanic Environments and Human Health Effects*

not disregard that all TEs can be toxic if consumed at high levels for long periods,

The main advances in trace element research have been made in soil sciences since soils are considered the most important environmental compartment functioning as a sink for TEs [7–9]. Trace elements are usually distributed over different soil compartments and their retention will depend on several soil characteristics, as

The main soil characteristics include pH, cation exchange capacity (CEC), particle size distribution, electrical conductivity, and organic matter content [10, 11]. These soil properties can promote the accumulation of TEs in soils or their depletion. The most adequate pH for the maximum TE availability is within 6.0–8.0; however, some TEs such as manganese, iron, boron, copper, and zinc are more available to plants when the soil is acidic (pH between 4.5 and 6.5), which contributes to manganese and boron toxicities in plants growing on acidifying soils [12]. The CEC is also a very important soil property as it can influence the soil structure stability, nutrient availability, soil pH, and the soil reaction to fertilizers and other ameliorants [13]. For example, negatively charged sites increase the CEC,

, and NH4+, while the positively charged sites increase

<sup>−</sup> [14]. All these soil properties, either

*DOI: http://dx.doi.org/10.5772/intechopen.90786*

**2. Trace elements in soil**

well as the parent rock material.

, Ca2+, Mg2+, Na+

<sup>−</sup>, NO3

result from anthropogenic activities, such as agriculture [15].

**2.1 Measurement of trace element levels in soils**

<sup>−</sup>, and PO4

avoiding misinterpretation of abnormally low or high TE contents [16].

combined or isolated, can promote the accumulation or the leakage of TEs in soils. The parent rock material also assumes high importance in TE availability; when parent materials have high trace element concentrations, the resulting soils also have high or even higher TE concentrations, particularly when the former also

Considering that specific soil characteristics can affect the TE availability, the use of universal background concentrations is inadequate, as it may not reflect the "normal" values for specific regions. In this way, each country should determine the background levels for each region with different geological substrates and establish normative values for environmental legislation based on these studies,

The soil background concentrations/levels will depend on the mineralogical composition of the parent rock material and on the weathering processes that have led to its formation, the granulometry fractions, and the organic matter content [17–19]. These background measurements, which represent natural concentrations in unpolluted pristine soils, are very difficult to assess because they require a soil free of contamination. Given this difficulty, the measurement usually applied is the geochemical baseline concentration that represents an expected range of element concentrations around medium normal sample mean [20]. Although the TE baseline concentration levels in the soil may differ between countries and/or geographical regions, their assessment has been recognized as the only means to establish reliable worldwide elemental concentrations in natural materials [21, 22].

The measurement of TE in soils requires well-planned sampling strategies to achieve accurate data. There are several defined protocols for soil sampling and many digestion techniques to optimize the TE quantification [23]. The conventional methods are based on a regular soil sampling design, with soil sample collection at a depth of 0–20 cm and subsequent chemical analysis of the sampled soils in the laboratory,

the retention of OH<sup>−</sup>, SO4

holding H+

disturbing the normal function of vital systems.

not disregard that all TEs can be toxic if consumed at high levels for long periods, disturbing the normal function of vital systems.
