**1. Introduction**

The internationally recognized Codex Alimentarius Commission defines honey as a naturally sweet substance produced by bees through the collection of flower nectar or secretions from living plants and the subsequent transformation of these collected materials with substances inherent to bees. This mix is deposited and dehydrated for storage, a process that results in the maturation of honey [1].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Honey is principally composed of a complex mix of carbohydrates, among which fructose and glucose account for 85–95% of the total sugars. Since glucose is less soluble than fructose, the proportions of these sugars in honey determine overall granulation, with higher fructose quantities lending to honey that remains longer in the liquid state [2, 3]. Other more complex sugars are formed through the bonding of two or more fructose/glucose molecules with trace polysaccharide residues. Honey also contains other substances to lesser degrees, including organic acids, amino acids, proteins, enzymes, minerals, fat-soluble vitamins, flavonoids with antioxidant properties, and hydroxymethylfurfural, a compound that indicates honey freshness [4–8]. Finally, honey can be further classified by melissopalynological analysis as either monofloral or polyfloral in origin. Monofloral honey is of greater commercial value due to 45% of solid residues being single-pollen in origin [9–12]. Altogether, the quality of honey depends on the presence and concentrations for each of the aforementioned compounds, as well as on classification as either mono- or polyfloral.

The close source-product association between plants-honey means that all honey inherit various characteristics of and share biological properties with their respective botanic sources [13]. Due to this, undesirable compounds or residues can be found in honey if the source plants were exposed to these substances, including those of anthrophic origin. Among the residues that alter the natural composition of honey are metals, which, depending on their concentration in food, can pose as a human health risk [14]. The most common route through which humans ingest and are exposed to metals is through the diet, although the presence of these chemical elements in the air also means intake through inhalation.

Some heavy metals are essential elements for normal growth of plants such as Co, Fe, Mn, Ni, Zn, and Cu and they have important roles in metabolism, but at higher concentrations, the same metals become toxic. Those increased levels can cause a decrease in percentage of biomass in vegetables and in many other cases, they lead to plant death. On the contrary, some heavy metals such as Pb, `Cd, Cr, and Hg have been marked with high toxicity for plants [15].

Metals have a density, (*d*) > 5 g/mL and atomic number > 20, with the exceptions of alkaline and alkaline earth metals. No more than 0.1% of the earth's crust contains metals. Although the term "heavy metals" primarily refers to elements with elevated cellular toxicity, this definition now extends to include micronutrients that, at high concentrations, represent a risk to human health. Heavy metals without known biological functions are the most dangerous due to high toxicities, including barium (Ba), cadmium (Cd), mercury (Hg), lead (Pb), strontium (Sr), and bismuth (Bi). Trace elements, or micronutrients, toxic at increased concentrations include boron (B), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), magnesium (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), and zinc (Zn) [16]. Due to the human health risk presented by these heavy metals and micronutrients, regulations exist for the maximum residual limits permitted in various foods destined for human consumption [17, 18].
