## 1 Introduction  
Heavy metals are considered serious inorganic pollutants due to their toxic effects and ability to accumulate in the environment [1]. Metals are non degradable and, therefore, remain indefinitely in aquatic and terrestrial environments. They can leach through soils eventually affecting groundwater or taken up by plants, including agricultural crops [2]. Lead (Pb), one of the most toxic and hazardous elements to human health [3], is ranked second on the 2017 Agency for Toxic Substances and Disease Registry (ATSDR) Substances Priority List [4]. Pb has deleterious effects on the nervous and cardiovascular systems, with its target organs being the brain and kidneys. Lead has been shown to restrict intelligent quotient (IQ) development [5], and is listed as a group 2A carcinogen by the International Agency for Research on Cancer (IARC) [6]. The impact produced by human activities result in the alteration of the natural balance of the system [7]. Mining is one of the most significant contributors of pollution in the environment by metals and metalloids [8]. Numerous studies have demonstrated that in many countries, areas surrounding mines are marked by significant soil and sediment pollution. For example, [PERSON] & [PERSON], found that mining soils in Zimbabwe had high concentrations of Pb (170.3 mg kg\({}^{-1}\)) [9]; [PERSON] et al. found that due to an average concentration value of 596.13 mg kg\({}^{-1}\), Pb should be controlled preferentially over Arsenic and Mercury in China's mining areas [10]. Similarly, in the Republic of Kosovo, the average concentration of Pb in the surface soils in mining and smelting areas was 450 mg kg\({}^{-1}\)[11]. In Aguascalientes, Mexico, [PERSON] et al. analyzed sediments from the San Pedro River and found a mean of 20.8 mg kg\({}^{-1}\)[12]. However, [PERSON] et al. analyzed soils and sediments from the mining areas around the Piedras Negras River, our study area, and found mean concentrations of 434.7 and 2200.8 mg kg\({}^{-1}\) respectively [13]. The mobility and bioavailability of heavy metals in the environment depends not only on their total concentration, but also on their association with the solid phase to which they are bound [14]. Speciation, a word borrowed from the biological sciences, has become a concept in analytical chemistry, expressing the idea that the specific chemical forms of an element should be considered individually [15]. When elemental speciation is not feasible, the term fractionation is in use, being defined as follows: process of classification of an analyte or a group of analytes from a certain sample according to physical (e.g., size, solubility) or chemical (e.g., bonding, reactivity) properties [15]. Sequential extraction methods are frequently used to assess operationally defined pools of trace elements, characterizing their liability on the basis of the dissolution behavior of the target binding phases in soils and sediments [16], show the potential risk of mobilization of metals in particulate phases [17]. According to the literature, the procedure by [PERSON] et al. [18] can be used on a broad array of soil types provided the metals tested are Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn. This is probably why the Tessier procedure is the most used method to date [19]. Moreover, the overall extraction efficiency of the Tessier scheme is much higher for Pb compared to the Community Bureau of Reference (BCR) scheme [20]. However, there are some disadvantages of Tessier method. Notably, it does not discriminate between metals associated with amorphous Fe and Mn oxides and those associated with crystalline oxides of Fe [21] and the lack of reference material hinders the comparison and validation of the procedure [21; 22]. However, the Tessier scheme is generally accepted as the most commonly used protocol followed closely by BCR [19]. On the other hand, many studies of soils and sediments try to relate the results of sequential fractionation procedures to bioavailability measurements [23].