## 1 Introduction
Lack of selectivity is manifested by incomplete dissolution of the intended phase by the extraction agents for example when the chemical system becomes overburdened, in (partial) dissolution of undesired phases resulting in overrating the targeted phase, and/or in readsorption and redistribution phenomena. Validation tests of sequential extractions have been a matter of debate for a long time and can be accomplished either by treating synthetic and/or pure mineralogical phases or by applying some kind of standard additions [13; 14; 15; 16; 17]. It has been suggested that extraction efficiency could be improved by monitoring some parameters. For example, incomplete dissolution of acid-soluble minerals due to strong acid/base buffering could be checked by measuring the pH of the solution before and after extraction [18]. [PERSON] et al. [19] suggested, therefore, a multiple successive extraction procedure with monitoring the mandatory parameters (pH, Fe and Mn concentration, and Eh) in metal release to determine the number of extractions required. This should lead, according to these authors, to a more reliable distribution pattern especially when dealing with heavily contaminated samples. [PERSON] et al. [20] suggested using low sediment-to-extract ratios (1/100) to ensure that each extractant did not become exhausted (e.g., to prevent that iron oxide dissolution is limited by oxalate concentration). The coal-burning plant Federico II of Brindisi (Apulia, southern Italy) discussed in this paper is outfitted with a partially-enclosed conveyor belt for the transport of the solid fuel to the coal-fired boiler. Coal sometimes, depending on its geographical origin, can be characterized by a high arsenic content that could have been transferred to the areas close to the power plant both by scattering of coal grains and/or by particles formed by combustion. This contingence was taken into account with a previous public agency funded investigation aiming to evaluate the environmental impact of the power plant on the surrounding area. Reported As concentration values were generally within the accepted safety limits, except for a single sampling point, where this earlier investigation detected extremely high values of As concentration (>1500 mg kg\({}^{-1}\), Table 1). This work, therefore, describes arsenic sequential extraction analysis performed on the 30 soil samples, deriving from 5 cores extracted in the circumscribed area where the earlier investigation detected anomalous values of As concentration, in order to confirm or deny the environmental significance of the data previously collected. Chemical analyses were performed in order to obtain the following information: (1) As availability in leaching test; (2) As sequential extraction by using different solvents; (3) As speciation analysis. Different sequential extraction schemes have been designed for the analysis of metals in soils and sediments [10; 21]. In this case, the speciation aims at understanding the distribution of a metal over the various sedimentary substrates such as carbonates, iron and manganese oxyhydroxides, organic matter, sulphides, silicates, etc. Under particular conditions some of these substrates will dissolve (for example the oxyhydroxides under reducing conditions and the carbonates under acidic conditions) or release adsorbed metals (for example when the electrolytic strength of the solution is increased). It is thus possible, by carefully selecting the composition of the extraction solutions, also called extractants, to destroy selectively specific soil or sediment substrates. Information obtained from sequential extraction procedures can be very interesting, although a prerequisite is that the analytical procedures are well-defined and accepted.