## 3 Results and Discussion
### Implication for the Contaminated Site Management  
As described in Section 2.4, the bioaccessibility was estimated for each soil sample starting from the bioaccessible concentrations measured with the two in vitro methods (i.e., UBM and SBET) and using the two different equations, (9) and (10). Figure 4 reports the comparison of the values of the bioaccessible fraction (BA\({}_{1}\)-UBM, BA\({}_{1}\)-SBET, BA\({}_{2}\)-UBM, and BA\({}_{2}\)-SBET) obtained for each soil sample. In the UBM case, the bioaccessible fraction was estimated by using the higher concentration among those measured in the gastric and the gastrointestinal phases, thus adopting a conservative approach. It has to be noticed that for the tested soil samples, the use of either the UBM or the SBET bioaccessible concentration did not notably affect the bioaccessibility when the results obtained with the same equation were compared. This means that, at least for the samples investigated in this work, despite the two methods following different procedures and  
Figure 4: Bioaccessibility of metals and metalloids contained in samples **A1**, **A2**, **S1**, and **S2** estimated adopting Equations (9) and (10). Striped bars represent values obtained from bioaccessible concentration lower than the limit of quantification. reagents and being carried out on different size fractions, the estimated bioaccessibility is basically the same. On the other hand, significantly different results were obtained using the two equations. Namely, the values obtained with Equation (10) (BA\({}_{2}\)), regardless of the in vitro method used, were at least one order of magnitude lower than those calculated with Equation (9) (BA\({}_{1}\)). This difference stems from the different assumptions behind the two equations. BA\({}_{1}\) did not account for the particle size distribution and was simply the ratio between the bioaccessible and total concentration measured on the same particle size fraction. In BA\({}_{2}\), the bioavailable concentration was normalized to the particle size fraction above 250 \(\upmu\)m or 150 \(\upmu\)m, for UBM and SBET, respectively, whereas the total concentration was also normalized to the soil fraction above 2 mm. As an example, we can look at the values obtained for lead in the different samples using the UBM. For sample A1, BA\({}_{1}\) was close to 1 and BA\({}_{2}\) around 0.5. This resulted from two counteracting effects (see Equation (10)). On the one hand, the particle size fraction below 250 \(\upmu\)m (2.4%) was lower than the one below 2 mm (12.2%), i.e., a ratio around 0.2; on the other hand, the total lead concentration in the <250 \(\upmu\)m fraction was higher than the one in the <2 mm fraction (836 mg kg\({}^{-1}\) vs. 351 mg kg\({}^{-1}\) respectively), i.e., a ratio of around 2.4. For sample A2, BA\({}_{1}\) was around 0.5, whereas BA\({}_{2}\) was around 0.1. In this case, the particle size fraction below 250 \(\upmu\)m (11%) was lower than the one below 2 mm (68.6%), i.e., around 0.16 ratio, whereas the total lead concentration in the <250 \(\upmu\)m fraction was slightly higher than the one in the <2 mm fraction (263 mg kg\({}^{-1}\) vs. 206 mg kg\({}^{-1}\), respectively), i.e., a ratio of around 1.3. The behavior observed for samples S1 and S2 was somehow in between those observed for A1 and A2. The bioaccessibility of lead in shooting ranges was investigated by numerous studies adopting different methods (see Table 2). [PERSON] et al. [35] investigated the Pb bioaccessibility in different sites characterized by various lead sources (Pb bullets and pellets, car battery Pb, gasoline Pb, diffuse Pb, made ground and city waste), observing that the shooting ranges showed the highest bioaccessibility. Generally, the bioaccessibility measured in shooting ranges falls within the range 45-100% [35, 36, 37, 38]. The results obtained in the present study, particularly those estimated with Equation (9), fit well with data available in the literature.