###### Abstract
The environmental regulations establish upper limits (threshold, alert, and intervention values) for heavy metal concentrations in water, soil, and sediment to preserve the local ecosystems. It is evident that contamination assessment based on pollution indices computed using mean upper crust values determined at the global level is inadequate for providing accurate results. This is because local conditions, dependent on geology, are not considered. Furthermore, implementing unnecessary remediation measures can even destroy ecosystem equilibrium [29; 30]. The substitution of mean upper crust values with local background values from a deep soil layer does not solve the problem, as the distribution of the analyzed metal is not homogeneous in soil layers due to weathering and pedogenesis processes, among other factors. This may result in an erroneous indication of contamination. It was recommended that raw data collected over a larger region be used instead to estimate the geochemical background range and identify geochemical anomaly patterns [31; 32]. The geochemical background is determined based on the median \(\pm\) 2 MAD (median absolute deviation) after outliers are removed with the aid of box-plot charts. It has been demonstrated that the median \(\pm\) 2 MAD is a superior method to the mean \(\pm\) 2 standard deviations for this purpose [33]. This method has been used in recent studies for the evaluation of data and the estimation of background intervals [34; 35; 36; 37]. In several studies conducted in Romania [38; 39], the values presented in [40; 41] have been used as background values for calculating indices in assessing trace element concentrations in soil and sediment. These values were employed in conjunction with comparing the limits set forth by Romanian legislation [42]. Additionally, the values of the Canadian sediment quality guidelines (SQGs), precisely the threshold effect level (TEL) and probable effect level (PEL) described in [43], were also used in a study [38]. The values from the Romanian legislation were employed as a geochemical background for trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in [44; 45; 46; 47] to assess the sediment's quality. It is noteworthy that Romanian legislation [42] also specifies limits for water quality evaluation. These limits were used to compute indices for trace elements [48; 49], nutrients, and other physico-chemical parameters in surface waters [2; 50]. Other studies on soil pollution [51] employed the natural abundances of chemical elements, designated as Clarks [52], and the average values determined in various soil types [53] for the calculation of specifically developed indices. The Clarks represent the average content of an element in the lithosphere, and they are widely used in mineral geochemical prospecting across Eastern Europe and Russia [54]. In other studies [55], the values indicated for soils in [26; 53] and Romanian legislation on soil were employed to calculate contamination/pollution indices. Romanian legislation on soil differentiates between normal, alert, and intervention values for sensitive and less sensitive categories of land use [56]. The values indicated in [26], as well as the maximum allowable concentrations for various European countries and the Dutch standard [57], were used in [58] to assess soil pollution due to mining in the Baia Mare area. A study in the eastern Black Sea [59] assessed the presence of minor and trace elements in soils, bottom sediments, and biota. The study also compared the values to the average upper continental crust values [24] and soil trace element levels in the Netherlands, Germany, Finland, the USA, and Russia. There is considerable variability [22; 23; 24; 25; 52; 53] in how geochemical background values for trace elements are defined and referenced regarding various media. These include averages of the continental upper crust or soil surface. These reference values are used in a multitude of publications to facilitate straightforward comparisons or the calculation of pollution indices.