## 4 Discussion
### Inter-Elemental Relationship and Related Groups  
In a Belgium study, Al, Si, Ti, Ca, K, Mn, and Fe which have loadings >0.5 on the first factor (see Table 4 in [82]) are interpreted as crustal. In Krakow, the origin of Al, Si, K, Mg, Ca, and Fe which are clustered separately (see Figure 7 in [92]) is interpreted as natural. Separation of a few aforementioned elements can also be found in other publications: e.g., Al, Fe, K, Mg [81], Al, Fe, and Mn [93]. Most of these elements are considered as crustal in review of various studies, too [94]. Iron was always among them, provided it was determined. But in the case of Klaipeda, Fe does not associate with all these crustal elements, and it is distinguished as their strict antagonist (see F1 TSP in Table S4). Cluster analysis confirms this, since cluster L4 composed of Fe accompanied by Cr is in the left branch of the dendrogram and is separated from other crustal elements in the right branch (Figure 7). Such separation of Fe from other crustal elements enables us to presume that it has its own emission source. The antagonism between Fe and crustal elements which is expressed in factor F1 TSP indicates that significant Fe input notably reduces the re-suspended part of other \"traditional\" crustal elements. This powerful source of Fe has clearly other origin than diffuse anthropogenic sources of Fe and associated with them elements which in Belgium were interpreted as \"traffic and metals\" (see the fourth factor in Table 4 [82]). In the dust of Klaipeda, similar Fe sources also exist, but are reflected in another factor, F5 TSP, as can be seen from significant at \(p\) < 0.05 loadings of Pb, As, Cr, Mn, Fe, and Ni on it. Almost all analytes in this list are also in aforementioned fourth factor, except Ni. Still, we cannot deny native source of Fe mentioned in all previously cited publications [81; 82; 92; 93] where positive correlation of Fe with other crustal elements has been shown. We can presume partial pedagenic origin of Fe in dust of Klaipeda basing on: (i) conclusions of these researchers, (ii) the fact that L4 cluster in the left branch of the dendrogram is the closest to the right branch and only two connections separate it from clusters R2 and R3 which include crustal elements, (iii) undeniable association of Fe with other crustal elements which is observed in topsoil (see Fe loadings on FTBT and dendrograms in our previous research of topsoil background composition [25; 87]) which serves as a source of re-suspension. But presently, Fe ore stevedoring seems to be not essential source of Cr, since the highest loading of Cr is on F5 TSP, i.e., it belongs to the group of elements leaded by Pb and As and accompanied by Cr, Mn, Fe, and Ni. Extremely high contents of Cr together with Fe have been observed in topsoil of the northern part of the city near Fe ore stevedoring terminal since 2005 [21; 95] up to today [96]. This part of the city has the oldest history and has been influenced by anthropogenic activity for the longest time. Lead was earlier an important traffic-related element because of leaded gasoline [97; 98]. The anomalies of Pb are the most conservative compared to other PHEs, i.e., best of all repeat their primary configuration, although the level of Pb in them inevitably decreases [14]. Relatively close to oldest part of the city (site \(i\) in Figure 1), one of the greatest factories of galvanic batteries in the former USSR has been operating since 1989, and it polluted the surrounding topsoil with Zn, Cu, As, Ni, Pb, Mn, Sr, and Cr [21]. Therefore, according to our available data, resuspension of formerly contaminated topsoil can be the most probable reason of elemental grouping in F5\({}_{\text{TSP}}\) and R1. The next factor F2\({}_{\text{TSP}}\) according to percentage of explained variance (12%) is significantly (\(p<0.01\)) loaded by Sr-P-Ca. Two of these three elements, i.e., P and Sr, form their own cluster L3 in the left branch at the lowest distance LD < 0.2.