## 5 Conclusions  
The threshold values for trace elements proposed in the in-force Romanian legislation [42] have limit values very similar to those of the Dutch standard, which have been developed for an area with a very different geology. Thus, it would be advisable to refine them in accordance with Romania's existing geochemical background values.  
This study proposes more adequate thresholds (upper geochemical background values) as follows:  
- As: 15 mg/kg;  
- Cd: 0.5 mg/kg;  
- Cr: 175 mg/kg;  
- Cu: 35 mg/kg;  
- Hg: 0.3 mg/kg (the same value as the Romanian legislation [42]);  
- Ni: 55 mg/kg;  
- Pb: 30 mg/kg;  
- Zn: 120 mg/kg.  
Seven of the eight investigated trace elements showed an important difference regarding the threshold value, the most prominent being Cr and Ni. The proposed threshold values reflect the geological background in Romania and, thus, should be included in the new national legislation regarding environmental protection.  
In order to establish more accurate threshold values for the eight critical trace elements examined in this study, as well as for other elements of interest, it is imperative to conduct a geochemical survey of the entire Romanian territory. This investigation can be facilitatedwithin the framework of the recently proposed soil legislation at the European level. The investigation should follow the protocol outlined in the Geochemical Atlas of Romania, using a more extensive sampling grid [60] and performing the analyses in a single accredited laboratory or under appropriate inter-comparison conditions. This approach will provide more accurate and up-to-date values for the geochemical background of Romania, facilitating environmental studies and mineral exploration. Consequently, this study may initiate the development of a more accurate geochemical survey of sediments in Romania, with the potential for replication in other regions.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15052458/s1](https://www.mdpi.com/article/10.3390/app15052458/s1)]([https://www.mdpi.com/article/10.3390/app15052458/s1](https://www.mdpi.com/article/10.3390/app15052458/s1)): Table S1: Trace elements concentration in different types of sediment samples from the Lower Danube Basin; Box-plots of nine sections from the Lower Danube; Box-plots of geochemical atlas 13,000,000; Archive containing larger maps for Figure 1; Archive containing larger maps for Figure 2; and The complete Geological Map of Europe for Figure 8.  
Conceptualization, A.-M.V.; methodology, A.-M.V.; software, A.-A.I.; validation, I.P., A.A.I. and V.E.A.; formal analysis, A.-M.V., I.P. and A.A.I.; investigation, A.-M.V., I.P. and A.A.I.; resources, L.L.B.; data curation, A.A.I.; writing--original draft preparation, A.-M.V.; writing--review and editing, I.P., A.A.I., V.E.A. and N.-S.A.; visualization, A.A.I.; supervision, I.P.; project administration, I.P.; funding acquisition, I.P. and L.L.B. All authors have read and agreed to the published version of the manuscript.  
This research was partly funded by Interreg Danube Transnational Programme SIMONA, project grant number DTP2-093-2.1, for sampling and chemical analyses and partly by the Ministry of Research, Innovation and Digitization of Romania through \"Program Nucleu\", PN 23-39-04-03 for writing and publishing.  
Not applicable.  
The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author.  
We are grateful to [PERSON] for his contributions to the SIMONA project, particularly regarding the sampling methodology and for his involvement in the suspended, bottom, and floodplain sediments collection campaigns.  
The authors declare no conflict of interest. The funders had no role in the study's design; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the result.