# Integrative Assessment of Sediment Quality in the Sao Francisco River (Mina Gerais, Brazil)
## 4 Discussion
The results in [48] show significant differences between quite unpolluted areas and anthropogenicallyimpacted sites along the Nysa Klodzka River (Poland), as well as high correlations with some chemical variables. The modified version of the IBMWP (Iberian biomonitoring working party) score was successfully applied by [49] to 50 Iberian rivers, showing strong correlations between this index and different physicochemical parameters. Both studies show results and relationships similar to those reported in the present work. Sediment quality assessment has demonstrated the importance of sediment characterization in terms of organic matter, grain size, metals [50, 51, 52, 53], and SEM-AVS-SEM [54] in determining the environmental quality conditions, mainly in heavily populated and industrialized regions. The results here obtained related to sediment characterization show three main different groups of findings: (i) station SF1 presented the lowest values of fines, SEM-AVSs, Al, Cu, Pb, Zn, and Hg, but the highest values of TOC, Cr, and Fe; (ii) station BG4 showed the lowest values of TOC, As, Co, Cr, and Ni, but the highest values of fines, nitrate, ammonium, ammonia, ammoniacal nitrogen, SEM-AVSs, and Al; (iii) the other two stations, SF3 and SF2, showed the highest Cu, Pb, Zn, and Hg concentrations, and the highest Co and Ni concentrations, respectively. As reported by [55], the nitrate values found in the Hindon River, which is also polluted by wastewater, were in the range of 96-245 \(\upmu\)g/L, i.e., lower values than those found in sediments from the BG4 station. Many rivers around the world are suffering contamination by industrial, agricultural, and domestic activities. The case study on the Axios/Vardar River in Southeastern Europe exposed the results of the water quality in an area surrounding a metal factory that receives domestic wastewater and agricultural runoff. In this case, the maximum values of nitrates and ammonium were 0.22 mg/L and 1.13 mg/L, respectively, which are again lower than those found in this study. The metal concentrations in that river were Pb (13.126 \(\upmu\)g/L), Zn (49 \(\upmu\)g/L), Cd (0.72 mg/L), and Cr (64 \(\upmu\)g/L), indicating that it was fairly less polluted than the river studied here (SFR). Taking into account the SEM-AVS results, all the sampling stations showed potential alterations in benthic organisms [19], showing SEM-AVS values higher than 0. Station BG4, had the highest value (3687.98), also had the highest alteration values of the calculated quality indices based on the benthic community structure (BMWP, S\({}^{\prime}\), N\({}^{\prime}\), d\({}^{\prime}\), H\({}^{\prime}\), and J\({}^{\prime}\)), as mentioned above. Moreover, according to the benchmarks of [3], the toxicity of our sediment samples was classified as unlikely (SF1 and ZM2 stations), uncertain (SF2 and SF3 stations), or likely (BG4 station). The highest concentrations of nitrogen species were analyzed in sediments from station BG4, which was located downstream of the Tres Marias WWTP. These results are in concordance with those reported by [56]. These authors concluded that wastewater contains significant amounts of ammonium, as only a small proportion is oxidized by conventional treatment plants [57]. Furthermore, as exposed by [58], sediments that are rich in organic matter and microbial biomass host the greatest number of denitrification processes, since they require sub-oxic conditions and a source of nitrate (from external inputs or the nitrification of ammonium). The link between cause (sediment contamination) and effect (macro-benthic community structure) was determined using BIOENV analysis. The obtained results indicate that a large proportion of the among-site variance in the abundance of benthic fauna along the studied river course was strongly associated with the measured environmental variables, particularly, nitrogen chemical species and metals Al and Zn.