# Integrative Assessment of Sediment Quality in the Sao Francisco River (Mina Gerais, Brazil)
## 4 Discussion  
This study identified the degradation in the surrounding area of the SFR course using the chemical measurement of sediments and macro-benthic community structure. This area, located between the Tres Marias reservoir and around 300 m downstream of the effluent discharge point of the refining factory, showed several sources of contamination. In this kind of situation with multiple stressors, it is necessary to assess the overall sediment quality, and the use of multiple lines of evidence with an integrative approach is recommended [31; 32; 33; 34; 35; 36]. The use of these multiple lines of evidence integrated with a weight-of-evidence approach (WOE) links the results obtained in each LOE, in this case, physicochemical parameters and benthic community structure indexes. Metal contamination has been extensively studied, but metal bioavailability and its effects are not commonly studied in this region [1; 2; 37; 38]. The environmental state of the SFR was evaluated in this study using different lines-of-evidence (LOEs), which were integrated using the BIOENV procedure. Benthic infaunal communities, as living components of sediments, represent the integrated response of the biological effects of pollutant contents on sediment samples. The results obtained using the classical descriptive parameters show the lowest values of Margalef richness (0.08) and Shannon-Wiener diversity (0.12), as well as the BMWP score system (23.34), at the BG4 station. Moreover, this station also showed the highest values of Pielou evenness (0.88). Furthermore, this station showed a significant (\(p<0.05\)) difference in the macro-benthic community structure results compared with those obtained for the other stations. Thus, the highest descriptive parameters were observed at different stations, showing, at SF3, the highest values of the abundance of taxa (6.40), Margalef richness (0.93), and Shannon-Wiener diversity (1.33). Significant differences (\(p<0.05\)) were only found in the BMWP score results obtained at the BG4 and SF2 stations, which can be observed in the MDS analysis (Figure 3). Furthermore, the SIMPER analysis showed two of three species (_Polypedium_ sp. and _Tanyatarsus_ sp.) that were classified as sensitive by [39], and the _Tunitarsus formosanus_ species, which was classified as sensitive [40; 41; 42]. Additionally, the other marked species (_Cryptochronomus_ sp. ), according to [43; 44], typically prefers well-oxygenated sandy substrates and is generally intolerant to polluted conditions. [_Polypedium trigonous_ species showed a positive relationship with most of the organic pollutants, such as TOM, ammonium, and nitrateas well as trace metals Zn, Cu, and Mn [45]. [PERSON]. [41] reported that _Polypedium_ sp. was very tolerant to metal contamination. Despite the use of biotic indices having some limitations, [PERSON]. [3] used the BMWP score system in this area with good results. Moreover, according to this index, the analyzed area of the SFR showed a 'low' environmental quality classification, except for the station located upstream of the factory, which showed a'regular' environmental quality classification. Based on these results, it can be considered that the factory exerts negative effects that are reflected in downstream stations. However, the BG4 station, which showed the worst quality classification, was located near the Tres Marias WWTP and far away from the influence of the mining factory. The community at this station seemed to be significantly affected (\(p<0.05\)) by this plant because of the discharge of urban waste, presenting a very different specific composition (abounding nematode and oligochaete species). Indeed, these species are well-known pollution bioindicators, and WWTPs can deposit large amounts of organic matter and nutrients into receiving waterways, leading to eutrophication [46] and temporary oxygen deficits [47]. The BMWP score system itself, or a modified version of this index, has been previously applied in other countries in order to study the water quality of rivers.