## 3 Results and Discussion
### Linking Contamination and Toxicity  
A PCA factor analysis was performed in order to assess the environmental quality of the study area from the Guadalquivir River, employing acute toxicity and chemical analysis. The application of principal component analysis indicated that the original set of variables could be narrowed down to three new factors that explained 100% of the total variance (Table 2). Factor analysis was performed to link the results of the five bioassays (Microto\({}^{\circledR}\) BSPT, _A. brevicornis_, both with _P. lividus_, and _T. tubifex_) with the concentration of the nine contaminants (Cu, Zn, Fe, Co, Ni, Cd, Pb, As, and organic carbon). The first principal factor (F1) explains 78.93% of the total variance and group responses of the sediment toxicity tests (excluding Microto\({}^{\circledR}\) and total growth rate measured in _T. tubifex_), metals, and organic carbon analyzed in sediments. However, this low loading of Microto\({}^{\circledR}\) in this factor could be due to the fact that this test is a screening bioassay; it is suggested that this biotest by itself may not be representative in certain cases of the full impact of a given pollutant on an ecosystem [17]. The second factor (F2) accounted for 14.31% of the total variance and was correlating the concentration of Cd in sediment with all the responses measured in the bioassays (by presenting positive loadings) except for total young number of _T. tubifex_ (which presented a negative value). This correlation between these metals and _T. tubifex_ parameters is in agreement with [40], who showed high sensitivity to copper and cadmium. The third factor (F3) accounted for 6.76% of the variance. This factor has  
Figure 3: Mean and SD of toxicity endpoints of the _T. tubifex_ bioassay: TGR (d\({}^{-1}\)), TYG, and mortality (%) at each station. Asterisk (*) indicates significant differences (_p_ \(<\) 0.05) between samples and the control (BAR). associated contamination by Co to _A. brevicornis_ and _T. tubifex_ mortality and TYG. Only _A. brevicornis_ mortality showed negative loadings. Previous results reported by [13] also related the contamination by Co to the _A. brevicornis_ mortality indicating a particular sensitivity of this species to Co.  
A graphical representation of the estimated factor values corresponding to each sampling station is presented in order to confirm the descriptions of these factors (Figure 3). Through the sediment toxicity test under laboratory conditions, it has been demonstrated that the environmental degradation due to metals in the Guadalquivir river water course can be translated into a potential ecological risk. The study here conducted assessments of the synergetic effect of all the contaminants present in the sediment analyzed. The integration of the results from the different lines of evidence makes it possible to address the extension of the metal contamination and the relationship between these metals (and other potential contaminants not measured) on the effects observed in the toxicity tests conducted. Based on the multivariate analysis results (Table 2 and Figure 4), different contamination and toxicity processes can be defined at each of the sediments studied here: sediments at station AR show the highest score value for Factor 1, Factor 2 being lowest and negative. The toxicity associated with metals is related to factor 1. This fact can be explained by two different sources of metals and the toxicity of them (Cd, and in lower weight Cu and As, from the negative value of Factor 2). It could be related to the presence of a dam 1 km upstream of the AR sample point that could explain potential phenomena of accumulation and thr release of different metals depending on the season. Sediments at station AL show the highest value score for Factor 2 and a negative value in Factor 1. Factor 2 includes correlations with toxicity test responses lower than F1 except for Microtax.