## 3 Results and Discussion
### Linking Contamination and Toxicity
This could be informative regarding the Microtax(r) responses in these sediments being lower in the rest of the toxicity tests, and as well as regarding a moderate toxic response in this sediment. The screening nature of this test has been reported [17]. In addition, the moderate toxicity observed in this station is related to a moderate correlation of three metals as well (Cu, Cd, and As), but not to the rest of the analyzed metals. Moreover, different sources of these metals could be included in the explanation of these correlations, and Cu, Cd, and As elements could be part of organic compounds, such as pesticides and fertilizers coming from agriculture activities which have a high economic impact in this area. Furthermore, agriculture has economic importance \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Variance \%** & **Factor 1** & **Factor 2** & **Factor 3** \\  & **78.93** & **14.31** & **6.76** \\ \hline _A. brevicornis_ mortality & 0.764 & 0.555 & \(-\)0.327 \\ _V. fischeri_ bioluminescence inhibition & & 0.954 & 0.301 \\ _P. lividus_ fertilization & 0.881 & 0.436 & \\ _P. lividus_ embryogenesis & 0.917 & 0.322 & \\ _T. tubifex_ mortality & 0.410 & 0.346 & 0.843 \\ _T. tubifex_ TYG & 0.874 & \(-\)0.413 & 0.378 \\ _T. tubifex_ TGR & & 0.982 & \\ Cu & 0.948 & 0.309 & \\ Zn & 0.974 & & \\ Fe & 0.960 & & \\ Co & 0.939 & & 0.332 \\ Ni & 0.956 & & \\ Cd & 0.948 & 0.301 & \\ Pb & 0.985 & & \\ As & 0.955 & 0.344 & \\ OC & 0.998 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Sorted rotated factor loadings of the original variables for the three principal factors results. Variables selected for the interpretation represented a loading of 0.30 or higher. in this area as reported by previous work [56]. In addition, the positive value of Factor 3 could confirm this different origin of the contamination of metals and the moderate toxicity observed in these sediments. Sediments at the station located nearby the city of Seville (SE) also show a positive score of Factor 1, informing about the contamination of metals and the toxicity associated with them. However, the values and correlations are lower than station AR and can be considered as intermediate in toxicity in this study. The negative values of Factors 2 and 3 confirm that sediments at this station are less contaminated than those at station AR. A previous sediment quality assessment was carried out with the biomarker responses of clams in the same stations [55]. AR and AL contamination resulted in the induction of biological stress, and SE contamination (As, Cd, and Cu) caused toxicity as biomarker effects. From these results, site-specific sediment quality guidelines can be derived for the area studied. These SQGs have been calculated following the procedure reported by [51] and slightly modified by [54]. The SQGs are shown in Table 3.  
These values have been compared with nationally and internationally accepted SQGs in order to establish a pollution range in this area, and with the aim of proving the validity of the use of these values to be applied in estuarine environments. In Table 4, this comparison can be observed in detail. Figure 4: Estimated factor scores from the sampling stations (Control, AR, AL, SE). The factor scores quantify the prevalence of each factor for every station and are established to define each factor. Comparing the results from this study with the different widely accepted SQGs, it is shown that not one of the metal concentrations founded in the Guadalquivir River fit with the action level proposed by these SQGs. However, the action level established in this study was proposed according to several laboratory bioassays, demonstrating sediment toxicity in all the cases with irreversible ecological effects. The SQGs calculated in the present study are in the interval of the international guidelines for all the metals [57]. Only Zn and Pb showed lower values for the guidelines than the rest of the international proposed guidelines. Ni showed guideline values close to the lower guidelines proposed by [58].