## 3 Results and Discussion
### Comparison of Results from PAH Analysis and Biological Survival Rates
azteca_. A possible reason is that the death of _H. azteca_ may be due to other classes of pollutants, or due to high content of TOC combined with free metal ions, which may decrease their bioavailability and, consequently, reduce their toxicity [47, 48, 49]. The literature mentioned that the concentration of heavy metals in porewater is high, not all of which comes from the isolation of heavy metals in sediments, but may be caused by the release of contaminated groundwater [50]. Studies have also pointed out that the copper concentration in the sediment porewater of lakes is positively correlated with organic matter content, but the mortality of chironamid larvae could not be explained by the copper concentration in the porewater [51]. Therefore, it is impossible to determine the cause of the mortality of _H. azteca_ based on the concentration of trace metals in the porewater alone. Interstitial Water Benchmark Units (IWBUs) and Interstitial Water Toxic Units (IWTUs) Used to Determine Toxicity in Sediment Porewater  
In the present study, the survival rates of _H. azteca_ and IWBUs were calculated as shown in Figure 7. The results of IWBUs (>1 means toxic) showed that 22 sample sites were toxic and 13 sample sites were not. The results of \(\Sigma\)IWTU showed that 77% of the sample sites exceeded 1.0 (Figure 8), benthic organisms were not protected, and adverse effects may occur. According to the survival rate of _Hyalella azteca_, 28 sample sites were \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sites** & **Cr** & **Ni** & **Cu** & **Zn** & **Pb** \\ \hline
**YS1** & 0.017 & ND & ND & 0.02 & ND \\
**YS2** & 0.045 & ND & ND & 0.164 & ND \\
**YS3** & 0.046 & ND & ND & 0.153 & ND \\
**YS4** & 0.005 & ND & ND & 0.102 & ND \\
**YS5** & 0.025 & ND & ND & 0.171 & ND \\
**DB1** & 0.019 & ND & ND & 0.249 & ND \\
**DB2** & ND & ND & ND & 0.027 & ND \\
**DB3** & 0.017 & ND & 0.007 & 0.431 & ND \\
**DB4** & 0.031 & ND & ND & 0.313 & ND \\
**DB5** & 0.038 & ND & ND & ND & 0.939 & ND \\
**SY1** & 0.042 & ND & ND & 0.223 & ND \\
**SY2** & 0.212 & 0.029 & 0.01 & 0.554 & 0.005 \\
**SY3** & 0.183 & 0.022 & ND & 0.574 & ND \\
**AGD1** & ND & ND & ND & 1.034 & ND \\
**AGD2** & 0.025 & ND & ND & 0.878 & ND \\ HJ1 & 0.009 & ND & ND & 0.065 & ND \\ HJ2 & ND & ND & ND & 0.191 & ND \\ HJ3 & ND & ND & ND & ND & ND \\ HJ4 & ND & ND & 0.007 & 0.018 & ND \\ HJ5 & ND & ND & ND & ND & ND \\ HJ6 & ND & ND & ND & 0.023 & ND \\ HJ7 & ND & ND & ND & ND & ND \\ LK1 & 0.014 & 0.02 & 0.007 & 0.167 & ND \\ LK2 & 0.149 & 0.185 & ND & 3.333 & ND \\ LK3 & 0.029 & ND & ND & 0.594 & ND \\ WR1 & ND & ND & ND & 0.159 & ND \\ WR2 & ND & ND & ND & 0.041 & ND \\ WR3 & 0.012 & ND & ND & 1.011 & ND \\
**WR4** & 0.036 & 0.256 & 0.126 & 3.609 & 0.045 \\ WR5 & ND & ND & ND & ND & 0.016 & ND \\
**WR6** & ND & ND & ND & ND & 0.034 & ND \\
**DG1** & 0.007 & ND & ND & 0.123 & ND \\
**DG2** & 0.009 & ND & ND & 0.406 & 0.007 \\
**DG3** & 0.007 & ND & ND & 0.178 & ND \\
**DG4** & ND & ND & ND & ND & ND \\ \hline \hline \end{tabular}  
* Unit: mg/L. ND < MDLC7 (0.006 mg/L), Ni (0.014 mg/L), Cu (0.006 mg/L), Zn (0.012 mg/L), Pb (0.004 mg/L).  
\end{table} 
Table 5: Concentrations of heavy metals in sediment porewaters. toxic and 7 sample sites were not. In this study, IWBUs and \(\sum\)IWTUs were used to predict the biological toxicity of the porewater of the sediment of eight streams in southern Taiwan, with an accuracy of 79% and 85% (number of IWBUs (\(\sum\)IWTUs)) > 1 site, and corresponding to the percentage of sites with _Hyallela azeca_ survival rate < 80%, showing that both porewater toxicity calculations for metal and organic compounds can be used as a tool for initial toxicity predictions. When the sample station coincided with IWBUs > 1 and IWTUs > 1, _H. azeca_ exposure to the sample also showed toxic effects (survival rate < 80%), showing that the combination of IWBUs and IWTUs indicators can more effectively predict the potential toxicity of porewater.