###### Abstract  
The amphipod (_Hyalella azteca_) and zebrafish (_Brachydanio rerio_) embryos were used for toxicological sediment porewater testing. Porewaters from 35 sampling stations of eight streams in southern Taiwan were screened for toxic effects and their relationship with 6 metal and 16 polycyclic aromatic hydrocarbons (PAHs). Concentration analysis results showed that the following PAHs, naphthalene, benzo(b)fluoranthene, dibenz(a,h)anthracene, acenaphthalene, and the heavy metal cadmium were not detected in 35 sampling stations. The highest detection rate of 94.1% was caused by the PAHs fluoranthene and pyrene. The highest detection rate of the metal zinc was 88.6% of 35 analyzed samples. The majority of samples (88%) were classified as level tier 1 according to USEPA national sediment inventory. This indicates the probability of adverse effects on aquatic life or human health. The results of a zebrafish embryo test showed that heart rate and survival were significantly reduced with all porewater samples. Therefore, fish exposed to contaminated river conditions may be affected in their cardiovascular functions. Looking at correlations between toxic effects of metals and PAHs, we found that phenanthrene, anthracene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, and benzo(a)pyrene were low, while fluorene was highly correlated with toxic effects of metals. iv 2021 26 August 2021 26 August 2021 30 August 2021  
organisms depend on their livelihoods, so porewater is considered as an important toxic exposure pathway for benthic organisms [8], but chemical data can also directly provide relevant information for the interpretation of sediment toxicity data [6]. In recent years, porewater has become a valuable tool for evaluating the mobility, bioavailability, and toxicity of various pollutants [8; 9; 10; 11]. Generally, indications provided from chemical analysis and biological exposure are used to evaluate whether--pollutants cause toxicity to organisms. Benthic communities are frequently used as indicators for watershed biomonitoring [12; 13]. More recently, scientists studied the distribution and toxic effects of heavy metals and PAHs [14; 15; 16; 17; 18; 19; 20]. Micropollutants such as metals and organics can affect benthic communities by altering their physiology as well as their structure [20; 21]. Polycyclic aromatic hydrocarbons (PAHs) are a class of the most important organic compounds containing stable aromatic rings as their molecular skeleton. They are lipophilic, carcinogenic, and have a tendency to adsorb to sediment particles [22; 23; 24]. They are not easy to degrade in the environment [23; 25]. The main sources of PAH contamination are oil spills and hospital and municipal discharge. PAHs also accumulate in the organs of fish or other aquatic organisms, possibly with different affinities to different organs and tissues (e.g., the concentration of PAHs in gill may be greater than in muscle) [26; 27]. This way, they are seriously endangering environmental integrity and human health. Approximately 130 PAHs have been identified [28]. The US EPA has classified 16 of the PAHs as priority-pollutants based on toxicity, their potential for human exposure, frequency of occurrence at hazardous waste sites, and the extent of information availability. These include: naphthalene, acenapthylene, acenapththene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[g,h,i] perylene, indeno [1,2,3-c,d]pyrene, and dibenz[a,h]anthracene [29]. Among them, benzo(a)pyrene is currently regarded as most toxic according to the toxic equivalent quantity (TEQ) due to its highest potency in terms of carcinogenicity [30]. Metals and metalloids are collectively referred to as heavy metals [31]. Some heavy metals, also called trace metals (e.g., Mn, Fe, Co, Ni), are essential to organisms, while other heavy metals (e.g., Cd, Pb, and Hg) are nonessential and usually toxic even in trace amounts [32].