## 3 Results and Discussion  
### HMs in the Sediments  
The concentrations of Hg, As, Cu, Pb, Cd, and Zn in surface sediments of the dumping area were 0.030-0.26, 7.90-19.8, 13.1-36.3, 17.4-54.7, 0.11-0.34, and 50.0-122 mg/kg, respectively, with an average of 0.080, 15.1, 24.5, 30.8, 0.21, and 97.6 mg/kg, respectively (Table 1). If the concentrations of pollutants in the sediments are lower than the threshold effect level (TEL), adverse biological effects are expected to rarely occur. If the concentrations of pollutants in the sediments are higher than the probable effect level (PEL), adverse effects are expected to frequently occur. If the concentrations of pollutants in the sediment are between the TEL and PEL, the probability of adverse biological effects is close to that of no adverse biological effects. In this study, the concentration of As in the sediments was higher than the TEL in each year, that of Cu was higher than the TEL except in 2013 and 2017, and that of Pb was lower than the TEL except in 2011 and 2012. The concentrations of Hg, Zn, and Cd were lower than the TEL. The concentrations of all HMs were lower than the PEL. The HMs in sediments from the dumping area may have adverse biological effects. The effect range low (ERL) and effect range medium (ERM) were proposed by the National Oceanic and Atmospheric Administration [27]. The results showed that the concentration of As was higher than ERL, and that of other HMs was lower than ERL and ERM. The concentrations of HMs in the surface sediments of all stations exceeded the background values of coastal sediments [26]. Hg, As, Cu, Pb, Cd, and Zn were approximately 2.7-, 1.9-, 1.6-, 1.5-, 3-, and 1.5-times higher than the coastal background values, respectively, indicating that the surface sediments of the dumping area have been slightly polluted over time. Although the concentrations of HMs in the sediments of the dumping area were higher than the background value, all the HMs except Hg fulfilled the class I standard of the Marine Sediment Quality Standard (MSQS) of China (GB 18668-2002). The quality of sediments in the marine dumping area was required to fulfill the class III standard of the MSQS. Therefore, the HM pollution was within an acceptable range. However, compliance with the sediment quality standards does not mean that HMs have no harm or risk, because the concentrations of HMs cannot fully reflect the pollution state [29], especially, the bioaccumulation and amplification of HMs in marine organisms pose potential health risks to human beings [30; 31]. The coefficient of variation (CV%) was used to explain the changes in HM concentrations in different years. It reflects the average degree of variation of each sampling \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Hg** & **As** & **Cu** & **Pb** & **Cd** & **Zn** & **References** \\ \hline
2011 & 0.050–0.090 & 14.2–17.4 & 20.2–31.5 & 29.7–32.3 & 0.15–0.21 & 108–117 & \\
2012 & 0.056–0.14 & 16.4–19.6 & 21.1–29.6 & 23.0–54.7 & 0.16–0.27 & 97.4–122 & \\
2013 & 0.054–0.086 & 16.1–17.8 & 19.8–36.3 & 19.9–36.0 & 0.16–0.34 & 66.1–116 & \\
2014 & 0.052–0.12 & 14.2–17.9 & 20.3–36.7 & 21.6–33.4 & 0.16–0.28 & 62.2–122 & This study \\
2016 & 0.053–0.26 & 14.2–19.8 & 21.8–25.4 & 25.4–32.8 & 0.22–0.32 & 88.6–119 & \\
2017 & 0.030–0.050 & 7.90–10.9 & 13.1–21.7 & 17.4–35.6 & 0.11–0.24 & 50.0–83.0 & \\ Average 1  \(\pm\) standard deviation & 0.080 \(\pm\) 0.041 & 15.1 \(\pm\) 3.20 & 24.5 \(\pm\) 4.40 & 30.8 \(\pm\) 7.70 & 0.21 \(\pm\) 0.061 & 97.6 \(\pm\) 20.5 & \\ Coefficient of variation (CV%) 3  \(\pm\) & 0.51 & 0.21 & 0.18 & 0.25 & 0.29 & 0.21 & \\ Class I 4  \(\pm\) & 0.2 & 20 & 35 & 60 & 0.5 & 150 & \\ Background & 0.03 & 7.7 & 15 & 20 & 0.07 & 65 & [26] \\ TEL 5  \(\pm\) & 0.13 & 7.24 & 18.7 & 30.2 & 0.68 & 124 & [27] \\ PEL 6  \(\pm\) & 0.7 & 41.6 & 108 & 112 & 4.21 & 271 & [27] \\ ERL 7  \(\pm\) & 0.15 & 8.2 & 34 & 46.7 & 1.2 & 150 & [28] \\ ERM 8  \(\pm\) & 0.71 & 70 & 270 & 218 & 9.6 & 410 & [28] \\ \hline \hline \end{tabular}
\end{table}