*3.4. Bioaccumulation of PCDD/Fs and DL-PCBs in Crabs*

Sediments, aquacultural water, aquatic plants, shore plants, and feed can all enter crabs, so pollutants from each aquacultural process can accumulate in crabs, posing a threat to our health. The above results showed that the DL-PCBs to PCDD/Fs concentration ratio in farm crabs was 191.62%. In sediments, aquacultural water, aquatic plants, shore plants, and feed, the DL-PCB to PCDD/F concentration ratios were 0.20%, 2.72%, 2.22%, 13.36%, and 2553.51%, respectively. In contrast, the concentrations of PCDD/Fs were higher in sediments, aquacultural water, aquatic plants, and shore plants than in crabs, while the concentrations of DL-PCBs were lower in sediments, aquacultural water, aquatic plants, and shore plants than in crabs (Figure S1). These results indicate that crabs bioaccumulate DL-PCBs more readily than PCDD/Fs and that raw materials used in feed may be contaminated with DL-PCBs.

To determine the key link responsible for the accumulation of pollutants in crabs, we conducted a correlation analysis of the residual pollutants in crabs and the potential sources, and the correlation coefficient R was used to measure the relationship between the crabs and potential sources. The correlation coefficient between crabs and sediment was 0.89 (R > 0.8), showing a strong correlation, while the correlation coefficient between crabs and aquaculture water was 0.28, showing a weak correlation and suggesting that the accumulation of PCDD/Fs and DL-PCBs in crabs in aquaculture mainly comes from sediments (Figure 6). PCDD/Fs and DL-PCBs can enter crabs through feed, water, aquatic plants, and shore plants; remain in crab tissues through distribution and metabolism; are excreted in feces and urine; and further migrate into sediments, increasing the exposure of crabs to pollutants.

**Figure 6.** Correlation analysis of the residual pollutants in Chinese mitten crabs and the potential sources.
