To investigate the contamination of PCBs in agricultural soils irrigated chronically with polluted water and the distribution and migration of PCBs under long-term irrigation, 100 farmland soil profile samples were collected in the Yellow River irrigation area in Inner Mongolia, China, to determine PCB content. Cluster analysis was used to identify possible sources of PCBs products, and the USEPA Health Risk Evaluation Model assessed the health risks posed by PCBs to humans. The results showed that the detection rates of eight monomers in the different soil layers of each sample site ranged from 5% to 90%, and the concentration ranged from not detected to 87.71 ng·g⁻¹. The PCBs content showed a vertical distribution rule of accumulation in the shallow layer, sudden decrease in the middle layer. Low-chlorinated PCBs were dominant in each soil profile. Source identification indicated that PCB pollution in the study area originated mainly from the Aroclor1242, Aroclor1248, Aroclor1016, Aroclor1232, and Aroclor1221 industrial products and domestic transformer oil. Finally, a health risk assessment demonstrated that child and adult groups in study area were exposed to negligible carcinogenic and noncarcinogenic risks.

As the largest group of synthetic dyes, azo dyes can pose various health and environmental risks due to their widespread use and challenging degradation. Laccases are efficient green biocatalysts for the degradation of organic pollutants. Herein, we report the in situ packaging of laccase in copper-doped zeolitic imidazolate framework-8 (ZIF-8) for the decolorization of reactive black 5, which is a model azo dye. The immobilization support (Cu5/mZIF-8) was obtained via lowering the precursor ratio of ZIF-8 and incorporating copper ions during the synthesis process. Cu5/mZIF-8 were found to be nanospheres with an average diameter of around 150 nm. Laccase encapsulated in Cu5/mZIF-8 showed an activity recovery of 75.6%, which was 2.2 times higher than that of the laccase embedded in ZIF-8. Meanwhile, the immobilized laccase (Lac@Cu5/mZIF-8) showed a higher catalytic activity in organic solvents than that of the free enzyme. In the presence of a mediator, Lac@Cu5/mZIF-8 could remove 95.7% of reactive black 5 in 40 min. After four consecutive cycles, the dye decolorization efficiency declined to 28%. About four transformation products of reactive black 5 were identified via LC-MS analysis, and the potential decolorization mechanism was proposed. The results indicated that the immobilized laccase could be used as an efficient biocatalyst in dye decolorization.