Field-scale bioremediation of dichlorodiphenyl trichloroethanes (DDTs) and polycyclic aromatic hydrocarbons (PAHs) contaminated farmland soil from the Shenyang North New Area of China was studied using the bacteria Arthrobacter globiformis. The additive effects of different concentrations of biosurfactant rhamnolipids (RLs) and anionic–nonionic mixed surfactant (SDBS–Tween 80) were evaluated. DDT and PAH removal rates by A. globiformis after 150 days of remediation were 52.1% and 21.9%, respectively. At the optimum RL concentration of 5 mg kg⁻¹, DDTs and PAHs had removal rates of 64.3% and 35.6%, respectively, at 150 days. This was 60.7% and 29.3% higher than the control; 36.9% and 19.8% higher than soil with RL-5 alone; and 12.2% and 13.8% higher than the A. globiformis treatment alone. RL-5 can enhance soil enzyme activity and A. globiformis reproduction during the DDT and PAH biodegradation processes. This study illustrates a highly efficient, low-cost in situ soil bioremediation technology that could have practical utility.

The Chaihe Pb-Zn mine, one of the largest Pb-Zn mines in northeast China, began to be exploited aggressively in 1966, but the degree of environmental impact is not well understood. Therefore, this study conducts a systematic study on the farmland areas upstream, downstream and around the lead-zinc mine, and metals, such as chromium (Cr), nickel (Ni), mercury (Hg), zinc (Zn), cadmium (Cd), lead (Pb), copper (Cu), and arsenic (As), were detected. The coefficient of variation (CV) indicated that, with the exception of Cu, Ni, and Cr, the metals in the surface soil were markedly affected by human activities. Enrichment factors further demonstrated that Hg, Cd, Pb, and Zn primarily originated from anthropogenic sources, while As, Ni, and Cr mainly stemmed from natural sources. Geoaccumulation index (I_geo) values disclosed that the contamination of Cd and Hg in the areas was particularly severe. The USEPA health risk model was employed to calculate the non - carcinogenic risk (HI) and carcinogenic risk (CR). In terms of health risk, the order of mean HI is as follows: Pb > As > Hg > Cd > Cr > Zn > Cu > Ni, and the order of mean CR is As > Pb > Cr > Cd > Ni. The results also illustrated that oral ingestion was the most important during the three exposure pathways, and children were shown to be prone to metal pollution. The CR for children, adolescents, adults, and total lifetime were acceptable, but HI for children, and total lifetime were unacceptable. Therefore, the results indicated significant contamination of Pb, Zn, Cd, and Hg in the surface soil around the Pb–Zn mine, offering valuable insights for enhancing ecological restoration and environmental protection efforts.

A novel bacterium, Arthrobacter globiformis DC-1, capable of degrading DDT as its sole carbon and energy source, was isolated from DDT-contaminated agricultural soil. The bacterium can degrade up to 76.3% of the DDT at a concentration of 10 mg/L in the mineral salt medium (MSM) within 1 day of incubation. The effects of various environmental conditions, such as the concentration of DDT, temperature, pH and additional carbon sources, on its growth and biodegrading capacity of DDT were investigated in the MSM. The A. globiformis DC-1 strain could efficiently grow and degrade DDT at a wide range of concentrations, with the maximum growth and degradation rate at 10 mg/LDDT, followed by inhibitory effects at higher concentrations (20 and 30 mg/LDDT). Mesophilic temperatures (25–30 °C) and a pH of 7–7.5 were the most suitable conditions for the growth and biodegradation. The presence of carbon sources significantly increased the growth of the DC-1 strain; however, degradation was inhibited in the present of glucose, sucrose and fructose, and peptone was determined to be the most appropriate carbon source for A. globiformis DC-1. The optimal DDT degradation (84.2%) was observed at 10 mg/LDDT, peptone as carbon source in pH 7.5 at 30 °C with 1 day of incubation. This strain could also degrade DDE, DDD and DDT simultaneously as the sole carbon and energy source, with degradation rates reaching 70.61%, 64.43% and 60.24% in 10 days, respectively. The biodegradation pathway by A. globiformis DC-1 revealed that DDT was converted to DDD and DDE via dechlorination and dehydrochlorination, respectively; subsequently, both DDD and DDE transformed to DDMU through further dechlorination, and finally, after ring opening, DDMU was mineralized to carbon dioxide. No intermediate metabolites accumulation was observed during the GC/MS analysis, demonstrating that the A. globiformis DC-1 strain can be used for the bioremediation of DDT residues in the environment.

Polycyclic aromatic hydrocarbons (PAHs) occur in the surface water of the Taizi River, China. The levels and composition patterns were studied by high-performance liquid chromatography and PAHs sources were analyzed using the isomer ratios of selected PAH compounds. In the flood period, concentrations of PAHs ranged from 1562.52 to 4176.15 ng/L with a mean of 2562.56 ng/L. In the dry period, concentrations ranged from 498.09 to 3218.27 ng/L with a mean of 1389.30 ng/L. The levels of sigma PAHs in the study area were higher than in other locations. The dominant PAHs were Baa in the flood period and Phe, Flu and Pyr in the dry period. The composition of PAHs was dominated by four-ring PAHs (51.72-82.69%) in the flood period and three-ring (28.25-50.10%) and four-ring PAHs (38.28-56.28%) in the dry period. The isomer ratios of Ant/(Ant + Phe), Flu/(Flu + Pyr) and compositional analysis were selected to identify the sources of PAHs. Coal combustion and traffic emission were the sources of PAHs in the surface water of the Taizi River, and the major source of PAHs was from combustion of coal.