The Yellow River Delta (YRD) is a typical agricultural and petrochemical industrial area of China. To assess the current status of phthalate esters (PAEs) of soil residues, soil samples (0∼20 cm) (n = 82) were collected in Bincheng District, at the geographic center of the YRD. PAEs were detected in all topsoil samples analyzed, which indicated that PAEs are ubiquitous environmental contaminants. Concentrations of 11 PAEs are in the range of 0.794∼19.504 μg g⁻¹, with an average value of 2.975 μg g⁻¹. It was presented that PAEs pollution in this area was weak and monotonously increasing along the rural–urban gradient. Higher concentrations were observed from roadsides (and/or gutters), densely anthropogenic activities areas (such as the urbanization and industrialization), and agriculture influence district, which mainly originated from construction waste, municipal sewage, agricultural waste and pesticide, discarded plastic effusion and atmospheric depositions. Concentrations of PAEs were weakly positivity correlated with soil organic carbon content and pH, which suggested both of them can affect the distribution of PAEs. The concentration of di (2-ethylhexyl) phthalate and di-n-butyl phthalate dominated in the 11 PAEs, with the average values of 0.735 and 1.915 μg g⁻¹, respectively, and accounted for 92.1 % of the whole PAEs’ concentrations. No significant differences of PAE congeneric profiles were observed between our work and others previously reported, which is consistent with the use of similar commercial PAEs around the world.

Biochar and beneficial microorganisms (BM) is considered promising soil amendment for saline-alkali amelioration and soil carbon storage.However, the effects of biochar combined with BM addition soil organic carbon (SOC) accumulation and microbial characteristics are less known in coastal saline-alkali soil. Herein, we investigated the SOC content and fractions, soil carbon enzyme activities, and microbial community composition in coastal saline-alkali soil, following three levels of biochar and BM addition. Compared to the control treatment, biochar and BM application effectively reduced soil salinity by 37.58–66.53% and increased soil NH₄⁺ by 9.49–121.16% and NO₃⁻ by 43.56–254.28%, respectively. Biochar integrated with BM addition significantly increased the content of SOC, soil mineral-associated organic carbon (MAOC), soil particulate organic carbon (POC), and carbon pool management index (CPMI) by 37.76–108.02%, 15.43–140.44%, 13.73–64.55%, and 81.11–154.61%, respectively, compared with CK treatment. Additionally, biochar and BM significantly enhanced the activities of soil carbon cycle enzymes, including α-1,4-glucosidase (14.54–124.45%), β-1,4-glucosidase (12.71–133.98%), and cellulose hydrolase (6.07–19.17%). Biochar and BM addition also improved the bacterial diversity and altered the microbial composition at the phylum level. The co-addition of biochar and BM improved SOC by decreasing soil salinity and, enhancing soil nutrient availability, soil carbon cycle enzymes, and microbial activity. Furthermore, the combination of 4% biochar and BM exhibited the highest MAOC/POC ratio, demonstrating the most significant impacts on enhancing SOC stability in coastal saline-alkali soil. This study highlighted that the combined use of biochar and BM could serve as a promising approach to fortify soil carbon pool content and stability in saline-alkali land.