Nitrogen input leads to the differential accumulation of polycyclic aromatic hydrocarbons in the low- and high-density fractions in sewage-irrigated farmland soil

Abstract

Because of a shortage of water resources, sewage irrigation has become a popular management tool for farmland soil in arid areas of China; however, this has led to the accumulation of polycyclic aromatic hydrocarbons (PAHs) in soil. Soil is an important component of ecosystems, and nitrogen is an important nutrient required for plant growth. Nitrogen input can alter the physical, chemical, and biological processes in soil and thus lead to changes in soil organic matter and organic pollutants. However, whether these changes affect the accumulation of PAHs and whether such accumulation differs in the low-density fraction (LF) and high-density fraction (HF) of soil remains unclear. In this study, the response of PAHs in soil to nitrogen input (0, 100, 200, and 300 kg N ha−1 yr−1, respectively), including differences in LF and HF, were investigated through field experiments in a typical sewage-irrigated area. The results showed that nitrogen input could increase the concentrations of PAHs in soil from (7.6 ± 1.1) × 103 to (10.4 ± 0.6) × 103 μg kg−1 and lead to striking differences between the LF ((5.06 ± 0.75) × 103 to (1.89 ± 0.18) × 103 μg kg−1) and HF ((2.54 ± 0.36) × 103 to (8.54 ± 0.44) × 103 μg kg−1). Given the significant increase in global nitrogen input, our findings have implications for the optimization and management of agricultural activities in sewage irrigation areas, such as soil investigation before fertilization, the use of soil improvers, and the improvement of soil planting measures.