Nitrogen addition increases the ecological and human health risks of PAHs in different fractions of soil in sewage-irrigated area

Abstract

Nitrogen (N) is one of the most important nutrients required by soil and crops. N addition improves soil quality and fertility. However, long-term N addition changes the soil environment, which may affect the adsorption and accumulation of organic pollutants in soil. The adsorption of pollutants by the light fractions (LF) and heavy fractions (HF) of soil, and their resulting risks, might differ. In addition, several organic pollutants, especially PAHs, accumulate in farmland soil under long-term sewage irrigation. However, few studies have examined the response of PAHs to N addition in soil in sewage-irrigated areas, including whether there is a difference in the response of the LF and HF of soil. Here, a long-term experiment was carried out in farmland soils in typical sewage-irrigated areas to reveal the adsorption and accumulation of PAHs in bulk soil, LF, and HF, and the human health and ecological environment risks posed by PAHs under different levels of N addition. Under long-term N addition, the concentration of PAHs in soil increased and fluctuated from 7598 μg kg−1 to 10,414 μg kg−1. Significant differences in the PAHs concentration in the LF (5048 μg kg−1 to 1889 μg kg−1) and HF (2536 μg kg−1 to 8521 μg kg−1) and the human health and ecological risks of soil with N addition in typical sewage-irrigated areas were observed. The HF of soil was characterized by low carcinogenic and ecological risks. The results of our research provide insight into possible management actions that could be taken to enhance the environmental protection and safety of agricultural production activities, such as sustainability fertilization.