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This study examines the characteristics and ecological risks of PAH pollution in soil from a retired coking plant and its effects on soil carbon cycling.

June 12, 2026Open Access

Characteristics, Ecological Risks, and the Impacts on Soil Carbon Cycling of PAH Pollution in the Soil of a Retired Coking Plant in Zaozhuang, Northern China

Key Points

This study examines the characteristics and ecological risks of PAH pollution in soil from a retired coking plant and its effects on soil carbon cycling.
Analyzed soil samples for PAH concentration and composition, focusing on high-molecular-weight PAHs.
Conducted metagenomic analysis to evaluate functional gene abundance related to soil carbon cycling.
Assessed ecological risk using the toxicity equivalent factor (TEF) method.
PAH concentration in surface soil ranged from 3.79 to 554 mg·kg−1, average 147.6 mg·kg−1; HMW-PAHs constituted 65.7% to 83.4% of total PAHs.
PAHs predominantly originated from coal and biomass combustion, indicating a severe ecological risk.
Alpha-amylase gene abundance in PAH-contaminated soil was significantly higher than in reference soil (p < 0.05).

Abstract

During the industrial restructuring in China, numerous outdated coking enterprises were phased out. Despite the cessation of production for several years, the soil in the production area of the retired coking plant remains heavily contaminated with polycyclic aromatic hydrocarbons (PAHs), which continue to adversely affect soil health. However, research on the pollution characteristics of soil PAHs under prolonged PAH exposure and the associated changes in functional genes related to soil carbon cycling is still inadequate. This study aims to identify the pollution characteristics and ecological risks of PAHs in the coking plant and to investigate the effects of long-term PAH contamination from abandoned coking plants on the functional genes involved in soil carbon cycling. It was found that PAHs in the soil were predominantly composed of high-molecular-weight PAHs (HMW-PAHs), which constituted 65.7% to 83.4% of the total PAH content. The total concentration of PAHs in the surface soil ranged from 3.79 to 554 mg·kg−1, with an average concentration of 147.6 mg·kg−1. Source analysis based on isomer ratios indicated that PAHs primarily originated from the combustion of coal and biomass. Utilizing the toxicity equivalent factor (TEF) method, we found that the PAH levels in the CA group exceeded the Serious Risk Concentration, indicating that PAH pollution poses a potential threat to the ecological environment. Metagenomic analysis revealed that the gene abundance of alpha-amylase in the CA group was significantly higher than that in the OLA group (p < 0.05), suggesting that prolonged exposure to PAHs has enhanced the starch hydrolysis capabilities of soil microorganisms. The findings of this study refine methods for assessing the risks associated with soil PAH contamination and provide a theoretical foundation for the risk management and reuse of retired coking plant sites.

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