Distribution, source, and ecological risks of polycyclic aromatic hydrocarbons in surface sediments from contaminated urban rivers across China

Sediments are one of the ultimate destinies of polycyclic aromatic hydrocarbons (PAHs) in the environment. This study aims to investigate the distribution, source characteristics, and ecological risks of PAHs in black-odorous urban river sediments, providing support for environmental safety assessment and pollution control.

A total of 173 surface sediment samples were collected and analyzed for 17 types of PAHs using gas chromatography-mass spectrometry (GC-MS). The sources of PAHs were identified using isomer ratio indicator analysis and a positive matrix factorization model (PMF). Furthermore, the health risks of the PAHs were assessed using the Sediment Quality Guidelines and the organic carbon normalization method.

The total PAH concentration ranged from 0.02 to 52 μg g⁻¹ dry weight. PMF and isomer ratio indicators revealed that the predominant sources were petroleum and fuel combustion. The ratio of perylene to pentacyclic aromatic isomers was < 10 in 75% of the samples. Most areas posed a low risk.

PAH concentrations exceeded those typically found in lakes and river surface sediments, ordinary industrial parks, and agricultural soils. However, no distinct spatial distribution was evident. The primary contributors were fossil, coal, and biomass fuel combustion. Moreover, the source of perylene exhibited spatial variability—natural biodiagenesis in South China and anthropogenic pyrolysis in North China. These suggest that as an index to trace the sediment footprint of large river influences, its environmental significance varied with different locations. The ecological risk assessment indicated that PAHs in most polluted urban river sediments posed low to moderate risks.