Polycyclic aromatic hydrocarbons and black carbon in intertidal sediments of China coastal zones: Concentration, ecological risk, source and their relationship

Polycyclic aromatic hydrocarbons (PAHs) and black carbon (BC) have attracted many attentions, especially in the coastal environments. In this study, spatiotemporal distributions of PAHs and BC, and the correlations between BC and PAHs were investigated in the intertidal sediments of China coastal zones. BC in sediments was measured through dichromate oxidation (BC_Cr) and thermal oxidation (BC_CTO). The concentrations of BC_Cr in the intertidal sediments ranged between 0.61 and 6.32 mg g^− 1, while BC_CTO ranged between 0.57 and 4.76 mg g^− 1. Spatial variations of δ¹³C signatures in TOC and BC were observed, varying from − 21.13‰ to − 24.87‰ and from − 23.53‰ to − 16.78‰, respectively. PAH contents of sediments ranged from 195.9 to 4610.2 ng g^− 1 in winter and 98.2 to 2796.5 ng g^− 1 in summer, and significantly seasonal variations were observed at most sampling sites. However, the results of potential toxicity assessment indicated low ecological risk in the intertidal sediments of China coastal zones. Greater concentrations of PAHs measured in the sediments of estuarine environments indicated that rivers runoff may have been responsible for the higher PAH pollution levels in the intertidal sediments of China coastal zones. Pearson's correlation analysis suggested that pyrogenic compounds of PAH were significantly related to BC, due to that both BC and these compounds derived mainly from the combustion process of fossil fuels and biomass. Overall, increasing energy consumptions caused by anthropogenic activities can contribute more emissions of BC as well as PAHs and thus improve the importance of BC in indicating pyrogenic compounds of PAHs in the intertidal sediments of China coastal zones.