Characteristics and source apportionment of methylated polycyclic aromatic hydrocarbons in sediments of reservoirs from the Qiantangjiang River, Wujiang River, and Pearl River

Methylated polycyclic aromatic hydrocarbons (MePAHs) pose more toxicity and persistence than their parent compounds, yet their contamination levels in reservoir sediments remain poorly understood. We analyzed 44 MePAHs in 72 surface and 199 core sediment samples from three watersheds in China: Qiantangjiang River (QTJ), Wujiang River (WJ), and Pearl River (PR). Total MePAH concentrations (ΣMePAHs) ranged from 19.7 to 1270 ng/g, with methylnaphthalenes and methyl phenanthrenes dominating. Temporally, the ΣMePAHs of surface sediments showed a pattern of dry season (340 ± 250 ng/g) > wet season (303 ± 189 ng/g). Spatially, the ΣMePAHs of surface sediments showed a pattern of WJ (444 ± 235 ng/g) > QTJ (253 ± 133 ng/g) > PR (199 ± 161 ng/g). ΣMePAHs were higher in the surface sediments, and sediment cores of the reservoirs upstream than downstream (383 ± 261 ng/g > 233 ± 113 ng/g, 340 ± 114 ng/g > 105 ± 43.5 ng/g, respectively), and ΣMePAHs varied with the depth of the sediment cores. Notable disparities in component profiles were evident between QTJ and PR sites at various locations, whereas WJ exhibited homogeneity in its component distribution. Spatial and temporal variations revealed unique patterns influenced by diverse sources and environmental factors. TOC was the main factor affecting MePAH concentrations. The influence of hydrological factors on MePAHs pollution in sediments outweighed that of social factors. MePAH isomers that replace methyl groups at specific positions (1,2 or 4-position) were present in much higher concentrations than other isomers in sediment. These findings deepen our understanding of MePAHs pollution in reservoir sediments and are instrumental in crafting effective pollution control strategies.