Effects of nonextractable residual formation on the study of historical PAH pollution and source contribution in a lake sediment core

Polycyclic aromatic hydrocarbons (PAHs) are common proxies for mirroring historical human activities and energy usage in sediment cores, but uncertainty exists about whether the formation of nonextractable residuals (NERs) might distort this information. This study investigated the influences of NER formation on the research of historical PAH pollution and source contribution within a sediment core of Tangxun Lake (Wuhan, China). To improve detection accuracy, a combined strategy coupling silylation and acid deashing was used to measure the NERs of Σ₁₅PAH, with concentrations of 48.08–266.27 ng g⁻¹, accounting for 30.6–64.5 % of the total PAHs (the sum of extractable fractions and NERs). The proportions were primarily influenced by the total PAHs and sediment aging duration, explaining 88.6 % and 1.9 % of the variability, respectively. The NER formation significantly altered the ring number composition of samples at depths of 21–39 cm. Furthermore, the ratios of Fla/(Fla + PYR) were conspicuously impacted, leading to shifts in source identification outcomes predicated on this ratio. The NER formation changed the majority of the percentile contribution values of biomass combustion, coal burning, and traffic emissions, especially for the first two sources in pre-1950s samples. Interestingly, a strong correlation between coal consumption (1980s–2020s) and the source attribution of coal burning was observed for the total PAHs (r = 0.53, p < 0.05), but not for extractable fractions (r = 0.34, p > 0.05). These findings emphasize the significant impact of NER formation on historical PAH pollution studies in sediment cores and the need to consider NERs in future research.