Aged polycyclic aromatic hydrocarbons as stratigraphic marker in the Anthropocene: Evidence from Tibetan Lake sediments

Jun Li; Ruwen Chang; Xiyu Ban; Guo-Li Yuan; Xinyu Du; Ge Yin; Tian Lin

doi:10.1016/j.watres.2023.120652

Aged polycyclic aromatic hydrocarbons as stratigraphic marker in the Anthropocene: Evidence from Tibetan Lake sediments

Water Res. 2023 Oct 15:245:120652. doi: 10.1016/j.watres.2023.120652. Epub 2023 Sep 19.

Authors

Jun Li¹, Ruwen Chang², Xiyu Ban², Guo-Li Yuan³, Xinyu Du⁴, Ge Yin⁵, Tian Lin⁶

Affiliations

¹ State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China; School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China.
² School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China.
³ State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China; School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China. Electronic address: yuangl@cugb.edu.cn.
⁴ College of Marine Ecology and Environment, Shanghai Ocean University, Shanghai 201306, China. Electronic address: mark8818@aliyun.com.
⁵ Shimadzu (China) Co., LTD, Shanghai, 200233, China.
⁶ College of Marine Ecology and Environment, Shanghai Ocean University, Shanghai 201306, China.

PMID: 37741038
DOI: 10.1016/j.watres.2023.120652

Abstract

Polycyclic aromatic hydrocarbons (PAHs) were supposed to serve as combustion marker reflecting the past energy use, but it was unclear whether their sediment records in the Anthropocene were "weathered" due to aging-induced formation of bound residues. In this study, the total concentration of PAHs (the sum of rapid desorption, slow desorption, and bound residue fractions) were determined in four dated sediment cores from eastern to central Tibet using multi-step sequential extraction method. The total 16 PAH concentrations were 11.8, 13.5, 18.9, and 29.4 ng/g dw (in average) in the Co Ngoin, Pung Co, Ahung Co, and Putok lakes, respectively. The stratigraphic records and estimated source contributions of PAHs in different areas of Tibet exhibited a coherent change in the mid-20th century in response to the Holocene-Anthropocene transition. The sediment PAHs also displayed a comparable pattern when the bound residue fraction was not accounted for, suggesting their effective retainability under natural aging conditions. This may be elucidated by the enduring forward and back conversions between slow desorption and bound residue fractions, which manifested similar time-dependent variations across PAH congeners. The distinct conversion tendencies of different congeners were predicted by the binding affinity of congeners to surface/inner regions of organic matter using molecular docking simulations. Our findings demonstrate the persistence of sediment PAH records under natural aging and validate the use of PAH documentary evidence for investigating the Anthropocene.

Keywords: Aging-induced transformation; Bound residue fraction; Combustion marker; Sediment record; Tibetan Plateau.