Historical record, source, and toxicity assessment of sedimentary organic matter using molecular composition of hydrocarbons in an urban lake, Wuhan, China

Abstract

The historical record of the spatial distribution, source, occurrence, and ecotoxicology of organic matter deposited in the past 100 years was investigated in a sediment core from an urban lake, in central China by analyzing different organic targets. These targets included total organic carbon (TOC), n-alkanes, representative petroleum biomarkers of terpanes and steranes, non-alkylated polycyclic aromatic hydrocarbons (PAHs), and their alkylated congeners (APAHs). Three sediment cores were collected from East Lake (Wuhan, China) in September 2013. The freeze-dried samples were Soxhlet extracted and cleaned up/fractionated into saturated and aromatic fractions. Gas chromatography equipped with mass spectrometry (GC-MS) was used to analyze the specific target groups. The TOC content of sediment was determined by an elemental analyzer after the freeze-dried sediments were pre-treated with 1 mol L−1 HCl to remove carbonate. The impact of human activities has become more serious since the 1960s as determined by analyzing the historical records of the measured parameters, due to the isolation of the study water body from the Yangtze River and the development of the local social economy. Higher plant wax was the major source of the identified n-alkanes; non-alkylated PAHs were more abundant than their alkylated congeners over the past 100 years. The source identification of n-alkanes, petroleum biomarkers, and PAHs suggested that the mixed sources, including biogenic and petrogenic input, and the incomplete combustion of biomass/solid fossil fuel have contributed to the organic matter in the study lake. The toxicity assessment suggested the presence of PAHs would not cause potential toxicity to the benthic organisms. The historical record of organic matter with different molecular compositions reflects the hydrodynamic condition of the study lake and the development of the local social economy. The mixed biogenic, pyrogenic, and petrogenic sources have contributed to the lake sediments. The detected PAHs did not have negative impacts to benthic organics. This study will provide valuable information to control organic contamination and guide potential remediation technologies in the future.