Field analysis of PAHs in surface sediments of the Pearl River Estuary and their environmental impacts

Abstract

Based on a monthly field survey in 2011 of the Pearl River Estuary, the dynamics of polycyclic aromatic hydrocarbons (PAHs) in surface sediments (depth < 5 cm) were explored. The seasonal variations in PAH level and composition were investigated in this study, as well as their environmental behaviors, the role of particles, and source apportionment. The concentration of the sum of 16 priority PAHs (defined as ∑₁₆PAHs) ranged from 0.32 to 1.10 μg/g, while that of the sum of 62 PAHs (defined as ∑_tPAHs) varied from 0.83 to 2.75 μg/g. The levels of both the ∑₁₆PAHs and ∑_tPAHs peaked in February, although the minimum levels appeared in different months—December and August, respectively. The seasonal difference in the ∑_tPAHs was significant (flood season, 7.69 μg/g; dry season, 10.51 μg/g). The 5-ring PAH compound (e.g., perylene) was the most abundant and was responsible for 35% of the total, which implied a terrestrial input source via the Pearl River. Sediment particles were predominantly composed of clayed sand, and sediment PAHs showed a greater tendency to be adsorbed onto the large-sized particles rather than the fine fractions. Total organic carbon (TOC) could considerably facilitate the sediment PAHs. Principal component analysis revealed that vehicle emission sources, petroleum sources, and combustion sources were the major anthropogenic contamination sources. The diagnostic ratios of various individual PAHs were also explored. These findings are particularly useful for understanding the geochemistry of organic pollutants in the complex estuarine environment.