Sources and diffusive air-water exchange of polycyclic aromatic hydrocarbons in an oligotrophic North-Patagonian lake

Polycyclic aromatic hydrocarbons (PAHs) are semivolatile organic compounds of environmental concern. This study aims to investigate the influence of local sources of anthropogenic PAHs and their air-water exchange fluxes in an oligotrophic North-Patagonian lake in Chile. The monitoring was carried out in Panguipulli Lake during a six-month period during the autumn and winter seasons (March to August 2017) using a high-volume air sampler and a pump system for water samples. We detected and quantified fifteen PAHs in the gas phase (mean ∑₁₅PAHs = 11.6 ng m^-3) and dissolved water phase (mean ∑₁₅PAHs = 961.8 pg L^-1). Methylphenanthrenes and pyrene dominated the concentrations of PAHs in the studied phases. To determine sources of PAHs we used the PAH ratios of Light Molecular Weight/Heavy Molecular Weight (∑LMW/∑HMW) and Phenanthrene/Anthracene (Phe/Ant). The PAH ratio results revealed a pyrogenic source. We estimated the air-water diffusive exchange fluxes and fugacity ratios for the studied compounds. In general, air-water diffusive exchanges of PAHs showed a net volatilization for the less hydrophobic (log K_OW < 4) and lighter PAHs (MW ≤ 170 g mol^-1), and a net deposition trend for the more hydrophobic (log K_OW 4-7) and higher molecular weight PAHs (MW ≥ 178 g mol^-1). We found a significant correlation between log water/air fugacity ratios and log K_OW of PAHs. Therefore, it is suggested that this oligotrophic lake acts as a sink by accumulating hydrophobic and mid-high molecular weight PAHs derived mainly from pyrogenic sources. This study is the first attempt to understand the sources and behavior of PAHs in oligotrophic lakes in the Southern Chile where information is scarce regarding the occurrence of PAHs.