Historical record of effects of human activities on absolute and relative concentrations of Polycyclic aromatic hydrocarbons (PAHs) in Lake Chao, China.

Polycyclic aromatic hydrocarbons (PAHs) are attracting concern because of their potential toxicity, posing serious threats to health of humans and ecosystems (Kim et al., 2013; Zhao et al., 2016). Generally, similar to other contaminants' behaviors (Wu et al., 2001; Zhang et al., 2007, 2008; Lu et al., 2009), PAHs result from natural organic matter and activities of humans, the latter's contribution usually outweighing the inputs from other sources (Fernández et al., 2000; Srogi, 2007). So far, more than 200 PAHs have been discovered, and among them 16 PAHs were classified as priority pollutants by the US Environmental Protection Agency (Xia et al., 2012; Sun et al., 2016). Most PAHs are hydrophobic and either nonbiodegradable or transformed to hydroxides that are slowly degraded. Due to their complex sources, PAHs have become ubiquitous in the environment (Kannan et al., 2005; Guo et al., 2011b; Nie et al., 2014; Ohura et al., 2015). Another reason for the persistence of PAHs is particularly due to their strong