The spatial differences found in PFAS
Correspondingly, higher levels of PFASs have been found in several areas such as the Haihe River, China where PFOS levels ranged from 1.80 to 7.30 ng g− 1 d.w. with a mean concentration of 5.20 ng g− 1 d.w. (Li et al., 2011) and in the Orge River, France, where the mean PFOS level was 4.30 ng.g− 1 d.w. (Labadie and Chevreuil, 2011). Considerably higher levels were also observed in the Huangpu River, Shanghai with mean PFOS levels of 34.60 ng g− 1 (range: 5.20–203 ng g− 1) (Bao et al., 2010). Additionally, AY 9944 samples from a wastewater canal of Pancevo (Serbia) exhibited PFOS levels up to 5.7 ng g− 1 d.w. and total PFASs up to 6.3 ng g− 1 (Beskoski et al., 2013). Higher levels of PFOS ranging from 0.5 to 30.1 ng g− 1 d.w. were found in sediment cores from Lake Ontario, although this was from 1952 to 2005 (Yeung et al., 2013). Among the highest concentrations of PFASs reported are those in areas with direct industrial emissions that have impacted fresh water systems with water concentrations reaching 1000 ng L− 1 (Lindstrom et al., 2011). Zhou et al. (2013), present a good example of this in a study where average sediment PFOS levels in the Tangxun Lake, China were measured at 74.4 ng g− 1 d.w. This lake is located near a production base of the nearby fluorochemical industry. Due to the wide diversity of PFASs, their extreme stability and spatial heterogeneity of PFASs burdens in the environment, monitoring studies are important to define areas of concern and routes of exposure.