Resumen de Distribution of perfluoroalkyl substances in the environment
Perfluoroalkyl substances (PFASs) are a large group of man-made chemicals that are widely used throughout society and found in the environment. These compounds are characterized by perfluorinated carbon chains of varying lengths with hydrophobic properties and containing an external polar and hydrophilic head. In general, the characteristics of PFASs are based on the length of the perfluorinated carbon chain that they contain. As the number of perfluorinated carbons increases in the molecule, the water solubility decreases and the better the surfactant properties, but will be more toxic for the environment due to their bioaccumulation in the organisms.
The main purpose of this Doctoral Thesis is to study the distribution and behavior of PFASs in different environmental compartments and to elucidate the interactions among them. In the first study of this Thesis, seventeen PFASs have been analyzed in the water-sediment-plant system along the Dongzhulong and Xiaoqing Rivers in China. The study area is affected by a fluoropolymer facility that belongs to the Dongyue group and is currently one of the major facilities of polytetrafluorethylene production in China. The second study is aimed to evaluate the environmental occurrence of PFASs in sediments, soils, and wildlife in the marine environment surrounding the Chafarinas Islands (South Spain) and the impact on gulls. The third study that composes this Thesis is aimed to evaluate the occurrence and 10-year temporal trend of seventeen PFAS in eggs of two gull species (Larus michahellis and Larus audouinii). These species are used as bioindicators of environmental pollution of Spain.
The results of this thesis show that the fate of the PFASs in the environment is explained by their physicochemical properties and the characteristics of the different study matrices. In freshwater systems, high amounts of PFASs in water and sediments close to the industrial discharge were detected, and concentrations decreased along the river due to dilution. In the water-sediment system, the results suggest that long-chain PFASs accumulated in sediment whereas short-chain PFASs remained in water all along the river. When including plants in the system, PFASs were taken up by plants and remobilized in the different plant compartments, and the uptake mechanisms differed among plant species. In the marine environment of the Chafarinas Islands, low levels of PFASs detected in soils, sediments, fish, and mussels reflected that the area is not directly impacted by PFASs. In this Thesis we also have estimated the bioaccumulation potential of PFASs, using gulls. We have estimated the intake based on fish-diet in gulls from Chafarinas. We observe that the release of PFAOS to the egg is 4.5% of the intake and we provide the basis for using gull eggs as biomonitors. In a final study of this Thesis, we evaluated the presence of PFASs in four main gull colonies in Spain. When comparing gull colonies, eggs from the Ebro Delta and Medes Islands, both located in the North-Eastern Mediterranean Sea, had a similar distribution of PFASs, while in Chafarinas and Atlantic Islands these PFASs were present at lower concentration levels and variability. In the Ebro Delta colonies, concentrations in eggs from L. audouinni were significantly higher than those found in L. michahellis, suggesting that fish diet influences PFAS bioaccumulation. Overall, ΣPFAS decreased in the 10-year study period but for individual compounds, trends were colony-species dependant.
This thesis permits to increase the knowledge about the processes that rule the behavior of PFASs in water, sediment, soil, and biota. Also, this thesis demonstrates the advantage of performing systematic monitoring schemes to determine the presence and fate of PFASs in the environment.
