Distribution of perfluoroalkyl substances in the environment

Abstract

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. The difference between perfluoroalkyl sulfonates (PFSAs) and perfluoroalkyl carboxylates (PFCAs) are found on the polar head of the chemicals. 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.

In recent years, the interest in PFASs has been growing due to their presence in humans and in wildlife species even from remote locations, which suggests a widespread global distribution of these pollutants. The highest concentration of PFASs has typically been documented in areas with direct industrial emissions. 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. Some studies indicate a presence of PFASs in sediments and soils and these can be a source of pollution for wildlife, and humans. 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 translocated in the different plant compartments, and the uptake mechanisms differed among plant species. Floating species show a higher concentration among plants because easily translocate long-chian PFASs direct from the water. Rooted species must compete with the sediment for PFASs uptake. Moreover, long-chain PFASs remain accumulated in the root compartment because of protein affinity while short-chain PFASs are more mobile and can be translocated to shoots. 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 PFOS 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, ∑PFAS 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.

El objetivo principal de esta Tesis Doctoral es estudiar la distribución y el comportamiento de las sustancias perfluoroalquiladas (PFASs) en diferentes compartimentos ambientales. En esta tesis se analizan diecisiete PFASs en el sistema de plantas de agua-sedimento a lo largo de los ríos Dongzhulong y Xiaoqing, en sedimentos, suelos y fauna de las Islas Chafarinas (Sur de España), y para finalizar se evalúan las tendencias temporales durante 10 años en huevos de dos especies de gaviotas consideradas bioindicadores de contaminación.

Los resultados de esta tesis muestran que la distribución de las PFASs en el medio ambiente se define por sus propiedades fisicoquímicas y las características de las diferentes matrices de estudio. En el sistema agua-sedimento, los resultados sugieren que la distribución de las PFASs depende de la longitud de la cadena. Las plantas absorben PFASs y los transfieren a diferentes compartimentos de las plantas. En el ambiente marino de las Islas Chafarinas, bajos niveles de PFASs se detectaron en suelos, sedimentos, peces y mejillones reflejando el poco impacto de estas sustancias en esa área. También se estimó el potencial de bioacumulación de las PFASs en gaviotas y se evaluó su presencia en huevos de diferentes colonias. Los huevos del delta del Ebro y de las islas Medas, ambos ubicados en el Mediterráneo nororiental, tenían una distribución de PFASs similar, mientras que en Chafarinas e Islas Atlánticas tienen a niveles de concentración muy bajos. En las colonias del Delta del Ebro, las concentraciones en huevos de L. audouinni fueron significativamente más altas que las encontradas en L. michahellis debido a diferencias en la dieta. En general, la concentración ∑PFASs disminuyó en el período de estudio, pero para los compuestos individuales las tendencias dependían de las colonias y especies.