Tree barks for retrospective measurement and source appointment of airborne perfluoroalkyl and polyfluoroalkyl substances

Abstract

Tree bark is a useful bioindicator of atmospheric pollution. It is specially suitable for airborne perfluoroalkyl and polyfluoroalkyl substances (PFASs) investigation due to persistence of ionic PFASs. The present work firstly systematically studied tree barks as a bioindicator of airborne PFASs. Comparison with the regular active and passive samplers found barks could produce long-term measurement of airborne PFASs, and could record the historical emission of PFASs with retrospective time frame as long as decades. Factors, e.g. tree type, trunk diameter, and sampling depth, can affect PFAS accumulation in barks, and these factors should be kept consistent during sampling. In a study area spatial distribution of airborne PFASs can be obtained by interpolation of bark results, and the concerned region can be located. Properties of the emission sources can be characterized, and the potential sources can be tracked based on the bark results. Their contributions can be further estimated by the source appointment strategies. In the economically and industrially developed study area of the present study, eight cities of southern Jiangsu Province of China, total ionic PFAS concentration of camphor bark samples collected in 34 sites was 0.44-359 ng/g dw (dry weight), dominated by perfluoroalkyl carboxylic acids (PFCAs). Two types of possible sources were characterized as with long-chained PFCAs and PFOA (perfluorooctanoic acid) as the main components respectively. The sources were appointed as fluoropolymer manufacturing and textile industries, the important PFAS application fields, and their relative contribution was estimated as 32.5% and 67.5% respectively. The present study can provide useful advice to the method framework of using barks for long-term occurrence investigation, concerned region location, and emission source appointment of airborne PFASs in a study area. Based on the bark results, effective strategies can be further made for PFAS pollution elimination and risk control.

Keywords: Atmospheric pollution; Bark; Bioindicator; Ionic PFASs; Neutral PFASs; Passive sampler.