Neutral polyfluoroalkyl substances in the global atmosphere.

Concentrations of neutral per- and polyfluoroalkyl substances (nPFAS) in the atmosphere are of interest because nPFAS are highly mobile percursors for perfluoroalkyl acids. Two calibration studies in Ontario, Canada and Costa Rica established the feasibility of using XAD 2-resin based passive air samplers (XAD-PAS) to reliably determine long term average air concentrations of nPFAS under temperate and tropical climatic conditions. The temporal and spatial distribution of nPFAS was investigated by analyzing XAD-PAS deployed for one year at between 17 and 46 sites on six continents between 2006 and 2011 as part of the Global Atmospheric Passive Sampling (GAPS) study. Higher levels of fluorotelomer alcohols (FTOHs) compared to fluorinated sulfonamides (FOSAs), and fluorinated sulfonamidoethanols (FOSEs) were observed at all sites. Urban sites had the highest levels of nPFAS compared to rural and remote sites, which is also apparent in a positive correlation of nPFAS levels with the proximity of a sampling site to areas of high population density. Levels of FOSAs and FOSEs tended to decrease during the six years of measurements, whereas an initial decline in the concentrations of FTOHs from 2006 to 2008 did not continue in 2009 to 2011. A comparison of nPFAS levels measured in national XAD-PAS networks in Costa Rica and Botswana revealed that the GAPS sites in Tapanti and the Kalahari are representative of the more remote regions in those countries. XAD-PAS derived absolute nPFAS levels at GAPS sites are lower than those measured using another PAS, but are within the range of levels measured with active air samplers. Agreement of relative nPFAS composition is better between samplers, suggesting that the discrepancy is due to uncertain sampling rates.

Mechanisms of heavy metal sorption on alkaline clays from Tundulu in Malawi as determined by EXAFS.

Chromium(III), copper(II), zinc(II), cadmium(II), mercury(II) and lead(II) cations are among the most common heavy metal pollutants in industrial waste waters. In our continued work on cost effective wastewater heavy metal removal agents and methods using local material, this study examines the interactions of chromium(III), copper(II), zinc(II), cadmium(II), mercury(II) and lead(II) cations with natural mixed clay minerals from Tundulu in Malawi using extended X-ray absorption fine structure (EXAFS) spectroscopy. The mixed clays were previously characterised and found to contain illite, low ordered kaolinite, mixed layer minerals and the non-clay mineral carbonate fluoroapatite with a mean pH(PZC) of 9.63. The EXAFS analyses provided qualitative evidence that oxygen atoms occupy the first coordination shells in all the studied central atoms. The metal species on the clay mineral surfaces seem to be adsorbates and/or precipitates of hydrolysis products. Chromium(III) forms a polynuclear hydrolysis complex on the mineral surface with Cr-O bond and Cr...Cr distances of 2.00 and 3.03 A, respectively, which is indicative of a chain structure with edge sharing CrO(6) octahedra. Copper(II) is bound to phosphate groups on the surface at low pH and has a first shell of coordinated oxygen atoms with Jahn-Teller distortion as revealed by different Cu-O bonds of 1.96 A for the equatorial ones, at 2.30 and 2.65 A for the axial oxygens, and a Cu-P distance at 3.29 A is distinguished as well. Upon treatment at neutral pH copper(I) oxide seems to be the main precipitation product on the clay surface. At neutral pH zinc(II) forms also polynuclear hydrolysis complexes with Zn-O bond and Zn...Zn distances of 2.01 and 3.11A, respectively, which shows the presence of edge sharing ZnO(4) tetrahedra. Cadmium(II) is adsorbed to the clay surfaces as a six-coordinated CdO(6) complex in octahedral fashion, but it is not possible to distinguish if cadmium is hydrated or partly hydrolysed. Mercury(II) is present as linear O-Hg-O units but without any observable Hg...Hg distance at high pH showing that mercury(II) is hydrolysed but not present as mercury(II) oxide. At low pH, linear O-Hg-Hg-O units are present showing that mercury(II) is reduced to mercury(I). No precise chemical environment around the lead(II) could be obtained for the lead(II) treated clays due to formation of different hydrolysis structures with multiple coordination numbers by lead(II) salts on the mixed clays.