The technique of diffusive gradients in thin films (DGT) is a fairly new and useful tool for in situ measurements of labile metal ions in water. The applicability of DGTs was investigated by comparing independently determined or estimated diffusion coefficients with DGT effective diffusion coefficients (D(DGT)) for 55 elements. The DGTs were exposed at a controlled fluid velocity of 0.1 m s(-1) and a concentration of 1 ng mL(-1) at four pH levels between 4.7 and 6.0, and the D(DGT) values were determined from the uptake by the sampler. The measured D(DGT) values for the elements Co, Ni, Cu, Zn, Cd, Pb, Al, Mn, and Ga were close to previously published values with some deviations for Pb and Zn. The uptake of V, Cr, Fe, U, Mo, Ti, Ba, and Sr varied with pH, and there were some experimental problems that require further investigations. A novel set of D(DGT) values for the lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Yb, Lu, Y) was established. The D(DGT) values for these were about 10-15% lower than for free ions in water and indicate that diffusion coefficients of metal ions in the agarose polyacrylamide diffusive hydrogel are 10-15% lower than in water. The high consistency of the data for the lanthanides establishes these elements as new performance test metals for the DGT sampler. The accumulation of the elements Li, Na, K, Rb, Mg, Ca, B, Tl, P, S, As, Bi, Se, Si, Sn, Sb, Te, Zr, Nb, Hf, Ta, W, Th, and Ag was low (D(DGT) lower than 10% of theoretical values). A more efficient elution procedure using concentrated nitric acid for the absorbent gel was established, with elution efficiencies between 95 and 100% for most metals. For deployment times of 24 h, detection limits from 0.001 to 1 ng mL(-1) were achieved with moderate precautions to prevent contamination.

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This paper reports the influence of environmental variables on soil concentrations of polychlorinated biphenyls (PCBs) and their global fractionation. Soils were sampled from remote woodland (coniferous and deciduous) and grassland locations on a latitudinal transect through the United Kingdom and Norway. Different processes control PCB concentrations and burdens in coniferous, deciduous, and grassland soil systems; these are discussed, with emphasis on the influence of canopy scavenging and soil organic matter (OM) content. In general, concentration differences between sites were 1-2 orders of magnitude for lighter PCBs and 2-3 orders of magnitude for heavier PCBs, when expressed on a pg g(-1) dry weight basis. These differences decreased by up to an order of magnitude when expressed as pg g(-1) OM. The dataset suggests that the more volatile PCBs are moving toward equilibrium with the OM burden of the soil compartment on a European regional scale, while the distribution of the "stickier", heavier homologues appears to still be primarily influenced by their preferential deposition closer to source areas. The relative concentration of the tri- and tetra-PCBs increases with latitude, while that of the hepta- and octa-PCBs decreases, consistent with the global fractionation theory. However, the regression slopes are quite shallow, with high scatter, implying that many environmental and soil-related factors (such as precipitation, organic carbon content and type, other soil properties, local sources, etc.) are also influencing the observed congener patterns. Temperature-driven fractionation, while clearly operating and detectable, needs to be considered in this broader context.