Humic acids role in Br accumulation along two ombrotrophic peat bog profiles

Scientific results about the role of peatlands as sink or source of bromine are rather antithetic. Although several attempts have been performed to correlate Br content and peat decomposition/humification, the role of humic acids (HAs) as possible sink of this element has not been previously investigated. Two peat cores (2H and 2T), collected from the ombrotrophic bog Etang de la Gruère (Switzerland), were divided in several slices from which humic acids were successively extracted. Bromine content was determined in both peat and corresponding HAs samples using an Energy-dispersive miniprobe X-ray fluorescence multielement analysis (EMMA-XRF). Data show a greater “affinity” of Br for HAs rather than for corresponding bulk peat samples, especially in the first 24 cm of depth where Br concentration in HAs is 3.5 times higher than the one in peat; in particular, approximately 40% (average value) of the total Br in peat is stably incorporated into HAs molecules. Further, the observed correlation between the Br content in HAs and the Pb enrichment factor in peat, especially in the upper part of both profiles, suggests a possible role of HAs as geochemical sink of Br atmospheric deposition. Consequently, humification processes occurring in peat could promote Br accumulation in HAs, thus reflecting the deposition rate of this trace element.