Barium in the O horizon of soils near Sundsvall, northern Sweden : From local minerals or from anthropogenic emissions?

Abstract: Concentrations of potentially toxic metals in surface soils are important to investigate before building new residential areas. Prior to development of a residential area in Sundsvall, northern Sweden, it was observed that barium (Ba) concentrations in the soil at the site exceeded the guideline value of 200 mg kg-1 outlined by the Swedish Environmental Protection Agency. In this study, I aimed at determining the reason for the high Ba concentrations in the O horizon of soils from this latter area. 49 O horizon samples were collected from two separate transects (about 36 km long). A total of 43 Scots pine (Pinus sylvestris) needles were collected from both transects to determine potential Ba accumulation in plants. The O horizon and pine needle samples were analyzed using X-ray fluorescence spectrometer (XRF) to determine Ba concentrations. The total mean concentration of Ba was 426±289 mg kg-1 without any relationship to industrial sources. Barium concentrations were negatively correlated to soil organic matter (r = -0.885). Correlations between Ba, aluminum (Al), silicon (Si) and potassium (K) was r = 0.565, r = 0.486 and 0.525, a finding that suggests a strong positive coupling to elements typically found in silicate minerals. Barium concentrations in pine needle samples were below limit of detection (<LOD) suggesting that “plant pumping” via roots to the soil surface was an unlikely explanation for high concentrations in the O horizon. I conclude that the minerals in the O horizon originate from inmixing from the underlying mineral soil, therefore, high Ba concentrations in the study area is likely due to naturally occurring minerals.