Soil-Solution Partitioning of Metals

ABSTRACT Soil- solution partitioning of metals determines the behaviour and toxicity of metals. Lead, copper, zinc and nickel are common pollutants, and due to historic metal deposition from the atmosphere, high levels of these metals have accumulated in upland organic soils in the UK. Atmospheric deposition of sulphur and nitrogen, and climate change, can affect soil solution pH and dissolved organic carbon (DOC) concentrations, and both pH and DOC are known to affect soil-solution partitioning of metals. In this thesis, metal concentrations were determined in archived soil and soil solution samples from a regional survey of upland sites in northern England with contrasting soils, and two experiments were undertaken to assess the effect of temperature and nitrogen deposition composition on metal concentrations in soil solution. In each case, a common objective was to assess whether variation in metal concentrations in soil solution could be explained by changes in soil solution pH and DOC concentration. Lead concentrations in soil solution were modified by heating, but not the composition of nitrogen deposition, and lead showed a strong affinity for organic matter in soils and soil solution. Zinc concentrations were affected by both heating and nitrogen deposition, with the strongest effect being through changes in pH. However, in the case of both zinc and nickel, there were also associations with DOC concentrations, indicating that the organic phase becomes more significant for partitioning of metals between soil and soil solution in organic-rich soils. For copper, there was little effect of heating or nitrogen deposition, and the strongest association was with nitrate, rather than pH or DOC, in soil solution. Future research should be focused on more comprehensive studies dealing with the relationship between DOC, pH, climate, nitrogen deposition and metal in the field, with supporting laboratory experiments.