Studies on the mobility of arsenic, copper and chromium in CCA-contaminated soil

IRG/WP 3571

J Bergholm

CCA contaminated soils from six Swedish preservation plants were investigated primarily to study the mobility of arsenic but also that of copper and chromium in the soils. The soil samples represented average types with different amounts of clay, organic matter, arsenic, copper, chromium and different pH. The total soluble amounts of the elements were measured. The pH dependent solubility and the water-soluble fraction were investigated. The fixation capacity of arsenic by treatment with iron and aluminium salts and the toxicity of CCA contaminated soils to ryegrass were also investigated. There is strong evidence that when the soils are contaminated by CCA solution or leachate, a fraction of the arsenic, copper and chromium is precipitated as copper and chromium arsenates or as other salts in the soils. The solubility of arsenic, copper and chromium is pH dependent and the release of these elements increases both with decreasing and increasing pH, with the lowest release at between pH 6 to 7. The elements are released at a constant rate in equilibrium and in proportion to the precipitated arsenates. The water-soluble fraction of the elements are higher in sandy than in clay rich soils. The mobility decreases in the order As>>Cu>Cr. It is possible to fix the arsenic in sandy soils with Fe(II) salts and this is most effective at about pH 5. The growth of ryegrass decreases when the arsenic content in the soil solution exceeds 0.25 mg/L and its growth is totally inhibited when the arsenic content exceeds 1 mg/L.


Keywords: ARSENIC; CCA; CHROMIUM; CLAY; COPPER; FIXATION; MOBILITY; pH; POLLUTION; PRESERVATION PLANTS; ORGANIC MATTER; SOIL; SWEDEN

Conference: 90-02-19/20 Cannes, France


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