Clay mineralogy and vertical distribution of cadmium in a soil profile in a reclaimed paddy field in Kyushu, Japan

We collected six soil samples from a soil profile in a reclaimed paddy field in Omuta, Kyushu, Japan and analyzed for basic chemical properties, clay mineralogy and total cadmium content. The all six soil samples resembled with regard to exchangeable cation composition and clay mineralogy. The total cadmium content on the whole soil basis was 5.1 and 3.5 mg kg^-1 for 0-15 cm and 15-35 cm layers, respectively, and it was in a relatively narrow range from 1.2 to 1.8 for the underlying layers. The cadmium content on the clay basis was also highest for the surface soil with a value of 19 mg kg^-1 and those for the underlying layers were fairly high with values from 9 to 12 mg kg^-1. According to physical chemistry of adsorption, the equilibrium concentration depends primarily on the adsorption per unit amount of adsorbent, the clay content as well as total cadmium content should be determined for assessing bioavailability of cadmium and remediation planning.