Total Cd in soil was determined by digesting the soil in a
mixture of nitric acid (HNO3), perchloric acid (HClO4)
(60%) and sulfuric acid (H2SO4) (5:2:1 by volume, 1 g of
soil in 20 mL of the mixture, heated to 200C for 2 h,
Baker and Amacher 1982a). Cadmium was extracted
with 0.1M hydrochloric acid (HCl) (20 g soil in 100 mL
of 0.1M HCl, 1 h shaking side-to-side; Baker and
Amacher 1982b), and the suspension was filtered
through No. 5 C filter paper.
A 0.2-g batch of rice grains, husked and unhusked,
and powdered soybean was digested in 4 mL of HNO3
and HClO4 (60%, 4:1 by volume) solution in a test tube
with a block digester. The digest was filled up to 10 mL
with 0.1% (v/v) HNO3. Cadmium in all the extracts was
analyzed using an atomic absorption spectro-photometer
(Shimadzu AA-6300) equipped with a graphite atomizer.