Static sorption experiments were carried out in acid-washed 50 ml plastic centrifuge tubes.
Stock solutions of Zn (10,000 mg l-1) and Cu (1000 mg l-1) were made with the corresponding
nitrate compound. The accuracies of the stock solutions were assessed by creating by
dilution, and analysing [Zn] test (theoretically 50 mg l-1) and [Cu] test (theoretically 10 mg l-1)
solutions, which contained no shell material.