Sequential extraction analysis of heavy metals in sediments of variable composition using nitrilotriacetic acid to counteract resorption

Artificial sediments were made that contained variable amounts (up to 20% by weight) of feldspar, calcite, Fe-oxide or organic matter. Analysis of samples spiked with Pb and Zn in the presence and absence of nitrilotriacetic acid (NTA) showed that 400 mg l(-1) of chelating agent greatly reduced or eliminated sorption in each case. Further study showed that this NTA concentration did not cause significant mineral dissolution. Resorption during sequential extraction analysis of artificial sediments is indicated by the fact that with NTA, levels of metals are higher in the first step and lower during subsequent steps, compared with levels obtained without NTA. However, the addition of 400 mg l(-1) of NTA to each extracting solution in the sequence appears to be effective for counteracting resorption in feldspathic, calcareous, ferruginous and carbonaceous sediments.