DIGESTS OR EXTRACTS - SOME INTERESTING BUT CONFLICTING RESULTS FOR 3 WIDELY DIFFERING POLLUTED SEDIMENT SAMPLES

Three sets of samples have been investigated in some detail. One set i s from a river polluted by mine workings, containing substantial level s of Fe, Mn,Cu, Zn and Ni with traces of many other metals. The second set consists of typical estuarine sediments contaminated from a wide range of industrial sources, and the third set consists of oily drilli ng cuttings from the sea bottom in the vicinity of a North Sea oil pro duction platform. These samples have been subjected to treatment 1) wi th EDTA at two different pH's (extracts) 2) with HNO3/H2O2 3) with HNO 3/HCl and 4) with HNO3/HCl/HF (digests). EDTA recoveries, compared to aqua regia digests, are often very reproducible, not dependent on pH, and usually significantly low. Nitric/peroxide and aqua regia digests often give very close results suggesting that these are meaningful val ues indicating the maximum levels of polluting metals in the sediments . However, the triple acid digest with HF does sometimes give higher v alues (and reasonable agreement for CRM's such as MESS-1) but with poo rer reproducibility.