A multi-technique investigation of copper and zinc distribution, speciation and potential bioavailability in biosolids

The use of biosolids in agriculture continues to be debated, largely in relation to their metal contents. Our knowledge regarding the speciation and bioavailability of biosolids metals is still far from complete. In this study, a multi-technique approach was used to investigate copper and zinc speciation and partitioning in one contemporary and two historical biosolids used extensively in previous research and field trials. Using wet chemistry and synchrotron spectroscopy techniques it was shown that copper/zinc speciation in the biosolids was largely equivalent despite the biosolids being derived from different countries over a 50 year period. Furthermore, copper speciation was consistently dominated by sorption to organic matter whereas Zn partitioned mainly to iron oxides. These data suggest that the results of historical field trials are still relevant for modern biosolids and that further risk assessment studies should concentrate particularly on Cu as this metal is associated with the mineralisable biosolids fraction.

► Complementary techniques were used to investigate Cu and Zn speciation in biosolids.
► Historic and contemporary biosolids with differing metal contents were examined.
► Similarities in Cu/Zn speciation were observed irrespective of biosolids provenance.
► Key binding environments identified were organic matter for Cu and Fe oxides for Zn.
► Similarities show historic field trial results are still relevant for biosolids management.