Bioavailability of Cu and Zn in raw and anaerobically digested pig slurry

The impact of anaerobic digestion on the bioavailability of copper and zinc from pig slurry was assessed. Both chemical and biological approaches were used independently on raw slurry (RS) and anaerobically digested pig slurry (DS). This work, using ultracentrifugation pellets from the same pig slurry before and after an anaerobic treatment, confirmed that Cu and Zn behave differently in terms of bioavailability, and contrasting results were obtained by chemical and biological assessments. A chemical approach combined a preliminary study of the pH effect on particulate/dissolved metal partitioning, sequential extraction, and biochemical fractionation. This approach tended to show a lower mobility of metals from digested slurry (DS). A biological approach was carried out with Zea mays and Vicia faba to study Cu and Zn uptake in soil amended with RS or DS. This assay could not differentiate the two slurries.