One of the processes preparing sewage sludge for agricultural utilisation is its biological processing using Eisenia fetida. The process is best applied to the sewage sludge composted with plant matter or other organic components. It allows a rapid and efficient change in compost properties, making it possible to obtain useful fertilisers, so-called vermicomposts. The investigations aimed to determine the effect of the levels of selected heavy metals in tannery composts and vermicomposts on the concentrations of these metals in the earthworm body and crop biomass. It was found that the copper, zinc, cadmium and chromium contents of the earthworm biomass depended on their contents of the substratum. The levels of heavy metals in the crops varied according to plant species, being as a rule lower in the vermicompost treatments than in the mineral or farmyard manure treatments. The plants stored the absorbed chromium primarily in their root systems. The excessive chromium content of vermicomposts did not cause its excessive accumulation in the crop biomass.

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