Compost is often proposed as a suitable material for the remediation of contaminated brownfield sites intended for soft end-use. In addition to vitalising the soil, it is also supposed to immobilise metals and so break contaminantreceptor pathways and reduce the ecotoxicity of the contaminants. However, some research has demonstrated contradictory effects between composts on metal immobilisation. In our study, five different composts were tested to examine both their metal retention and

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... reduction capabilities on three different metal contaminated soils. Leaching tests, a plant growth test with Greek cress (Lepidium sativum), an earthworm (Eisenia fetida) survival and condition test and a bacterial toxicity test using Vibrio fischeri were carried out. The batch leaching tests results showed that spent mushroom compost caused an increase in metal concentration in the leachates while LimeX70 compost caused a decrease. The variation in behaviour between different composts for each soil was somewhat random, so a generic conclusion could not be drawn. Toxicity tests showed significant reduction of metal bioavailability and toxicity. Our results also suggest that more rigorous tests should be undertaken to understand the mechanisms involved in metal complexation using different compost types, in order to optimise the use of compost for remediation.