Transport and transformation of heavy metals during earthworm composting process and the corresponding influencing factors
In order to study the transport and transformation characteristics of heavy metals(HMs)during the process of earthworm composting,six groups of composting substrates were prepared by combining different proportions of cow manure(350～400g),straw(150～200g),and calcium superphosphate(25～75g),followed by addition of earthworms with different masses(50～150g).Changes in the total contents and occurrence forms of HMs(Cu,V,Mn,As,Zn,and Cr)in the substrate were investigated.In comparison to the treatment groups with addition of 50g and 100g earthworm,significantly lower contents(P＜0.05)were observed for the group with 150g earthworm addition in terms of total Cu(27.00mg/kg),oxidizable Cu(22.03mg/kg),total Zn(288.89mg/kg),reducible Zn(22.03mg/kg),total V(5.22mg/kg),residual V(8.87mg/kg)and total Cr(26.79mg/kg),respectively.Four weeks of earthworm composting increased the contents of total Cu,total V,total Zn,and the bioavailability of Mn and Zn,but decreased the contents of total Mn,total As and the bioavailability of Cu and V.Both the pH and organic matter content in the substrate were identified to be the key factors influencing the observed changes in the total amount and occurrence forms of HMs during the composting process.Based on the assessment of potential risk index and risk assessment coding,it is suggested that the risk of soil contamination by HMs induced by compost amendment is relatively small.
livestock manureearthworm compostingheavy metalstransport and transformationbioavailability
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