Speciation Analysis Method of Heavy Metals in Organic Fertilizers: A Review

Heavy metals in organic fertilizers pose a risk to the agricultural ecosystem. The environmental risk of heavy metals depends not only on the total amount but also on the speciation. Hence, more information on heavy metals speciation in organic fertilizers is needed to avoid adverse effect. At present, the speciation information of heavy metals is usually obtained by the single-extraction method and sequential extraction method. Common heavy metals that have received attention include Cu, Zn, Pb, Cd, Cr, Hg and As. There is a lack of reviews on speciation analysis methods for heavy metals, specifically in organic fertilizers. This work aims to comprehensively review the methods, explore the problems of the sequence extraction procedure and summarize the factors affecting the distribution of heavy metals speciation. Each sequence extraction procedure of heavy metals in organic fertilizers is described in detail, and the affecting factors are proposed. The review could contribute proposing the directions of optimizing the sequence extraction procedure of heavy metals in organic fertilizers in the future.