IntroductionComposting has become increasingly important for solid waste disposal, because it provides an efficient and environment friendly method to reduce the volume of waste. The composting process also can detoxify harmful organic substances and pathogens, and provides a material of agricultural importance.1,2Recently however, there have been concerns over its safe application in the ecosystem due to the introduction of industrial or municipal solid waste (MSW) to composting waste, which may increase its heavy metal content. When measuring the element content in compost, the quantification of the chemical forms is essential for estimating the mobility and bioavailability of the elements in the composts. Various sequential extraction protocols had been proposed and utilized to allow fractionation of the elements into operationally defined geochemical phases for the analysis of soils and sediments.3,4More recently, these procedures have been applied to compost.5–8It has also been shown that this time-consuming process can be speeded up substantially if an ultrasonically accelerated version of sequential extraction is utilized.9Using this rapid method it was found that elements such as Zn, Mn and As had a high potential mobility in compost, whereas other elements such as Pb, Cu, Fe, and Cr exist mainly in immobilized forms. This approach to measuring elemental mobility has however been criticized for various reasons. The first step of the procedure often involves extraction with 0.1 mol l−1acetic acid which is a relatively strong extractant and as it removes all the water-, acid soluble and exchangeable forms together it cannot give information about the current mobility as opposed to the potential mobility of the sample.10Another major criticism is that the extraction schemes are performed under pseudo-equilibrium conditions and therefore the information on the availability of the element is only based on thermodynamic considerations.11The leaching property of a waste material is an important criterion for the management of waste. Many leaching tests are developed as standard methods for evaluating the potential impacts of waste material on the environment.12For example, the Environmental Protection Agency of the United States have developed a toxicity characterization leaching procedure (TCLP) which is frequently used to evaluate the mobility of both organic and inorganic components present in contaminated soil and other waste materials.13,14Leaching experiments can also be used as a complementary tool to assess the mobility of heavy metals and metalloids in compost. With leaching procedures, the experiments can be carried out so as to mimic various natural scenarios such as rainfall giving more realistic information about the element mobility.10,15Leaching experiments are also useful for the evaluation of possible clean-up techniques for compost as changes in environment conditions may lead to the risk of heavy metals being released to the environment.15Compost may therefore have to be cleaned up before application to land or even before the composting process has been carried out.7One way to clean up the compost is to use a flushing technique with leaching reagents. This approach has been more frequently investigated for cleaning heavy metal contaminated soil.16–18Further kinetic information can be obtained from leaching experiments by recording the amount of leached elementversusleaching time for a given reagent. Several authors consider this approach is more likely to give a more real distribution of elemental species as found in the natural environment.19,20By applying a non-linear regression model, the leached species can be categorized into two types,i.e.those which are easily extracted (labile species) and those which are extracted more slowly (non-labile species).20,21There is no report of such kinetic speciation methods having been applied to compost samples.Finally a retention experiment was carried out to assess the ability of compost to adsorb microelements in water. The aim of this experiment was to see if the application of compost in remediation technologies could be expanded to cleaning up water contaminated with heavy metals.