To understand fate and behaviour of heavy metals in soils, first we had to know something about their geochemical properties. For this you can read two ''bibles'' of heavy metals: one is Biogeochemistry of Trace Elements (Kabata-Pendias A., Pendias H) the second one is old book of Polański and Smulikowski called Geochemistry. You have also some Chemical elements Compendium (for example of Bobrowska-Grzesik et al. from 2013-in English of course). But for really good understanding of metals behaviour You need also know something about fractions/forms of tchem in soils. Because heavy metals have their specific affinity to different soil constituents (organic matter, iron oxides, manganese oxides, minerals). If You Have all informations about geochemistry, and availability or mobility of heavy metals and then You take in to consideration soil properties You will know for sure, how heavy metals, and why are bahaving in Your examinated soils :)