In aquatic and soil systems,trace metals exist in a number of forms,soluble or particulate,that determine their effect on ecosystems.It is accepted that based on the content of total heavy metal alone,it is not feasible to make any good prediction of its biological effect.Consequently,in establishing environmental criteria for and executing risk assessment of heavy metals,more and more attention is being given to taking into account their bioavailability.Metal bioavailability and toxicity have long been recognized as a function of water chemistry.And models were proposed to describe its mechanisms,such as Free Ion Activity Model(FIAM),Gill Site Interaction Model(GSIM)and Biotic Ligand Model(BLM).Based on FIAM and GSIM,by taking into account the effects of chemical speciation of heavy metals in water and their competition with cations for biotic lig-ands,BLM was successfully used to predict bioavailability and toxicity of metals in waterbody.USEPA has recently adopted BLM in developing its water quality criteria for copper.In this paper,a complete introduction is presented to the conceptual model of BLM in aquatic environment,its development and application of software,and a review made of extrapolating BLM to the sediment and soil environments,with emphasis on the terrestrial biotic ligand models(t-BLM)for plants,soil animals and microor-ganisms.A conceptual model of t-BLM was proposed and its methodology discussed.T-BLM which integrates soil physicochemical properties,metal speciation,bioaccumulation and toxicity response,will serve as a new tool to develop the more rational soil quality criteria and to conduct risk assessment of heavy metals.