Plant-availability of metals in biosolids-treated soils may be mathematically described by Mt = C x [1 - e- (k x t)] where Mt (mg kg-1) is the cumulative metal removal from the biosolids-treated soils by growing and harvesting plants for t years, C is the total phytoavailable metal pool of the soil (mg kg-1) at t = 0, and k is the metal absorption rate coefficient (yr-1). The total available metal pool, C, is defined as metals extractable by organic acids in the rhizosphere of growing plants and k is related to the kinetics of metal release by organic acids. Half-life of the available metals in biosolids-amended soils may be derived from k.Experiments were conducted to characterize the concentration and composition of the organic acids. A successive extraction method was used to extract metals from biosolids-treated soils for determinging C and k. In this manner, the plant available metals of the biosolids-treated soils are defined by the total available metals, half-life, and duration of plant growing.