Plant-availability of metals in biosolids-treated soils may be mathematically described by M t = C x 1 - e - (k x t) ] where M t (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 bioslids-treated soils are defined by the total avialble metals, half-life, and duration of plant growing. Examples showed that the total available metals of the biosolids-amended were 18 to 39, 0.12 to 2.0, 7.4 to 13, 24 to 46, 1.2 to 2.1, and 43 to 53% of the total Cd, Cr, Cu, Ni. Pb, and Zn in the soils. This publication can also be purchased and downloaded via Pay Per View on Water Intelligence Online - click on the Pay Per View icon below