Figure 1: Percentages of metal extracted (means ± SD where ) from control and biosolid-treated Romona soil by the organic acid mixtures. Obtained at Moreno Field Station of the University of California, Riverside, CA. From 1976 through 1981, composted biosolids were applied at dry weight rates of 0 (control), 22.5, and 180 Mg ha−1 yr−1, respectively. Some of the observations were below detection limits (nd) of the AAS for Pb = 0.001 mg kg−1.