Heavy metal content of tomatoes fertilized with biosolids
Biosolids recycle plant nutrients, but may contain other constituents, such as heavy metals, that could contaminate food crops through plant uptake. The study was conducted to quantify heavy metal uptake. Tomatoes (Solanum lycopersicum, var. Better Boy), grown in a greenhouse in a mined sand containing sphagnum peat [90:10 (sand:peat), by volume], were fertilized with a biosolids fertilizer (Milorganite®), supplemented with K, and with several specialty organic fertilizers (Tomato Tone®, Dr. Earth®), and the soluble fertilizer Miracle-Gro®, all at the same rate of N, except that a 0.5x and 1.5x rate of biosolids was included. A 1x biosolids treatment without added K also was included in the study. The greatest fresh weight of tomatoes was obtained with Tomato Tone® fertilizer. The 1.5x rate of biosolids produced significantly (P < 0.05) lower fruit yield, but that treatment, and the 1x biosolids rate, produced greater yield than Dr. Earth® and Miracle-Gro. Although the biosolids contained more As, Cd, Mo, Ni, and Pb than the specialty organic fertilizers, and presumably more than the soluble fertilizer, even at the 1.5x rate of biosolids there were no significant differences (P < 0.05) among the four fertilizers in the concentrations of these elements in the tomato fruits. The Dr. Earth® fertilizer contained more Cu, and approximately the same amount of Zn as the biosolids, but the concentration of these two elements was not different in the tomato fruits produced by the four fertilizers.