Cadmium uptake by lettuce from soil amended with phosphorus and trace element fertilizers

Some phosphorus and trace element fertilizers may contain elevated amounts of toxic metals such as cadmium (Cd) and repeated uses of the fertilizers at high rates over time may increase Cd uptake by plants. This greenhouse study investigated the availability to leaf lettuce (Lactuca sativa L.) (Royal Green) of Cd in a western phosphate rock (PR), and a zinc (G-Zn) and an iron (IR) fertilizers that are by products of industrial wastes. The water-soluble CdCl2 was included in the study for comparison. Applications of Cd from the fertilizers or CdCl2 up to 16 times the Canadian Standards for maximum annual Cd loading limit increased soil total Cd. This was true also for the labile Cd extractable by DTPA (diethylenetriaminepentaacetic acid) or 0.05 M CaCl2 for all Cd sources except IR. Lime and Cd source and rate all affected Cd availability in the soil and accumulation by the plant. The added Cd from CdCl2 was more labile and readily available to the plant than the added Cd from the PR or G-Zn. Lettuce-Cd was best described by CaCl2-Cd (r(2) = 0.782), followed by DTPA-Cd (r(2) = 0.686), with soil total Cd being least effective in predicting lettuce-Cd (r(2) = 0.186). If soil total Cd has to be used in describing Cd accumulation by the plant, it should be included with pH in a stepwise multiple regression. The Cd transfer coefficient for the fertilizers should be measured based on labile Cd extractable by CaCl2 or DPTA, instead of soil total Cd. The labile-based Cd transfer coefficient could improve the assessment of the risk of human exposure to the metal in the fertilizers through consumption of the food crop.