Availability to lettuce of arsenic and lead from trace element fertilizers in soil

Some waste-derived trace element fertilizers may contain elevated amounts of arsenic (As) and/or lead (Pb), and the impact of their use on As and Pb accumulation in soil and uptake by plants should be investigated. This greenhouse study examined how increasing rates of an iron (IR) fertilizer, containing 4806 mg kg(-1) of As, and a zinc fertilizer (G-Zn), containing 18080 mg kg(-1) of Pb, and liming affected As and Pb availability and uptake by lettuce (Lactuca sativa L.) in a silt loam soil. Additions of As as As2O3 and Pb as PbCl2 to the soil were included for comparison. Soil total and NaHCO3-extractable As increased with increasing inputs of As regardless of As source. This was true also for soil total and DTPA-extractable Pb. Sufficient oxidation of arsenopyrite (FeAsS) in the IR could have occurred, resulting in 36.4% of total As in IR being extractable by NaHCO3. Only extremely small fractions of the added As from IR (5 x 10(-3)%) and of the added Pb from G-Zn (7 x 10(-3)%) were accumulated in the plant. Source had an effect on As, but not Pb, accumulation by lettuce. The lower accumulation of As by the plant from IR than from As2O3 could be attributed to a high molar ratio of Fe to As (419) in the readily labile As fraction to render As in IR less available than As in As2O3. The molar ratio of Fe to Pb in the readily labile fraction of Pb in G-Zn was zero, which limited the influence of Fe on the accumulation of Pb from G-Zn despite its extremely high total Fe (18.3%) content. The transfer coefficients of the added As (0.013) and Pb (0.014) over all sources and lime rates were very low. Since nearly all of As and Pb added from the fertilizers remained in the soil, effects of long-term use of the products on As and Pb accumulation in the soil and uptake by the plant remain to be studied.