Juan P. Flores- Márgez, E. Jaramillo- López, Naomi W. Assadian, George D. Di Giovanni, Federico Pérez- Casio and Manoj K. Shukla
The potential risk of transfer of heavy metals from wastewater and biosolids to forage, livestock and ultimately to human is a serious issue. A field experiment was designed to assess the uptake of Cd, Cr, Ni and Pb from water and soil boat forage, and from oat forage to sheep tissues. Treatments consisted of application of lime-stabilized biosolids at the rates of 0, 25 and 50 Mg ha-1 dry weight basis along with a conventional rate of N fertilizer. Oat (Avena sativa L.) was planted in 300 m2plots irrigated with reclaimed wastewater and twenty sheep were grazed. Kidney, liver and muscle were analyzed for metals concentrations. Soils treated with biosolids had significant less soluble Cr and Pb, but higher total Cr concentration than the control. Soluble and exchangeable forms in soil were higher for Cd (32.3%) than for Cr, Ni and Pb (5.4, 3.2 and 3.5%). Nickel and Pb concentrations were often higher than Cd, but Cr was not detected by the chemical analysis. Sheep ingested more Ni and Pb, but there were no significant treatment effects on metals concentrations in animal tissues. Cd concentration increased by 9.22% in kidney and 5.2% in liver for the sheep grazed in the treatment with 50 Mg biosolids ha-1than the sheep not grazed on experimental plots. No metal bio-accumulation in sheep tissues was observed at toxic levels. Agricultural use of reclaimed wastewater and biosolids does not appear to represent a significant risk of metal contamination, but studies are needed to evaluate the risks associated with longer grazing periods, and plant care should be taken in expanding and implementing results of this study as biosolids characteristics vary from WTP to another.
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