Bio-Availability of Heavy Metals in Soils Treated with Lime-Stabilized Biosolids and Irrigated with Wastewater.
Juan Pedro Flores-Margez1, Esaul Jaramillo-Lopez1, Naomi Waissman Assadian2, George D Di Giovanni2, Federico Perez-Casio1, and Baltazar Corral-Diaz1. (1) Univ Autonoma de Ciudad Juarez, Avenida Henry Dunant # 4016 Circuito Pronaf, Ciudad Juarez, Mexico, (2) Texas A&M Univ, 1380 Circle A&M, El Paso, TX 79927
The potential risk of heavy metals transfer from wastewater, soil and biosolids to forage, livestock and ultimate to human health is a serious demand by the society at the border Mexico-USA. A field experiment was designed to assess the transfer of Cd, Cr, Ni and Pb from soil to oat forage, and forage to sheep tissues. Treatments consisted of lime-stabilized biosolids at rates of 0, 25 and 50 Mg ha-1 dry weight basis and a conventional rate of N fertilizer using a randomized complete block design with four replications. Forage oat was planted in plots of 300 m2 where sheep were grazed during the fall-winter seasons. Chemical fractionation of metals in soil consisted of total, soluble, exchangeable, carbonate bound, oxide bound, organic bound, and residual fractions. Biosolids treatments had significant less soluble soil Cr and Pb, but higher total Cr concentration than the other treatments. Soluble & exchangeable fractions in soil were 32, 5.4, 3.2 and 3.5% for Cd, Cr, Ni and Pb, respectively, and oat samples had 0.07, 0, 6.69, and 5.88 mg kg-1 Cd, Cr, Ni, and Pb. Sheep ingested more Pb and Ni than Cr and Cd, but there was not significant treatment effect on metals concentrations in meat, kidney and liver tissues. The series Pb > Ni > Cr > Cd was similar to the series showed for irrigation wastewater. A single rate of biosolids did not represent a significant risk to oat forage and sheep tissues. However, as heavy metals are added from wastewater to soils permanently, more studies are needed to assess metals accumulation and their bio-availability for longer grazing periods in alkaline soils.