Trace Metal's in Vegetables Grown in Soil Amended with Exceptional Quality Biosolids.

Biosolids quality, in terms of metal concentration, has improved tremendously after the initiation of industrial pre-treatment programs and promulgation of the 40 CFR Part 503 biosolids regulations (Part 503). However, concerns remain that heavy metals may pose a risk to human health through the consumption of crops grown on soils receiving biosolids as a source of nutrients. Lettuce, zucchini, and tomatoes selected as representative of the major vegetable groups were grown for three years (2011 to 2013) on soil amended with annual application of exceptional quality (EQ) biosolids at two rates of 25 and 50 Mg ha^-1 to quantify trace metals uptake. The concentrations of all the nine Part 503 regulated metals in the edible portion of in all the three vegetables were either similar or lower in the biosolids treatments than control except for Zn, which was higher in zucchini and tomatoes. The concentration of Pb in the 2013 zucchini crop declined with increasing biosolids rate. Measured concentrations of Cd and Ni in lettuce, tomatoes, and zucchini were significantly lower than the predicted concentrations based on uptake coefficients used in the Part 503 risk assessment. Measured Zn concentration in tomatoes and zucchini was higher than the predicted concentration. Both measured and predicted concentrations of Cd, Ni, and Zn were far below the safe lifetime concentrations (SLCs) in all the three vegetables, which are considered safe for consumption by home gardeners. Overall, the measured concentrations of trace metals at the highest cumulative biosolids loading rate were approximately 54% lower than the respective SLCs. Results from this study show that land application of EQ biosolids does not pose any potential risk to human health through uptake of trace metals in vegetables.