Changes in Cd bioavailability in metal spiked soils amended with biosolids: results from a wheat seedling bioassay

Abstract

Three contrasting soils were collected from the Canterbury region in New Zealand and treated with a one-off application of Cd (1, 5 and 10 mg/kg applied as sulphate), in the presence and absence of biosolids applied at a rate equivalent to 400 kg N/ha. Soils were then incubated for two weeks and 24 weeks at a constant temperature of 25 ± 2 °C in the absence of light. A seedling bioassay, using wheat (Triticum aestivum) was undertaken to assess changes in plant Cd concentrations and soil solution Cd chemistry during incubation. Six measurements of Cd availability were also employed to determine which test yielded the strongest correlation with plant Cd concentrations. Overall, Cd concentrations in shoots were significantly reduced on average by 30% in plants grown in Cd spiked soils amended with biosolids compared to unamended soils, even though no significant changes were detected in measures of Cd solubility. Of the six methods examined, Ca(NO₃)₂ extraction yielded the strongest correlation with plant Cd, and a comparison between relationships determined for biosolids amended and unamended soils revealed no significant difference (p = 0.625). Consequently, this result provides evidence that Cd bioavailability as measured by Ca(NO₃)₂ is not altered in the presence of biosolids.