Calcium water treatment residue reduces copper phytotoxicity in contaminated sandy soils

Calcium water treatment residue (Ca-WTR), an industrial by-product, was found to be effective in decreasing Cu availability in contaminated soils and transport to the environment. In this study, a greenhouse study was conducted to test the ability of Ca-WTR to reduce the toxicity and uptake of Cu by ryegrass (Lolium perenne L.) and lettuce (Lactuca sativa L.) as indicator crop plants in Cu-contaminated sandy soils. Eight weeks growing period was observed in Alfisol and Spodosol amended with different levels of Ca-WTR (5-100 g kg(-1) soil). Plant biomass yields increased with WTR application rates at the low levels (5-20 g kg(-1) for Alfisol, pH 5.45 and 5-50 g kg(-1) for Spodosol, pH 4.66), and decreased at the high levels (>20 g kg(-1) for Alfisol and >50 g kg(-1) for Spodosol). The maximum growth of ryegrass with Ca-WTR was 133% and 149% of the control (without Ca-WTR) for the original Alfisol and Spodosol (without spiked Cu), respectively, while the corresponding values for lettuce was 145% and 206%. Copper concentrations in ryegrass shoots decreased significantly with increasing Ca-WTR application rates. For lettuce, Cu concentration decreased only at high Ca-WTR rates (>50 g kg(-1)). In addition, ryegrass had a greater potential for Cu uptake and translocation than lettuce in both soils.