Three coal combustion byproducts, fly ash (FA), scrubber sludge (SS) and gypsum (G), added to soil at rates of 0, 20, 40 and 80 g/kg only limited annual ryegrass (Lolium multiflorum) growth at the 80 g/kg rate. FA and SS increased selenium (Se), arsenic (As) and molybdenum (Mo) concentrations in ryegrass but only Se from FA would present a potential food chain risk. G did not significantly increase ryegrass concentrations of Se, As and Mo and should not produce elevated trace element levels in plant material or the environment when added to sail at high rates.

Our previous work provided evidence that application of coal combustion products (fly ash and bed ash) at rates exceeding liming requirements may cause considerable degradation of organic N in soils. To investigate the influence of such application rates on the fate of soil organic matter, we studied the effects of different amounts (0, 20, 40, and 80 g kg(-1) soil) of bed ash and ay ash on the mobilization of organic C in soil. The studies showed that whereas fly ash mobilized little or no organic C when applied at rates as high as 80 g kg(-1) soil, bed ash caused substantial mobilization and loss of soil organic C when applied at or above the rate of 20 g kg(-1) soil. Chromatographic and spectroscopic methods were used to characterize the different forms of carbon mobilized in soil amended with combustion products. These studies showed that various forms of organic C were mobilized by bed ash treatments such as carbohydrates, phenolic substances, humic substances, and amino acids. We found that the total amounts of soil organic C mobilized by bed ash treatments were related to increased soil pH and with the losses of C associated with increases of soluble humic substances. The losses of organic C from soils treated with bed ash were found to be as high as 15.5% of the total soil organic C. These studies also provided evidence for stabilization of some forms of soil organic C by Ca2+ from bed ash.