Storage of household and greenhouse ashes on the surface of sandy soils: consequences for the soil environment.

Abstract

In households and greenhouses, fuel combustion generates ashes that are sometimes deposited on the of soil surface. The consequences of the deposition of such wastes on soil properties are not well known. Therefore, this study determines these geochemical processes (effects of the deposition of household and greenhouse ashes on buried sandy soils) and soil-forming processes. The study reveals that the deposition of household ashes increases the pH of buried Arenosols, while greenhouse ashes do not raise the pH of buried soil. The increased pH of buried soils caused by household ashes arises from calcite dissolution, Ca and K mobilisation, and Ca and K trapping by coatings on quartz grains. In turn, pozzolanic reactions and the crystallisation of gypsum (or a mixture of calcite and gypsum) on the surface of coke in greenhouse ashes limit Ca leaching downwards in the soil profile. Soil horizons with household and greenhouse ashes are characterised by relatively high contents of metal(loid)s. Furthermore, the mobilisation of metal(loid)s is evidenced from horizons containing both types of combustion wastes downwards in the soil profiles. The contents of Mn, Ti, Zn, Cd, Sr, As, Cr, V, and Ba in sandy horizons buried by household ashes are higher than the contents of these elements in soils, reflecting the local geochemical background. For sandy horizons buried by greenhouse ashes, the enrichment of Cd, Sr, As, Cr, and Ba is noted as being relative to soils from a local geochemical background. Therefore, this study demonstrates that household and greenhouse ashes need special attention because of their potential negative environmental effects. The incineration of household ashes (and greenhouse ashes) with municipal wastes, and metal(loid)s recovery from the resulting ashes is a promising management strategy for these types of combustion wastes instead of storing them around households.