Levels of 137Cs and 40K in wood ash-amended soils

Abstract

Wood ash is a residual material produced at an annual rate of 1.5–3.0 million tons by wood burning power plants in the USA. Up to 80% of the wood ash generated in northeastern USA is landspread on agricultural soils. Recently, concern has arisen regarding the 137Cs content of wood ash and levels of 137Cs of wood ash-amended soils. The 137Cs originated primarily from above ground nuclear weapons testing in the 1950s and 1960s. This study examined the total and pH 3, NH 4OAc extractable levels of 137Cs and 40K in three soils incubated in the laboratory with 0, 3 and 9 g of wood ash on a calcium carbonate equivalence basis kg −1 soil. The wood ash contained 137Cs and 40K at 3920 and 21700 pCi kg −1, respectively. At the regulated wood ash application rate limit, 3 g wood ash (calcium carbonate equivalent basis) kg −1 of soil, there was no statistical difference from the control treatment in both total and soluble 137Cs and 40K levels. For one soil, there was an increase in the 137Cs level when wood ash was amended at 9 g wood ash (calcium carbonate equivalent basis) kg −1 soil. The 137Cs was strongly bound to the cation exchange sites of the soils with the average fraction soluble in pH 3, NH 4OAc solution at 4.8% in the mineral soils and 0.9% in the organic soil. Considering the current limits on permitted wood ash application rates to soils, there was no statistically significant effect on the levels of 137Cs or 40K found in wood ash-amended soils.