Fate and Mobility of Radium-226 in Municipal Wastewater Sludge Following Agricultural Landspreading

Executive Summary: A field study was conducted to evaluate the fate of radium-226 applied incidentally during the landspreading of municipal sludge. Survey results were compared to data available in the literative and were used to develop policy. Those communities in which a violation of the combined radium drinking water standard existed, and which produced a sludge that is landspread were sought. For selected communities, sludge spreading sites and corresponding control sites were chosen based on their sludge application history and the soil properties. Composite soil samples for both the plow layer and the soil layer immediately below it were obtained. When possible, plant tissue was obtained and separated between the fruit or grain and the remaining above ground biomass.

Data indicated that soil radium activity levels were not elevated as a result of landspreading of sludge containing radium. Native radium levels appear to be related to clay content. No evidence that radium presented a threat to the groundwater was obtained. When soil radium activity levels in the lower soil increment exceeded those in the upper increment, clay levels in the lower increment were correspondingly higher.

The existence of an arcopetal gradient for radium in plants was supported. No elevation of radium activity in plant grain or fruit was observed. However, in some instances elevated radium was found in the above ground biomass in corn, soybeans and alfalfa. Plant radium activity levels did not appear to be directly related to soil radium activity levels. Plant radium levels were higher when plants were grown in soils which had lower clay contents and lower pH. This suggested that soil factors dictated plant uptake of radium.

Radium mobility is influenced by soil factors; this suggests that selection for and management of soil factors is a viable method of reducing radium mobility and minimizing environmental concerns. A set of guidelines to facilitate the safe land application of sludge contained in radium were developed and are included in this report.