Abstract

Crop uptake of 226Ra over a range of key New Zealand agricultural and horticultural growing areas was analysed to establish the dietary implications of an increase in soil 226Ra activity concentrations. Thirty crop samples, covering both feed and food commodities, were quantified for 226Ra activity concentrations, and concentration ratio (CRs) from the soil activity were calculated. The calculated CRs correlated with international default values for estimating crop uptake. Variation in CRs established that there was no increase in the crop activity concentration, relative to soil 226Ra from pasture foliage at a fertiliser impacted site, with a gradient of soil 226Ra activity concentrations. Based on the calculated CRs, the upper bound of the theoretical range of dietary exposures to 226Ra was 78.1 μSv/yr for teenage boys. Future forecasting of the increased dietary dose of 226Ra that might occur at the current soil loading rate, based on current fertiliser activity concentrations, confirmed that long-term loading of soil with 226Ra is unlikely to present a dietary risk. The forecast model calculated that the increase in dietary ionising radiation burden is unlikely to reach thresholds requiring regulatory intervention for two millennia.

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