The effect of sustained release boli with ammoniumiron(III)-hexacyanoferrate(II) on radiocesium accumulation in sheep grazing contaminated pasture.

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Sustained release boli with the cesium binder ammonium iron(III)-hexacyanoferrate(II) (AFCF) were tested under practical conditions for sheep grazing on pastures contaminated with radiocesium (134Cs+137Cs) from the Chernobyl fallout. Two types of AFCF boli were developed: boli without a protective surface coating intended to last 4-8 wk; and boli coated by a wax-mixture with an extended duration of 10-12 wk. From 1989 to 1993 we measured the effect of wax-coated and uncoated boli administered at various times during the grazing season to a total of 3,248 animals. Reductions in radiocesium levels in meat of sheep were measured by in vivo monitoring. Administration of AFCF boli without a wax-coating reduced the mean radiocesium levels in lambs by 43-75% over a 4-8 wk period, and administration of the wax-coated AFCF boli reduced the mean radiocesium levels by 48-65% over a 9-11 wk period. The coefficients of variation in meat radiocesium levels were similar in treated and control groups at the end of the observation period, showing that the reduction of meat radiocesium values was homogenous throughout the treated groups. The boli giving sustained release of AFCF is a labor-saving and cost effective countermeasure for sheep grazing radiocesium contaminated pastures.