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Toxicity to birds

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Mallard ducks have been studied as representative of terrestrial non-predatory organisms that consume plant food. Pendleton et al. (1995) monitored body tissue levels on diets with 1600 mg-B/kg for up to 48 days. Boron levels were higher on day 32 than on day 4 and differed among all tissues, with the highest levels in blood (average 50.2 mg/kg), followed by brain (31.4 mg/kg) and liver (24.9 mg/kg). Pendleton et al. did not report BAF values directly; however the reported data do permit calculation of the ratio of boron concentration in the tissue to boron in the diet, which represents a BAF. Pendleton et al reported that the diet contained 1600 ppm added boron. The tissue/food ratio (BAF) was thus less than 0.1. Pendleton et al. noted that boron was rapidly eliminated within 1 day on a “clean diet. ”

Stanley et al. (1996) also reported boron concentrations in mallard egg and livers after feeding boron-added diets. Adult duck livers contained 4.6 mg B/kg and 8.5 mg B/kg when fed diets with 450 and 900 mg B/kg, respectively. Duck eggs contained 6.5 and 11 mg B/kg, and duckling liver contained 7.6 and 13 mg B/kg for the same diets. The tissue: food ratio (BAF) was thus less than 0.1 for all tissues.

Data also exist for herbivorous mammals that confirm rapid elimination of boron. Assuming first order kinetics for elimination, the half-life was estimated to be approximately one hour for mice and less than 12 hours for rats (Farr and Konikowski 1963; Ku et al. 1991, 1993). In rabbits, 50 to 66% of an orally administered dose of boric acid was excreted in the urine in the first 24 hours after dosing (Draize and Kelley, 1959). In cows, Owen (1944) observed essentially quantitative recoveries of boron in the urine and faeces of animals fed daily rations fortified with borax.

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