Abstract-Particles of white phosphorus (P 4 ) in pond sediments at Eagle River Flats, Alaska, USA, a military artillery range are acutely toxic to dabbling ducks and swans. We determined if toxicity of P 4 to ducks varied by its form (i.e., dissolved or particulate) or particulate size. Residual P 4 in the digestive tracts of ducks was measured to assess risks posed to predators and scavengers of ducks. Farm-reared mallards were treated with 12 mg P 4 /kg body weight, either dissolved in oil, or as numerous small, or one to two large particles. At the first major convulsion, ducks were euthanized and the quantity and location of P 4 in the digestive tract were determined. These data were compared to data from dead ducks collected from the artillery range. Dissolved, small, or large particles of P 4 produced similar acute toxicity. Residual P 4 in digestive tracts was greatest in ducks treated with small particles and was as great as 3.5 mg P 4 . Similar quantities of residual P 4 were found in dead ducks collected at Eagle River Flats. For dabbling ducks, P 4 particle size is not as important as the dose ingested. For predators, the P 4 contents of the entire digestive tract is important for assessment of the risk of poisoning.