Lead in young herring gulls: paradoxical effects of exercise on tissue concentrations

Exposure to lead prenatally and early in life affects physiological, behavioral, and intellectual development in humans and other animals. The movement and storage of lead within tissues and organs and its elimination from the body influence the amounts reaching sensitive target organs such as the developing brain. In this study, young herring gulls, Larus argentatus, were used to examine the effect of mild exercise on the deposition of lead in bone, to clarify possible differences between free-ranging birds in nature and confined birds in the laboratory. Forty 2-day-old chicks were randomly assigned to one of four groups: lead treatment with and without exercise, and controls with and without exercise. Chicks in the lead treatment group received a single intraperitoneal injection of lead acetate solution (100 mg/kg); weight-matched control chicks were injected with an equal volume of isotonic saline at the same age. Chicks in the exercise groups were taken outside and encouraged to move about for 2.5 h/d; others were confined in standard cages. Chicks were sacrificed at 45 d of age and lead was analyzed by graphite furnace atomic absorption. The interaction of exercise and lead dose significantly influenced the amount of lead in the three bones examined (rib, humerus, tibiotarsus), but not in the other tissues. For the lead-treated birds, mean bone lead levels were lower in the exercised versus nonexercised birds, while the reverse was true for control chicks. The data suggest that lead storage can be partly ameliorated by exercise, that young chicks would be the most affected by lead, and that older chicks that move and have larger territories in which to move may suffer lesser effects than those in dense territories.