Effects of lead in nestling black-crowned night-herons (Nycticorax nycticorax) experimentally dosed in the field

Lead is a known environmental toxicant, and poisoning resulting from the ingestion of lead shot has been well-documented in many species of waterfowl. However, much less is known regarding exposure and effects of free environmental lead in species of birds other than waterfowl. In an attempt to evaluate toxicity of lead to herons and to determine the usefulness of feathers as a non-invasive exposure-monitoring tool, black-crowned night-heron nestlings were dosed with lead to determine its distribution among tissues, and its effects on biochemical biomarkers, growth, and survival. Five-day-old heron nestlings (one per nest) at Chincoteague Bay, Virginia were given a single intra-peritoneal injection of dosing vehicle (control; N=7) or one of three lead solutions (as lead nitrate) (10, 50, or 250 mg/kg body weight of nestling; N=7 per dose) chosen to represent levels below, at, and above those found in moderately-polluted environments. All nestlings treated with lead exhibited dose-dependent inhibition of delta-aminolevulinic acid dehydratase (ALAD) activity compared to controls, and nestlings treated with the highest concentration showed a reduced carcass weight compared to controls. Of several measures of oxidative stress that were analyzed, significant differences were found between low- and high-dosed nestlings in hepatic total thiol and protein-bound sulfhydryl concentrations. No differences in survival were detected between dosed nestlings, controls, or uninjected siblings. Lead concentrations in several matrices, including feathers, are being determined to assess distribution among tissues and will also be examined for relationships with measures of effect.