Lead pellet retention time and associated toxicity in northern bobwhite quail (Colinus virginianus)

Abstract

Birds are exposed to Pb by oral ingestion of spent Pb shot as grit. A paucity of data exists for retention and clearance of these particles in the bird gastrointestinal tract. In the current study, northern bobwhite quail (Colinus virginianus) were orally gavaged with 1, 5, or 10 Pb shot pellets, of 2-mm diameter, and radiographically followed over time. Blood Pb levels and other measures of toxicity were collected, to correlate with pellet retention. Quail dosed with either 5 or 10 pellets exhibited morbidity between weeks 1 and 2 and were removed from further study. Most of the Pb pellets were absorbed or excreted within 14 d of gavage, independent of dose. Pellet size in the ventriculus decreased over time in radiographs, suggesting dissolution caused by the acidic pH. Birds dosed with one pellet showed mean blood Pb levels that exceeded 1,300 µg/dl at week 1, further supporting dissolution in the gastrointestinal tract. Limited signs of toxicity were seen in the one-pellet birds; however, plasma δ-aminolevulinic acid dehydratase (d-ALAD) activity was persistently depressed, suggesting possible impaired hematological function.

Evidence of High Tolerance to Ecologically Relevant Lead Shot Pellet Exposures by an Upland Bird

“…Since the model's publication, ecological risk assessors have come to assume that because of the model's focus, death follows from the ingestion and retention of one shot pellet (USFWS 2002a,b). Importantly, all one-pellet dosed birds (n = 10) survived in the 28-day Kerr et al (2010) study, suggesting that small upland birds can tolerate this dosage of incidental lead particle ingestion. In dosing northern bobwhites with up to three pellets at a time in the present study, exceeding what may be a realistic grit-ingestion rate (see Discussion), dose-response curves for blood lead concentration and δ-ALAD activity could be established.…”

“…In place of having the shiny grey-black metallic luster of unused pellets, spent shot pellets develop a crust of white, grey, or brown material (Jorgansen and Willems 1987) from the formation of lead oxides, carbonates, and other soluble lead compounds produced by weathering (Sever 1993). Other than a study by Kerr et al (2010) and a 7-day study involving five birds of one sex by Vyas et al (2001), spent shot has not been employed in any force-feeding pellet experiment. Heretofore, a few researchers incorporated pellet-weathering features in their experimental designs, but these efforts did not simulate the true ecological site condition (McConnell 1968;Rocke et al 1997).…”

“…This study is a follow-up investigation of the Kerr et al (2010) effort, a survivorshiporiented, range-finding, pellet-dosing study with the northern bobwhite. The Kerr et al (2010) study implemented two high-dose lead pellet groups, and required euthanization of the groups early in the experiment; hence, dose-response curves for blood lead concentration and δ-ALAD activity could not be established.…”

“…The Kerr et al (2010) study implemented two high-dose lead pellet groups, and required euthanization of the groups early in the experiment; hence, dose-response curves for blood lead concentration and δ-ALAD activity could not be established. The study queried whether a single pellet dosed to the gizzard would be lethal.…”

“…In dosing northern bobwhites with up to three pellets at a time in the present study, exceeding what may be a realistic grit-ingestion rate (see Discussion), dose-response curves for blood lead concentration and δ-ALAD activity could be established. The fuller understanding of lead shot pellet toxicity presented in this article was realized by using the pellet retention time data from Kerr et al (2010), obtained from radiography conducted in the same laboratory as part of a study that employed an identical experimental design.…”