Relative Toxicity of Lead and Five Proposed Substitute Shot Types to Pen-Reared Mallards

Abstract

A 30-day toxicity test was made to determine the relative toxicity of lead, a tin-lead alloy, zinc, nickel, teflon-coated steel, and tin, all in shot form, to pen-reared mallard drakes. All of the 15 ducks dosed with lead died. Twenty-seven percent of 15 dosed with alloy, and 20 percent of 15 dosed with zinc also died. Ten of the remaining zinc-dosed ducks showed signs of distress, including losses of muscular control and body weight. There were no deaths among 15 ducks dosed with nickel, 15 dosed with teflon-coated steel, and 15 dosed with tin. Seventy-three percent of those dosed with nickel shot eliminated all shot before the end of the 30-day period. Acid-fast intranuclear inclusion bodies were present in the kidneys of mallards dosed with commercial lead shot, or with tin-lead alloy shot, but not in the kidneys of birds given nickel, tin, or teflon-coated steel shot. Atypical, pale, acid-fast bodies were found in kidneys of 1 of 15 birds dosed with zinc. An iron-containing pigment, which stained positive with the Prussian blue technique, was present in variable amounts in almost all livers. Zinc-dosed ducks that died or were killed while still showing signs of zinc intoxication had higher iron levels in the liver than ducks that had recovered from zinc intoxication. Mortality of waterfowl due to lead poisoning has been recognized for many years. Despite several research studies (Green and Dowdell 1936, Dowdell and Green 1937, and Jordan and Bellrose 1950) no satisfactory substitute for the presently used commercial lead shot has been developed. In 1965 the Patuxent Wildlife Research Center began a research project aimed at the development of a non-toxic shot. In 1966 the Sporting Arms and Ammunition Manufacturers' Institute and the Patuxent Wildlife Research Center undertook this study as a cooperative research project. Metals or alloys proposed as possible substitutes for lead are first tested for their acute toxicitx to pen-raised mallards. Candidate materials found to be non-toxic are then tested for possible effects on reproduction, for ballistical properties, and for killing power. The results of the first group of candidate materials tested were reported by Irby et al. 1967, and Locke et al. 1967. 1 Present address: Department of Forestry and Wildlife Management, University of Massachusetts, Amherst. This paper reports the results of the acute toxicity tests for another group of candidate materials, and is part of a series of studies designed to develop a non-toxic shotgun pellet. We acknowledge the assistance of John L. Sincock, Ralph Andrews, Larry T. Young, and Robert G. Heath, all of the Pa uxent Wildlife Research Center. MATERIALS AND METHODS The birds tested were 18-month-old mallard drakes (Anas platyrhynchos) reared at the Patuxent Wildlife Research Center. One hundred and five birds were included in the experiment. For 9 months prior to the study they were kept together in a single pen and fed a mixture of commercial duck pellets and mixed grains. During the study they were kept in groups of five in 21 pens 30 x 15 x 6 ft high and offered cracked corn, quartz, and oystershell grit ad libitum. Each pen contained a feeding trough and a watering trough at ground level, with flowing water continually maintained at a depth of 10 inches.