The Hazards of Secondary Poisoning from Zinc Phosphide to Selected Vertebrate Species
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University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 12-1972 The Hazards of Secondary Poisoning from Zinc Phosphide to Selected Vertebrate Species Herbert B. Bell University of Tennessee - Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Part of the Animal Sciences Commons Recommended Citation Bell, Herbert B., "The Hazards of Secondary Poisoning from Zinc Phosphide to Selected Vertebrate Species. " Master's Thesis, University of Tennessee, 1972. https://trace.tennessee.edu/utk_gradthes/765 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Herbert B. Bell entitled "The Hazards of Secondary Poisoning from Zinc Phosphide to Selected Vertebrate Species." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Science, with a major in Wildlife and Fisheries Science. Ralph W. Dimmick, Major Professor We have read this thesis and recommend its acceptance: Michael R. Pelton, Eyvind Thor Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) November 10, 1972 To the Graduate Council: I am submitting herewith a thesis written by Herbert B. Bell entitled liThe Hazards of Secondary Poisoning from Zinc Phosphide to Se 1ected Vertebrate Sped es. II I recommend that it be accepted for nine quarter hours of credit in partial fulfillment of the requirements for the degree of Master of Science, with a major in Wildlife Management. ajoi Professor f' ~.I We have read this thesis and recommend its acceptance: ~.l~£L) ~, ~ k-~ ~~.~ Accepted for the Council: \~aCV::dvi~ a~lor for Graduate Studies and Research THE HAZARDS OF SECONDARY POISONING FROM ZINC PHOSPHIDE TO SELECTED VERTEBRATE SPECIES A Thesis Presented to the Graduate Council of The University of Tennessee In Partial Fulfillment of the Requirements for the Degree Master of Science by Herbert B, Bell December 1972 ACKNOWLEDGMENTS . I am grateful to Dr. Ralph W. Dimmick, Associate Professor of Forestry, The University of Tennessee, who served as director of research during all phases of this study. I would like to express appreciation to the following members of The University of Tennessee for their helpful assistance, and careful editing of the manuscript: Dr. Michael R. Pelton, Assistant Professor of Forestry, and Dr. Eyvind Thor, Professor of Forestry. Appreciation ;s extended to Dr. John C. Rennie, Assistarlt Professor of Forestry, The University of Tennessee, for assistance in statistical analyses and interpretation. Mr. Tommy Hines, Research Supervisor, Oklahoma Game and Fish Commission, and Mr. Lou Yates, a biologist aide of the Tennessee Game and Fish Commission, are thanked for assistance during several phases of the field and laboratory work. I am especially grateful to my wife, Carolyn, for her patience and assistance. Facilities and financial support for this study were provided by The University of Tennessee, Tennessee Game and Fish Commission, and the Hiwassee Land Company. Calhoun, Tennessee. 1 i 1058089 ABSTRACT . The objectives of this study were to determine: (1) the effects of weather upon toxicity of grains treated with zinc phosphide, (2) the acceptance by prairie voles of weathered bait, (3) the LDso of zinc phosphide on selected rodent species, and (4) the potential hazard of secondary pOisoning to predators fed prey pOisoned with zinc phosphide. The rate of loss of zinc phosphide from the bait vehicle was significantly greater during the first week of exposure than in the succeeding three weeks; approximately 34 and 31 percent of the toxic material was lost in April and November, respectively, during the first week the bait was placed in the field. White mice (Mus musculus) were fed weathered bait to evaluate the biological significance of weathering on the rodenticide. The number of mice dying was inversely correlated with the time the bait was exposed to weathering. Bait exposed four weeks was believed to be ineffective. Acceptance of the bait by white mice apparently was not influenced by the length of its exposure in the field, Mice accepted bait which had been weathered one and four weeks as readily as fresh bait. The LDSO of zinc phosphide for white mice was determined to be 2S.77 ! 12.16 mg/kg. The LDSO of zinc phosphide for prairie voles was 16.23 ! 0 mg/kg. The potential hazards of secondary poisoning from rodents killed ; ; i iv with zinc phosphide were investigated for three species of predators, red fox (Vulpes fulva), gray fox (Urocyon cinereoargentus), and great harried owls (Bubo virginianus). No predators died from consuming poisoned voles, though some behavioral irregularities developed during the feeding trials. TABLE OF CONTENTS CHAPTER PAGE I. INTRODUCTION . .. 1 II. LITERATURE REVIEW. 3 III. MATERIALS AND METHODS. 7 IV< RESULTS AND DISCUSSION 10 Effect of Weathering on the Rodenticide 10 Erosion of Zinc Phosphide from the Bait , 10 The Effect of Weathering on Bait Efficiency. 16 Bait Acceptance . 16 Bait Effectiveness • (I !Ii 0- 17 Oral LDSO of Zinc Phosphide for White Mice and Prairie Voles ........ 19 Indirect Poisoning of Predators 0 21 V. SUMMARY. 27 LITERATURE CITED . 30 VITA • 0 • • • • 33 v LIST OF TABLES TABLE PAGE I. The Effect of Exposure to Weather on Erosion of Zinc Phosphide from Oat Groats OOOCZOO" 11 II. A Factorial Analysis of the Zinc Phosphide Present on 10 Zinc Phosphide Treated and Black Dyed Oat Groats of the April and November Bait Experimental Periods 12 III. Temperature and Precipitation on the Test Area April 8-May 5, 1970 and November 20- December 17, 1970 .... 14 IV, The Effect of Weathering on Bait Efficiency as Reflected by Proportion of Mice Dying at Various Levels of Bait Consumption . , . 18 V, The LD50 Dosage of Zinc Phosphide for White Mice and Prairie Voles Calculated According to Wei 1 ( 1952 ) . 20 VI. Weight of Voles and Zinc Phosphide Dosage Consumed by Predators . • • • • . • 0(;00000(l0 22 vi CHAPTER I INTRODUCTION Rodent activities have since biblical times been in direct conflict with man's activities and control methods to reduce rodent activities have been devised. They usually fall into two groupings: (1) ecological control methods and (2) chemical control methods. Phillip F. Allen (1942) cites some of the proven ecological methods: tillage practices, grazing of cover crops, destruction of cover by fire, flooding, encouragement of natural enemies* changing flora by use of fire, changing flora by use of grazing. and diversion to habitats immune from injury. The second major grouping comprises three major types: repellents, antifertility agents, and the most popular, economic poisons. According to Rudd and Genelly (1956), ANTU (Alpha Naphthy1thioura), thallium, barium, carbonate, Castrix, phosphorus, piva1, red quill, 1080 (sodium f1uoroacetate), warfarin, and zinc phosphide are the primary economic poisons or rodenticides used in the United States. Thallium, 1080, and zinc phosphide popularity materialized because small quantities of the rodenticides are effective animal field controls. Although some of the rodenticides, including the most popular~ do exhibit some degree of selectivity. they are primarily nonspecific; that is, they will kill any vertebrate species depending largely on the amount of poison consumed by the individual of that species. Often non-target species may be killed when rodenticides are used over large areas. 1 2 Zinc phosphide is the accepted poison for small field rodents in the United States today. However, when coated on cereal grains to form 'a bait, zinc phosphide has reportedly killed non-target species (Rudd and Genelly 1956). In Tennessee a commercial zinc phosphide bait, oat groats treated with 1.S percent zinc phosphide and black dyed, is presently being studied for field control of prairie voles (Microtus ochrogaster). Several questions remain to be answered concerning the use of this rodenticide in the field. The objectives of this study were to determine: (1) the effects of weather upon the toxicity of grains treated with zinc phosphide, (2) the acceptances by prairie voles of weathered bait, (3) the LDSO of zinc phosphide on selected rodents, and (4) the potential hazard of secondary pOisoning to selected predators fed prey poisoned with zinc phosphide. CHAPTER II LITERATURE REVIEW Zinc phosphide was used widely during World War II by federal and state agencies to control rat populations in the United States (Mallis 1969:79), During the early 1950 1 s, the poison gained popularity in California as an effective means for controlling ground squirrels (Citellus beecheyi and £. oreganus) and meadow mice (Microtus spo) which were damaging orchards, grain crops, and hay crops (Storer 1953:5). Recently in Tennessee the poison was used to control prairie voles (Microtus ochrogaster) which were damaging Virginia pine (Pinus virginiana) plantations (Hines and Dimmick 1970). Merck Index (1952) describes the pOison as a dark-gray lustrous or dull powder possessing a faint phosphorus odor. If strongly heated (llOO°C) with the exclusion of air, it melts and finally sublimes. It;s very stable when kept dry, and ;s insoluble in water and alcohol, but is soluble in HCl and H2S04 with the evolution of phosphine gas: zinc phosphide + oxidizing agent ~ salt + phosphine gas, The commercial phosphide is only 80 to 85 percent pure, the remaining content consisting of some metallic zinc, phosphite, and phosphate. Historically, rodent control methods were selected on the basis of economic feasibility and effectiveness for controlling the target species (Allen 1942:130). Recently, however, another feature has 3 4 gained significance in the selection of control methods.