Grantee Research Project Results
Final Report: Improving Ecological Risk Assessment of Pesticides for Nontarget Terrestrial Vertebrates
EPA Grant Number: R825347Title: Improving Ecological Risk Assessment of Pesticides for Nontarget Terrestrial Vertebrates
Investigators: Wolff, Jerry O. , Edge, W. Daniel
Institution: Oregon State University
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1997 through December 31, 1999
Project Amount: $358,354
RFA: Exploratory Research - Environmental Biology (1996) RFA Text | Recipients Lists
Research Category: Biology/Life Sciences , Aquatic Ecosystems
Objective:
Our objectives were to field test assumptions of the Quotient Method. The specific objectives and hypotheses were:1. Given an alternative, will animals move away from a spray zone into an unsprayed zone long enough to reduce exposure and risk? We hypothesized that mammals will not move from established home ranges to avoid contaminated vegetation.
2. Will birds and mammals respond differently to equivalent concentrations of a pesticide applied as granular and flowable formulations? We hypothesized that a granular application will have a greater negative impact on birds and less of an impact on mammals than will a flowable application.
3. What are the effects of environmental variables such as rainfall on exposure of a pesticide to mammals? We hypothesized that rainfall shortly after application will have a greater negative impact on voles than would dry conditions.
4. How do altered adult sex ratios affect juvenile recruitment, growth rates, and timing of sexual maturation. We hypothesized that high densities of adult females would suppress juvenile female recruitment, growth rates, and delay sexual maturity.
Summary/Accomplishments (Outputs/Outcomes):
Our findings are summarized by experiment below.Experiment 1. We used 50 radio collared gray-tailed voles, Microtus canicaudus, to determine if voles would abandon home ranges that had been treated with Guthion? 2S and move to adjacent uncontaminated areas. We spray half of four enclosures with Guthion? 2S, four enclosures were sprayed completely and four enclosures were retained as controls. We radio-collared four adult females within each enclosure and tracked the animals for 2 weeks before and after spray day. We found voles would not abandon home ranges and that voles in control, half-sprayed and full-sprayed enclosures moved the same distances. This experiment, reported in Wang (2000) and Wang, et al. (1999a and b), suggests that voles may be able to find uncontaminated areas within their home ranges that allow them to avoid exposure to a contaminant.
Experiment 2. We used gray-tailed voles, Microtus canicaudus, and northern bobwhite quail, Colinus virginianus, as experimental model species to field test whether small mammals and birds respond differently to equivalent concentrations of a pesticide applied in granular and flowable formulations. In mid-May 1998, we placed voles into 15, 0.2-ha enclosures planted with a mixture of pasture grasses. In mid-July, we placed quail into the same enclosures with the voles. In late July, we applied the organophosphorus insecticide diazinon in five treatments: a control (all habitats sprayed with water), liquid formulation of diazinon at 0.55 kg/ha, liquid formulation of diazinon at 1.11 kg/ha, broadcast of granular diazinon at 1.11 kg/ha, and broadcast of granular diazinon at 2.22 kg/ha. The diazinon treatment in liquid and granular formulations did not depress population size, growth rate, or survival of voles. We found a significant difference in the survival rate of the quail between the controls and treatments. Granular diazinon caused a measurable decline of quail survival, although the liquid application at an equivalent rate did not significantly affect quail survival. Our results suggest that ground feeding birds are more susceptible to granular insecticides than flowable applications, but voles were not susceptible to either formulation at the rate we used. This experiment is detailed in Wang (2000) and Wang, et al. (2001b).
Experiment 3. The Quotient Method (QM), a pesticide risk assessment model used by the U.S. Environmental Protection Agency (EPA), assumes that the expected environment concentration of a contaminant is a function of application rate immediately after pesticide application. The QM does not take into account weather conditions (e.g., rainfall) at the time of spray. We used gray-tailed voles, Microtus canicaudus, as an experimental model species to field test this assumption of the QM by simulating a 0.25-cm rainfall. In June 1999, we placed voles into 16, 0.2-ha enclosures planted with a mixture of pasture grasses. In early August, we applied 2.44 kg/ha of the insecticide Guthion? 2S (azinphos-methyl) in four treatments: dry control, wet control ("rain"), dry treatment (sprayed with Guthion? 2S, no "rain"), and wet treatment (sprayed with Guthion? 2S and "rain" within 24 hours). We used four replicate populations for each treatment. Survival probabilities of male voles in dry treatment enclosures declined throughout the rest of study following pesticide application, while survival probabilities displayed short-term increases in other treatments. Rainfall improved male survival and may have mitigated the adverse effects of Guthion? 2S. We also detected significant time by treatment interactions on population size and population growth rates of voles. Our results indicate that the Guthion? 2S treatment depressed population size and growth rate in the dry treatment. However, rainfall may have reduced the risk of Guthion? 2S to voles. Our study suggests that the QM is robust to the assumption that rainfall does not increase exposure of voles to Guthion? 2S in grasslands. However, the interaction between rainfall and Guthion? 2S application resulted in a deviation from the predicted risk. We report the results of this experiment in Wang (2000) and Wang, et al. (2001a).
Experiment 4. In previous experiments, we have documented survival rates that differed among males and females gray-tailed voles. Differential survival rates have important implications for demographic changes in populations exposed to contaminants. The Quotient Method assumes that mortality does not vary among individuals exposed to a contaminant. We manipulated adult sex ratios such that we had four replicate, high-density populations of three treatments: male-biased, female-biased, and equal sex ratios. Male-biased population size was significantly lower than control or female-biased populations. Recruitment of male and female juveniles was lower in female-biased populations than in the other two treatment groups. Juvenile females took significantly longer to breed in female-biased populations than in the other two treatments. Decreased juvenile recruitment appears to result from post-partum mortality and may result from infanticide by adult females competing for offspring-rearing space. High populations of males had no measurable affect on demography. Experimental populations of 100 females/ha had no measurable effect on vole demography whereas 150 females/ha did. Juvenile recruitment is inversely density-dependent, but in that most wild populations of voles do not exceed 100 breeding females/ha, it is unlikely that one sex has a greater regulatory effect on vole demography than the other sex. Differential mortality has the potential to alter population dynamics in exposed populations. These results are being prepared for submission to the Journal of Mammalogy.
Journal Articles on this Report : 9 Displayed | Download in RIS Format
Other project views: | All 17 publications | 10 publications in selected types | All 10 journal articles |
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Caslin TM, Wolff JO. Individual and demographic responses of the gray-tailed vole to vinclozolin. Environmental Toxicology and Chemistry 1999;18(7):1529-1533. |
R825347 (1999) R825347 (Final) |
Exit Exit |
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Edge WD, Schauber EM. Factors affecting risk assessment of small mammals to pesticides. Environmental Toxicology and Chemistry 2000;19(11):2735-2741. |
R825347 (1999) R825347 (Final) |
Exit Exit |
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Schauber EM, Edge WD. Statistical power to detect main and interactive effects on the attributes of small-mammal populations. Canadian Journal of Zoology 1999;77(1):68-73. |
R825347 (1999) R825347 (Final) |
Exit Exit |
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Sheffield LM, Crait JR, Edge WD, Wang G. Response of American kestrels and gray-tailed voles to vegetation height and supplemental perches. Canadian Journal of Zoology 2001;79(3):380-385. |
R825347 (Final) |
Exit |
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Wang G, Wolff JO, Edge WD. Gray-tailed voles do not move to avoid exposure to the insecticide Guthion® 2S. Environmental Toxicology and Chemistry 1999;18(8):1824-1828. |
R825347 (1999) R825347 (Final) |
Exit Exit |
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Wang G, Edge W, Wolff JO. A field test of the quotient method for predicting risk to Microtus canicaudus in grasslands. Archives of Environmental Contamination and Toxicology 1999;36(2):207-212. |
R825347 (1999) R825347 (Final) |
Exit |
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Wang G, Edge WD, Wolff JO. Response of bobwhite quail and gray-tailed voles to granular and flowable diazinon applications. Environmental Toxicology and Chemistry 2001;20(2):406-411. |
R825347 (Final) |
Exit |
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Wang G, Edge WD, Wolff JO. Demographic uncertainty in ecological risk assessments. Ecological Modelling 2001;136(1):95-102. |
R825347 (1999) R825347 (Final) |
Exit Exit Exit |
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Wang G, Edge WD, Wolff JO. Rainfall and Guthion 2S interactions affect gray-tailed vole demography. Ecological Applications 2001;11(3):928-933. |
R825347 (Final) |
Exit Exit |
Supplemental Keywords:
agriculture, exposure, ecological effects, ecology, indicators, mammalian, modeling, Northwest, Oregon, OR, toxics, zoology., RFA, Health, Scientific Discipline, Toxics, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, exploratory research environmental biology, Chemical Mixtures - Environmental Exposure & Risk, Environmental Chemistry, pesticides, Chemistry, Ecological Effects - Environmental Exposure & Risk, Risk Assessments, Ecological Effects - Human Health, Biology, Ecological Indicators, risk assessment, ecological exposure, ecological risk assessment, pesticide exposure, terrestrial vertebrates, mutagenic properties, field experiments, quotient model, wildlife populations, chemical mixtures, ecological assessment, mitigating factors, toxic environmental contaminantsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.