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Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Wildlife and Fisheries Science

First Advisor

Lester D. Flake

Second Advisor

Walter G. Duffy


The effects of phorate, an organophosphorus insecticide, on mallard (platyrbynchos) ducklings and aquatic macroinvertebrates was studied in littoral mesocosms in South Dakota wetlands. In 1991 and 1992, four mesocosms were constructed in each of three wetlands. In each wetland, one mesocosm was a reference and phorate concentrations of 1.2, 2.4, and 4.8 kg/ha were applied to treatment mesocosms. The effects of phorate on the Microtox system was also examined. Phorate concentrations in the water dissipated over the one-month study, while its metabolites, phorate sulfone and phorate sulfoxide, increased. Phorate was the primary chemical present in the sediment. Chemical analysis of both water and sediment were highly variable. Phorate caused direct mortality to ducklings at all treatment concentrations. Ducklings in reference mesocosms survived longer (P < 0.05) than those in treated mesocosms in both years. Ten-day old ducklings were more sensitive to phorate than 21-day old ducklings. Treated ducklings that survived phorate treatments suffered sublethal effects. Both brain and blood cholinesterase (ChE) activity of treated ducklings was reduced significantly (P < 0.01) from reference ducklings. Some treated ducklings had brain and blood ChE activity reduced more than 50% from reference birds. Blood ChE activity was a more sensitive indicator than brain ChE activity of effects from phorate treatment. Phorate concentrations present in the mesocosms caused mortality to amphipods and chironomids throughout the study. Leeches and snails were resistant to phorate concentrations and had no significant mortality. Index netting indicated that few living macroinvertebrates were present in mesocosms after phorate treatment and populations recovered only slightly after one month. Macroinvertebrate taxa that were sensitive to phorate included: Odonata, Hemiptera, Culicidae, Heliidae, Ephemeroptera, Acarina, Coleoptera, stratiomyidae, and Hydracarina. Invertebrate taxa that were tolerant to phorate included: Hirudinea, Gastropoda, Oligocheata, and Ostracoda. Microtox results were inconsistent with field mortality data. Microtox often indicated no toxicity, even though both invertebrates and ducklings were dying. Phorate concentrations in wetlands can cause direct mortality to ducklings, have sublethal effects such as reduced ChE activity, and have indirect effects by reducing invertebrate populations. Phorate is highly toxic to wetland invertebrates and can have negative effects on wetland ecosystems. Caution should be used when interpreting the results of Microtox readings when evaluating wetlands for pesticide contamination.

Library of Congress Subject Headings

Mallard--Effect of pesticides on
Invertebrates--Effect of pesticides on
Pesticides--Environmental aspects--South Dakota
Wetland ecology


Includes bibliographical references (pages 87-101)



Number of Pages



South Dakota State University


Copyright © 1993. Charles D. Dieter. All rights reserved.