Dissertations and Theses @ UNI

Award Winner

Recipient of the 2003 Outstanding Master's Thesis Award - Second Place.

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Open Access Thesis


Insecticides--Environmental aspects--Iowa; Organophosphorus compounds--Environmental aspects--Iowa; Aquatic insects--Effect of water pollution on; Indicators (Biology);


Organophosphorous (OP) insecticides are widely used around the world to control pests. These insecticides can enter streams and rivers and impact nontarget aquatic organisms by inhibiting acetylcholinesterase (ACE), a nervous system enzyme necessary for normal behavior and survival. However, these contamination events are usually brief and often missed by chemical analyses attempting to detect OP insecticides. Although ACE activity has been used as a bioindicator of OP insecticide exposure in humans and wildlife for many years, few studies have investigated using aquatic insect ACE activity as a potential bioindicator of OP insecticide contamination in streams. This study used the mayfly lsonychia bicolor (Ephemeroptera: Isonychiidae) because, in the United States, it is widely distributed in stream riffles throughout the Midwest and East.

In the first experiment methods for quantifying ACE activity in I. bicolor head capsules were developed and optimized. Results indicated that: 1) Triton X-100 detergent (0.5%) significantly increased ACE activity; 2) a 0.0418 molar solution is the optimum acetylthiocholine iodide concentration to use with a 200:1 dilution of I. bicolor head capsules; and 3) the optimum assay reaction temperature is approximately 32°C.

The second experiment investigated potential differences in baseline field ACE activities, and nutrient and temperature effects on I. bicolor ACE activity. Results indicated that: 1) initial ACE activities from the three field populations were significantly different; 2) after 30 days in stream microcosms the activities were similar; 3) nutrient supplements have no effect on ACE activity during short-term, stream microcosm tests; and 4) maximum ACE activities occur at 19 and 25°C.

Two separate experiments used laboratory stream microcosms to investigate I. bicolor ACE inhibition following 48 h exposures to chlorpyrifos. Results from those experiments indicated that 10.0 µg/L chlorpyrifos significantly inhibits ACE activity and causes mortality.

The final study involved monitoring ACE activity at field sites in Northeast Iowa, USA, during 2000 (15 sites) and 2001 (10 sites). In addition, one site on the Cedar River and three sites on the Volga River were more intensively monitored to investigate seasonal effects and the effects of precipitation, respectively. These studies found that: 1) I. bi color ACE activities from the Volga and Upper Iowa Rivers were impacted relative to Cedar River sites; 2) ACE activities were lower during cooler seasons; and 3) storm events did not produce a readily discernible pattern of effects on ACE activities. Overall, these laboratory and field studies support continuing the development and use of I. bicolor ACE activity as a biomarker of OP insecticide contamination in streams.

Year of Submission


Year of Award

2003 Award

Degree Name

Master of Science


Department of Biology

First Advisor

Kurt W Pontasch, Chair


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Date Original


Object Description

1 PDF file (xii, 171 pages)



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