Title page for ETD etd-09182008-063530
|Type of Document
||Hall, Ellen L.
||Pesticide distribution in water, sediment, and fish of the Occoquan Watershed
||Master of Science
|Dietrich, Andrea M.
|Godrej, Adil N.
|Grizzard, Thomas J.
|Date of Defense
About 50 synthetic organic chemicals (SOCs), including pesticides
and polyaromatic hydrocarbons (PAHs), have been identified as possible
contaminants in the Occoquan Watershed. Since 1982, water, sediment,
and fish samples have been collected from the streams and reservoirs of
the watershed 2-4 times per year. The Occoquan Watershed Monitoring
Laboratory (OWML) collected samples and analyzed for a targeted set of
compounds. Beginning in 1993, new SOC screening methods consisting of
solid-phase extraction (SPE) followed by gas chromatography with mass
spectrometric detection (GC/MS) were developed for water and sediment
samples. A similar method for fish tissue was developed in this study
using methanol extraction with C-18 and alumina SPE cleanup. Method
detection limits (MDLs) ranged from 0.03-0.37 mg/kg wet weight and
recoveries in matrix spikes ranged from 15-92%.
Very few SOCs in OWML's database were found at levels above
method detection limits. In water, atrazine was the most commonly
detected compound (87 detections out of 610 samples analyzed). It was
also found in 8 sediment samples and 1 fish organ sample. Atrazine
concentrations were highest in the spring; summer provided the most
frequent detections. Detections occurred at multiple locations during the
same sampling period; stations furthest west (nearest to agricultural areas)
tended to show the highest values. Rainfall events were associated with
23% of atrazine detections. The raw and finished water samples from the
two water treatment plants in the basin showed that the average atrazine
removal by conventional treatment was 37%.
|| Approximate Download Time
| 28.8 Modem
|| 56K Modem
|| ISDN (64 Kb)
|| ISDN (128 Kb)
|| Higher-speed Access
next to an author's name indicates that all
files or directories associated with their ETD
are accessible from the Virginia Tech campus network only.
If you have questions or technical
problems, please Contact DLA.