Fate and effects of triallate in a prairie wetland

View/ Open
Date
1996Author
Désy, Julie
Type
ThesisDegree Level
MastersMetadata
Show full item recordAbstract
Extensive use of pesticides in the Canadian prairies, where cropland is
interspersed with wetlands, increases the potential for contamination of aquatic
ecosystems. Triallate is a widely used herbicide for the control of wild oats and it is
frequently detected in aquatic systems. Because triallate is toxic to aquatic organisms
and has the potential to persist in sediment, its impact on natural systems needs to be
evaluated. The purpose of this research was to determine the fate of triallate in wetlands
and its effect on selected aquatic organisms representing different trophic levels. Four
littoral enclosures were built in a prairie pond; each was divided in half creating paired
treatment and control cells. Triallate was applied at a concentration of 250 µg/L,
representing a worst-case contamination by runoff. Time-specific concentrations of
triallate in water, sediment and biota were measured. Triallate disappeared quickly from
the water and partitioned to the sediment. Volatilization and uptake by organisms may
have contributed to decreasing water concentrations. Levels in water decreased sharply
in the first 3 days following application coupled with rising sediment concentrations.
Levels in amphipods and aquatic plants also increased. Effects of triallate were evaluated
for phytoplankton, periphyton, zooplankton (Daphnia pulex) and amphipods (Hyalella
azteca). Biomass of phytoplankton and periphyton was not affected by triallate. Daphnia pulex and Hyalella azteca suffered reduced body size and reproduction.
However, some of the results were inconsistent among enclosures. Microcosm and
laboratory experiments were performed to complement the field study and demonstrated
the toxicity of triallate to phytoplankton and D. pulex. Sublethal effects of triallate were
manifested by reduced body size and reproduction in D. pulex exposed to 125 µg/L of
triallate. These findings agree with results obtained in the field study.
The present interim guideline (0.24 µg/L) for the protection of aquatic life
appears to be adequate. In natural systems, triallate binds to dissolved and particulate
organic matter and partitions quickly to sediment, reducing the amount present in
solution and therefore the exposure to aquatic organisms. However, triallate persists in
sediment for a longer time period and the toxicity of triallate associated with sediment has
not been evaluated.