Submitted to: Bulletin of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2007
Publication Date: 1/10/2007
Citation: Smith Jr, S., Lizotte Jr, R.E., Moore, M.T. 2007. Toxicity assessment of diazinon in a constructed wetland using Hyalella azteca. Bulletin of Environmental Contamination and Toxicology. 79(1):58-61. DOI:10.1007/s00128-007-9215-6. Interpretive Summary: Constructed wetlands are used to mitigate pesticide runoff from agricultural fields into receiving water bodies and have been successful in reducing the concentrations of non-point source pollutants. Such wetlands thus serve to enhance water and ecosystem quality . Aqueous and sediment phases in constructed wetlands have separate roles, as either sinks or sources, in determining the effectiveness of wetlands in mitigating pesticide toxicity. For these reasons, the importance of elucidating potential effectiveness of wetlands in reducing pesticide (diazinon) toxicity to aquatic organisms (Hyalella azteca) is addressed. We found that the responses of Hyalella azteca to diazinon contamination of wetland water and sediment can move from a sink during initial pesticide influx to a source affecting non-target aquatic organisms for days to weeks after entering the wetland. Additional studies are planned to further define this source/sink phenomenon.
Technical Abstract: This study examined the use of a 3-cell constructed wetland to mitigate ecological impacts of simulated diazinon runoff from agricultural fields to receiving aquatic systems by using standard 48 h aqueous and sediment bioassays with the freshwater test organism, Hyalella azteca. Chemical analysis revealed spatial and temporal variation in diazinon concentrations within aqueous and sediment samples among all three wetland cells. Eight hours after dosing, all wetland cells had measurable amounts of diazinon within the aqueous phase, but diazinon was not detected in sediment within the sediment retention pond (first cell). Aqueous and sediment diazinon concentrations typically decreased with increasing time periods due, in part, to material degradation and desorption. By 27 d, the first and third cells showed little to no measurable amounts of diazinon. Spatially, lowest aqueous and sediment diazinon concentrations occurred within the wetland area closest to the injection point, the sediment retention pond (cell 1). Greatest aqueous and sediment diazinon concentrations occurred within the primary wetland cell (cell 2) and, to a lesser extent, the finishing wetland cell (cell 3). Such a pattern shows rapid flow of water and associated pesticide out of the initial wetland cell and slower movement into the remaining two cells. Hyalella azteca 48 h survival in aqueous exposures varied temporally and, to a lesser extent, spatially in conjunction with measured diazinon concentrations. Aqueous survival decreased significantly from time 0 h in all three wetland cells up to 7 d after diazinon dosing. By 15 d post-dosing, cell 1 showed an increase in survival (13%). By 27 d, water from cell 1 showed a further increase in survival and survival in cell 2 increased from 0% to 3%. Based upon responses of Hyalella azteca to aqueous and sediment diazinon contamination, sediment diazinon can move from contaminant sink during initial pesticide influx to a source of diazinon contamination affecting non-target aquatic organisms for days to weeks after entering a constructed wetland. Further studies are needed to elucidate the relationship between aqueous and sediment phases in pesticide contamination within aquatic systems and associated effects on non-target aquatic organisms.