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The response of biota in experimental stream channels to a 24-hour exposure to the herbicide Velpar L

Schneider, J., Morin, A., Pick, F.R.
Environmental toxicology and chemistry 1995 v.14 no.9 pp. 1607-1613
hexazinone, toxicity, invertebrates, nontarget organisms, chlorophyll, population density, streams, water pollution, toxicology, algae and seaweeds, adverse effects, biomass production
Outdoor experimental stream channels were used to examine the short-term impact of Velpar L on periphyton and macroinvertebrates. Velpar L was added to five channels for 24 h while five additional, alternating channels served as controls. The concentration and the duration of the Velpar L treatment were chosen to mimic the pulse of herbicide carried to streams during rain events subsequent to Velpar L spraying. The mean concentration of hexazinone, the active ingredient, in the treatment channels varied over time from 145 micrograms L-1 to 432 micrograms L-1. Periphyton chlorophyll-a-specific productivity was reduced by 80% during the Velpar L addition. Within 24 h after the termination of the Velpar L addition, periphyton productivity returned to control levels. The 4-h EC50 value, 3.6 micrograms L-1 of hexazinone, for chlorophyll-a-specific productivity was lower than published bioassay results from single species tests. Mean periphyton biomass (chlorophyll-a per unit area of gravel substrate) and mean macroinvertebrate biomass, density, length, and drift were not significantly affected by the Velpar L addition. Although it appears that lotic systems are resilient to short-term exposure to Velpar L, the effects of repeated and chronic exposures on stream biota remain unexplored.