Combined effects of discharge, turbidity, and pesticides on mayfly behavior: experimental evaluation of spray-drift and runoff scenarios.
The effects of the pyrethroid-insecticide cypermethrin (CYP), increased flow speed (Flow), and increased suspended particles (Part) on drift behavior and activity of mayfly nymphs (Baetis harrisoni) were investigated both individually and in combination in a laboratory stream microcosm. Spray-drift trials were performed by exposing the nymphs to 1 microg/L of CYP. During runoff trials (CYP x Part), contaminated sediment containing 2,000 microg/kg of CYP was introduced to the microcosm at a concentration of 500 mg/L. Both trials were carried out under high-flow (CYP x Flow and CYP x Part x Flow) and low-flow (CYP and CYP x Part) conditions, and for all cases, control experiments were performed. Drift rate, drift density (for any treatments with increased flow), and activity were used as behavioral endpoints. Multifactorial analysis of variance shows that CYP exposure significantly increased the drift, whereas Part and Flow trials significantly decreased the drift (p < 0.05). In addition, activity decreased significantly under high-flow conditions. The CYP x Part and CYP x Flow treatments resulted in increased drift rate and drift density, respectively, whereas Part x Flow and CYP x Part x Flow treatments resulted in decreased drift density. The CYP x Part and CYP x Flow trials had a significant antagonistic, interactive effect on drift rate and drift density, respectively, with measured levels being lower than expected levels. The reduction in bioavailability of CYP in the presence of increased flow and sediment levels suggests that mayflies are more likely to be affected by spray-drift exposure (CYP) than by runoff exposure (CYP x Part x Flow). Results indicate that mayflies reacted actively in response to flow conditions and passively in response to pesticide exposure.
Dabrowski
James M
JM
Freshwater Research Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa. dabrowj@dwaf.gov.za
Bollen
Anne
A
Schulz
Ralf
R
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D007313:Insecta / Q000187:drug effects*; D007306:Insecticides / Q000737:chemistry / Q000633:toxicity*; D009758:Nymph; D011722:Pyrethrins / Q000737:chemistry / Q000633:toxicity*; D013019:South Africa; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000009:adverse effects*
D007306:Insecticides; D011722:Pyrethrins; D014874:Water Pollutants, Chemical; C017160:cypermethrin