Effects of time-variable exposure regimes of the insecticide chlorpyrifos on freshwater invertebrate communities in microcosms

Abstract

The present study compared the effects of different time-variable exposure regimes having the same time-weighted average (TWA) concentration of the organophosphate insecticide chlorpyrifos on freshwater invertebrate communities to enable extrapolation of effects across exposure regimes. The experiment was performed in outdoor microcosms by introducing three different regimes: a single application of 0.9 µg active ingredients (a.i.)/L; three applications of 0.3 µg a.i./L, with a time interval of 7 d; and continuous exposure to 0.1 µg a.i./L for 21 d. Measurements showed that the TWA(21d) concentration in the continuous-exposure treatment (0.098 µg/L) was slightly lower than in the three-application (0.116 µg/L) and single-application (0.126 µg/L) treatments. The application of chlorpyrifos resulted in decreased abundances in the arthropod community, with the largest adverse effects reported for the mayfly Cloeon dipterum and cladocerans Daphnia gr. longispina and Alona sp., while smaller effects were observed for other insects, copepods, and amphipods. At the population level, however, the mayfly C. dipterum only responded to the single-application treatment, which could be explained by the toxicokinetics of chlorpyrifos in this species. At the end of the experimental period the invertebrate community showed approximately the same effect magnitude for all treatment regimes. These results suggest that for this combination of concentrations and duration of the TWA, the TWA concentration is more important for most species than the peak concentration for the assessment of long-term risks of chlorpyrifos.

Ecological impacts of time-variable exposure regimes to the fungicide azoxystrobin on freshwater communities in outdoor microcosms

“…The results suggest that long-term effects can be assessed by comparing TWA rather than peak concentrations, even if the dynamics of the pulses are different. Zafar et al (2011) also found similar relationships between long-term effects and TWA concentrations for most invertebrate species exposed to chlorpyrifos in microcosm under different exposure profiles with the same TWA concentration. They also concluded that for the applied combination of concentration dynamics, the TWA concentration was a more adequate predictor for long-term risks of chlorpyrifos for most species than the peak concentration.…”

“…This followed a similar microcosm study with the insecticide chlorpyrifos, which concluded that for most species, but not for all, the TWA concentration was more important than the peak concentration in explaining the longer-term effects (Zafar et al 2011). The aim of the present study was to compare the effects of four different exposure regimes (two chronic, maintained exposure profiles, one repeated pulsed, and one single pulsed exposure regime) for the fungicide azoxystrobin.…”

“…More pronounced effects may be expected when this concentration is maintained. Therefore, the intention was for the concentration in CAT 10 to be equal to the 42d-TWA in SAT 33 and FAT 16 (calculations according to Zafar et al (2011)). However, azoxystrobin proved to be more persistent in our microcosms and consequently the TWA concentration of the SAT 33 and FAT 16 were 15 μg/L instead of 10 μg/L, and therefore this TWA concentration fell in between CAT 10 and CAT 33 .…”

Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States

“…Since the publication of the Giesy et al review, results of several cosm studies of CPY have featured prominently in comparisons of cosm studies, single-species laboratory toxicity tests, and regulatory benchmarks across classes of insecticides (Brock et al 2000(Brock et al , 2006Maltby et al 2005 ;van Wijngaarden et al 2005b ). Several newer cosm studies have broadened the scope of conclusions about chlorpyrifos effects on aquatic communities to a wider range of locations and environmental conditions (Daam et al 2008a , b ;López-Mancisidor et al 2008a , b ;van Wijngaarden et al 2005a ;Zafar et al 2011 ). The body of evidence from cosm studies is consistent in supporting the conclusion that concentrations of 0.1 μg CPY L −1 or less cause no ecologically signifi cant effects on aquatic communities.…”

“…In further studies, macrophyte-dominated outdoor Dutch ditch cosms were treated with CPY under three different exposure regimes: a single application of 0.9 μg L −1 , three applications of 0.3 μg L −1 at 7-d intervals, and continuous application of 0.1 μg L −1 for 21 d using a pump (Zafar et al 2011 ). The three exposure regimes were designed to produce similar 21-d time-weighted averages of 0.1 μg L −1 .…”