Environmental Engineering Reference
In-Depth Information
insecticide cypermethrin (0.05 mg/L) over a 2-week period, in freshwater enclo-
sures. They recorded no combined direct or indirect effects of the two compounds
on periphyton and phytoplankton communities. Van den Brink et al. (
2009
) evalu-
ated the chronic (8 week) effects in microcosms of a mixture of the triazine herbi-
cide atrazine and the organochlorine insecticide lindane at ive equivalent
concentrations, ranging from 0.01 to 5 times the EC
50
of the most sensitive standard
test organism (
Scenedesmus subspicatum
for atrazine and
Oncorhynchus mykiss
for
lindane). Results were that phytoplankton chl
a
increased, following an increase in
Cyclotella
species, at the highest treatment rate during weeks 5 and 6. The authors
suggested that the effects of atrazine on phytoplankton were lower than expected
and were counteracted by reduced grazing pressure from lindane-induced effects on
zooplankton. Effects on periphyton were only detectable at the species level. At the
highest treatment level, the effects produced were characterized as increased popu-
lation density of the chlorophyceae genus
Characium,
and decreased population
densities of the diatom genus
Achnanthes
and the cyanobacterium
Oscillatoria
redeckei
. This result suggests that a cause-effect relationship existed at the highest
treatment level. The authors hypothesized that the pesticide mixture affected both
top-down and bottom-up regulation mechanisms.
Herbicides and Fungicides
Villeneuve et al. (
2011
) and Tlili et al. (
2011
) investigated the responses of per-
iphytic communities to pesticide mixture exposures of the herbicide diuron and
the fungicides azoxystrobin or tebuconazole, respectively. However, the main
objective of these two studies was not to examine the interactions between the
tested compounds. Rather, it was to assess the inluence of low regimes (Villeneuve
et al.
2011
) or compare chronic versus acute exposure effects (Tlili et al.
2011
),
using pesticide mixtures and concentrations classically encountered in a vineyard
watershed. Therefore, even if the direct effects of diuron on periphytic communi-
ties were clearly detectable in the two studies, it was not possible to evaluate
if simultaneous exposure to a fungicide modulated the response of the impacted
communities.
2.2.4
Successive Treatments
One strategy to assess the fate and ecological effects of agricultural pesticide treat-
ments is to simulate the events that often transpire to contaminate surface waters
during actual pesticide application programs. The simulation procedure consists
of emulating real agricultural application scenarios by making successive treat-
ments with various pesticides to study the effects of residues leached into aquatic
ecosystems. By employing ditch mesocosm studies over a period of 30 weeks,
Arts et al. (
2006
) tested the effects of 15 separate spray treatments to potatoes with
various compounds (prosulfocarb, metribuzin, lambda-cyhalothrin, chlorothalonil,
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