Environmental Engineering Reference
In-Depth Information
between 0.02 and 10 mg/L. Ricart et al. (
2009
) also observed changes in diatom
composition of periphyton that were exposed for 29 days to low concentrations of
diuron. Their work showed that the most sensitive end point was diatom biovol-
umes, which signiicantly decreased in the presence of diuron within 8 days, even in
the treatments receiving the lowest concentration (i.e., 0.07 mg/L). This result was
in accordance with that of Leboulanger et al. (
2011
), who reported a decrease in
phytoplankton biovolumes following a 5-day exposure to 2.2 and 11 mg/L diuron.
Using three successive treatments of 5 mg/L of diuron, Knauert et al. (
2009
)
observed that the herbicide signiicantly affected phytoplankton density and
diversity, during 5 weeks of constant exposure. The most sensitive species were the
cryptophyceae
Chroomonas acuta
and
Cryptomonas erosa
et
ovata
. Diuron exhib-
ited a dissipation half-life of 43 days, allowing the phytoplankton community to
recover both abundance and diversity during the 33-173 day posttreatment period.
Chronic Versus Acute Effects
Tlili et al. (
2008
) assessed the response of chronically contaminated bioilms
(32 days, 1 mg/L diuron) to short pulses of diuron exposure (3 h; 7 and 14 mg/L).
They detected several effects, including a signiicant increase in chl
a
luorescence
in periphyton chronically exposed to 1 mg/L diuron, increases in biomass and pho-
tosynthetic carbon incorporation, and changes in algal community structure
(assessed by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis
(PCR-DGGE) on 18S rDNA gene fragment and pigment analysis). Diuron pulses
(single or double pulses at 7 or 14 mg/L) inhibited carbon incorporation in all bio-
ilm communities, especially in the control microcosm. Nevertheless, the different
pulses only affected community composition in control bioilms, revealing that the
impact on a bioilm of a pulsed acute exposure to diuron depends on whether com-
munities had previously been exposed to this herbicide.
PICT Assessment
McClellan et al. (
2008
) observed an increase in community tolerance for long-term
concentrations of 0.08-10 mg/L diuron, whereas a chronic exposure of 50 mg/L was
intolerable for periphyton, which was severely disturbed. Interestingly, the authors
emphasized the fact that the observed threshold concentration of 0.08 mg/L, which
caused effects on periphyton biomass and composition, as well as a shift in com-
munity tolerance, could not be predicted by extrapolation methods such as SSD or
acute-to-chronic effect ratios.
An increase in periphtyon tolerance was also recorded by Tlili et al. (
2010
), fol-
lowing a 3-week exposure to 10 mg/L diuron. Their work revealed that phosphate
concentration didn't inluence diuron tolerance induction in the exposed communi-
ties as Guasch et al. (
2007
) had shown with atrazine. Nevertheless, Tlili et al. (
2008
)
did not detect PICT in periphyton exposed for 32 days to 1 mg/L diuron. According
to the authors, the lack of PICT processes could be due to the regular supply of
nonexposed microorganisms in the contaminated microcosms that was provided by
water renewal during the experiment.
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