Lethal and sub-lethal chronic effects of the herbicide diuron on seagrass

Negri, Andrew P., Flores, Florita, Mercurio, Phil, Mueller, Jochen F. and Collier, Catherine J. (2015) Lethal and sub-lethal chronic effects of the herbicide diuron on seagrass. Aquatic Toxicology, 165 73-83. doi:10.1016/j.aquatox.2015.05.007

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Author Negri, Andrew P.
Flores, Florita
Mercurio, Phil
Mueller, Jochen F.
Collier, Catherine J.
Title Lethal and sub-lethal chronic effects of the herbicide diuron on seagrass
Journal name Aquatic Toxicology   Check publisher's open access policy
ISSN 1879-1514
Publication date 2015-08-01
Year available 2015
Sub-type Article (original research)
DOI 10.1016/j.aquatox.2015.05.007
Open Access Status File (Author Post-print)
Volume 165
Start page 73
End page 83
Total pages 11
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2016
Language eng
Formatted abstract
Photosystem II herbicides from agricultural sources have been detected throughout nearshore tropical habitats including seagrass meadows. While PSII herbicides have been shown to inhibit growth in microalgae at low concentrations, the potential impacts of chronic low concentration exposures to seagrass health and growth have not been investigated. Here we exposed two tropical seagrass species Halodule uninervis and Zostera muelleri to elevated diuron concentrations (from 0.3 to 7.2 μg l−1) over a 79-day period followed by a 2-week recovery period in uncontaminated seawater. PAM fluorometry demonstrated rapid effect of diuron on photosystem II (PSII) in both seagrass species at 0.3 μg l−1. This effect included significant inhibition of photosynthetic efficiency (ΔF/Fm′) and inactivation of PSII (Fv/Fm) over the 11 week exposure period. Significant mortality and reductions in growth was only observed at the highest exposure concentration of 7.2 μg l−1 diuron. However, biochemical indicators demonstrated that the health of seagrass after this prolonged exposure was significantly compromised at lower concentrations. For example, the drop in C:N ratios (0.6 μg l−1) and reduced δ13C (1.7 μg l−1) in seagrass leaves indicated reduced C-assimilation from photosynthesis. Critically, the energetic reserves of the plants (as measured by starch content in the root-rhizome complex) were approximately halved following diuron exposure at and above 1.7 μg l−1. During the 2-week recovery period, the photosynthetic capacity of the seagrass improved with only plants from the highest diuron treatment still exhibiting chronic damage to PSII. This study shows that, although seagrass may survive prolonged herbicide exposures, concentrations ≥0.6 μg l−1 diuron equivalents cause measureable impacts on energetic status that may leave the plants vulnerable to other simultaneous stressors. For example, tropical seagrasses have been heavily impacted by reduced light from coastal flood plumes and the effects on plant energetics from light limitation and diuron exposure (highest in flood plumes) are very similar, potentially leading to cumulative negative effects.
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Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2016 Collection
National Research Centre for Environmental Toxicology Publications
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Citation counts: TR Web of Science Citation Count  Cited 4 times in Thomson Reuters Web of Science Article | Citations
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Created: Tue, 16 Jun 2015, 00:14:57 EST by System User on behalf of National Res Centre For Environmental Toxicology