Herbicides: A new threat to the Great Barrier Reef

Australian Centre for Tropical Freshwater Research, James Cook University, Townsville, Queensland 4811, Australia.
Environmental Pollution (Impact Factor: 4.14). 05/2009; 157(8-9):2470-84. DOI: 10.1016/j.envpol.2009.03.006
Source: PubMed

ABSTRACT The runoff of pesticides (insecticides, herbicides and fungicides) from agricultural lands is a key concern for the health of the iconic Great Barrier Reef, Australia. Relatively low levels of herbicide residues can reduce the productivity of marine plants and corals. However, the risk of these residues to Great Barrier Reef ecosystems has been poorly quantified due to a lack of large-scale datasets. Here we present results of a study tracing pesticide residues from rivers and creeks in three catchment regions to the adjacent marine environment. Several pesticides (mainly herbicides) were detected in both freshwater and coastal marine waters and were attributed to specific land uses in the catchment. Elevated herbicide concentrations were particularly associated with sugar cane cultivation in the adjacent catchment. We demonstrate that herbicides reach the Great Barrier Reef lagoon and may disturb sensitive marine ecosystems already affected by other pressures such as climate change.

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    • "We found the two investigated strains to vary considerably in their response to diuron. Effect concentrations inhibiting effective quantum PSII yield (DF/Fm 0 ) (Tables 1 and 2) in the investigated Symbiodinium cultures were lower than reported for most other cultured microalgae (Magnusson et al., 2010), in the range of reported environmental concentrations (Kennedy et al., 2012; Lewis et al., 2009) and below current water quality guideline values for the GBR (GBRMPA, 2010), suggesting that populations of freeliving Symbiodinium may be at risk from herbicide exposure. The observed sensitivity of the clade D cultures to diuron could be especially consequential, as free-living Symbiodinium provide a pool for infection for larvae of many coral species not deriving symbionts through vertical transfer (parent to egg) (Coffroth et al., 2006). "
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    ABSTRACT: Most reef building corals rely on symbiotic microalgae (genus Symbiodinium) to supply a substantial proportion of their energy requirements. Functional diversity of different Symbiodinium genotypes, endorsing the host with physiological advantages, has been widely reported. Yet, the influence of genotypic specificity on the symbiont's susceptibility to contaminants or cumulative stressors is unknown. Cultured Symbiodinium of presumed thermal-tolerant clade D tested especially vulnerable to the widespread herbicide diuron, suggesting important free-living populations may be at risk in areas subjected to terrestrial runoff. Co-exposure experiments where cultured Symbiodinium were exposed to diuron over a thermal stress gradient demonstrated how fast-growing clade C1 better maintained photosynthetic capability than clade D. The mixture toxicity model of Independent Action, considering combined thermal stress and herbicide contamination, revealed response additivity for inhibition of photosynthetic yield in both tested cultures, emphasizing the need to account for cumulative stressor impacts in ecological risk assessment and resource management. Copyright © 2015. Published by Elsevier Ltd.
    Environmental Pollution 09/2015; 204. DOI:10.1016/j.envpol.2015.05.013 · 4.14 Impact Factor
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    • "Herbicide resistance and its side effects are the two main concerns, which are partially caused by the high levels of herbicide residues (Bruggeman et al. 2014; Délye et al. 2013). Moreover, inappropriate use of the herbicides potentially impact nontarget organisms in aquatic ecosystem and nonfarming areas (Boutin et al. 2014; Jacobsen and Hjelmsø 2014; Lewis et al. 2009). Mesotrione is a selective herbicide for preemergence and postemergence control of a wide range of broad-leaved and grass weeds in maize (Mitchell et al. 2001). "
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    ABSTRACT: The degrading microorganisms isolated from environment usually fail to degrade pollutants when used for bioremediation of contaminated soils; thus, additional treatments are needed to enhance biodegradation. In the present study, the potential of sugarcane bagasse as bacteria-immobilizing support was investigated in mesotrione biodegradation. A novel isolate Bacillus pumilus HZ-2 was applied in bacterial immobilization, which was capable of degrading over 95 % of mesotrione at initial concentrations ranging from 25 to 200 mg L(-1) within 4 days in flask-shaking tests. Scanning electron microscope (SEM) images showed that the bacterial cells were strongly absorbed and fully dispersed on bagasse surface after immobilization. Specially, 86.5 and 82.9 % of mesotrione was eliminated by bacteria immobilized on bagasse of 100 and 60 mesh, respectively, which indicated that this immobilization was able to maintain a high degrading activity of the bacteria. Analysis of the degradation products determined 2-amino-4-methylsulfonylbenzoic acid (AMBA) and 4-methylsulfonyl-2-nitrobenzoic acid (MNBA) as the main metabolites in the biodegradation pathway of mesotrione. In the sterile soil, approximately 90 % of mesotrione was degraded after supplementing 5.0 % of molasses in bacteria-bagasse composite, which greatly enhanced microbial adaptability and growth in the soil environment. In the field tests, over 75 % of mesotrione in soil was degraded within 14 days. The immobilized preparation demonstrated that mesotrione could be degraded at a wide range of pH values (5.0-8.0) and temperatures (25-35 °C), especially at low concentrations of mesotrione (5 to 20 mg kg(-1)). These results showed that sugarcane bagasse might be a good candidate as bacteria-immobilizing support to enhance mesotrione degradation by Bacillus p. HZ-2 in contaminated soils.
    Applied Microbiology and Biotechnology 09/2015; DOI:10.1007/s00253-015-6935-0 · 3.34 Impact Factor
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    • "PSII herbicides can also limit primary production in seagrass by reducing photosynthetic efficiency and/or causing damage to PSII (Flores et al., 2013; Haynes et al., 2000; Ralph, 2000; Seery et al., 2006). Since herbicide exposure peaks during flood periods (Lewis et al., 2009; Smith et al., 2012) there is mounting concern that persistent low concentrations of PSII herbicides in nearshore waters of the GBR may contribute to seagrass decline (Waterhouse et al., 2012; Waterhouse et al., 2013). "
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    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 7.2μgl(-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 0.3μgl(-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 7.2μgl(-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 (0.6μgl(-1)) and reduced δ(13)C (1.7μgl(-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 1.7μgl(-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 ≥0.6μgl(-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. Crown Copyright © 2015. Published by Elsevier B.V. All rights reserved.
    Aquatic Toxicology 05/2015; 165:73-83. DOI:10.1016/j.aquatox.2015.05.007 · 3.45 Impact Factor
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