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. 2018 Oct 15;15(10):2255.
doi: 10.3390/ijerph15102255.

Sediment Facilitates Microbial Degradation of the Herbicides Endothall Monoamine Salt and Endothall Dipotassium Salt in an Aquatic Environment

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Free PMC article

Sediment Facilitates Microbial Degradation of the Herbicides Endothall Monoamine Salt and Endothall Dipotassium Salt in an Aquatic Environment

Md Shahidul Islam et al. Int J Environ Res Public Health. .
Free PMC article

Abstract

Endothall dipotassium salt and monoamine salt are herbicide formulations used for controlling submerged aquatic macrophytes and algae in aquatic ecosystems. Microbial activity is the primary degradation pathway for endothall. To better understand what influences endothall degradation, we conducted a mesocosm experiment to (1) evaluate the effects of different water and sediment sources on degradation, and (2) determine if degradation was faster in the presence of a microbial community previously exposed to endothall. Endothall residues were determined with LC-MS at intervals to 21 days after endothall application. Two endothall isomers were detected. Isomer-1 was abundant in both endothall formulations, while isomer-2 was only abundant in the monoamine endothall formulation and was more persistent. Degradation did not occur in the absence of sediment. In the presence of sediment, degradation of isomer-1 began after a lag phase of 5⁻11 days and was almost complete by 14 days. Onset of degradation occurred 2⁻4 days sooner when the microbial population was previously exposed to endothall. We provide direct evidence that the presence and characteristics of sediment are of key importance in the degradation of endothall in an aquatic environment, and that monoamine endothall has two separate isomers that have different degradation characteristics.

Keywords: aquatic weed; biodegradation; irrigation canal; irrigation channel; mesocosm; persistence.

Conflict of interest statement

This research was funded in part by the distributor of endothall in Australia, UPL Australia Ltd. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Figure 1
Figure 1
Extracted ion chromatogram of endothall, in two formulations. Endothall concentrations of isomer-1 are 10 mg L−1 in both cases.
Figure 2
Figure 2
Endothall isomer-1 (a) and isomer-2 (b) concentrations in mesocosms for each treatment. Values represent average over three replicates. Plots represent various combinations of endothall formulation, source of water and sediment, presence or absence of sediment, and microbe augmentation. Note different y-axis scales between left and right panels. (1) Treatments containing dipotassium endothall without microbe augmentation. (2) Treatments containing monoamine endothall (without microbe augmentation). (3) Treatments containing monoamine endothall with sediment, ±microbe augmentation. Note: a subset of treatments is shown in both (2) and (3). Legend provided in top right panel: Water sources represented by line style; endothall form (DE = Dipotassium endothall, ME = Monoamine endothall), sediment presence or absence (±sed) and pre-exposure to endothall (±aug), represented by shape and full of symbols.

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