African Wildlife & Environment Issue 84 2023

CONSERVATION

IS IT WISE TO REMOVE HYACINTH FROM EUTROPHIC DAMS?

aerosolized cyanobacterial toxins causes a significant health risk that is not yet fully understood for humans. The work done by Hu and others published in 2022, concludes that, “BMAA and microcystin are consistently detected in HAB (Harmful Algal Bloom) waters, although their concentrations do not always correlate with the severity of the health impact, suggesting the potential contribution from additional toxins present in the aerosolized HAB water. This study demonstrates, for the first time, the health risk of exposure to aerosolized HABs, and further highlights the critical importance of understanding the toxicity of aerosolized cyanobacteria HAB particles and determining the immediate and long term health impacts of HAB exposure”. This is cause for concern, because the human health risk of aerosolized toxins, originating from HAB waters, is not yet fully understood. For example, a study published in 2022 by Lee and others in the journal Environmental Health , reports a statistical correlation between HAB waters and neurodegenerative disease, within a 5-km radius of the eutrophic water body. A specific finding notes, “(while) the role of toxic HAB in neuropathy is still controversial, the statistical results of this study imply a significant correlation between HAB incidence and the occurrence of neurodegenerative diseases”. It recommends additional epidemiological studies to further determine the correlation between a range of toxins found in HAB water, and the range of neurodegenerative disease manifesting within a defined radius of such waterbodies. This cutting-edge research into aerosolised toxins arising from eutrophic water is cause for concern. It suggests that communities living within a defined radius of eutrophic waters, are at greater risk of a There is a growing trend to remove water hyacinth, often driven by enthusiastic members of the public. There are even attempts to destroy the plants by spraying floating mats with herbicide. While undoubtedly well intended, these interventions are generally blind to the basic science underpinning the management of eutrophic waters. This article opens that debate by presenting recently reported human health trends that decision makers might need to consider before authorizing such activities.

Dr Anthony Turton

In 2015, the South African Journal of Science published a paper by Mathews and Bernard that quantified the extent to which South African dams have become eutrophic. This summarized many years of cutting-edge remote sensing research, which has demonstrated the capacity to detect cyanobacterial blooms from satellites located in space. This credible research indicated that two thirds of our large dams are now eutrophic. In 2014 Mathews demonstrated that the gross trophic status through chlorophyll-a quantification can be accurately determined in both eucaryote (DNA-based) and procaryote (cyanobacteria without a distinct nucleus) dominant waters, through a peer reviewed publication in the journal Remote Sensing and the Environment. This means that the space-derived data has real value in informing decisions about the management of eutrophic waters, because it can distinguish different types of algae. This is important, because the depth of our cumulative knowledge on cyanobacterial blooms in South Africa has established that our dominant genera of blue-green algae are Anabaena and Microcystis , both procaryotes. It has been established, with little room for doubt, that these two genera produce potent toxins – anatoxin and microcystin. It has also been established that beta-methylamino L-alanine (BMAA) is the active ingredient of microcystin. Hu and others noted in 2022 that the human health risk arising from exposure to aerosolized algal blooms is poorly understood, but they demonstrated that an animal model, the fruit fly Drosophila melanogaster , when exposed at an early age, resulted in long-term impact among all age cohorts. Their work demonstrated that once-off exposure to

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