Low Levels of Contaminants Stimulate Harmful Algal Organisms and Enrich Their Toxins

Abstract

A widespread increase in intense phytoplankton blooms has been noted in lakes worldwide since the 1980s, with the summertime peak intensity amplifying in most lakes. Such blooms cause annual economic losses of multibillion USD and present a major challenge, affecting 11 out of the 17 United Nations Sustainable Development Goals. Here, we evaluate recent scientific evidence for hormetic effects of emerging contaminants and regulated pollutants on Microcystis sp., the most notorious cyanobacteria forming harmful algal blooms and releasing phycotoxins in eutrophic freshwater systems. This new evidence leads to the conclusion that pollution is linked to algal bloom intensification. Concentrations of contaminants that are considerably smaller than the threshold for toxicity enhance the formation of harmful colonies, increase the production of phycotoxins and their release into the environment, and lower the efficacy of algaecides to control algal blooms. The low-dose enhancement of microcystins is attributed to the up-regulation of a protein controlling microcystin release (McyH) and various microcystin synthetases in tandem with the global nitrogen regulator Ycf28, nonribosomal peptide synthetases, and several ATP-binding cassette transport proteins. Given that colony formation and phycotoxin production and release are enhanced by contaminant concentrations smaller than the toxicological threshold and are widely occurring in the environment, the effect of contaminants on harmful algal blooms is more prevalent than previously thought. Climate change and nutrient enrichment, known mechanisms underpinning algal blooms, are thus joined by low-level pollutants as another causal mechanism.

Monitoring, Regulation, and Mitigation of Cyanotoxins in the Environment to Protect Human Health and Wildlife

“…Toxic cyanobacteria are dominant organisms in harmful algal blooms. Harmful algal blooms have intensified worldwide since the 1980s due to anthropogenic (e.g., fertilizer use, population growth, and gross domestic product) and climatic (e.g., temperature, wind speed, atmospheric pressure, and rainfall) factors, and blooms are often more intense in less developed regions, such as in Asia, South America, and Africa . These factors suggest an enhanced risk for increased exposure to cyanotoxins, which differs among regions.…”

“…These factors suggest an enhanced risk for increased exposure to cyanotoxins, which differs among regions. Anthropogenic contaminants in the environment can also stimulate the synthesis of cyanotoxins and their release in the environment, but recent studies indicated that the ingestion of anthropogenic chemicals by cyanobacteria can lead to the synthesis and release of novel cyanotoxins with the potential to lead to massive deaths of wild animals …”

“…The use of novel DNA-based nanosensors may facilitate a more effective and faster identification and sensing of cyanotoxins in the future . These could also be coupled with proteomic and transcriptomic analyses of cyanobacteria to characterize potentially new toxins, especially because the current scientific literature lacks such studies at small doses of stress . The active engagement of the public in the monitoring activities of local environmental institutions within a citizen-science approach could help in such programs to expand the coverage of waters regularly observed for harmful algal blooms.…”

“…Mitigation efforts that should be implemented include the application of existing algaecides at early stages of harmful algal bloom formation, to prevent expansion of cyanobacteria and restrict the synthesis and release of cyanotoxins. There are various effective algaecides, such as CuSO 4 , H 2 O 2 , ultraviolet, and KMnO 4 , but careful selection of the most ideal doses is needed to avoid undesired stimulation of cyanobacteria due to insufficiently large doses . This complicates the mitigation efforts because large doses of algaecides might severely affect organisms other than target algae, and thus, the selection of doses should be done case-specifically and considering effects on local nontarget organisms.…”

“…Harmful algal blooms have intensified worldwide since the 1980s due to anthropogenic (e.g., fertilizer use, population growth, and gross domestic product) and climatic (e.g., temperature, wind speed, atmospheric pressure, and rainfall) factors, and blooms are often more intense in less developed regions, such as in Asia, South America, and Africa. 4 These factors suggest an enhanced risk for increased exposure to cyanotoxins, which differs among regions. Anthropogenic contaminants in the environment can also stimulate the synthesis of cyanotoxins and their release in the environment, 4 but recent studies indicated that the ingestion of anthropogenic chemicals by cyanobacteria can lead to the synthesis and release of novel cyanotoxins with the potential to lead to massive deaths of wild animals.…”