The following post is one of a series previewing the research that will be presented at the SETAC Europe Annual Meeting in Rome, Italy (13-17 May 2018).
A guest post by Gemma Giménez Papiol
How do toxic natural compounds such as microalgae toxins or plant secondary metabolites affect water quality, ecosystem functioning, and human health? For the majority of natural toxins—of which there are at least 25,000 different compounds—we do not know! Natural toxins include some of the worlds’ most toxic substances. They may be produced either within water bodies or by plants and other organisms from which the toxins may transfer via soils to receiving waters, or they can enter the human food web via filter-feeding organisms such as clams and mussels. Many of the compounds are polar, leading to high mobility in the environment; the nonpolar components can remain in body compartments for longer and become a serious threat to human health. We are in the strange situation that except for a few 100 of these toxins, we have no monitoring data and no insight with environmental fate and toxic effects, and with a lack of tools for assessing exposure and health impacts. In this session we will shed new light on the subject and discuss future priorities for studies of the large group of emerging natural toxins.
Microalgae toxins are produced by microalgae in freshwater and marine environments. They are related to microalgae proliferations, known as harmful algal blooms (HABs). Microalgae proliferation is favored by environmental conditions, especially the increase of nutrients—mainly nitrogen and phosphate—in aquatic ecosystems, a natural phenomenon called eutrophication. However, anthropogenic activities contribute to the increase of nutrient input to water bodies, resulting in them becoming highly eutrophic. Cyanotoxins (produced by cyanobacteria, mainly in freshwater) are classified into hepatotoxins, neurotoxins, and dermatotoxins, based on molecular structure and toxicity. Marine toxins are classified according the poisoning symptoms, the vector, or their structure; therefore, there are amnesic shellfish poisoning (ASP) toxins, paralytic shellfish poisoning (PSP) toxins, ciguatera fish poisoning (CFP) toxins, or lipophilic toxins, as examples. HABs have been evidenced worldwide as well as their toxic, social, environmental, and economic effects.
Plant secondary metabolites are bioactive compounds produced by terrestrial plants. Their role is to protect plants from other species, as herbivores, or to compete with other plants (“chemical weapons”). They are released from plant to soil via wash-off or plan litter (roots and leaves); therefore, the source is not continuous. Many of them are polar compounds that leach easily to drains and groundwater. Their final concentration in the water depends on the rate of transfer from the plant, the rate of abiotic and microbial degradation, and the timing of meteorological events such as rain (wash-off).
The presence of these toxins in water supply reservoirs increases the costs of the water treatment and/or the stoppage of water supply for human consumption, and their potential presence in seafood has necessitated the development of monitoring programs worldwide to guarantee food safety. To the already reported direct toxic effects such as hepatotoxicity, liver failure, DNA damage, oxidative stress, decreased reproduction and survival in aquatic organisms, impairments to gonadal development in aquatic organisms, disordered hormone conversion in mice and neurodevelopment toxicity, effects due to bioaccumulation and biomagnification, transfer in the food web, transfer to offspring, and teratogenic effects must also be added.
Currently, the only protection is to avoid the ingestion of contaminated water or food. In order to face the big challenges posed by natural toxins to human health and ecosystems, research, monitoring, and new management strategies are necessary. Analytically, natural toxins present unknown structures (as opposed to the known structures of synthetic chemicals) and many congeners. For instance, there are 248 identified microcystin (MC, a cyanotoxin) congeners so far, but the regulation differs between the US (several congeners and total MCs are monitored by ELISA techniques) and Europe (the congener MC-LR will soon be included as a parameter in drinking water monitoring). The scarcity of standards and Certified Reference Materials not only limits their chemical analysis but also the generation of risk values for aquatic life. For instance, the determination of LC50s, IC10s and NOECs for protection of wildlife in aquatic environments is not possible. These, and other challenges, will be discussed in the session “Natural toxins and harmful algal blooms (HABs): analysis, toxicity, and risks.”
Session information: “Natural toxins and harmful algal blooms (HABs): analysis, toxicity, and risks”
May 17, 2018 | 8:30 – 12:25 | Room O