Key messages

• Assessment of reproduction and embryotoxicity in pond snails by mycotoxins commonly present in wastewater
• Assessment of cyanobacterial toxicity to marine and freshwater invertebrates on life history
• Assessment of cyanobacterial toxicity in combination with chemical pollution to green algae 

Overview

The EU uses regulations as a method to set threshold values for the concentration of natural toxins such as microcystins ↗, yessotoxin ↗ and saxitoxin ↗ to ensure they remain safe for human consumption. Microcystins are toxins produced by cyanobacteria ↗ in freshwater, while yessotoxin and saxitoxin are marine biotoxins associated with harmful algal blooms.

While there are regulations in place to protect human health, there is a gap in regulations regarding safe exposure levels for aquatic species from an environment health perspective.

In aquatic ecosystems, invertebrates have a crucial role in the food chain and the overall functioning of the ecosystem, as they are primary consumers and serve as food for higher trophic levels. Microalgae are in turn the primary food source for these invertebrates, which are positioned on an even lower level in the trophic chain forming the very base of aquatic ecosystems. Studying the effects and risks natural toxins have on aquatic organisms, such as invertebrates and microalgae, lays the cornerstone of assessing the need for regulations and toxin mitigation measures.

By investigating the toxicity of naturally occurring toxins alone or in combination on aquatic organisms, this project aims to make an impact on the regulatory landscape concerning the protection of marine and freshwater environments. Within EU legislation, this project draws on the Marine Strategy Framework Directive ↗ and the Water Framework Directive ↗. Additionally, the results of this project will also serve as a basis for further regulating nitrogen and phosphorus pollution ↗ within the EU, as these contribute to eutrophication ↗, a key driver of harmful algae bloom.  

Achievements & Results

The study investigated the effects of various natural toxins and environmental conditions on aquatic organisms. Here are the key findings:

• Toxicity of Mycotoxins: Several mycotoxins commonly found in wastewater, such as zearalenone and deoxynivalenol ↗, were tested for their effects on pond snail embryos. Toxicity levels were detected at concentrations well above environmental levels.  
• Impact on Tiny Crustaceans: Two marine toxins, yessotoxin and saxitoxin, were shown to reduce the number of offspring produced by the estuarine copepod N. spinipes. This impact became even stronger when water temperatures were elevated, highlighting the potential risks of climate change in amplifying toxin effects.
• Toxin Levels in Natural Waters: Measurements of four algal toxins in natural seawater (yessotoxin, saxitoxin, domoic acid, and microcystin-LR) found that, in the absence of algal blooms, their concentrations are below levels shown to cause harmful effects in this study.
• Effects on Green Algae: Testing the effects of microcystin-LR and cylindrospermopsin on green algae (C. vulgaris) revealed that growth was affected only at relatively high concentrations (4 to 40 mg/L) after 4 to 7 days of exposure. 

Policy relevance

• Drawing attention to the need of further regulations on threshold values of naturally occurring toxins in the aquatic environment
• Providing scientific support to prioritize specific toxins and sensitive species across marine and freshwater habitat based on effect assessments