Global Distribution of Freshwater Paralytic Shellfish Poisoning Toxins (“Saxitoxins”) 1967–2025: Implications, Limitations, and Application to Risk Assessment

Abstract

Paralytic shellfish poisoning (PSP) toxins (PSPTs) (“Saxitoxins”) are a class of neurotoxins identified globally in freshwater and marine systems but are understudied in freshwater environments. We collected literature reports of PSPTs in natural systems from their first discovery in 1967 until 2025, with the aim of summarizing their occurrence. Freshwater PSPTs were commonly reported (>20% of waterbodies in 14/21 studies), with complex congener profiles including 21 primary congeners. Saxitoxin (STX) represented only 18% of the total, suggesting that methods focused primarily on STX are not adequately protective of environmental health. The most common PSPT producing genera were species of Aphanizomenon, but over 40% of reports could or did not assign a producer to the identified toxins. While there were many analytical methodologies incorporated by localized studies, those investigating multiple waterbodies (>6) tended to use only one analytical method. Our exposure assessment was inhibited by this subset of studies having study-specific limitations, severely restricting the use of these data for risk assessment. Toxicological uncertainty further hampered risk assessment – dose–response data for acute consumption of PSPTs has been generated and assessed, but questions remain about the accuracy of the no-observed-adverse-effect-level. Chronic/sub-chronic PSP toxicity data has been collected in animal models but there are no regulatory guidelines that utilize these for guidance values. The evidence indicates that PSPT production potential is widespread in freshwater environments, but most existing data do not accurately assess environmental concentration. Given these uncertainties, there is significant potential for harm from exposure to freshwater PSPTs.