Risk Assessment of Marine Algal Toxins on Humans and Dugongs

Abstract

Algal toxins can have a significant impact on human and ecological health as the toxins accumulate in the food chain and are consumed by both humans and marine organisms. This study focussed on the following marine algal toxins that were present at the study sites: okadaic acid (OA), domoic acid (DA), gymnodimine (GD), pectenotoxin-e (PTX-2) and PTX-2 seco acid (PTX-2SA). The study sites investigated for potential algal toxin exposure were selected from the waters around North Stradbroke Island, Queensland, Australia, where shellfish are harvested by the local population, and where dugongs are known to feed on seagrass. Samples were collected monthly for two consecutive years. The species of toxinproducing algae present at the sites studied were Pseudo-nizschia sp., Dinophysis caudata, D. acuminata and Prorocentrum lima. The occurrence of Dinophysis species was observed to be dependent on the season while Pseudo-nitzschia sp was present both in colder and warmer months. Data on the dose-response analysis were extracted from published literature. This data was categorised into whole organisms, human and animal cell lines, and compared to one another. For further toxicodynamic studies, human cell lines were dosed with known concentrations of the toxins: OA, DA and GD. These cytotoxicity and microarray analyses were performed to observe the effects of toxins on gene regulation. A more extensive analysis was performed using GD alone. Expression of numerous genes was affected, and real time polymerase chain reaction reactions were performed to confirm the regulation of those genes. Gymnodimine was demonstrated to affect genes within pathways relating to oxidative phosphorylation, apoptosis, MAPK and Wnt signalling pathways. The cytotoxicity and microarray data and the data accumulated from the published literature were combined to form a comprehensive database of both chronic and acute effects. The database was then referred to for the dose-response analysis for the risk assessment. The exposure data attained from field sampling in the current study was analysed against the doses for any shown effects. Total daily intake for humans and dugongs sourcing food from around the island were calculated and health risks were estimated by incorporating tolerable daily intake, guideline values and total daily intake. The risk characteristics of algal toxins on the health of humans (consuming shellfish) and dugongs (consuming seagrass) indicated that acute health risks were unlikely, unless an outbreak of toxic algae (algal bloom) were to occur. Since there were no occurrences of algal blooms during the study period, high levels of toxins were not detected in any of the collected shellfish, phytoplankton or seagrass samples. However, if such blooms were to occur around the island, the phytoplankton could potentially produce algal toxins at high enough concentrations to cause acute toxic effects in the consumers. The current study has also demonstrated that there is a potential for chronic, long term health effects from consuming shellfish and seagrass around the island. The presence of low-level concentrations of algal toxins in the food sources can lead to chronic effects. Toxins such as OA are known tumour promoters. For dugongs, which feed on seagrass on daily basis, the potential for chronic effects is high. It was demonstrated that GD also possesses toxicological characteristics that may enhance the possibility of tumour promotion because of its effect of down-regulating parts of the apoptosis pathway, which may prevent cell death and as a consequence, lead to uncontrolled cell growth.