PERSISTENCE AND DEGRADATION OF CYANOBACTERIAL PARALYTIC SHELLFISH POISONS (PSPS) IN FRESH-WATERS

Paralytic shellfish poisons (PSPs) extracted from the cyanobacterium A nabaena circinalis persisted for over 90 days when incubated in freshw ater. The primary transformation reaction was desulfocarbamoylation of the predominant, low toxicity C-toxins, to the more potent decarbamoy l-gonyautoxins (dc-GTXs). This transformation caused an initial increa se in sample toxicity, in spite of an overall decrease in total toxin concentration (on a molar basis) with time. Incubation of PSPs in irri gation drainage water resulted in a six-fold increase in toxicity afte r 10 days, with the solution remaining more toxic than the original so lution for over 60 days. The dc-GTXs thus formed, and the gonyautoxins (GTXs) present in the original sample, degraded slowly for the durati on of the 90 day incubations. Similar results were recorded when PSPs were incubated with sterile deionised water, and with sterile deionise d, protein precipitated water, but the build-up of dc-GTXs proceeded a t a slower rate than with the drainage water. The other reaction noted to be significant was the slow epimerisation of the less stable beta- epimers (C2, GTX3) to alpha-epimers (C1, GTX2). The degradation of C-t oxins, gonyautoxins (GTXs) and dc-GTXs could be modelled by simple fir st-order loss kinetics. When PSPs were incubated at 90 degrees C, the same loss processes and reaction order was observed. The failure of pr otein precipitation and high temperature to alter the reaction process es, indicates that desulfocarbamoylation of C-toxins, and degradation off GTXs and dc-GTXs is chemically, and not enzymatically, mediated. U pon the collapse of PSP producing A. circinalis blooms, and the subseq uent release of toxins into the water column, contaminated water may b ecome more toxic in the short term before the eventual degradation of PSPs to non-toxic products. Unless significant dilution occurs, PSP co ntaminated waters may contain toxins for more than 3 months. (C) 1997 Elsevier Science Ltd.