Variability of mouse bioassay for determination of paralytic shellfish poisoning toxins

Toxic shellfish extracts and paralytic shellfish poison (PSP) standard solutions, tested over a range of pH levels, storage conditions, and temperatures, were monitored for toxin concentration, using the mouse bioassay and thin layer chromatography (TLC). A comparison of PSP toxin concentrations in toxic shellfish extracts and PSP standard solutions when dilution was varied suggests that other factors in the shellfish extracts contribute to the toxicity in mice; the closet agreement was at the death time range of 5-8 min. The toxicities of PSP standard solutions at pH levels ranging from 2 to 6 and held at 4 degrees C for various times were relatively constant; however, there was a gradual decrease in toxicity with pH 6 solutions. Also, standard solutions (pH 6) held at 4 degrees C for 28 days showed a 50% decrease in toxicity when the pH was adjusted to 2. TLC analyses of PSP standard solutions and toxic shellfish extracts revealed multiple spots at the Rf ranges of saxitoxin/neosaxitoxin and gonyaulax toxins I-IV. PSP standard solutions usually had a single spot in the saxitoxin/neosaxitoxin area. No attempt was made to confirm the identity of these compounds. Previously tested toxic shellfish extracts with subsequent pH adjustment to 1.5 and additional heat treatment (100 degrees C for 5 min) showed no appreciable difference in mouse toxicity. The use of antifoaming agents during the acid extraction step did not affect the final amounts of PSP obtained.