Zinc from oyster tissue as causative factor in mouse deaths in official bioassay for paralytic shellfish poison

Toxicity (extreme weakness, body temperature drop, cyanosis, some slow deaths) in test mice, upon intraperitoneal injection of standard-method paralytic shellfish poison (PSP) extracts of some PSP-free oysters, is consistent with the relatively high levels of zinc in these extracts. As a rough guideline, the threshold for a toxic response corresponds to a drained tissue zinc level of over 900 micrograms/g. The identification of zinc as the substance responsible has been supported by inducing toxicity in control extracts by spiking with nontoxic levels of zinc, and by eliminating toxicity from toxic extracts by chemical removal (precipitation, ion exchange) of metals.