Paralytic shellfish poisoning results from consumption of seafood naturally contaminated by saxitoxin and its congeners, the paralytic shellfish toxins (PSTs). The levels of such toxins are regulated internationally, and maximum permitted concentrations in seafood have been established in many countries. A mouse bioassay is an approved method for estimating the levels of PSTs in seafood, but this is now being superseded in many countries by instrumental methods of analysis. Such analyses provide data on the levels of many PSTs in seafood, but for risk assessment, knowledge of the relative toxicities of the congeners is required. These are expressed as “Toxicity Equivalence Factors” (TEFs). At present, TEFs are largely based on relative specific activities following intraperitoneal injection in a mouse bioassay rather than on acute toxicity determinations. A more relevant parameter for comparison would be median lethal doses via oral administration, since this is the route through which humans are exposed to PSTs. In the present study, the median lethal doses of gonyautoxin 5, gonyautoxin 6, decarbamoyl neosaxitoxin and of equilibrium mixtures of decarbamoyl gonyautoxins 2&3, C1&2 and C3&4 by oral administration to mice have been determined and compared with toxicities via intraperitoneal injection. The results indicate that the TEFs of several of these substances require revision in order to more accurately reflect the risk these toxins present to human health.

Nodularin is a cyanobacterial toxin predominantly produced by Nodularia spumigena Mertens. This cyanobacterium has been associated with fish, bird, and animal deaths, and the toxin can contaminate fish and shellfish intended for human consumption. With climate change, blooms of Nodularia spumigena are becoming more frequent and more widespread, meaning that the risk this cyanobacterium poses to human health must be evaluated. However, toxicity information is scarce, meaning that data from the closely related toxin class, microcystins, are currently used instead. In the current study, the LD₅₀ of nodularin-R by intraperitoneal injection was found to be 50 µg/kg, consistent with previous reports. For the first time, the LD₅₀ of nodularin-R by oral administration was determined using the voluntary consumption of laced cream cheese (7.5 mg/kg), which is similar to that reported for microcystin-LR (10.9 mg/kg). The use of microcystin toxicology data in food safety assessments for nodularin, therefore, seems reasonable—but it is critical that an oral repeated-dose study is performed on nodularin to better understand the risk posed by this toxin through chronic exposure.