Factors Influencing the Toxicity, Detoxification and Biotransformation of Paralytic Shellfish Toxins - Reviews of Environmental Contamination and Toxicology - page 17

and human health. In general, nutrient concentration, the nutrient ratio and environ-
mental parameters are known to infl uence harmful algal blooms (HABs) and the
cellular toxicity they cause. However, the linkage among nutrients (organic and inor-
ganic), environmental parameters, PST toxicity and PST composition are still poorly
understood. Further investigations are needed to elucidate how certain environmental
parameters, certain nutrients and their proportions act to regulate the production of
PSTs in HAB species.
Filter feeding bivalves are the primary vector of paralytic shellfi sh poisoning.
The bioaccumulation of PSTs in bivalves is associated with shellfi sh sensitivity to
the toxins. Sensitive shellfi sh usually accumulate lower toxin levels, while insensi-
tive species accumulate toxins to an extremely dangerous level. To ensure the safety
of seafood products, shellfi sh fi sheries are closed by regulators if any edible portion
of shellfi sh is found to have levels of PSTs equal to or exceeding 0.8 ʼ g STXeq per 100g
tissue shellfi sh fl esh. The closures of such facilities are often long and sometimes
indefi nite. Therefore, for the benefi t of processors, it is important that scientists
understand the mechanism and rate of uptake of PSTs, as well as their elimination
rate from different bivalve species. Understanding the kinetics of uptake and elimi-
nation will enhance our ability to balance protecting public health, while preserving
the economic viability of the seafood industry.
There is clear evidence that PSTs are biotransformed by bacterial isolates from
bivalves. However, a vast knowledge gap exists about the enzymatic pathways of
how the PSTs are biotransformed to less toxic versions of themselves by the bivalves
or by the bacteria that infest the bivalves. In addition, little is known of the factors,
either environmental or otherwise that affect PST biotransformation. In particular,
research is needed to elucidate the factors that infl uence both non-enzymatic and
enzymatic transformation of PST by bacteria. Specifi c bacterial strains should be
examined that can be utilized in the bivalve culture industry or elsewhere to degrade
or detoxify PSTs. Development of novel methods of detoxifi cation is essential from
both the consumer human health and industry economic viability perspectives.

8 Summary

Saxitoxin and related compounds are potent marine neurotoxins, and are often
associated with paralytic shellfi sh poisoning (PSP) incidents. In marine waters,
dinofl agellates belonging to the genera Alexandrium , Gymnodinium and Pyrodinium
are the agents that cause PSP. The growth rate, PST (paralytic shellfi sh toxin) con-
centration and composition produced by these PST-generating dinofl agellates are
highly infl uenced by dietary nutrient concentration, nutrient composition and other
environmental factors. With the exception of fi lter-feeding bivalves, all marine
organisms are vulnerable to the effects of the PSTs. The suspension-feeding bivalves
are the primary vectors for transferring the PSTs that pose a health hazard to humans
and other food web consumers. Different bivalve species produce different levels
of PSTs. The toxin levels in these bivalves species depends mainly on how much of