Scallops, toxins

Figure 5.60 Calibration curves for the diarrhetic shellfish poisons in (i) standard solutions in methanol (O), and (11) standard solutions in poison-free scallop extract solutions ( ) (a) pectenotoxin-6 (b) okadaic acid (c) yessotoxin (d) dinophysistoxin-1. Reprinted from J. Chromatogr., A, 943, Matrix effect and correction by standard addition in quantitative liquid chromatographic-mass spectrometric analysis of diarrhetic shellfish poisoning toxins , Ito, S. and Tsukada, K., 39-46, Copyright (2002), with permission from Elsevier Science.

A matrix extract was prepared from poison-free scallop and spiked at the level of 200 ngg of scallop hepatopancreas. The toxins were determined by using LC-MS with calibration employing external standards prepared in methanol. The matrix extract was then spiked further with 300 ngg of each of the toxins and redetermined. The results obtained for each analyte are summarized in Table 5.17 and show that, when using the external calibration method, the values obtained range from 138 to 170 ngg a reduction in accuracy of between 15... 

Not all these polyether occur together in the same shellfish samples. OA was the major toxin in the mussel specimens from most of the European countries (42), while DTXl was the major toxin in mussel in Japan and in Sogndal, Norway (43). Scallops in Japan show the most complicated toxin profile. Furthermore, the relative ratio of the toxins varied regionally, seasonally, and annually. Pectenotoxins were detected, however, only in Japanese shellfish. Distribution of toxins is summarized in Table I. 

Coupled with successful primary prevention are ongoing monitoring programs for the organisms and their toxins, both in the environment and in the seafood. The molluscan shellfish (i.e., oysters, clams, mussels, and scallops) are the species associated with shellfish poisonings. The absence of characteristics such as abnormal taste, smell, or appearance precludes sensory inspection for these toxins. Instead, ensuring seafood safety relies on testing seawater and the seafood itself The assays used to detect toxins in seafood have evolved as analytic methods and instrumentation have improved. The American Public... 

Imai, I., et al., Monitoring of DSP toxins in small-sized plankton fraction of seawater collected in Mutsu Bay, Japan, by ELISA method relation with toxin contamination of scallop. Mar. Pollut. Bull., 47, 1-6, 114, 2003. 

Figure 12. Using toxin molecules as benthic tracers of presence of toxin producing dinoflagellates in cyst form. The scallop is used as the signal recorder/integrator.

In addition to these passive processes shellfish have been shown to actively modify the saxitoxins. Shimizu has shown (40) that scallops can remove both the N-l-hydroxyl and 11-hydroxysulfate groups from the saxitoxins. Sullivan has shown ( ) that enzymes in littleneck clams can remove the sulfamate or carbamate side chain, yielding the decarbamoyl toxins. This activity was not detected in either mussels or butter clams. With both sorts of modification the products are compounds that have higher potency and are likely to be bound in shellfish more strongly. 

Toxicity in deep water scallops throughout the year has been recognized for many years (44, 46, 47). More importantly, the levels of toxicity in the scallop digestive gland were shown to increase dramatically (sometimes by a factor of 2 or 4) during winter months when tamarensis motile cell populations were low or undetectable. Bourne ( ) postulated that cysts were the toxin source, an opinion also favored by Jamieson and Chandler (47) in a more recent study. It has since been confirmed that G. tamarensis cysts are indeed toxic, and this has led to a proliferation of explanations for toxicity episodes based on cyst ingestion. 

Despite this progress, the evidence linking cysts to shellfish toxicity remains circumstantial and care should be exercised before attributing toxin increases to this mechanism. The major problem is that it has yet to be demonstrated that shellfish can remove toxin from cysts. The feeding studies mentioned earlier (which do not yet include scallops 35) indicate that many viable G. tamarensis cysts can be isolated from the fecal pellets of mussels and soft-shelled clams fed cyst suspensions. There is certainly some cyst mortality as well (Figure 5), but whether this is also associated with toxin retention by the shellfish has yet to be demonstrated. It is reasonable to expect that the assimilation of toxin from cysts will not be a highly efficient process. 

Another problem with wintertime toxicity data is that toxin levels are reported per 100 gm of tissue. Studies of the deep sea scallop Placopecten magellanicus indicate that the size of the digestive gland can vary through the year (51). Thus a constant amount of toxin in a gland would look variable when normalized to 100 gm of tissue, with the highest relative toxicity during winter months when the tissues are the smallest. It would appear, however, that this error is small (perhaps 20-30%) relative to the 2 to 4-fold toxin increases typically reported between seasons in scallops (4, 47). 

When the homogenates of toxic scallops were incubated, other drastic changes in the toxin profile were observed (10) proportionally gonyautoxin-I - IV and neosaxitoxin decreased and saxitoxin increased. In another instance, the analysis of Mytilus exposed to the 1980 red tide at Sonoma County, California, showed the almost exclusive presence of neosaxitoxin in mussels collected just after the red tide and a gradual increase of saxitoxin (Krueger, Meyer and Shimizu, unpublished). These observations suggested the possible... 

Materials. The following shellfish specimens were collected for toxin analysis from the northeastern part of Honshu, Japan, during the infestation period the mussel Mytilus edulis at Miyagi Prefecture, the scallop Patinopeoten yessoensis at Aomori Prefecture, the short-necked clam Tapes japonioa at Fukushima Prefecture, and Gom-phina melanaegis at Ibaraki Prefecture. 

Shellfish (filterfeeding mollusks) Mussels, clams, oysters, scallops Several kinds of toxin taken up from plankton (dinoflagellate) See below ... 

Suzuki, T, Igarashi, T, Ichimi, K., Watai, M., Suzuki, M., Ogiso, E., and Yasumoto, T. 2005a. Kinetics of diarrhetic shellfish poisoning toxins, okadaic acid, dinophysistoxin-1, pectenotoxin-6 and yessotoxin in scallops Patinopecten yessoensis. 

Since the early Japanese studies on DSP, the toxins in mussels and scallops were suspected to be different. The main diarrhetic toxin found in scallops was found to be a mixture of 7-(9-acylderivatives of dinophysistoxin-1 (DTX-1), ranging from tetradecanoic acid (C14 0) to docosahexaenoic acid (C22 6to3), and designated as dinophysistoxin-3 (DTX-3) (Yasumoto et al. 1985). These acylated forms have never been found in marine microalgae, and so it was presumed that they originated in the bivalve by acylation (Lee et al. 1989). Direct evidence of this biotransformation by shellfish was obtained by artificially feeding scallops with D. forth collected from the sea (Suzuki et al. 1999). 

Suzuki, T, Mitsuya, T, Imai, M., and Yamasaki, M. 1997. DSP toxin contents in Dinophysis forth and scallops collected at Mutsu Bay, Japan. JApplPhycol 8 509-515. 

The consumption of shellfish (scallops and mussels) harvested during late spring to early summer fiom the northeastern region of Japan quite often results in what is commonly known as diarrhetic shellfish poisoning. An initial chemical investigation of the toxic mussels resulted in the identification (86) of okadaic acid [108], dinophysistoxin 1 (DTXj) [109] and two toxins of unknown structures. In a later study (87), chemical structures of three new polyether toxins, dinophysistoxin- 3 (DTX3)[110], pectenotoxin-1 [111 ] and pectenotoxin-2 [112] were reported. 

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