Abstract:
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In this work we studied the toxicity in clams from the Gulf of Gabes, Tunisia (Southern
Mediterranean). Samples from two stations (M2 and S6) were collected monthly from
January 2009 to September 2010, and analyzed by the official control method of
mousse bioassay (MBA) for lipophilic toxins. All samples were also analyzed with the
LC-MS/MS method for the determination of lipophilic toxins, namely: okadaic acid
group, pectenotoxins, yessotoxins and azaspiracids, spirolides and gymnodimines
(GYMs). The results showed prevalence of GYMs since it was the only toxin group
identified in these samples with a maximum of 2,136 μg GYM -A kg-1 (February 2009
at M2). Furthermore, GYMs showed persistence in the area, with only one blank sample
below the limit of detection. Interestingly, this blank sample was found in June 2009
after an important toxic episode which supports the recent findings regarding the high
detoxification capability of clams, much faster than that reported for oysters. In
comparison, good agreement was found among MBA, the LD50 value of 80-100 μg kg-1
reported for GYM- A, and quantitative results provided by LC-MS/MS. On the contrary
to that previously reported for Tunisian clams, we unambiguously identified and
quantified by LC-MS/MS the isomers GYM- B/C in most samples. Phytoplankton
identification and enumeration of Karenia selliformis usually showed higher densities at
site M2 than S6 as expected bearing in mind toxin results, although additional results
would be required to improve the correlation between K. selliformis densities and
quantitative results of toxins. The prevalence and persistence of GYMs in this area at
high levels strongly encourages the evaluation of the chronic toxic effects of GYMs.
This is especially important taking into account that relatively large quantities of GYMs
can be released into the market due to the replacement of the official control method
from mouse bioassay to the LC-MS/MS for lipophilic toxins (Regulation (EU) No
15/2011), and the lack of Regulation for this group of toxins. |