Environmental Engineering Reference
In-Depth Information
strongly bind to their siphon tissues (Beitler and Liston
1990
). Generally, fast detoxifi ers
are those species that remove or detoxify the toxins at rates between 6% and 17%
per day. At such rates, safe levels are attained within 1-10 weeks (Table
3
). In con-
trast, slow detoxifi ers (those that exhibit toxin elimination rates of
≤
1%/day) take
several months or even years to attain safe levels (Bricelj and Shumway
1998
).
Detoxifi cation in bivalves begins with a fast initial depuration phase, followed by a
slow depuration phase (Chou et al.
2005
; Xie et al.
2013
; Choi et al.
2003
). The ini-
tial fast depuration results from evacuation of unassimilated toxin and toxigenic
cells, whereas the slower depuration phase represents loss of toxins that had been
assimilated and incorporated into tissues (Silvert et al.
1998
).
The PST level in each organ does not remain constant over time. During toxifi ca-
tion, the proportion of toxin contained in bivalve viscera remains fairly constant, but
decreases steadily during the detoxifi cation process (Donovan et al.
2008
; Kwong
et al.
2006
; Martin et al.
1990
). The hepatopancreas and viscera exhibit the highest
rate of toxin elimination, whereas the foot and adductor muscles display the slowest
rate (Bricelj et al.
1991
). The different clearance rates results from the PSTs having
been redistributed from the hepatopancreas to other tissues during the detoxifi cation
process (Bricelj and Cembella
1995
). The non-visceral tissues of purple clam begin
to accumulate PST (i.e., GTX) on day 16-20 from the initial exposure as a result of
translocation from the digestive gland to muscle tissue (Chou et al.
2005
). The Purple
Clam transfers toxins from the digestive gland to the foot and adductor muscles
earlier than other clam species, because the half-life of the PSP toxin is shorter in
this species (Chou et al.
2005
; Chen and Chou
2001
). In the surfclam,
S. solidissima
,
the rank order of various tissue pools, in terms of detoxifi cation rates, is as follows:
viscera > gill > foot adductor muscle (Bricelj and Cembella
1995
). The hepatopan-
creases, viscera, gills, foot and adductor muscles of green mussels were reported to
accumulate 40%, 34%, 17% and 10% of PST, respectively, after 7 days of detoxifi -
cation (Kwong et al.
2006
). Accumulation rates of PST in different compartments
also depend on the types of toxin involved (Kwong et al.
2006
; Bricelj and Cembella
1995
). For example, elimination of C2 toxin was shown to be effi cient from all
organs. However, elimination of GTX4 was relatively slow from gills and viscera,
because the toxin was retained by those organs. Kwong et al. (
2006
) reported that
the elimination of STX and neoSTX from foot and adductor muscles was delayed
because the PSTs were redistributed from other organs.
5
Analysis Methods for Paralytic Shellfi sh Toxins
PST analysis is mainly achieved through bioassay (
in vivo
mouse bioassays),
in
vitro
cell assays,
in vitro
functional assays (receptor binding assay), chemical assays
(HPLC and LC-MS) and immunosorbant assays (immunoassays).
Search WWH ::
Custom Search