Page 3 - Dolphin_Tuna_Shark_1996

Butyltins in Dolphin, Shark, and Tuna 21

Table 1. Concentrations of butyltin compounds (ng/g wet wt) in adult degradation activity a concentration gradient of DBT >>
male bottlenose dolphins from Italian coast of the Mediterranean Sea TBT -> MBT has to be expected. The concentration ratios of
TBT, DBT and MBT in the blubber is typical for an organ with
Carcass
almost no or less capacity for alkyltin dealkylation. Further-
decomposition Tissue Fat (%) MBT DBT TBT BTs a
more, MBT is relatively more polar (hydrophilic) than DBT
Moderate Blubber 18 55 16 41 110
and, therefore, eliminated rapidly from the liver.
Liver 7 150 800 250 1200
The most commonly documented effect of butyltins in mam-
Moderate Blubber 8 25 9 14 48
mals was immune suppression (Snoeij et al. 1989). The resis-
Fresh Blubber 27 65 42 210 320
tance against Aeromonas hydrophilia was decreased in fish
Liver 17 200 1600 400 2200
exposed to butyltins (de Vries et al. 1991). It is not known
whether the concentrations of BTs found in these diseased
~BTs = MBT+DBT+TBT, i.e., total butyltins (BTs) is the sum of
mono-(MBT), di-(DBT), and tributyltin (TBT) dolphins had any effect on the immune system, suggesting the
need for further studies.
noides) tissues collected from Japanese coastal waters for BTs
showed the highest concentrations in liver with lower concentra-
BIuefin Tuna
tions in kidney, muscle, blubber and brain (Iwata et al. 1995).
Accumulation of butyltin compounds in dolphin livers is differ-
Concentrations of BTs in tuna ranged from 67 to 540 ng/g wet
ent from organochlorines, which preferentially accumulate in
wt (mean: 210 ng/g) in liver and 16-230 ng/g wet wt (mean:
lipid rich blubber (Tanabe et al. 1981). On the other hand,
62 ng/g) in muscle (Table 2). Similar to dolphins, liver had
butyltin accumulation in the liver of dolphins is similar to
higher concentrations than muscle in tuna fish. Butyltin concen-
several trace metals, which prominently concentrate in the liver
trations in tuna liver were about 8-fold lower than in dolphins.
or kidney (Honda et al. 1982). Preferential enrichment of butyl-
It has been shown that the butyltin concentration in fish liver
tin compounds in the liver may be associated with the presence
was an order of magnitude higher than in muscle (Kannan et
of increased amounts of metal binding proteins such as glutathi-
al. 1995b). Butyltin concentrations in tuna were lower than
one, which conjugates with several electrophilic compounds
those reported in mussels collected from La Spezia and Taranto
and plays a role in the detoxification of potential alkytating
harbors along the Italian coasts (Caricchia et aL 1991) and
agents and certain xenobiotics. The accumulation of butyltin
comparable to those reported from Barcelona harbor, Spain
compounds in the liver of vertebrates and the midgut or hepato-
(Tolosa et al. 1992). Similarly, BT concentrations in tuna were
pancreas of invertebrates has been shown (Davies et al. 1986;
comparable to those reported in several fish from the Gulf of
Gibbs et al. 1990; Stroben et aI. 1992; Kannan et al. 1995a,
Gdafisk, Baltic Sea (Kannan and Falandysz 1995).
1995b). Although the number of samples is small, the results
Analysis of mono-, di-, and tributyltin compounds in tuna
indicate considerable accumulation of butyltin compounds in
showed the presence of highest concentrations of DBT in the
higher trophic vertebrate marine organisms.
liver, while TBT and MBT were the prominent species in the
The concentrations of BTs in the blubber of bottlenose dol-
muscle (Figure 2). The concentrations of DBT in tuna liver
phins are comparable to those reported for marine mammals
were lower than those in dolphin livers. Lower concentrations
collected from the North Pacific, except for a finless porpoise
of MBT in liver than in muscle suggests metabolism by the
(N. phocaenoides) collected along the Japanese coast of the Seto
liver followed by transfer of metabolites to other tissues.
Inland Sea, which was two to three times higher in concentration
The toxicity of butyltin to fish depends on the developmental
(Iwata et al. 1995). The residue BT concentrations in dolphin
stage. It has been shown that yolk sac fry stage was the most
tissues were higher than those observed in bivalve mollusks
sensitive to the toxic effects of TBT (de Vries et al. 1991). The
collected from Mediterranean coastal waters (Alzieu et al. 1991;
resistance to bacterial challenge by fish was decreased even at
Caricchia et aI. 1991; Tolosa et al. 1992; Cocchieri et al. 1993),
TBT water concentrations around 10 ng/L (de Vries et al, 1991).
but lower than in carnivorous gastropods from the same area
Investigations relating body concentrations and toxic action of
(Axiak et al. 1995).
butyltins are necessary to assess the toxic implications of the
TBT was the predominant compound in the fresh blubber,
butyltin concentrations found in fish.
while DBT predominated in the liver (Figure 2). The higher
lipophilicity of TBT compared with DBT and MBT may explain
its predominance in the blubber. However, in the blubber of
Blue Shark
the two dolphins, which were moderately decomposed at the
time of sampling, MBT levels were comparable to the TBT
concentrations (Table 1). Transformation of TBT to MBT dur- Concentrations of BTs in shark ranged 1-9 ng/g wet wt (mean
ing the decomposition of carcasses might have elevated the 3.4 ng/g) in the subcutaneous fat, 20-36 ng/g wet wt (mean:
proportion of MBT in these samples. Dibutyltin was the pre- 30 ng/g) in the liver and 75-220 ng/g (mean: 140 ng/g) in the
dominant compound in the liver (71%), while MBT was in
kidney (Table 3), suggesting higher accumulation in kidney
minor amounts (9%). Metabolism of TBT by hepatic micro-
than in liver. Renal BT concentrations were 3-7 times higher
somal monooxygenase enzymes (Lee 1985) may lead to the
than hepatic concentrations. Higher concentrations in kidney.
production of MBT and DBT. Although, the complete metabo-
may be associated with the modified physiological function of
lism of TBT is expected to lead to higher concentrations of
this organ in sharks. It is also probable that the kidney of sharks
MBT than DBT, the rate of debutylation of DBT to MBT by
might contain elevated levels of glutathione, which plays a role
the microsomal monoxygenase system is considered slower
in conjugating with metals/metalloids. Higher concentration of
than of TBT to DBT. Consequently, in organs with high TBT butyltins in kidney than in liver was similar to the pattern