Worldwide Occurrence of Organotins from Antifouling Paints and Effects in the Aquatic Environment - Antifouling Paint Biocides - page 90

nases (CYP) [139], and glutathion S -transferases [140]. TBT was shown to
have a strong inhibitory effect in vitro [141, 142] and in vivo on hepatic mi-
crosomal CYP in fish [139, 143] and molluscs [144]. Similar effects have been
shown for TPT [139]. Organotins act by binding to amino acids in the cata-
lytic site of the CYP enzyme. The interaction with microsomal monooxyge-
nase systems results in the loss of biotransformation capabilities. In addition,
this may lead to inhibition of CYP19 (aromatase) and the formation of impo-
sex in marine gastropods.
Perturbation of calcium homeostasis is involved in the cytotoxic action of
organotins. Calcium ions play a critical role in chemical-induced toxic cell
killing and programmed cell death (apoptosis). Elevated calcium concentra-
tions appear to be responsible for cell death and stimulation of apoptosis by
1-10 M TBT, in particular in thymocytes [145], resulting in immunotoxic-

ity, or neurotoxicity in the case of trimethyltin. Organotins induce apoptosis
by increase of intracellular Ca 2+ , followed by generation of reactive oxygen
species in mitochondria which causes oxidative stress, activation of caspases
and finally results in DNA fragmentation and apoptosis [146].
Organotins act also as potent cell membrane toxicants leading to pertur-
bations of plasma membranes and membrane proteins. Therefore, cells as
a whole are affected by toxic organotins [147-149] and are found to be corre-
lated with in vivo acute fish toxicity [26, 149], and the octanol-water partition
coefficient [148]. In mussels induction of stress proteins (heat shock pro-
teins) has also been shown [150]. Recently, a cDNA microarray technique was
applied for the analysis of global gene expression profiles in TBT exposed
ascidians [151]. More than 200 genes showed strong differential expression
after 24 hexposureto100 nM TBT. These genes encode proteins involved
in stress response, detoxification, oxidoreduction reaction, biosynthesis and
catabolism. This is a clear indication of pronounced molecular effects of TBT
at the gene expression level.

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5.2
Effects on Aquatic Life

TBT and TPT induce a number of physiological, morphological and toxi-
cological effects in aquatic organisms. Numerous studies have shown that
triorganotins are acutely and chronically toxic at low environmental levels.
Aquatic life in highly polluted areas is significantly affected. The two most
pronounced cases are the shell thickening and growth anomalies in oys-
ters [1], and the occurrence of imposex in neogastropods, both occurring at
low ng L -1 [130]. The discovery of shell deformations in oysters resulted in
regulation of TBT-containing antifouling paints. TBT act by inhibition of cal-
cification in oysters at concentrations as low as 2 ng L -1 TBT [152]. Anomalies
in larvae and inhibition of reproduction was also observed [153]. Growth of
oysters and molluscs was severely reduced by 240 ng L -1 [154].