Worldwide Occurrence of Organotins from Antifouling Paints and Effects in the Aquatic Environment - Antifouling Paint Biocides - page 89

groups at the tin atom, with maximum toxicity for trisubstituted compounds
and decreasing toxicity with increased length of the organic moiety [3]. Of
particular importance is the high toxicity of TBT, TPT and tricyclohexyltin
derivatives, which have high fungicidal, bactericidal, algicidal, and acarici-
dal properties. Trisubstituted organotins are extremely toxic to aquatic life
for a large variety of organisms as shown in vivo and in vitro [4]. The most
sensitive species known so far are oysters and neogastropods, affected at
ng L -1 levels of TBT. In both cases the impact of TBT has economical (oys-
ters) and ecological consequences on the population level. Ecological effects
on many snail species are found globally in contaminated coastal regions
with shipping activity. Many ecotoxicological studies on organisms of differ-
ent evolutionary level have been reported [1, 24, 125-130], and show rather
large species sensitivity differences. Lowest effect concentrations are in the
range of 1-10 ng L -1 [1, 2, 10, 130], which are among the lowest yet found
for chemicals. Invertebrates and fish are affected as well, although at higher
concentrations of 100-10 000 ng L -1 . The acute toxicity data basis is rather
large [4, 131]. However, long-term or chronic effects on individual organisms
are sparse and effects on the structure and function of aquatic ecosystems still
unclear.

5.1
Modes of Action

TBT and TPT exert a number of important cellular, biochemical and mo-
lecular effects acting via different modes of action at M concentrations. The

inhibition of oxidative phosphorylation and ATP synthesis in mitochondria is
a key process having been described decades ago [132-134]. Triethyltin acts
at concentrations as low as 0.1

µ

M. Moreover, inhibition of photophosphory-
lation in chloroplasts, perturbation of calcium homeostasis [135], inhibition
of ion transport through the cellular membrane by inhibition of ATPase [136],
and inhibition of enzymes such as ATPases and cytochrome P450 monooxy-
genases (CYP) are among the biochemical processes affected by organo-
tins [137]. Organotins act as ionophores, able to catalyze the ion exchange
resulting in uncoupling of oxidative phosphorylation. Moreover, organotins
have been known to act as potent inhibitors of the F 1 F 0 -ATP synthase. These
enzymes in the mitochondrial membrane play a fundamental role in cellu-
lar energy metabolism and are constituents of nearly every living cell from
bacteria to humans. The ATP synthases are rotary enzymes composed of
two motors that are connected by a common shaft to exchange energy. TBT
inhibits ATP hydrolysis by the Na + -translocating or H + -translocating ATP
synthase in bacteria [138]. The subunit a ion channel is the specific target site
for ATPase inhibition by organotins [138].
Triorganotins also interact with various intracellular enzymes that may
result in toxicity, namely with the cytochrome P450 dependent monooxye-

µ