Environmental Engineering Reference
In-Depth Information
Commission's moves, the IMO Convention has not been ratified by member
countries to date, and therefore has not yet entered into force as of 2005.
In this review, recent data on the environmental contamination and eco-
toxicology of organotins is given, focusing on the advancement in the last
decade. Earlier insights given in a broader sense on many different aspects of
organotins in the environment [4] are supported by recent data. In the last
decade, studies mainly focused on monitoring of larger geographical areas
using sediment and biological samples, particularly in Asian countries. An-
other focus lied in the monitoring and understanding of the mechanisms
behind the masculinization of marine gastropods (imposex). Progress in the
last decade has mainly been made in the global assessment of the organotin
pollution using both chemical analysis and biomonitoring using imposex as
abiomarker.
One of the most important conclusions lies in the recognition that the
organotin contamination is global, reaching developing countries, which
seems to be linked to economic growth. However, despite regulations,
organotin contamination of harbors and marine environments persists.
2
Bioavailability
The aqueous chemical speciation of organotins is important for their environ-
mental behavior, and consequently for bioavailability and toxicity. Organo-
tins undergo pH-dependent hydrolysis in water and their speciation is
also dependent on dissolved ions. Trisubstituted organotins form positively
charged diaquo complexes R 3 Sn(H 2 O) 2 + at pH < p K a , and these monovalent
organometallic cations behave as weak acids. Acidity constants (p K a )of6.25
and 5.20 were determined for TBT and TPT, respectively [20]. The domin-
ant TBT and TPT species at pH < p K a is the cation, whereas at pH > p K a the
neutral hydroxide species TBTOH and TPTOH, respectively, dominates. In
thepresenceofchlorideions(seawater),R 3 SnCl species occur. Hence, at en-
vironmental pH conditions, mono-, di-, and trisubstituted organotins exist
predominantly as neutral hydroxides in aqueous solution.
The speciation of organotins is pH-dependent and has consequences for
their bioavailability, a fundamental parameter in ecotoxicology. Significant
partitioning into biota occurs via uptake through membranes by hydropho-
bic mechanisms via uncharged species (both TBTOH and TBTCl). Several
octanol-water partition coefficients (log K ow ) for organotins were given [4],
including 4.10 for TBTOH and 3.53 for TPTOH [21]. TBTOH and TPTOH
are relevant for uptake, bioaccumulation [22, 23] and toxicity toward aquatic
organisms [22, 24, 25], including fish cells [26], where a positive correlation
between the in vitro cytotoxicity and log K ow was found. The influence of
the pH and dissolved organic matter (DOM) was demonstrated in our studies
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