Environmental Engineering Reference
In-Depth Information
with frogs [24], Daphnia magna ,yolksaclarvaeoffish Thymallus thymal-
lus [22], and the midge Chironomus riparius [25]. Trisubstituted organotin
cations are less toxic than the neutral hydroxides, and this goes along with
their pH-related K ow . Significantly higher bioconcentration occurred at pH 8
than pH 5 or 6, which is related to the fact that these compounds mainly, but
not exclusively, accumulate as hydroxides [22]. Toxicity was also significantly
increased at pH 8, where TBT occurs predominantly as TBTOH (95%) [21].
This is correlated with higher K ow at pH 8 [22].
Figure 1 shows that bioconcentration of TBT in C. riparius larvae is sig-
nificantly higher at pH 8 than pH 5 due to the prevalence of bioavailable
TBTOH. TPT bioconcentration was significantly higher due to the lack of
significant metabolism, occurring with TBT [25]. These pH dependent differ-
ences are mainly based on the aqueous phase speciation. This was also shown
in yeast [27], where uptake and toxicity of TPT was reduced considerably at
pH 3.5. TPT + uptake was restricted to cell wall sorption, while TPTOH caused
an increase in the order in the cell phospholipid bilayer and diffuses into
the cell. The neutral TBTCl and TPTCl were more toxic than the hydroxides.
Similar to our studies [26], toxicity in yeast was correlated with lipophilicity.
The distribution of TBT and TPT between water and DOM is pH-
dependent and highest distribution ratios with maxima occur close to the
acidity constant [21]. Sorption is governed by complexation of the cation
(TBT + ,TPT + ) by negatively charged ligands of DOM mainly at low pH, but
also on hydrophobic partitioning of hydroxid species to nonpolar groups (hy-
drophobic interactions) at ambient pH. Figure 2 shows that DOM leads to
a concentration-related reduction in the TBT bioaccumulation in Chirono-
Fig. 1 Bioaccumulation of TBT and TPT in Chrionomus riparius at different pH. At pH 8,
TBT occurs predominantly as TBTOH (98%), whereas at pH 5, TBT is present primarily
as positively charged TBT + (fraction of 95%). After [23]
Search WWH ::




Custom Search