Organometallic Compounds - Organic Pollutants: An Ecotoxicological Perspective - page 172

categories: (1) high-energy and (2) low-energy. A negative correlation was found
between high-energy behaviors and total mercury concentration in the blood of
adult loons. High-energy behaviors included foraging for chicks, foraging for self,
swimming and flying, preening, and agonistic behaviors. There was also a strong
negative correlation between mercury levels in female loons and reproductive suc-
cess (Burgess and Meyer 2008, Evers et al. 2008). In a laboratory investigation,
adverse effects were observed when loon chicks were dosed with levels of methyl
mercury comparable to the highest levels of exposure recorded in the preceding
study (Kenow et al. 2007). There was evidence of demyelination of central nervous
tissue and reduced immune function when the chicks were fed fish containing 0.4
μg/g of methyl mercury or more.
The mink ( Mustela vision ) is a piscivorous mammal that also has been exposed to
relatively high dietary levels of methyl mercury in North America in recent times. In
a Canadian study, mink trapped in Yukon territory, Ontario, and Nova Scotia were
analyzed for levels of mercury and abundance of muscarinic, cholinergic and dop-
aminergic receptors in the brain (Basu et al. 2005). A correlation was found between
total Hg levels and abundance of muscarinic receptors, but a negative correlation
was found between total Hg and abundance of dopaminergic receptors. Thus, it was
suggested that environmentally relevant concentrations of Hg (much of it in methyl
form) may alter neurochemical function. The highest levels of mercury contamina-
tion were found in mink from Nova Scotia that had a mean concentration of total Hg
of 5.7 μg/g in brain, 90% of which was methyl mercury.

8.3 organotIn comPoundS

8.3.1 c h e m i c a l p r o p e r T i e s
Like mercury, tin is a metal that has a tendency to form covalent bonds with organic
groups. The compounds to be discussed here are tributyl derivatives of tetravalent
tin. The general formula for them is

[n-C 4 H 9 ] 3 Sn-X, where X is an anion.

The most important of the compounds from an ecotoxicological point of view, and
the one that will be used here as an example, is tributyltin oxide (TBTO). Its struc-
ture is shown in Figure 8.5.
TBTO is a colorless liquid of low water solubility and low polarity. Its water solu-
bility varies between <1.0 and >100 mg/L, depending on the pH, temperature, and
presence of other anions. These other anions determine the speciation of tributyltin
in natural waters. Thus, in sea water, TBT exists largely as hydroxide, chloride, and
carbonate, the structures of which are given in Figure 8.5. At pH values below 7.0,
the predominant forms are the chloride and the protonated hydroxide; at pH8 they
are the chloride, hydroxide, and carbonate; and at pH values above 10 they are the
hydroxide and the carbonate (EHC 116).
The K ow for T TBTO expressed as log P ow lies between 3.19 a nd 3.84 for distilled water,
and is about 3.54 for sea water. TBTO is adsorbed strongly to particulate matter.