TBTO

Wester PW, Canton JH (1987) Histopathological study of Poecilia reticulata (guppy) after long-term exposure to bis(tri-/7-butyltin)oxide (TBTO) and di-n-butyltindichloride (DBTC). 

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 structure is shown in Figure 8.5. 

TBTO is a colorless liquid of low water solubility and low polarity. Its water solubility 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 for TBTO expressed as log Pq lies between 3.19 and 3.84 for distilled water, and is about 3.54 for sea water. TBTO is adsorbed strongly to particulate matter. 

When TBTO is released into ambient water, a considerable proportion becomes adsorbed to sediments, as might be expected from its lipophilicity. Studies have shown that between 10 and 95% of TBTO added to surface waters becomes bound to sediment. In the water column it exists in several different forms, principally the hydroxide, the chloride, and the carbonate (Figure 8.5). Once TBT has been adsorbed, loss is almost entirely due to slow degradation, leading to desorption of diphenyl-tin (DPT). The distribution and state of speciation of TBT can vary considerably between aquatic systems, depending on pH, temperature, salinity, and other factors. 

Mechanistic studies have shown that TBT and certain other forms of trialkyltin have two distinct modes of toxic action in vertebrates. On the one hand they act as inhibitors of oxidative phosphorylation in mitochondria (Aldridge and Street 1964). Inhibition is associated with repression of ATP synthesis, disturbance of ion transport across the mitochondrial membrane, and swelling of the membrane. Oxidative phosphorylation is a vital process in animals and plants, and so trialkyltin compounds act as wide-ranging biocides. Another mode of action involves the inhibition of forms of cytochrome P450, which was referred to earlier in connection with metabolism. This has been demonstrated in mammals, aquatic invertebrates and fish (Morcillo et al. 2004, Oberdorster 2002). TBTO has been shown to inhibit P450 activity in cells from various tissues of mammals, including liver, kidney, and small intestine mucosa, both in vivo and in vitro (Rosenberg and Drummond 1983, Environmental Health Criteria 116). 

Rosenberg, D.W. and Drummond, G.S. (1983). Direct in vitro effects of TBTO on hepatic cytochrome P450. Biochemical Pharmacology 32, 3823-3829. 

Atactic poly(methyl methacrylate/methacrylic acid), the copolymer of methyl methacrylate (MMA) and methacrylic acid (MAA), was synthesized "directly" as a prepolymer to be esterified with bis(tri-n-butyltin) oxide (TBTO). Two formulations of poly (MMA/MAA) were synthesized, a 1 1 and a 2 1 MMA and MAA copolymer whose syntheses differ only in the proportion of monomer reacted. 

Penninks108 assessed the evaluation of a safety factor to determine a Tolerable Daily Intake (TDI) value for the environmental contaminant bis(tributyltin)oxide (TBTO). The... 

Food concentration normal with no overt adverse signs of TBTO exposure noted in adults. Decreased hatchability and increase in percent of chicks found dead in the shell were noted at 60 and 150 mg/kg food. Egg production and eggshell thickness normal. Abnormal blood chemistry and hepatic EROD noted in parent birds treated with TBTO (Coenen etal. 1992)... 

Holm, G., L. Norrgren, and O. Linden. 1991. Reproductive and histopathological effects of long-term experimental exposure to bis(tributyltin)oxide (TBTO) on the three-spined stickleback, Gasterosteus aculeatus Linnaeus. Jour. Fish Biol. 38 373-386. 

Schwaiger, J., F. Bucher, H. Ferling, W. Kalbfus, and R.D. Negele. 1992. A prolonged study on the effects of sublethal concentrations of bis(tri- -butyltin)oxide (TBTO) histopathological and histochemical findings in rainbow trout (Oncorhynchus mykiss). Aquat. Toxicol. 23 31 -48. 

Triebskom, R., H.R. Kohler, J. Flemming, T. Braunbeck, R.D. Negele, and H. Rahmann. 1994a. Evaluation of bis(tri-n-butyltin)oxide (TBTO) neurotoxicity in rainbow trout (Oncorhynchus mykiss). I. Behaviour, weight increase, and tin content. Aquat. Toxicol. 30 189-197. 

Ward, G.S., G.C. Cramm, P.R. Parrish, H. Trachman, and A. Slesinger. 1981. Bioaccumulation and chronic toxicity of bis(tributyltin)oxide (TBTO) tests with a salt water fish. Pages 183-200 in D.R. Branson and K.L. Dickson (eds.). Aquatic Toxicology and Hazard Assessment fourth conference. ASTM Spec. Tech. Publ. 737, American Society for Testing and Materials, Philadelphia, PA. 

Certain organotins, such as di- -octyltin dichloride (DOTC) and tributyltin oxide (TBTO), alter the structure and function of the thymus and consequently affect pri-... 

A review of the literature on chemical-induced immunosuppression in rats and mice, exposed during the pre- and/or postnatal period, was compared to exposure of adults. Five known immunosuppressants (i.e., TCDD, TBTO, DES, Pb, and diazepam) were reviewed. The data revealed that the developing immune system was more sensitive to chemical exposure than the mature immune system. Based on these evaluations, the authors concluded that it was reasonable to assume that testing only in adults would not provide a sufficient level of sensitivity to define immunotoxicity in the neonate 132. In summary, this chapter provides compelling evidence that the developing, compared to the mature, immune system is more vulnerable to perturbation. 

Abbreviations PAH = polyaromatic hydrocarbon, TCDD = Tetrachlorodibenzo-p-dioxin, PCB = polychlorinated biphenyl, PBB = polybrominated biphenyl, TBTO = tributyltin oxide, DBTO = dibutyltin oxide, TPT = triphenyltin. 

Each of the above liquid residues was tritrated against standard sodium hydroxide, using phenolphthalein as indicator. Identical titer values were obtained the same titer value was also given by the original solid residue of unreacted TBTA (0-1). Such an observation of identical titer Values should be expected if the conversion of TBTA, by reaction with sodium chloride, is solj.ly to TBTCl. However, any side reaction leading to TBT hydroxide or TBTO will result in lower titer values since these tin compounds, unlike TBTA or TBTCl cannot be titrated like weak acids. Clearly, the side reactions are not noticeable in these experiments. Hydrolysis is not competitive under the conditions of this study, probably because chloride concentration never drops below 10-1 whereas hydroxide concentration is always below 10 s. (It was noticed that the pH of the aqueous layer in each case had risen from 6.5 to 9.0.)... 

Conventional Systems. In the conventional antifouling compositions, the organotin compound (TBTO, TBTF, TBTC1, TBTOAc) is mechanically mixed into the paint vehicle. When the TBT species is completely soluble in the polymer matrix, factors (a) and (b) become unimportant in most cases. The mobile species is already present its diffusion in the matrix, phase transfer and migration across the boundary layer into the ocean environment may be represented by Figure 2a. When the organotin compound forms a dispersed second phase, rate of its dissolution in the polymer matrix becomes another factor to consider. 

Hydrolysis. NMR results show that TBT carboxylates undergo fast chemical exchange. Even the interfacial reaction between TBT carboxylates and chloride is shown to be extremely fast. The hydrolysis is thus not likely to be a rate determining step. Since the diffusivity of water in the matrix is expected to be much greater than that of TBTO, a hydrolytic equilibrium between the tributyltin carboxylate polymer and TBTO will always exist. As the mobile species produced diffuses out, the hydrolysis proceeds at a concentration-dependent rate. Godbee and Joy have developed a model to describe a similar situation in predicting the leacha-bility of radionuclides from cementitious grouts (15). Based on their equation, the rate of release of tin from the surface is ... 

This is in agreement with the results of Bennett and Zedler (12) they have pointed out that conventional urethane, vinyl and epoxy systems show widely divergent release rates. Whereas the vinyl system lost TBTO at a rate of 1-2 yg/cm2/day and polyurethane at 25 yg/cm2/day, the epoxy system virtually lost no tin. 

Miller has shown that TBTO will prevent fouling attachment at leaching rates as low as 1.25 yg/cm2/day (18). It is thus reasonable to assume that fouling commences when the rate of release falls below 0.5 yg Sn/cm2/day. Based on this, the effective dif-fusivities are calculated, using Crank s rate equation. The calculated effective diffusivities are then substituted in the integral form of Crank s equation to estimate the amount of Sn lost. 

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