The toxicity of organotin compounds of the general formula RnSnX(4-n) depends strongly on the type of organic substituent R and on the degree of substitution n. The residues X, not bound through a tin-carbon bond, are however of much smaller influence. Furthermore, there is evidence that hydrolysis of tributyltin esters will occur under environmental as well as under physiological conditions to TBTO or its corresponding derivatives. Thus TBTO can be considered a model substance in the risk evaluation for tributyltin compounds TBTX. Along with industrial hygiene considerations of TBTO and tributyltin esters, the strong local irritation and high toxicity in aerosol form when testing undiluted material must be noted. However, the tolerance of model wood preservatives containing 1% w/w TBTO, 2% W/W TBTN and 2% w/w TBTL on the skin of human volunteers after single exposure was not different from that of the vehicle alone. Vapours of TBTO, tributyltin naphthenate and benzoate proved to be practically non-toxic in single exposure studies with rats. After repeated administration of TBTO to rats in the feed (4 and 13 weeks) and in aerosol form (4-5 weeks) toxicity to lymphatic organs predominated. After aerosol exposure additionally severe irritation of the respiratory tract occurred. No adverse reactions were observed in rats exposed for 4-5 weeks to vapour practically saturated with TBTO. With both application routes (oral and inhalation) no indications were found of damage to the nervous system, as is the case for lower homologues of the trialkyltin series. Our results of testing for genotoxic potential in micro-organisms, human lymphocytes and in the micronucleus test in mice do not indicate a mutagenic or carcinogenic potential. Further mutagenicity data from a WHO/IARC multi-centre study are in part contradictory. They do, however, not indicate a definite mutagenic hazard. Moreover in teratogenicity studies in mice and rats TBTO did not show embryotoxic including teratogenic properties at dose levels that were not toxic to the dams. From the no-effect level in the 4-5 week inhalation study a 24 hour exposure limit value for humans can be derived. This acceptable room air concentration can be compared with results of a model study, in which the concentration over wood blocks treated with preservants containing 1.5 and 3.0% tributyltin naphthenate was measured. Based on this evaluation there are no objections to a large surface application of wood preservatives of the tested composition in room interiors. Nevertheless the general rule should be observed, that formulations containing biocides should be used only where there is a definite necessity for them.

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