The evaluation of data-derived safety factors for bis(tri-n-butyltin)oxide

In this report the evaluation of a safety factor is assessed, according to the decision tree suggested by Renwick (1991a,b), to determine a Tolerable Daily Intake (TDI) value for the environmental contaminant bis(tri-n-butyltin)oxide (TBTO). Based on available literature the nature of the most sensitive parameter of TBTO-toxicity was perceived to be on lymphoid organs and lymphoid function. Subsequently, safety factors were derived in relation to published data on inter-species and inter-individual differences in both kinetics and dynamics of TBTO. Lack of information on human data concerning the nature of toxicity as well as kinetics and dynamics of TBTO finally resulted in a safety factor of 100. A TDI of 5 or 0.25 mg/kg bw per day was assessed based on reductions of lymphoid organ weights (thymus) or lymphoid function (resistance to T. spiralis), respectively. In addition, based on available data in rodents on kinetics and dynamics of TBTO, it is suggested that a combined TDI value for both tri- and dibutyltin compounds might have to be considered.