Published studies in which rats were exposed to CdCl2 in standard chow or dnnking water were analyzed to compare the relative bioavailability of cadmium from the two media. Relative bioavailability was assessed from estimates of the rate of accumulation of cadmium in kidney cortex or liver. Data were grouped into tiers based on study design and reponing of data: Tier 1, identical experimental protocols and dosage can be estimated: Tier 2, very similar or identical protocols and dosage can be estimated: Tier 3, protocols may differ and dosage can be estimated; and Tier 4, protocols may differ and dosages cannot be estimated (but concentration of cadmium in food or water is reponed). Tiers were nested, such that Tier 4 contained all relevant studies; Tier 3 included data sets from Tiers 1 and 2: and Tier 2 included the data set from Tier 1. Data within Tiers 1, 2, and 3 were subjected to a linear regression analysis with dosage as the independent variable and tissue accumulation rate as the dependent vanable to determine whether bioavailability of cadmium was significantly different based on medium of administration. The results of this analysis show the following: (1) In rats receiving food and drinking water ad libitum, the bioavailability of cadmium in drinking water is not significantly different (P > 0.05) from the bioavailability of cadmium in food when dosages are less than 4 mg/kg body wt/day. (2) Cadmium decreases food and water consumption: therefore, assessments of relative bioavailability should be made based on actual dosage rather than exposure levels. (3) Diet composition and status of the gastrointestinal tract are probably a more important determinant of the bioavailability of cadmium than is the exposure medium. (4) Studies of the effect of total diet composition on bioavailability of cadmium may be more relevant than are studies of the effect of the exposure medium. It is concluded from this analysis that the bioavailability of cadmium in food is not different from that in water when diet is provided ad llbltum. Therefore, we recommend that distinct RfDs for cadmium in food and dnnking water should not be based on the assumption that the bioavailability of cadmium in drinking water is greater than that of cadmium in food.

[Departement_IRSTEA]EEE [TR1_IRSTEA]E35-Techniques et gestion d'équipements publics pour l'eau et les déchets | Water mains renewal often occures with net reorganizing, but in the next years, real renewal works will have to be undertaken because of the ageing and the damages in the networks. New tools will be necessary to put in place estimated proceeding and a new planing process. The economic optimization of the date-lines is an exemple of this . The method is to minimize the total cost of renewal and maintenance for each pipe in order to find the optimal renewal date. The modelling of the failures and the evaluation of the different costs necessary to estimate these spendings. The modelling of the failures relies on a probabilist approach developped by the CEMAGREF and the ENGEES. The evaluation of the costs pointes out the problem of the taking into consideration from the social costs bounded to a failure. Real cases show the difficulty of their taking into account but also the ned to keep them. | Le renouvellement des canalisations d'eau potable est souvent intervenu dans le cadre des restructurations de réseaux. Les prochaines années verront se multiplier des opérations de renouvellement stricto sensu, directement liées au vieillissement et à la dégradation de ces réseaux. De nouveaux outils seront nécessaires pour instaurer une démarche prévisionnelle et donc une nouvelle logique de programmation. L'optimisation économique des échéances en est un exemple. Cette démarche vise à minimiser le montant total des dépenses liées au maintien en service et au renouvellement de chaque canalisation en vue de déterminer une date optimale de renouvellement. La détermination des dépenses nécessite la modélisation de l'évolution des défaillances et l'évaluation des différents coûts à prendre en compte. La modélisation de l'évolution des défaillances se fait par une approche probabiliste élaborée par le CEMAGREF et l'ENGEES, la détermination des coûts pose le problême de l'incorporation des coûts indirects liés à une rupture. L'étude de cas concrets montre l'intérêt et les limites d'une telle approche.

Water mains renewal often occures with net reorganizing, but in the next years, real renewal works will have to be undertaken because of the ageing and the damages in the networks. New tools will be necessary to put in place estimated proceeding and a new planing process. The economic optimization of the date-lines is an exemple of this . The method is to minimize the total cost of renewal and maintenance for each pipe in order to find the optimal renewal date. The modelling of the failures and the evaluation of the different costs necessary to estimate these spendings. The modelling of the failures relies on a probabilist approach developped by the CEMAGREF and the ENGEES. The evaluation of the costs pointes out the problem of the taking into consideration from the social costs bounded to a failure. Real cases show the difficulty of their taking into account but also the ned to keep them. | Le renouvellement des canalisations d'eau potable est souvent intervenu dans le cadre des restructurations de réseaux. Les prochaines années verront se multiplier des opérations de renouvellement stricto sensu, directement liées au vieillissement et à la dégradation de ces réseaux. De nouveaux outils seront nécessaires pour instaurer une démarche prévisionnelle et donc une nouvelle logique de programmation. L'optimisation économique des échéances en est un exemple. Cette démarche vise à minimiser le montant total des dépenses liées au maintien en service et au renouvellement de chaque canalisation en vue de déterminer une date optimale de renouvellement. La détermination des dépenses nécessite la modélisation de l'évolution des défaillances et l'évaluation des différents coûts à prendre en compte. La modélisation de l'évolution des défaillances se fait par une approche probabiliste élaborée par le CEMAGREF et l'ENGEES, la détermination des coûts pose le problême de l'incorporation des coûts indirects liés à une rupture. L'étude de cas concrets montre l'intérêt et les limites d'une telle approche.