Le plomb particulaire dans l'eau du robinet: source, occurrence, enlevement et bioaccessibilite

The first part of this project consisted of sampling campaigns carried out in locations representative of the environment in which children are exposed to lead, such as residences with a lead service line (LSL) in Montreal and a large building representative of schools in Laval. The main objective was to generate distributions of particulate lead concentrations, and to identify the parameters that influence the occurrence of particulate lead at the tap. Extreme total lead concentrations measured in the large building were associated with a major contribution of particulate lead, which was mainly caused by the corrosion of brass fixtures and faucets in the building. The comparison of the results obtained with the different sampling protocols carried out in the residences showed that a sampling performed after 30 minutes of stagnation is not adapted for the detection of particulate lead. On the contrary, random daytime sampling, or sampling after an overnight stagnation, was more adequate. Creating hydraulic disturbances increased dramatically the particulate lead concentrations measured at the tap after 5 minutes of flushing. Therefore, it appears important to collect samples at a high flow rate that is more representative of consumer usage patterns, to avoid underestimating the concentrations of exposure.;Considering the very high particulate lead concentrations measured in the residences resulting from hydraulic disturbances, and especially those measured in the large building, the second part of the project consisted of validating a method to remove particulate lead at the tap. The focus was on validating at the tap treatment that could be applied immediately at a reasonable cost to protect the consumer before the implementation of long term solutions. Two studies were carried out on point-of-use devices (POUs): a pilot study and a field study. Three types of POUs (pour-through, tap-mounted, under-the-sink) were tested at pilot scale using Montreal tap water, and were tested in an accelerated mode up to 120% of the manufacturer's prescribed capacity. The POUs tested were NSF-53 certified for lead before the modification of the protocol in 2007. Under-the-sink and tap-mounted POUs, composed of a carbon block of low porosity, showed excellent efficiency to remove particulate lead levels, and an acceptable efficiency to reduce dissolved lead concentrations according to the NSF-53 criteria.;The field study was carried out in the large building sampled for lead levels in tap water. Five identical under-the-sink POUs previously tested at pilot scale were installed at five taps in the large building. The POUs were monitored over one year for the removal of dissolved and particulate lead in tap water of the building. Their impact on the microbiological quality of tap water was also evaluated. Results showed excellent efficiency of the POUs to remove particulate lead and dissolved lead concentrations. Total lead levels in POU effluent water were significantly lower than those measured during the pilot study, demonstrating a good efficiency of the POUs under typical consumption patterns in a large building over a period of one year.;The last part of this project was initiated by a thorough research and critical review of the existing literature on bioaccessibility and bioavailability of lead in soil and dust particles. The procedures adequately calibrated for children exposure assessment were identified, and the test presenting the highest level of validation was selected for adaptation and application to lead particles from tap water.;The results of particulate and dissolved lead concentrations at the tap of residences with an LSL, and from the large building were then used as input to the IEUBK model to estimate the BLL of children less than 7 years old. The concentrations of particulate lead were adjusted taking into account their bioaccessibility previously evaluated at the laboratory. Lead levels in soil, dust, and diet, as well as ingestion rates relative to each of these sources entered in the IEUBK model were constant and representative of the latest values from studies conducted in Canada. Simulations were run successively, by increasing progressively the particulate lead concentration in tap water according to its distribution, in order to determine a threshold at which particulate lead would contribute significantly to exposure. Results clearly showed that exposure to particulate lead in large buildings with particulate lead issues, is comparable to the exposure to lead associated with the presence of LSLs. It appears therefore urgent to quantify particulate lead levels in large buildings with adequate sampling protocols and analytical procedures, particularly in buildings serving vulnerable populations, such as pediatric hospitals, primary schools and daycare. (Abstract shortened by UMI.).