Abstract: Relative Contribution of Potential Modes of Surface Dust Lead Contamination in the Homes

Lead contamination in the shipbuilding and ship repair industries has resulted from the use of leadbased paint and from welding processes. Previous studies have shown that workers involved in these tasks are especially prone to increased blood lead concentrations. The repair of wooden boats in Thailand also involves the use of lead but in the form of powdered lead oxide (Pb 3 O 4 , plumboplumbic oxide, or red lead) as a component in the caulking material. Workers are directly exposed to lead when mixing caulking materials and when sealing boat hulls. A previous study has reported that 67% of boat caulkers had high blood lead levels (>40 μg/dl). Furthermore, households in communities adjacent to boatyards have been shown to have elevated dust lead concentrations, and children’s blood lead concentrations in these communities were high and correlated closely with static measures of household surface dust lead concentration. Remedial measures aimed at reducing the burden of childhood lead contamination in these communities could be directed at reducing the levels of lead contaminating household surfaces, reducing the magnitude of child-lead contact or both. An effective strategy for reducing lead contamination of household surfaces requires an understanding of the dynamics of dust lead deposition in the household. Such understanding is only poorly provided by static measures of lead loading alone, such as the mass of lead wiped from a given area at any one time. Better understanding could be acquired by measurements of the rate at which lead is deposited on household surfaces, espeAbstract: Relative Contribution of Potential Modes of Surface Dust Lead Contamination in the Homes of Boatyard Caulkers: Orrapan UNTIMANON, et al. Bureau of Occupational and Environmental Diseases, Ministry of Public Health, Thailand— Objectives: The aim of this study was to quantify the relative contributions to surface lead contamination of boat-caulkers’ houses of three contamination modes, namely “take-home” lead from the caulker, “natural” spatial dispersal from boatyard to household and “redistribution” of accumulated lead-laden dust within the house. Methods: Boat-caulkers’ houses situated in areas surrounding boat repair yards were recruited. Caulkers’ houses that were located close together were divided into location-matched pairs, within which one was randomly assigned to be given a cleaning and designated a CL house, and the other was to be left uncleaned and designated a NCL house. Geographically isolated caulker’s houses were randomly assigned to one of the two categories. The nearest non-boatyard worker’s house (NB) was additionally recruited for each set. The surface lead loading rate (SLLR), defined as the mass of lead deposited in dust per unit area of surface per unit time, was measured over a period of 3 mo in all houses, and the data were modeled using linear mixed effects regression. Results: Adjusted values of SLLR differed only slightly between CL and NCL houses (0.96 to 1.02 times) but were between 1.65 and 2.03 times higher in CL and NCL houses than in NB houses depending on proximity to the boatyard and between 2.12 and 2.61 times higher in houses within one km of a boatyard than in more distant houses depending on category of house. Conclusions: Newly deposited dust lead likely resulted from the take-home and spatial dispersion modes. The contribution of Relative Contribution of Potential Modes of Surface Dust Lead Contamination in the Homes of Boatyard Caulkers