Application of lead monitoring results to predict 0–7 year old children's exposure at the tap

Abstract

Dwellings with/without a lead service line [LSL] were sampled for lead in tap water in Montreal, during different seasons. Short-term simulations using these results and the batchrun mode of the Integrated Exposure Uptake Biokinetic (IEUBK) model showed that children's exposure to lead at the tap in the presence of an LSL varies seasonally, and according to the type of dwelling. From July to March, for single-family homes, the estimated geometric mean [GM] blood lead level [BLL] decreased from 2.3–3.6 μg/dL to 1.5–2.5 μg/dL, depending on the children's age. The wide seasonal variations in lead exposure result in a minimal fraction (0–6%) of children with a predicted BLL >5 μg/dL in winter, as opposed to a significant proportion (5–25%) in summer. These estimations are in close agreement with the BLLs measured in Montreal children in fall and winter, and simulations using summer water lead levels illustrate the importance of measuring BLLs during the summer. Finally, simulations for wartime residences with long LSLs confirm the need to prioritize the control of this lead exposure from tap water.

Introduction

Neurodevelopmental effects have been measured in young children at low blood lead levels [BLLs], which makes it difficult to establish a safe threshold (Canfield et al., 2003; European Commission, 2011). Consistent with these findings, the Centers for Disease Control recently established a new reference value of 5 μg/dL based on population BLLs, and plans to review this value every four years (CDC, 2012). Children's exposure to lead [Pb] comes mostly from their diet but also from dust, soil, air, paint, and tap water. The reduction of Pb levels in food and gasoline resulted in the steady decline in BLLs in recent years. Also, remedial action has been performed to decrease the Pb levels in soil and dust at contaminated sites, although some of these sites still remain (USEPA, 2006). Considering the general decrease in Pb in these sources and the reduction of the BLL reference value, Pb in tap water may constitute the remaining significant contributor to children's exposure.

Lead service lines [LSLs] constitute a major source of Pb in tap water. Their replacement is expensive and legally complex because of shared ownership between the municipality and the home owner. Flushing is a remediation method usually prescribed to reduce Pb levels below the 10–15 μg/L reference levels, although not a long-term solution. Also, even if LSLs are replaced, the benefits can be uncertain if the replacement is partial (Triantafyllidou and Edwards, 2011), or if long-term deposits were generated in the premise piping [PP] when the LSL was in place (Schock, 2005). Other sources include solders, brass fixtures, and faucets (Schock, 1990). Such sources, although containing far less Pb content than LSLs, can generate high Pb concentrations at the tap as well as Pb particles accumulations behind the tap, which could be highly relevant for exposure, especially in the case of large buildings (Deshommes and Prévost, 2012).

In several studies, an association has been observed between the presence of an LSL and increased BLLs in young children (Levallois et al., 2013; Brown et al., 2011; Edwards et al., 2009). The dissolution of Pb from an LSL is governed by water quality, and increases with stagnation time and temperature. Water temperature can vary widely across a distribution system and in PP, and may strongly influence Pb concentration at some taps (Schock, 1990). Regulatory Pb sampling is therefore often prescribed during summer, and consequently most of the Pb data available corresponds to this warmer period (Cartier et al., 2011; Deshommes et al., 2010). However, considering the seasonal variations of BLLs observed in children exposed to soil and dust mostly during the summer (Laidlaw et al., 2005; USEPA, 1996; Yiin et al., 2000), we suspect that similar trends in children's BLLs could occur following exposure to Pb in tap water. However, the extent of these variations has not yet been assessed.

The objectives of this study were: (i) to evaluate if results from tap water sampling can reveal the presence/absence of an LSL; (ii) to compare Pb sampling results for different seasons, and different types of dwellings with/without an LSL; (iii) to evaluate new sampling approaches and discuss their relevance for children's exposure; and (iv) to assess, using the Integrated Exposure Uptake Biokinetic [IEUBK] model, the effect of seasonal variations of Pb in tap water on the BLLs of young children living in homes with/without an LSL.