Overview
This cross-sectional risk assessment measured lead and cadmium concentrations in four types of water sources used by primary schools in southern Thailand: bottled water, tap water, filtered tap water, and raw surface water. Tap water samples were collected after a 5-minute flush (not first-draw), so the concentrations represent post-flush rather than worst-case stagnation exposures. Despite detectable lead in tap and raw water samples, chronic daily intake calculations using Thai-specific exposure parameters (6-year exposure, 35 kg children, 2 L per day) produced hazard quotients below 1.0 for all source types. However, 18.2 percent of tap water samples exceeded the WHO provisional guideline value of 10 µg/L (0.010 mg/L) even after flushing, indicating that flushing alone did not reliably bring concentrations below the international threshold.
Key numbers
Lead concentrations by water source type (mg/L; 1 mg/L = 1,000 µg/L):
- Bottled water: range not detected to 0.018 mg/L (0 to 18 µg/L); 91.7 percent at or below 0.01 mg/L (10 µg/L); 8.3 percent above 0.01 mg/L
- Tap water (post-5-minute flush): range not detected to 0.025 mg/L (0 to 25 µg/L); 81.8 percent at or below 0.01 mg/L; 18.2 percent above 0.01 mg/L
- Filtered tap water: range not detected to 0.005 mg/L (0 to 5 µg/L); all samples at or below 0.01 mg/L (100 percent compliance)
- Raw surface water: range not detected to 0.040 mg/L (0 to 40 µg/L); 66.7 percent at or below 0.01 mg/L; 33.3 percent above
LOD for lead: 0.002 mg/L (2 µg/L) by graphite furnace atomic absorption spectrometry.
Cadmium concentrations: all source types had hazard quotients below 1; maximum cadmium 0.0049 mg/L (4.9 µg/L).
Hazard Index (all source types, based on CDI calculations): below 1.0 for lead and cadmium combined at all source types, indicating the population-level average exposure was below threshold for non-carcinogenic effects.
Methods (brief)
Cross-sectional sampling at 44 schools in four districts. Tap water collected after 5-minute flush. Graphite furnace atomic absorption spectrometry (PerkinElmer Analyst 800); samples filtered through Whatman Grade 541 prior to analysis. LOD for lead 0.002 mg/L (2 µg/L); LOD for cadmium 0.0001 mg/L. Chronic daily intake calculated using standard USEPA exposure factors adapted for Thai primary school children (body weight 35 kg, ingestion rate 2 L per day, 6-year exposure period).
Evidence fitness
Supports: characterizing post-flush water lead concentrations at Thai primary schools; assessing population-level non-carcinogenic risk under a central-tendency exposure scenario; demonstrating that filtration effectively reduces lead at the point of use.
Does not support: estimating worst-case first-draw (maximum stagnation) lead exposures in this setting, as tap water was sampled post-flush; applying these findings to other Asian or global school settings without comparable plumbing age and source water profiles; concluding safety at the individual high-exposure level, since hazard index below 1.0 is a population average that does not exclude elevated risk in individual children consuming more water or attending schools with the highest tap water concentrations.
Limitations
Tap water was sampled after a 5-minute flush, not at first draw; concentrations may substantially underestimate morning stagnation exposures at schools where water sits overnight or over weekends. Hazard index calculations use central tendency exposure factors; children who consume more water or attend schools with the highest measured concentrations may face individual HQ values above 1.0. The study covered four districts of a single province; local geology, plumbing materials, and source water chemistry differ across Thailand and limit generalization. No blood lead measurements were taken to validate the exposure model.
Related evidence
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