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Spatial indoor radon distribution in Mexico City
Francisco Franco-Marina1, Jaime Villalba-Caloca, Nuria Segovia
1National Institute of Respiratory Diseases in Mexico City, Subdirección de Investigación Sociomédica, INER, Calzada de Tlalpan 4502, Colonia Sección XVI, Mexico D.F. CP 14080, Mexico. ffrancom@prodigy.net.mx
The Science of the Total Environment
|November 25, 2003
Summary
This study mapped residential radon levels in Mexico City using nuclear track detectors. High radon concentrations were found in southwestern areas, near inactive volcanic mountains, informing exposure assessments for health studies.
Area of Science:
- Environmental Health Sciences
- Geospatial Analysis
- Epidemiology
Background:
- Radon is a naturally occurring radioactive gas that can accumulate indoors.
- Accurate spatial assessment of residential radon is crucial for epidemiological studies on lung cancer risk.
- Mexico City Metropolitan Area presents a unique environment for studying indoor radon distribution.
Purpose of the Study:
- To conduct a spatial analysis of indoor radon concentrations in the Mexico City Metropolitan Area.
- To assign estimated radon exposure levels for an ongoing case-control study.
- To identify geographical areas with high residential radon levels.
Main Methods:
- A probabilistic household survey sampled 501 dwellings for indoor radon measurement using solid-state nuclear track detectors (LR 115).
- The city was partitioned into nine zones, with simultaneous surveys conducted across all zones.
- Geostatistical techniques, including kriging interpolation and surface contouring, were employed for detailed spatial distribution mapping.
Main Results:
- The highest adjusted geometric mean radon concentration (136 Bqm⁻³) was observed in the southwest zone, with 46% of households exceeding 200 Bqm⁻³.
- Radon levels were influenced by room placement, floor level, and ventilation habits, but not building materials.
- Areas with very high radon concentrations (>111 Bqm⁻³, up to 288 Bqm⁻³) were identified in southern and western zones, often near inactive volcanic mountains.
Conclusions:
- Geostatistical methods provide reasonable estimates of average spatial residential radon distribution in Mexico City.
- The identified high-radon areas, particularly in the southwest, require attention for potential health risk assessment.
- This indirect exposure assessment method is cost-effective for epidemiological studies but may introduce non-differential misclassification error.