Radon potential mapping: Sensitivity to input weighting selection

Transcription

1 Radon potential mapping: Sensitivity to input weighting selection Mark Bennett, SILK Lab, Dalhousie University Dr. Daniel Rainham, SILK Lab, Dalhousie University John Drage, NSDNR, Halifax NS SILK LAB

2 My Background - Undergrad degree in Biology, GIS Cert. - Focus on Systems Biology and Geo-Statistics - Currently working for: - IWK Perinatal Epidemiology Research Unit - Statistics Canada RDC Program - Spatial Information for Health Knowledge Lab - Various research groups at Dalhousie University - MSc. Student in Community Health & Epidemiology SILK LAB

3 Research Questions What impact does input weighting have on the distribution of radon probability? Does a new weighting better explain the variability of indoor radon based on measurements? SILK LAB

4 Can indoor radon levels be predicted with environmental factors? - What is radon, the health consequences and pre-existing risk map - Small introduction to radon - Known and suspected health complications - NSDNR radon risk map - Sensitivity analysis of map with variable weightings - What proportion of the cells change class with new weights? - Is the model sensitive to weight changes? - Do new weightings predict a higher or lower risk? Where? - Strength of association between predicted risk and measured radon - Percentage of exceeding values in risk classes - Regression of score vs radon measurements SILK LAB

5 What is Radon? Health Canada recommends a value of less than 200 Bq/m 3 in homes. Health Canada, 2014 Lung Association of Canada, 2014 Canadian Nuclear Safety Commission, 2011 SILK LAB

6 How Does Radon Enter a Home? Water pipes Negative Pressure Unsealed windows Diffusion through soil Unfinished floors Small cracks in foundation Lung Association of Canada, 2014

7 Health Consequences Increase in radon, leads to a 16% higher chance of lung cancer (Chen et al., 2012) 2nd leading cause of lung cancer (Chen et al., 2012) Correlation with myeloid leukemia (Henshaw et al., 1990) Correlation with kidney Cancer (Durrani SA., 1993) Higher incidence cell carinomas (Wheeler BW et al., 2012) Correlations with bone cancer (Collman et al., 1991) Wikimedia Commons

8 NSDNR Radon Risk Map - Nova Scotia Department of Natural Resources - 250m x 250m resolution - Equal weighting factors - Developed with ArcGIS O Reilly et al., 2010

9 Can indoor radon levels be predicted with environmental factors? - Sensitivity analysis of map with variable weightings - What proportion of the cells change class with new weights? - Is the model sensitive to weight changes? - Do new weightings predict a higher or lower risk? Where?

10 Model Weighting Calculation Mask to remove ND and water 3 Input layers from NSDNR Orig_filt Geology Bedrock Variable weighting combinations Soil Perm Weighted Sum Wgt_sum Raster Calculator ND_remv Airborne Uranium FINAL Int Fin_tab###.txt Export XY Final_pnt.shp Raster to point Change result to an integer Raster to point and exported as text file

11 Model Class Change Calculations Orig_mask (New_wgt orig_wgt)*mask 111_reclass Raster Calculator #:#:# - 1:1:1 Results from weighting model #:#:#.tiff Reclassify #:#:# Reclass Bin into three risk classes

12 Percent Class Change Percent of Cells to Change Class < 10% Change 10% and <15% Change Model ID 15% Change

13 Model Sensitivity Cumulative Changes - Roughly 40% of cells underwent change at least once throughout all model permutations - 17% of cells changed 25% or more Percent Pixel Changed 58% 4%

14 Norm Difference Overall Risk Classification Score Model ID

15 Direction of Change Hotspots Predominantly Lower Risk Predominantly Higher Risk

16 Can indoor radon levels be predicted with environmental factors? - Can you predict indoor radon levels with environmental predictors? - Percentage of exceeding values in risk classes - Regression of score vs radon measurements

17 Radon Measurements - Three sources of data to measure indoor radon levels: 1) Health Canada - Federal building monitoring program and cross sectional study 2) Nova Scotia DNR Provincial data collected within homes 3) Commercial Data Two local testing companies, and Lung Association of NS - Geocoded onto map by postal code/address, or provided to us with coordinates N

18 Percent Percentage of >200 Bq/m 3 in Risk Class c132 c133 c131 c121 c232 c331 c231 c221 c123 c322 c223 c332 c122 c233 c111 c321 c211 c323 c112 c113 c212 c213 c312 c311 c313 Low Risk Model ID Medium Risk High Risk

19 R Squared Value Weighted Sum Values vs Measured Rn Model ID

20 Can indoor radon levels be predicted with environmental factors? Model Assumptions - Professional opinion - Subjective assignments Explanatory Factors - Construction materials - Age of house - Surrounding till/fill - Household behaviour (negative pressure) Receptor

21 Research Questions What impact does input weighting have on the distribution of radon probability? There is a significant impact based on input weighting. Does a new weighting better explain the variability of indoor radon based on measurements? Variation is better explained with a new model by almost double SILK LAB

22 References Chen J., Moir D. and Whyte J. Canadian population risk of radon induced cancer: A reassessment based on the recent cross-canada radon survey. Radiation Protection Bureau. Health Canada Collman GW., Loomis DP. And Sandler DP. Childhood cancer mortality and radon concentration in drinking water in North Carolina. British journal of Caner 63(4) Durrani SA. Radon as a health hazard at the home: What re the facts?. Nuclear Tracks and radiation measurements. Vol 22 issue v Henshaw DL., Eatough JP. and Richardson RB. Radon as a causative factor in induction of myeloid leukemia and other cancers. The Lancet volume 1 issue Wheeler BW., Allen J., Depledge MH. And Curnow A. Radon and skin cancer in Southwest England: An Ecologic Study. Epidemiology 23(1) SILK LAB