Department of Epidemiology & Public Health General Principles of and Examples of Environmental Exposure Assessment Kees de Hoogh Andrea Ranzi
Outline First half • Definition of exposure • Different exposure pathways • Exposure misclassification • Air pollution Second half • Examples of air pollution exposure assessment in studies • Use of satellite data • Other studies 24-4-2018 Environmental Exposure Assessment 2
What is exposure? National Research Council : an event consisting of contact at a boundary between a human and the environment at a specific contaminant concentration for a specified interval of time. Ott : the existence of a person and an agent (contaminant) in the same microenvironment at the same time (in potential contact with each other). Jaycock : the product of (concentration), (time), and (duration), or rate of transport of toxicant (mg/cm 2 -min) 24-4-2018 Environmental Exposure Assessment 3
Human Health Effects of Pollution 24-4-2018 Environmental Exposure Assessment 4
Exposure processes • Ingestion of contaminants in groundwater, surface water, soil, and food. • Inhalation of contaminants in air (dust, vapor, gases), including those volatilized or otherwise emitted from groundwater, surface water, and soil. • Dermal contact with contaminants in water, soil, air, food, and other media, such as exposed wastes or other contaminated material. • External exposure to radiation. 24-4-2018 Environmental Exposure Assessment 5
Environment - Health Source: Exposure Science in the 21 st Century – National Academy of Sciences, 2012 24-4-2018 Environmental Exposure Assessment 6
How can we assess exposure? 24-4-2018 Environmental Exposure Assessment 7
Exposure pathways contaminated site Source: Public Health Assessment Guidance Manual Exposure Evaluation: Evaluating Exposure Pathways ATSDR (Agency for Toxic Substances and Disease Registry) http://www.atsdr.cdc.gov/hac/PHAManual/ch6.html 24-4-2018 Environmental Exposure Assessment 8
Exposure pathways contaminated site Source: Public Health Assessment Guidance Manual Exposure Evaluation: Evaluating Exposure Pathways ATSDR (Agency for Toxic Substances and Disease Registry) http://www.atsdr.cdc.gov/hac/PHAManual/ch6.html 24-4-2018 Environmental Exposure Assessment 9
Calculating Exposure Doses Source: Public Health Assessment Guidance Manual Exposure Evaluation: Evaluating Exposure Pathways ATSDR (Agency for Toxic Substances and Disease Registry) http://www.atsdr.cdc.gov/hac/PHAManual/ch6.html 24-4-2018 Environmental Exposure Assessment 9
Example – Exposure through Soil ingestion ➢ For example, consider adult ingestion of soil with a non-carcinogenic contaminant concentration of 100 milligrams per kilogram (mg/kg) and a daily soil ingestion rate of 100 milligrams per day (mg/day). Assume the person is on site 5 days per week, 50 weeks per year, for 30 years. First calculate the exposure factor: ➢ EF = (F x ED) / AT ➢ EF = ([5 days/week x 50 weeks/year] x 30 years) / (30 years x 365 days/year) ➢ EF = 0.68 ➢ Next calculate the exposure dose: ➢ D = (C x IR x EF x CF) / BW ➢ D = (100 mg/kg x 100 mg/day x 0.68 x 10 -6 kg/mg) / 70 kg ➢ D = 9.7 x 10 -5 mg/kg/day Source: Public Health Assessment Guidance Manual Exposure Evaluation: Evaluating Exposure Pathways ATSDR (Agency for Toxic Substances and Disease Registry) http://www.atsdr.cdc.gov/hac/PHAManual/ch6.html 24-4-2018 Environmental Exposure Assessment 11
Exposure modelling ➢ Interpolation Models spatial pattern of exposure on the basis of • monitored (georeferenced) data with or without covariates e.g. kriging in soil pollution or inverse distance weighting in air pollution exposure modelling ➢ Source-receptor modelling Models exposure by simulating relationships between • source and receptor e.g. dispersion modelling in air pollution exposure modelling 24-4-2018 Environmental Exposure Assessment 12
What makes a good exposure measure? • Specific • Accurate • Robust • Flexible • Representative • Practical 24-4-2018 Environmental Exposure Assessment 13
Exposure misclassification Models are a simplified representation of reality: • Every model makes assumptions and generalisation about processes, interactions and feedbacks in the reality it describes • Exposure models make assumption about spatial patterns of environmental hazard concentrations and the individual or population under study • Various aspects of uncertainty associated with each method of estimating exposure 24-4-2018 Environmental Exposure Assessment 14
Air pollution ” Air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.” Definition according to WHO Primary pollutants Secondary pollutants + O 2 + Ozone (O 3 ) Nitrogen oxides (NO x ) Particulate Matter (PM) «Smog» Carbon monoxide (CO) Peroxyacetylnitrat (PAN) Sulfur oxides (SO x ) Volatile organic compounds (VOC) 24-4-2018 Environmental Exposure Assessment 15
Where does it come from? 24-4-2018 Environmental Exposure Assessment 16
Sources of particulate air pollution Natural Anthropogenic � Combustion � Abrasion Indoor sources Long distance transport! 24-4-2018 Environmental Exposure Assessment 17
Particulate Matter (PM) PM size fractions: Ultrafine particle PM 2.5 Particle 1 mm = 1000 µm PM 10 Aerodynamic diameter Diesel particle < 10 µm → PM 10 Federal Commission for Air Hygiene, Bern 2007 R. Kägi, EMPA < 2.5 µm → PM 2.5 < 0.1 µm → Ultrafine particle (UFP) ½ diameter of a human hair (50 µm) 24-4-2018 Environmental Exposure Assessment 18
How can we measure air pollution? 24-4-2018 Environmental Exposure Assessment 19
Health effects 24-4-2018 Environmental Exposure Assessment 20
Who is affected by air pollution? Big problem in mega cities Big problem in middle and low income countries But also a problem in Europe - no threshold of toxicity for PM! Beijing, January 2014 PM 2.5 > 500µg/m 3 Beelen et al. 2013 3.5 million premature deaths / year WHO guidelines for PM 2.5 attributed to household annual mean: 10 µg/m 3 air pollution from solid fuels! 24-hour mean: 25 µg/m 3 WHO, 2011 IHME, GBD 2010 24-4-2018 Environmental Exposure Assessment 21
Where are we And where do we measure? exposed? • We spend majority of time indoors • New buildings => better insulation to save energy 24-4-2018 Environmental Exposure Assessment 22
Where do we monitor air pollution Annual mean PM 10 concentrations in Europe in 2008 24-4-2018 Environmental Exposure Assessment 23
What can measurements tell us 24-4-2018 Environmental Exposure Assessment 24
Environmental modelling: Modelled NO2 concentration: 3-day simulation over Europe 24-4-2018 Environmental Exposure Assessment 25
…..and across the world ➢ Donkelaar et al, 2010 24-4-2018 Environmental Exposure Assessment 26
Methods • Proximity based methods • Spatial interpolation • Dispersion modelling • Land Use regression 24-4-2018 Environmental Exposure Assessment 27
Principle of interpolation and geostatisics Tobler’s first law of geography: Everything is related to everything else ...but near things are more related than distant things 24-4-2018 Environmental Exposure Assessment 28
Modelling methods for point data Approach Example Description Proximity Voronoi Creates areas around each point tesselation containing locations nearest to that point Creates zone (buffer) of specified distance around point Buffering Distance Inverse-distance Weights each location in terms of inverse functions weighting distance from monitoring site Global Trend surface Fits global surface through data points interpolators analysis Local Kriging Fits series of local surfaces through data interpolators points 24-4-2018 Environmental Exposure Assessment 29
Interpolation Actual surface and sample points ▪ Trend surface analysis ▪ Inverse distance weighting Surface modelled as disjunct surface ▪ Spline ▪ Local polynomials ▪ Kriging Which method is the most Surface modelled as inverse distance appropriate? ▪ Informed by good understanding of the data Surface modelled as a systematic (global) surface ▪ Validate with another dataset ▪ Measure of the certainty or accuracy of the predictions Surface modelled as a locally smoothed surface 24-4-2018 Environmental Exposure Assessment 30
Inverse distance weighting Values at unsampled locations are a function of values at sampled locations within a specified zone of influence (e.g. radius). The weighting (or influence) of surrounding locations are usually a function of inverse distance. � � � Z Z j i i 2 i 5 Z j is the value (we are trying to predict) at location j 1 λ i is the weighting for location i 4 Z i is the sampled value at location i N 3 � � � p p 1 / d / 1 / d i i i � i 1 d i is the distance between prediction location j and each measured location i P is the power function for distance (typically ‘2’) 24-4-2018 Environmental Exposure Assessment 31
Inverse distance weighting N � � � 1 Weights always sum to 1 i 2 � i 1 5 1 4 λ 3 d 24-4-2018 Environmental Exposure Assessment 32
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