## Environmental Issues in Public Health

Hui Hu Ph.D.

Department of Epidemiology

College of Public Health and Health Professions & College of Medicine

July 25, 2017

Introduction

Measurement

Intervention

# P = G + E

Phenotype

Genome

Environment

T2DM, Cancer, LBW, PTD

Polymorphisms

Infectious agents

Nutrients

Pollutants

Drugs

### Genome

• There are exquisite tools that have been developed to sequence the human genome and to interrogate individual susceptibility through genome-wide association studies (GWAS)

• Thousands of GWAS

### Exposome

• However, there was a lack of comparable tools in relation to exposure assessment
-  almost uniquely focused on single exposure-health effect relationships and no global view of how various types of exposures co-exist and jointly affect health

• A similar platform for discovery should exist for E
- why?

• Heritability: the range of phenotypic variability attributed to genetic variability in a population
-  indicator of the proportion of phenotypic differences attributed to G
\sigma_P^2=\sigma_G^2+\sigma_E^2
$\sigma_P^2=\sigma_G^2+\sigma_E^2$
H^2={{\sigma^2_G}\over {\sigma^2_P}}
$H^2={{\sigma^2_G}\over {\sigma^2_P}}$

### Exposome

• To draw attention to the critical need for more complete environmental exposure assessment
-  environment is defined in this context as 'non-genetic' factors
-  exposome complements the genome

• The exposome is composed of every exposure to which an individual is subjected from conception to death
-  the nature of those exposures
-  their changes over time

• Expanded and dynamic exposure assessment across multiple domains

• Integration of data on exposure and response across multiple scales of variation

• Use of the resulting high dimensional information on multiple exposure-response relationships for data-driven discovery

### Three domains of exposome

• Three broad domains of non-genetic exposures:
-  internal
-  specific external
-  general external

Source: Wild CP. The exposome: from concept to utility. International journal of epidemiology. 2012 Feb 1;41(1):24-32.

### Three domains of exposome (continued)

• There is overlap in the three domains
-  physical activity can either be internal or specific external

• The domains can also be considered as intertwined
-  the internal may at least partially be a response to the external

• Measures in one domain or another may reflect to differing degrees one component of the exposome:
-  the urban environment (general external)
-  air pollution (specific external)
-  inflammation (internal)

Source: Wild CP. The exposome: from concept to utility. International journal of epidemiology. 2012 Feb 1;41(1):24-32.

Individual's Health

Behavior and Intrinsic Biological Factors

The Total Environment

Natural

Built

Social

• May cause skin cancer and melanoma
• Recent studies also showed associations between UVR and increased mortality due to CVD, cancer, and respiratory diseases

• Natural radioactive decay of uranium
• May cause lung cancer

Air pollution:

• Clean Air Act (1970, 1990)
• Outdoor air pollution:
6 criteria air pollutants - PM, SO2, CO, NOx, O3, Pb
• Indoor air pollution: tobacco smoke, combustion products, radon gas

Climate change:

• Extreme temperature and precipitation
• Associated with increased mortality and morbidity

Food access, Walkability, and Greenness

• Associated with physical activity, obesity, and cardiometabolic outcomes

• No safe level of lead exposure has been identified
• Even low levels of lead can cause neuropsychiatric function and potentially lead to behavior problems

Education, Poverty, and Safety

• Important health determinants

## Measurement

### Natural Environment

• Natural environment includes all things naturally occurring on Earth

• Physical, chemical, and biological components or contaminants in soil, air, water

• Exposure to these agents are usually unknown or unsensed by the exposed individual
-  the exposure cannot be recalled or recorded by the study subject
-  it can only be documented through measurements in the environment

### Two types of errors

• Error variance (lack of precision) in the measure
-  individual levels of exposure are over- or underestimated but the mean exposure of a group is correct
-  usually leads to attenuation of the observed relationship of the exposure to outcome

• Systematically incorrect estimation of exposure levels
-  the mean exposure level for a group is over or under-estimated
-  can lead to over- or underestimation of the risk at a fixed level of exposure

### Examples

• A study trying to assess the association between exposure to magnetic field and childhood asthma

• The authors obtained geocodes for all the participants, and linked them to the data from electrical utility companies which include all existing and historical 132-400 kV overhead trasmission lines.
-  they assigned each home exposure levels 0 μT, 0.1 μT, 0.2 μT, or 0.4μT

• Objectivity: depends on two steps
-  the sampling of the environment
-  the measurement procedure proper

• In some case, both steps can be highly objective (e.g. measure the concentration of gaseous air pollution using personal sampler)

• Often only the second step is objective, while identification and selection of the sample involves substantial subjectivity
-  rely on information provided by the study subject to identify environmental materials to be sampled (e.g. use residential history to assess air pollution exposure)

### Advantages of environmental measurements (continued)

• Analytic specificity and sensitivity

• If the exposure is a mixture of chemical, measurements specific for a single chemical may be inappropriate if
-  that chemical is not the one responsible for the biological effect under study,
-  and its concentration is not highly correlated with that of the active agent or with the total activity in the mixture

• Cost and feasibility of use on a large scale

### Advantages of environmental measurements (continued)

• Individualized:
-  can be achieved only when personal sampling is practicable over repeated and extended periods of time

• In many cases, it can only be approximated by average measurements over time or groups of persons
-  estimating air pollution exposure using a stationary air monitor

• Errors in obtaining the original specimens from the environment and in sub-sampling for lab analysis may be the main source of error in environmental measurements

### Sampling and measuring present exposures

• Two main purposes:

-  to be used as such in prospective cohort studies aimed at relating present exposure to future disease occurrence

-  to be entered as one element in the process of estimating past exposure within cross-sectional, retrospective cohort, or case-control studies

### Methods of environmental sampling

• Measurement at fixed points within the environment and inferring individual exposure from the concentration of contaminants measured in the parts of the environment covered by each sampler

• Measurement of the immediate and continually changing environment of individual subjects by some form of personal sampling
-  this is preferred since it takes into account the subject's position in the environment, and concentrations of the environmental agent there, and behaviors which may modify exposure in particular circumstances

### Selecting subjects for environmental sampling

• Continuous sampling of the environment of each subject throughout all periods of exposure relevant to the study
-  relatively simple in some settings: e.g. film-badge monitoring of exposure to ionizing radiaiton
-  usually impracticable and unnecessary

• Sampling both subjects and exposure time

• Two main approaches:
-  random selection of subjects and then grouping those appearing to share common levels of exposure to the environmental agent
-  pre-definition of strata presumptively homogeneous with respect to the exposure and sampling randomly within the strata

### Sampling and measuring past exposures

• Measurements of present exposure in the environment are applicable to cross-sectional, case-control, or retrospective cohort studies only when it can be reasonably assumed that measurements in the present environment are highly correlated with the past

• Records of past measurements of relevant exposures can be sought.

• Three scenarios:
-  complete data
-  incomplete data
-  data unavailable

• It is practically impossible to monitor all agents present in the environment

### Complete past measurements

• Usually, the measurements on natural environment available were collected to check compliance with regulatory standards

• Important to ascertain the purpose of the measurements and the frame within which they were collected
-  they determine the way in which the samples were selected and the way they reflect the pattern of exposure of the study subjects

• Example:
-  measurements of only a fraction of the mixture of interest
-  measurements only in "maximum risk employees"

### Incomplete past measurements

• Incomplete:
-  lack of spatiotemporal coverage
-  measured by sub-optimal methods
-  measured only some correlate of the exposure of interest

• Methods to address these problems:
-  spatiotemporal interpolation
-  calibration and conversion
-  predictive models

### Built Environment and Social Environment

Built Environment

• Emcompasses all man-made surroundings that provide the setting for human activity

• Examples:
-  green space
-  sidewalks/trails
-  parks/recreational services
-  food access

Social Environment

• Important health determinants

• Examples:
-  demographics
-  economy
-  social capital
-  safety

## Intervention

### Group Discussion

• Read the article below (https://ehp.niehs.nih.gov/125-A65/).
• What do you think about population-level vs. individual-level environmental interventions? Discuss their strengths and limitations.

By Hui Hu

# PHC4101-Summer2017

Slides for the Guest Lecture, Summer 2017, PHC4101 Public Health Concepts

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