An Introductory Lecture to Environmental Epidemiology Part 1. Introductory Examples.

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An Introductory Lecture to Environmental
Epidemiology Part 1. Introductory Examples.

• Mark S. Goldberg
• INRS-Institut Armand-Frappier, University of
  Quebec, and McGill University
• July 2000

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The author

• Dr. Mark Goldberg obtained his MSc in 1985 and
  his PhD in 1991 from McGill, both degrees in
  epidemiology and biostatistics.
• Dr. Goldberg is an associate professor at the
  INRS-Institut Armand-Frappier, University of
  Québec, and is adjunct professor at McGill
  University. He currently holds a health research
  scientist award from Health Canada.

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• His main interests are in occupational and
  environmental epidemiology, including cancer in
  textile manufacturing workers, health effects of
  exposures from municipal solid waste landfill
  sites, the relationship between ionizing
  radiation and cancer and reproductive outcomes,
  and the connection between tobacco smoking and
  back pain.

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• Currently, he is conducting research into the
  short- and long-term effects of air pollution,
  environmental case-control studies of breast
  cancer, and a study of waiting times for
  treatment of breast cancer in Quebec. Dr.
  Goldberg has published about 40 papers in
  scientific peer-review journals, is the recipient
  of research funds from a number of organizations,
  and sits on a number of scientific review panels.

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Objectives

• This is the first in a five-part series of an
  introductory lecture on environmental
  epidemiology. The goal of the lecture is to
  provide the student with a basic understanding of
  the elements of environmental epidemiology.
  Throughout the lecture, examples from the
  literature are used to illustrate the basic
  methods. It is assumed that the student is
  familiar with basic epidemiology and with
  regression techniques.

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Environmental Epidemiology

• The study of the determinants of the
  distributions of disease that are exogenous to
  and nonessential for the normal functioning of
  human beings
• Adapted from Hertz-Piccioto (in Rothman and
  Greenland, 1998)

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Types of Environmental Exposures

• Point sources
• Pollution from factories, municipal solid waste
  sites
• Line sources
• EMF exposures from high tension power lines
• Pollutants from internal combustion engines
  around motorways

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• Area sources
• Long-range transport of combustion products from
  traffic
• Volatile organic compounds contaminating
  underground water reservoirs

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Example Cancer Rates Near a Solid Waste Landfill
Site

• Ecological Analysis (Goldberg et al., Arch
  Environ Health 199550417-24)
• Landfill site opened in 1968
• 100,000 persons lived within 2 km of the site
• In 1993, it contained about 36x106 Tons of
  domestic, commercial, industrial waste

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• Rates for men and women living in zones around
  site 1981-1988
• Zones defined by 3-character postal codes (fairly
  large areas)
• Putative upwind and downwind zones
• Putative unexposed zone far from the site

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• The High zone surrounds the landfill site to
  about 1 mile.
• The High A zone is downwind and the High B
  zone is upwind because of the crude geographic
  identifiers, there is a region directly
  surrounding the site that is in both sub-zones.
• The Medium zone is further away from the site
  and exposure was likely to be very limited.

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Map of the site showing the different exposure
zones
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• Poisson regression adjusted for age and year, by
  sex
• Reference zones selected from the unexposed
  areas to ensure similarities for
• average household income
• proportion of immigrants
• proportion first language was French
• unemployment and poverty rates

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• Matching was not entirely successful, as some key
  factors were dissimilar (e.g., percentage of
  persons with an Italian family background)

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• Analytic study(Goldberg et al., Arch Environ
  Health 199954291-6)
• Multi-site cancer case-control study of
  occupation, men, 1979-85
• Distance from site and by geographic zones (at
  time of interview)

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• Logistic regression for each site of cancer,
  adjusted for occupational and nonoccupational
  risk factors
• Age, family income, cigarette smoking, alcohol
  consumption, ethnicity, place of birth, body mass
  index, consumption of vitamins, occupational
  salubrity

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Relative Risks for Cancer
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Relative Risks for Liver Cancer from the
Case-control Analysis
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Conclusions

• 1) Slightly different results obtain using
  different methodologies. Populations were
  somewhat different, although there was an
  overlap.
• 2) The results are inconclusive, except perhaps
  for liver cancer. Vinyl chloride monomer is one
  of the constituents of the biogas, and this is an
  accepted liver carcinogen.

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• 3) Further studies are needed at other landfill
  sites. Results from such studies may be difficult
  to generalize if the constituents of the biogas
  differs and if exposure patterns in populations
  vary considerably.

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Another Ecological Example

• The following example is a complex longitudinal
  cohort study undertaken for the purposes of
  determining whether air pollution affects
  pulmonary function. The analysis presented here
  is for mortality and the comparison is between
  six cities in the US. As in the preceding
  case-control study, this study can be viewed as
  an ecological study standardized for personal
  risk factors.

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Example Harvard Six-cities Study (Dockery et al,
NEJM 19933291753-9)

• Prospective cohort study of about 8,000 subjects
  selected randomly from 6 US cities with different
  levels of air pollution
• Subjects followed every two years and lung
  function and questionnaires administered
  periodically
• Ambient air exposures assessed from special
  fixed-site monitoring stations (particles,
  sulfates, gaseous pollutants)

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• Mortality analyses, comparing mean annual levels
  in each city for years near start of followup
• Assumed that subjects did not move during
  followup and that the rank ordering of cities for
  levels of air pollution was invariant of followup
  time
• Stratified Cox proportional hazards models to
  estimate cause-specific relative risks

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Mortality rates by level of pollution by city and
by pollutant
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Estimates of Relative Rates of Mortality,
Comparing Most Exposed to Least Exposed City

• This analysis is a Cox regression analysis
  comparing the most polluted city (Steubenville)
  to the least polluted city (Portage). The range
  of exposures for fine particles is about 18.6
  µg/m3. A wide range of key risks factors were
  included in the statistical model.

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References

• Environmental Epidemiology
• Hertz-Piccioto, I. Environmental Epidemiology,
  in Rothman and Greenland Modern Epidemiology,
  Second edition, Lippincott-Raven Publishers,
  1998, Philadelphia, Chapter 28, pages 555-583.