Managerial Epidemiology: Week 6

Chapter 13

Epidemiologic Aspects

of Work and the

Environment

Learning Objectives

• Define the term environmental epidemiology

• Give examples of environmental agents that are associated with human health effects

• Provide examples of study designs used in environmental epidemiology

• State methodologic difficulties with research on environmental health effects

Environmental Epidemiology

• Study of disease and health

conditions (occurring in the

population) that are linked to

environmental factors

• Environmental exposures—outside

the control of the exposed individual

Two Examples of Environmental

Catastrophes

• Deepwater Horizon oil spill, Gulf of

Mexico, April 20 to July 15, 2010

• Fukushima nuclear reactor meltdown

following earthquake in Japan, March 11,

2011

Human Exposures to

Environmental Hazards

• Chemical agents

• Electromagnetic radiation

• Ionizing radiation

• Heavy metals

• Air pollution

• Temperature increases from global

warming and climate change

Health Effects Attributed to

Environmental Exposures

• Cancer

• Infertility

• Reproductive impacts

• Infectious diseases such as malaria

• Occupation-specific adverse

outcomes

Study Designs Used

• Descriptive study designs

– Helpful for setting priorities

– Hypothesis formulation

• Analytic study designs

– Effects of low-level exposures

– Exposure-effect relationships

– Retrospective cohort designs

Hazardous Agents in the Work

Environment

• Ionizing radiation

• Infectious agents

• Toxic substances

• Drugs

• Carcinogenic agents

Health Effects Associated with

Work Environment

• Health risks for pregnant workers and

the unborn fetus

• Various lung diseases

• Dermatologic problems

• Bladder cancer among dye workers

• Leukemia among workers exposed to

benzene

Study Designs Used in

Environmental Epidemiology

• Descriptive studies provide information

for setting priorities, identifying hazards,

and formulating hypotheses for new

occupational risks.

• Etiologic studies can be used to show

exposure-effect relationships.

Retrospective Cohort Studies

• Various end points are used to study

the effects of occupational exposures.

– Morbidity: self-reports of symptoms and

results of clinical examinations

– Mortality: comparison of mortality rates

of exposed workers with nonexposed

workers in the same industry

Collection of Exposure Data • Employment records often are used

and may include:

– Personal identifiers to permit record

linkage

– Demographic characteristics

– Work history

– Information about potential confounding

variables, e.g., medical history, smoking

habits

The Healthy Worker Effect

• Observation that employed

populations tend to have a lower

mortality experience than the general

population.

• The healthy worker effect may reduce

the measure of effect for an exposure

that increases morbidity or mortality.

Ecologic Study Designs

• One use is the study of the health effects of air pollution.

• Researchers measure the association between average exposure to air pollution within census tracts and the average mortality in those census tracts.

• Unable to controI for individual factors, e.g., smoking habits

Case-Control Studies

• Compared with cross-sectional

study designs, case-control studies

can provide more complete

exposure data.

• However, precise quantitation of

exposure and unobserved

confounding may be difficult to

achieve.

Toxicologic Concepts Related

to Environmental Epidemiology

• Dose-response

• Threshold

• Latency

• Synergism

Dose-Response Curve

• Graph that is used to assess the

effect of exposure to a chemical or

toxic substance upon an organism.

Threshold

• The lowest dose at which a

particular response may occur

Latency

• The time period between initial exposure and a measurable response

• Latency can range from seconds (acute toxic agents) to years (mesothelioma).

• The long latency of health events in environmental research makes the detection of hazards difficult.

Synergism

• A situation in which the combined effect of several exposures is greater than the sum of the individual effects.

• Example: Study conducted among asbestos insulation workers demonstrated a synergistic relationship between asbestos and smoking in causing lung cancer.

Types of Agents

• Chemical agents

• Metallic compounds

• Electric and magnetic fields

• Ionizing radiation

• Allergens and molds

• Dusts

• Physical and mechanical energy

Chemical Agents

• Many types used at home and at

work

–Household cleaning agents

–Automotive chemicals

–Paints

–Pesticides

–Bisphenol A (BPA) in plastics

Chemical Agents (cont’d)

• Potential effects on human health

through acute toxicity, direct skin

irritation, contact dermatitis, or

long-term effects such as cancer

Pesticides: Used to Control

Pests

• Insecticides

• Herbicides

• Rodenticides

Four Classes of Insecticides

• Organophosphates

• Organocarbamates

• Pyrethroids

• Organochlorides

(organochlorines)

Organochloride Insecticides

• DDT

– Toxic to wildlife and persistent in

the environment

• Lindane

• Chlordane

Chemical Agents (cont’d)

• Asbestos

– Strictly speaking, a mineral fiber

– Was used commonly for ship building, construction, insulation, and automobiles

– Associated with asbestosis, mesothelioma, and lung cancer

Metallic Compounds

• Arsenic

• Mercury

• Lead

Metallic Compounds (cont’d)

• Arsenic

– A crystalline metalloid

– Exists as inorganic compounds in the

environment

– Many uses

• Used as a preservative for residential

lumber outlawed

– Potential carcinogen, e.g., bladder

cancer

Metallic Compounds (cont’d)

• Mercury

– Used for the treatment of syphilis, as an agricultural fungicide, and in dental amalgams

– Responsible for Minamata disease, which occurred in the mid-1950s in Minamata Bay, Japan

• A neurological condition linked to the

consumption of fish contaminated with

mercury

Metallic Compounds (cont’d) • Lead

– Once widely used in paint and gasoline

– Associated with serious central nervous system effects even at low levels

– Has adverse effects on intelligence,

behavior, and development

– Between 1988 and 2002, percentage of

children with elevated blood lead levels declined steeply

Electric and Magnetic Fields

• Sources include power lines, microwave ovens, stoves, clocks, cellular phones.

• Los Angeles and Swedish studies found an association between residential proximity to power lines and childhood cancer risk.

• U.S. and Norwegian studies found an increased risk for male breast cancer among male electrical workers.

Ionizing Radiation

• Consists of either particle energy (e.g., highly energetic protons, neutrons, and α and β particles) or electromagnetic energy (e.g., γ-rays and X-rays)

• Sources of ionizing radiation can be natural or synthetic.

Ionizing Radiation (cont’d)

• Natural sources--examples are radon and cosmic rays.

– Radon is one of the largest sources of human exposure to ionizing radiation and may be the cause of about 21,000 deaths from lung cancers in the U.S.

• Synthetic sources--examples are medical x-rays and nuclear generators.

Allergens and Molds

• Allergens--substances that provoke

an allergic reaction in susceptible

individuals

• Allergic reactions range from

dermatitis, asthma, and itchy eyes to

anaphylactic shock.

Physical and Mechanical

Energy

• Include agents associated with

unintentional injuries

• Unintentional injuries are a leading cause

of death within the age group 1-44 years

in the U.S.

• Also include such factors as noise,

vibration, and extremes of temperature

Global Warming

• Possible association with extreme

heat waves

• Climate changes in the eastern

U.S.

• Deaths associated with heat

waves

Monitoring and Surveillance of

Occupational Hazards • Hazard surveillance--characterization of known

chemical, physical, and biologic agents in the

workplace

• Sentinel health event--a case of unnecessary

disease, unnecessary disability, or untimely

death whose occurrence is a warning signal

that the quality of preventive or medical care

may need to be improved

Environmental Hazards Found

in the Work Setting

• Biologic hazards--Hospital employees, sewage workers, and agricultural workers may be exposed to hazardous biologic agents. For example, HIV may infect hospital workers through accidental needle sticks.

• Mineral and organic dusts--Examples include coal dust (mining and black lung disease) and rubber dust (COPD).

Environmental Hazards Found

in the Work Setting (cont’d)

• Vapors and fumes are likely to become

increasing hazards due to the growing use

of chemical substances.

• Vapors--Include organic solvents such as

benzene, which may cause cancer and

damage internal organs (particularly the

liver)

Mineral and Organic Dusts

• Silicosis

• Pulmonary emphysema

• Chronic obstructive disease

• Coal workers’ pneumoconiosis

Industrial Chemicals

• Exposure in occupational settings

is up to 100 times higher than in

the ambient environment.

• Vinyl chloride—angiosarcoma of

the liver

• Pesticides

Noteworthy Community

Environmental Health Hazards

• Hazardous waste sites

• Air pollution

• Nuclear facilities

• Drinking water

Sick Building Syndrome

• Dryness of the skin and mucous

membranes

• Mental fatigue

• Headaches

• Symptoms diminish when affected

person leaves the building.

Hazardous Waste Sites

• Notorious sites in the U.S. include: Love Canal, NY; Valley of the Drums, KY; Times Beach, MO; Stringfellow acid pits, CA; Casmalia Waste Disposal Facility, CA.

• Of great concern is the contamination of water supplies by toxic wastes.

• Some possible adverse effects of hazardous waste exposure include birth defects, neurologic disease, and cancer.

Air Pollution

• Constituents of air pollution include sulfur oxides, particles, ozone, and lead and other heavy metals.

• Lethal air pollution episodes have occurred worldwide.

• Studies conducted in New York City, St. Louis, and Tennessee have shown a correlation between increases in daily mortality and increased air pollution.

Environmental Tobacco

Smoke (ETS)

• Nonsmokers who work in a smoking environment have reduced pulmonary function compared to nonsmokers in a smoke-free work environment.

• ETS causes 3,000 lung cancer deaths annually among nonsmokers.

• ETS is associated with children’s

bronchitis, pneumonia, and asthma.

Nuclear Facilities

• Include weapons production plants, test sites, and nuclear power plants

• Studies of living in close proximity to nuclear installations have shown conflicting results regarding cancer rates.

– Following the Chernobyl nuclear power plant accident, thyroid cancer rates increased near the reactor.

Drinking Water

• Chemical plants and nuclear facilities

may contaminate ground water.

• Chlorination of water supply has helped

to decrease the incidence of

gastroenteric diseases.

• Lead and asbestos particles may be

present in water and have potential for

toxicity.