ENH 121 Chapter Notes - Chapter 1: Environmental Hazard, Exposure Assessment, Meteorology
Course CodeENH 121
Chapter 1: Environment, Health and Risk
•Global warming, population growth, habitat destruction and resource depletion
have produced a widely acknowledged environmental crisis.
•These long term environmental pre thioblems are not amenable to quick technical
fixes and will require profound social changes for their solutions.
•The environmental crisis:
•Human beings are altering the basic operations of the earth’s atmosphere,
geosphere and biosphere.
•Four prominent biologists have noted with concern that “human alteration of earth
is substantial and growing.
•Between one third and on half of the land surface has been transformed by human
•There is a decline in frog populations around the world.
•The health and reproductive success of amphibians is being damaged by
interactions between an increase in the intensity of ultraviolet light, traces of
globally distributed toxic chemicals, competition from introduced predator
species and infections caused by virulent fungi and bacteria.
•Declining health of frogs, birds and thousands of other organisms may be the
clearest indication of environmental threats to human health.
•Today’s environmental degradation is rapidly creating an unprecedented global
crisis. The driving forces are population growth and industrialization.
•Human activity increased the atmospheric concentration of carbon dioxide by
nearly 30%, doubled the concentration of methane and introduced long lived
ozone destroying chlorofluorocarbons into the stratosphere.
•Human and Ecosystem Health:
•From a medical standpoint health is viewed as an attribute of the individual.
•An ecosystem based health perspective takes into account the health related
services that the natural environment provides and acknowledges the fundamental
connection between an intact environment and human health.
•An ecosystem health stance is a nonanthropocentric, holistic worldview
increasingly shared by biological scientist.
•In the anthropocentric view of the world, humans are the most important of all the
species and should have dominion over nature.
•Has been concluded that the earthy is warming and that green house gases are part
of the cause.
•Health and the environment:
•The health effects of global changes are often indirect and difficult to asses, and
the quality of evidence for the health related outcomes of global environment
change varies widely.
•The health science necessary to understand global environmental change is
increasingly interdisciplinary and requires collaboration over long periods among
meteorologist, chemists, biologists, agronomists and health scientists.
•The sciences of global change frequently relies on computer models to suggest the
direction and magnitude of change, but politicians and policy makers are loath to
commit resources to predicted but unproven future outcomes.
•Environmental degradation exaggerates the imbalance between population and
resources, increases the costs of development and worsens the extent and severity
•Interaction between poverty, population growth and environmental degradation
impede sustainable economic development and worsen population health.
•Changes in natural system may be sudden and nonlinear.
•Two recent developments have drawn renewed attention to the health risks of
industrial chemicals known as persistent organic pollutants (POPs): the
indemnification of medical waste as a significant
•Medical waste incineration is a major source of dioxin and mercury released into
•The second development is the emerging toxicological field of endocrine
•Risk and Caution: Some Definition
•a risk is a potential threat to health and life
•How we assess, perceive, communicate and manage risk is termed risk analysis. o
•Risk analysis is a substantive, changing and controversial field.
•Risk assessments provide probability figures that apply to populations, not to
•Exposure refers to the intensity and duration of contact with a substance or with a
physical agent such as ultraviolet, x-ray or microwave radiation.
•Inhalation, skin absorption, and ingestation are the possible routes of exposure.
• The exposure disease model involves four elements: the exposure to the
substance, the dose the patient actually absorbed the biological effect of the
absorbed dose and the clinical disease that results.
•Numbers are derived from a process called risk assessment, which has four
•1. Hazard identification, which involves identifying health hazards in the
environment and characterizing their physical and chemical properties, the
environmental and biological fates, and their abilities to cause disease.
•2. Exposure assessment, which involves estimating human exposure from air
water, food, or skin contact with the hazardous agent.
•3. Dose-response assessment, which involves characterizing the potential of a
substance to cause disease a function of the exposure or dose.
•4. Risk characterization, which integrates information on the agent’s toxicity,
likely routes of exposure and dose response assessment into an estimate of the
agents probable effects on the health of the population.
•Clinical and epidemiological studies offer the most direct means of assessing
human health risk associated with hazardous exposures.
•Toxicologist rapidly admit that laboratory animals differ from humans in a variety
of ways: humans are larger, live longer, frequently suffer from two or more
disease at a time, receive different exposure then lab animals, metabolize more, or
execrate the agent differently.
•From experimental evidence, laboratory animals and human have more
physiological, biochemical and metabolic similarities than differences.
•Extrapolating Results to Humans:
•Many risk estimator’s prefer to use mathematical models to characterize the
underlying dose-response curve.
•In carcinogenesis, risk estimators typically use one of three classes of models.
•1) Tolerance distribution models assume that each individual in a population has a
threshold below which he or she will not respond, and that thresholds vary among
•2) Mechanistic models, based on the assumption that cancer originates within a
single cell, attempt to characterize the process of transformation mathematically.
•3) time to tumour models are occasionally used to low dose extrapolation when
data on the time between initial exposure and detection of a tumour in an
individual animal are available
•Refinining Risk assessment:
•Risk assessment is going through a period of rapid development.
•Exposure assessment, thought to be one of the most challenging steps in the
process, is being refined to consider environmental degradation and accumulation,
ingestion of contaminated soil and foligate by cattle, deposition rates of
parculates, dermal uptake, biomagnification, pharmacokinetics in humans,
exposures to schedules and the dietary changes that take place over a lifetime.
•Risk assessment is also beginning to emphasieze as mentioned above,
reproductive and development toxicity, neurotoxicity and immunotoxicity, as well
•Closely linked to risk assessment and risk perception is risk communication- the
ways in which the existence and the relative magnitude of a hazard are
•Physicians and public Health Professionals:
•In answering question regarding toxic exposure or the other environmental health
risk, a physicians needs to call on a number skills, including the ability to evaluate
and assess the nature and the extent of the patients exposure to an environmental
hazard, the ability to asses the degree to which the hazards presents a health threat
and the ability to assess the degree.
•First step is to stop further environmental degradation. This will require major
shifts from policies that conrol pollution and repair damage to policies that seek to
prevent the generation of pollution and environmental damage in the first place.
•Second step will be to change the relationship between developed and developing
•Third initiatives are to develop long term educational strategies that will change
the mindsets of individuals and institutions with respects to protecting the
environment and promoting health.