HSCI 204: Human Health and The Environment

Introduction to environmental health, The health burden from environmental hazards, Exposure assessment & environmental epidemiology, Toxicology & risk assessment, Air Quality, Pesticides

Hierarchy of Exposure Controls

Framework used in occupational and environmental health to reduce or eliminate exposure to hazards

• Ranks control strategies from the most to least effective

John Snow

• Investigated a severe cholera outbreak by mapping out deaths in a neighbourhood

• Noticed many cases were around the Broad Street water pump

  • Showed how disease could be traced to a specific environmental exposure

  • Public health intervention could help cases

Richard Doll

• The epidemiologist best known for helping establish the link between smoking and lung cancer (along with Austin Bradford Hill)

• Used a long-term cohort study, which showed a strong dose-response relationship

Bradford Hill’s Guidelines for Causation

• Strength of Association - stronger associations are more likely to be causal

• Consistency - the association must be shown repeatedly in different studies, populations, etc.

• Specificity - a specific exposure leads to a specific cause

• Temporality - exposure must occur before the disease

• Dose-response - greater exposure leads to greater risk

• Coherence - association fits with existing knowledge (lab data, pathology, history)

• Plausibility - there is a biologically reasonable mechanism

The Age of Pestilence and Famine

This stage was dominated by the constant threat of disease and food scarcity — prevented sustained population growth

• Only after societies advanced in agriculture, sanitation, and medicine did they move into the next stage

The Age of Receding Pandemics

This stage was when societies began to gain control over major causes of death — leading to longer life expectancies and stable population growth

• Advancement in agriculture, sanitation, and medicine

The Age of Man-Made Diseases

Pattern of disease shifts from infectious outbreaks to chronic, long-term conditions

• People live longer because infectious diseases declined, but lifestyle and degenerative disease became the main health challenge

Epidemiological Triangle

Shows that disease is rarely caused by one factor alone and prevention can target any part of the triangle (occurs through interaction of three components)

• Remove the agent

• Vaccinate the host

• Modify the environment

Epidemiological Transition

Describes how the main causes of diseases and death shift as societies develop economically and socially

• Mortality shifting from infectious to chronic/lifestyle disease

Environmental Risk Transition

Describes how environment-related health risks change as a country develops economically and industrializes

• Household related risk (poor sanitation. indoor air pollution) to community-wide risks (industrial pollution, climate change)

Global Burden of Disease (GBD)

Quantifies health loss from various disease, injuries, and risk factors so that health systems can be improved (eliminating disparities)

DALYs

Measures total burden of disease — # of years lost due to sickness/disability (YLD) and premature death (YLL)

• DALY = YLD + YLL

Population Attributable Fraction

Measure of the percentage of cases/deaths in a population that would be eliminated if a specific risk factor were removed

• Cases that would not happen if exposure was gone

The Prevention Paradox

When the majority of cases of disease come from a population at low/moderate risk and only a minority come from the high risk population

• Large # people at risk give rise to more cases than a small # who are at high risk (overall population health — exposure increases)

Shifting The Curve

Refers to moving an entire population’s health outcome to improve overall health — not just the high-risk individuals

• Lowering risk factors

• Improving health outcomes

• Altering the trajectory of a disease outbreak

Clinical Strategy

Physicians diagnose people with signs or symptoms of a disease and prescribe a drug or perform surgery

Population Strategy

Scientists attempt to identify and reduce upstream risk factors in populations that cause disease (attacking and limiting the root cause)

What is exposure assessment?

The process of estimating how much of a substance/environmental hazard people are exposed to

• How often

• Through which route

Acute

• Short-term “bursts” of elevated exposure (hours to days)

• May be followed immediately by symptoms or exacerbation of existing condition

Chronic

• Longer-term periods of exposure (years to lifetime)

• Often lower concentrations/doses

• May be associated with onset of new disease (sometimes after a latency period)

Exposure Routes

• Dermal; skin contact with a harmful substance

• Inhalation

• Ingestion

• Mother → Fetus

Why are exposure assessments conducted?

To identify, measure, and evaluate the exposure to the substance/hazard

• Determines potential health risks and helps set safety standards and regulations

Uses of Exposure Info

• Epidemiology

• Risk Assessment/Impact Assessment

• Surveillance, evaluation of exposure trends

• To identify sources/determinants of exposure

• To compare with regulations and guidelines

Direct Methods of Exposure Assessment

Are a better estimate for exposure, but are more expensive and time consuming — not often feasible on a large scale

• Personal Measurements

• Biomarkers

Indirect Methods

Are a poorer estimate for exposure, but are cheaper and less time consuming — little to no participant demand

• “Area” Measurements

• Questionaries

• Models

Biomarkers

Measures pollutant/metabolite in biological material (urine, breathe, blood, etc.)

• ex. breathalyzer

• Estimates dose and incorporates multiple routes of exposure

Why is exposure assessment important?

• Risk depends on both how hazardous a substance is and the exposure

• Without exposure, there is no risk and it allows us to estimate real-world health risks and set protective public health standards

Problems with exposure misclassification

A type of information bias in epidemiological studies (incorrectly categorized regarding participant exposure)

• Results in inaccurate data — false conclusions about the connection between exposure and health outcome

Role of exposure prevalence in determining population-level impacts of an environmental risk

It shows how risky it is, determining which groups are most affected — helps create intervention strategies

• Minimize and hopefully eliminate a risk

Effect of Exposure Errors

• Exposure estimation errors can bias epidemiological studies and will often be “toward the null”

• Can cause exposure-health relationships to be underestimated

Why are exposure controls at the source generally more preferable than controls at the level of the individual?

It addresses the upstream determinants of health

• No exposure = no risk

Key Ideas in Epidemiology

• Not everyone who is exposed to a hazard will develop disease/illness from that exposure

• Not every case is the result of the exposure of interest

• Correlation does not imply causation

Observational Designs Studies

• Cross-sectional

• Case-control

• Cohort

• Time Series

Experimental Design Studies

• Randomized Control Trial

• Natural Experiments

Cross-Sectional Study

Analyze data from a population or subset at a single, specific point in time

Case-Control Study

Compares individuals with a specific disease or outcome (“cases”) to similar individuals without it (“controls”) to identify past exposure or risk factors.

Cohort Study

Follows a specific group of people (cohort) over a period of time to understand the relationship between exposure and an outcome

Time Series Study

Uses stats to analyze and model data points collected at regular intervals (e.g. weekly, monthly, etc.) to identify patterns, trends, and shifts over time

Randomized Control Trial

Used to measure the effectiveness of new treatments or interventions

• One group receives the treatment (drug) and the other doesn’t (control)

• Considered the “gold standard” study design

Natural Experiment

Involves the unobstructive, real-time observation of subjects (people or animals) in their natural environment without any interference or manipulation

Why are randomized controlled relatively uncommon in environmental epidemiology?

They are often unethical, impractical, or unfeasible for the study — more useful in clinical medicine (ex. testing a drug) rather than observational studies

Why is it important to assess exposure carefully?

It’s important because risk is a function of both hazard and exposure

• Even if a extremely harmful substance has little risk if the exposure is near zero, but a moderately harmful substance can have high risks if the exposure is high.

• If exposure is assessed poorly it could waste resources and create public mistrust.

Relative Risk

Measures the likelihood of an event (disease/injury) occurring in an exposed group compared to a non-exposed (control) group

Odds Ratio (Effect Estimates)

Quantifies the strength of association between exposure and outcome

• Compares the odds of the event occurring in an exposed group vs a non-exposed group

Acting too early vs. too late

Early:

• Waste resources, causes harm (ex. vaccine hesitancy), lose public trust

Late:

• Suffer avoidable death, disease, and/or disability

Precautionary Principle

A strategy for approaching potentially dangerous innovations or actions when scientific knowledge is incomplete

• “Better safe than sorry”

Toxin

A compound of natural origin that exerts notable adverse effects on biological systems

Toxicant

A synthetic compound that exerts notable adverse effects on biological systems

Route of a Toxicant

1. Absorption — crosses biological barrier

2. Distribution — toxicant is distributed within the body

3. Metabolism — metabolite may be more toxic than parent compound

4. Excretion — toxicant leaves the body

Teratogenicity

Ability to cause birth defects

Mutagenicity

Ability to cause heritable changes in DNA (mutations)

Neurotoxicity

Toxic to nerves or nervous system

What is a threshold in a dose-response relationship?

The lowest dose of a substance at which a harmful effect begins to appear - no measurable adverse effects

Why is a threshold important?

• threshold — small amounts are generally “safe” and we can focus on keeping the exposure below the threshold

• no threshold — any exposure could cause harm, which leads to stricter regulations/management

Lethal Dose 50

The dose of a chemical which produces death in 50% of a population of test animals to which it is administered

• Used to compare the acute toxicity of different compounds

NOAEL

No observed adverse effect level

• The highest dose at which he adverse effect is NOT observed

LOAEL

Lowest observed adverse effect level

• The lowest dose at which the adverse effect is observed

• The effect does not have to be death

Reference Dose

The estimate of the amount of a substance a person can be exposed to every day over a lifetime without likely experiencing harmful health effects

• Safe daily exposure level for non-cancer effects

Point of Departure

The dose at which “bad things” (adverse health effects) start to happen

Hazard

Something capable of causing an adverse effects

Risk

Probability that the hazard will cause an adverse effect under specific exposure conditions

Risk Assessment

The process by which hazard, exposure, and risk are determined

Risk Managment

The process of weighing policy alternatives and selecting the most appropriate regulatory action based on the results of risk assessment (and social, economic, political concerns)

Risk Perception

How people interpret, understand, and respond to a risk — how risky people believe something is

Where can you gather toxicology info?

• ATSDR

• International Agency for Research on Cancer (IARC)

• IRIS database

What info does a dose-response curve provide?

• If the substance has a threshold

• The NOAEL and LOAEL

• How much of the substance was used (the dosage)

• How well the substance works (the response)

How do dose-response curves for essential nutrients and non-nutritive toxicants differ?

Essential Nutrients:

• U-shaped graph

• At low doses, adverse health effects occur (deficiency)

• At high doses, the nutrient acts as a toxin

Non-Nutritive Toxicants:

• S-shaped graph

• At low doses, no adverse effects are detected (some do not have thresholds)

• At high does, adverse effects increase

What are the four major components of a risk assessment?

1. Hazard Identification — what adverse health effects are associated with the environmental contaminant of concern

2. Dose-Response Assessment — what’s the relationship between dose and probability of adverse health effects

3. Exposure Assessment — what’s the current exposures or doses in the population of interest

4. Risk Characterization — nature and magnitude of the risk to human health

How does traditional risk assessment differ between carcinogens and non-carcinogens?

Carcinogens:

• Assumed to be a non-threshold (any exposure carries some risk)

Non-Carcinogens:

• Assumed to have a threshold below which no adverse health effect occurs

PM_2.5

Particulate matter that is 2.5 micrometers in diameter or smaller

• Around the size of a RBC — can travel deep into human lungs (into alveoli and remain there)

How are particulate matter concentrations expressed?

Micrograms cubic meter of air (ug/m³)

Outdoor Air Pollutants

• Particulate Matter

• Ozone (O₃)

• Sulfur Dioxide (SO₂)

• Nitrogen Oxides (NO and NO₂)

• Carbon Monoxide (CO)

Household (Indoor) Air Pollution

Caused by the indoor burning of unprocessed solid fuels

• Carbon Monoxide (CO)

• Radon

Spatial patterns of traffic related air pollution concentrations

More concentrated in dense, populated areas and major roads (ex. downtown Vancouver)

Major health effects through ambient air pollution

• CVD (49.0%)

• Chronic Lung Disease (13.3%)

• Respiratory and other infections (8.8%)

• Neurological Conditions (8.3%)

• Diabetes (8.3%)

• Maternal/Neonatal (7.4%)

• Cancers (5.5%)

Major health effects through household air pollution

• Maternal/Neonatal (25.7%)

• CVD (24.6%)

• Respiratory and other infections (15.6%)

• Diabetes (3.6%)

• Neurological Conditions (1.8%)

• Cataracts (1.7%)

• Cancers (1.3%)

How are air pollution exposures and health risks distributed globally and locally?

• Globally — higher risk and exposure in developing regions and disadvantaged neighborhoods (poor ventilation, burning solids for fuel, etc.)

• Locally — higher risk and exposure in lower income neighborhoods, communities near highways, and areas close to factories

Harvard Six Cities Study

Public health study that followed many adults across six U.S cities and examined different health changes, while air monitoring stations measured particle levels

• People living in cities with high air pollution were more likely to experience adverse health effects (ex. premature death)

• Found that PM_2.5 were the most dangerous because of their ability to penetrate deep into the lungs/bloodstream

The UGAAR Study

Randomized control trial in Mongolia that investigated if using portable air purifiers at home during pregnancy could improve birth outcomes — half the group was given an air purifier, the other half was not

• Purifiers reduced PM_2.5 in households

• Babies had an increase in average birthweight

Main health concerns associated with radon and CO exposure

Both are a colourless and odorless gas that can accumulate in homes — is able to cause death at high levels as well as other adverse health effects

• Radon is carcinogenic

• CO can bond to hemoglobin in RBCs (can’t transport O₂)

Why is radon a problem in households?

Radon can accumulate indoors after seeping from soil (uranium in soil, breaks down to form radon), rock, and water through foundation cracks or gaps in construction (is also a carcinogen)

What is the energy ladder?

Model describing how households switch from traditional, inefficient, solid fuels (wood, coal, dung) to cleaner more efficient energy sources (LPG, electricity) as their income and socio-economic status rise

• Shows how lower-income communities are at higher risk to household air pollution

Why are pesticides used?

• To control pests in order to protect food supplies and ensure high agricultural yields

• Protects crops from weeds, disease, and insects

Why are organophosphate insecticides more favoured that organochlorine insecticides?

Organophosphates

• Less persistent (degrade faster in the environment) — reduces long-term accumulation

• Higher acute toxicity to humans

Organochlorines

• Very persistent (can remain in the environment for years)

• Lower acute toxicity to humans

• Banned in many regions

Five main chemical classes of insecticides

1. Organophosphates

2. Carbamates

3. Organochlorines

4. Pyrethroids

5. Neonicotinoids

Advantages of environmental persistence of pesticides

Extended residual activity — provides long-term control of pests and reduces the need for frequent reapplications (cost effective)

Disadvantages of environmental persistence of pesticides

• Widespread contamination — chemical can remain in the soil and water for extended periods of time

• Could cause harm to non-pests (could carry into water sources and harm different ecosystems)

Spray Drift

The unintentional, airborne movement of pesticides outside the intended target area during or shortly after the application

• Caused by wind, droplet size, humidity, etc.

Health effects caused by chronic exposure to pesticides

• Mostly associated with organophosphates

• ~3-5 million unintentional poisonings (20,000 deaths)

• Mainly in low-middle income regions

• 2 million internal poisonings (150,000 pesticide suicide deaths annually)

Trade-offs in using DDT (organochlorine) for malaria control

Some trade-offs for the effectiveness and low cost comes with significant human health risks and environmental persistence

Rachel Carson’s concerns with widespread use of chemicals

• She was concerned with the widespread, and often secretive use of synthetic chemical pesticides (DDT) in the post WW2 era

• She argued these chemicals were used with little to no investigation with their long-term effects

Why does Rachel Carson remain a polarizing figure for decades after the publication of silent spring?

Her work directly challenged a powerful chemical industry and the post WW2 ideology of domination through technology and industrialization

What chemical class of pesticides accounts for the majority of poisonings?

Organophosphate

• High acute toxicity to humans

• Used frequently in agriculture and households

• Act as irreversible inhibitors of the enzymes that breaks down acetylcholine (causing the overestimation of nerve receptors)

Glyphosate

A widely used herbicide that works by blocking an enzyme pathway that plants need to grow, which humans don’t have — it was originally considered relatively low toxicity to people

• Has been on the news because of cancer concerns and lawsuits, being classified as a probable carcinogen

Regrettable Substitution

Occurs when a hazardous chemical is replaced with a substitute that is equally or more harmful to human health or the environment (ex. organochlorine → organophosphate)

Salmonellosis

• Associated with poultry, meat, and eggs — consumption of contaminated foods (fecal material from unwashed hands)

• Higher mortality among young and elderly (~3%)

E.coli

• Present in the intestinal tracts of cattle (excreted through fecal material)

• Associated with undercooked beef or raw milk (unpasteurized)

  • Hemorrhagic colitis (bloody stools), hemolytic uremic syndrome (RBC destruction, blood clots in kidneys, kidney failure)

Listeriosis

• Bacteria found in soil and water

• Associated with soft cheese, meats, and vegetables

  • High fatality rate (~20-30%) — pregnant women (and fetuses), young and elderly, and immunocompromised

HACCP

Hazard Analysis Critical Control Point (food safety system)

• Preventative management system used in the food industry to manage the distribution from raw material production to final consumption (stopping hazards before they occur)

Surface Water

All water naturally open to the atmosphere (rivers, lakes) — less desirable for drinking