hsci 204

Cohort Studies:

Cohort studies begin by identifying a group of participants who do not have the disease of interest.

Researchers then observe these participants over time to track the development of new cases of the disease.

Cohort studies proceed from exposure to outcome.

They can study rare exposures and determine the temporal relationship between exposure and outcome.

Cohort studies can be expensive and time-consuming, especially prospective cohort studies, and are not useful for studying rare diseases.

Case-Control Studies:

Case-control studies start by identifying participants based on their disease status (cases) and a comparison group without the disease (controls).

Researchers then look backward in time to determine who had the exposure.

Case-control studies proceed from outcome to exposure.

They often require smaller sample sizes and are useful for studying rare diseases.

Exposure assessment can be difficult due to the retrospective nature of the study, and they are not useful for studying rare exposures.

Exposure Assessment: This process identifies who is exposed to what, in what amount, when, where, and how frequently. It considers both the exposure pathway (the course a pollutant takes from source to subject) and the exposure route (how a substance enters the body, such as dermal, inhalation, or ingestion).

Epidemiology: This field investigates the effects of exposures on human populations. It seeks to define exposure-health relationships and identify susceptible groups.

Toxicology: This branch of science studies the adverse effects of substances on biological systems.

Risk Assessment: This method determines the hazard, exposure, and resulting risk.

2. Acute vs. Chronic Exposure

Acute Exposure: This refers to short-term, high-concentration exposure over hours to days. It may lead to immediate symptoms or worsen existing conditions.

Chronic Exposure: This involves long-term, low-concentration exposure over years to a lifetime. Effects may include the onset of new diseases, potentially after a long latency period.

These terms describe both the nature of the exposure and the health effects that result.

3. Exposure Pathways and Interventions

Environmental Risk Paradigm: Pollutants move from emissions to exposure, dose, and ultimately, an effect.

Points of Intervention: Interventions to reduce exposure can occur at the source, along the exposure pathway, or at the individual level. Reducing emissions is the most effective approach.

4. Exposure Assessment Methods

Direct Methods: These involve personal measurements and biomarkers. While providing a more accurate estimate of exposure, they are expensive, time-intensive, and demanding on participants.

Indirect Methods: These include area measurements, questionnaires, and models. They are less expensive and can be applied to larger populations, but may be less accurate.

5. Application of Exposure Information

Exposure data is crucial for:

Epidemiological studies.

Risk and impact assessments.

Surveillance of exposure trends.

Identifying exposure sources and determinants.

Comparing exposures to regulatory guidelines.

6. Epidemiological Study Designs

Observational Studies: These include cross-sectional, case-control, cohort, and time series studies.

Experimental Designs: These involve randomized controlled trials and natural experiments. Randomized studies are rare in environmental health.

7. Toxicology: Key Concepts

Toxicokinetics: This describes how the body processes toxic substances (absorption, distribution, metabolism, excretion).

Dimensions of Toxicity: Key factors include the toxicant and target organ, dose, exposure route, timing, and duration.

Quantifying Toxicity: Common measures include LD50 (lethal dose for 50% of the population), NOAEL (no observed adverse effect level), and LOAEL (lowest observed adverse effect level).

The dose makes the poison.

8. Risk Assessment and Management

Risk Assessment: This involves determining the hazard, exposure, and risk.

Risk Management: This involves selecting the most appropriate action based on risk assessment, alongside social, economic, and political factors.

9. Risk Perception

Risk perception affects both individual and policy choices. It represents an intuitive judgment regarding the nature and magnitude of health risks.

Lay people's judgments of risk are related more to hazard characteristics.

Both experts and non-experts contribute valuable insights in risk assessment.

10. Prevention Strategies

Prevention Paradox: A large number of people at a small risk may result in more disease cases than a small number at high risk.

Shifting the Curve: This involves reducing exposure across an entire population.

Action Thresholds: Decisions on when to act are based on the precautionary principle versus definitive causality

Exposure Assessment Methods

Direct Methods: Personal measurements and biomarkers, which provide better estimates of true exposure but are expensive and demanding.

Indirect Methods: Area measurements, questionnaires, and models, which are less expensive but may provide poorer estimates of true exposure.

Biomarkers: Measuring pollutants or metabolites in biological materials to estimate dose and incorporate multiple routes of exposure.

Temporal Variation: Concentrations vary in time.

Spatial Variation: Concentrations vary from place to place.

4. Epidemiology Study Designs

Observational Designs:

Cross-Sectional: Assessing exposure and outcome at a single point in time.

Case-Control: Identifying participants based on disease status and then determining prior exposure.

Cohort: Identifying participants without the disease and observing them over time to assess new cases.

Time Series: Analyzing changes in exposure and health outcomes over time.

Experimental Designs:

Randomized Controlled Trial: Randomly allocating participants to intervention or control groups.

Natural Experiments: Observing the effects of naturally occurring changes in exposure.

Relative Risk: A ratio of risks used in cohort studies to measure the association between exposure and outcome.

Odds Ratio: A measure of association used in case-control studies.

Bias: Systematic deviation of results or inferences from truth.

5. Toxicology

Toxicokinetics: What happens to a toxic substance in the body, including absorption, distribution, metabolism, and excretion (ADME).

Toxin: A compound of natural origin that exerts adverse effects on biological systems.

Toxicant: A synthetic compound that exerts adverse effects on biological systems.

Dimensions of Toxicity: Factors determining the likelihood and severity of a toxic effect, including toxicant, target organ, dose, route, timing, and duration.

LD50 (Lethal Dose 50): The dose of a chemical that produces death in 50% of a test animal population.

NOAEL (No Observed Adverse Effect Level): The highest dose at which an adverse effect is not observed.

LOAEL (Lowest Observed Adverse Effect Level): The lowest dose at which an adverse effect is observed.

Reference Dose (RfD) / Acceptable Daily Intake (ADI): Acceptable intake at a fraction of the NOAEL to provide a margin of safety.

6. Risk Assessment and Management

Hazard: Something capable of causing an adverse effect.

Risk: Probability that a hazard will cause an adverse effect under specific exposure conditions.

Risk Assessment: Process by which hazard, exposure, and risk are determined.

Risk Management: Process of weighing policy alternatives and selecting the most appropriate regulatory action.

IARC (International Agency for Research on Cancer): An agency within the World Health Organization that evaluates evidence of carcinogenicity.

7. Risk Perception

Technical/Quantitative Risk: Function of hazard, exposure, susceptibility.

Perceived Risk: An intuitive judgment about the nature and magnitude of a health risk.

8. Prevention Strategies

Prevention Paradox: A large number of people at a small risk may give rise to more cases of disease than the small number at high risk.

Shifting the Curve: Lowering the entire distribution of a risk variable by some measure in which all participate.

Precautionary Principle: Taking precautionary measures when an activity raises threats of harm to human health or the environment, even if some cause and effect relationships are not fully established scientifically

Air Pollution

A. Historical Context & Evolution:

• Air pollution is not a modern phenomenon. It's been an issue at the household level since the habitual use of fire ~300,000 to 400,000 years ago.

• Industrialization and urbanization significantly increased air pollution levels and their impact.

• Air pollution regulations have a long history, with recognition of air pollution as a "nuisance" as early as the 1200s in England. The Clean Air Act of 1956 in England was a significant step, partly in response to a deadly 1952 pollution event.

• Energy source changes (coal to oil to natural gas) have influenced air quality in high-income countries, leading to "Significant Improvement in Air Quality".

B. Outdoor Air Pollution:

• "Criteria" Air Pollutants: The lecture identifies key pollutants including particulate matter (PM), ozone (O3), sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon monoxide (CO). These are widely measured and regulated.

• Particulate Matter (PM): The lecture emphasizes the importance of PM size, noting "Particle Size Matters".

• Ozone: "Good up high, bad nearby" – highlighting the dual nature of ozone.

• Traffic-Related Air Pollution: Traffic is identified as a significant source, creating spatial gradients of pollution exposure.

C. Burden of Disease (Ambient Air Pollution):

• Air pollution has significant health impacts, even in high-income countries.

• Cause-Specific Impacts: A large portion of the disease burden from PM2.5 comes from its impact on cardiovascular health. Other impacts include diabetes, chronic lung disease, cancers, and respiratory infections.

• Premature Mortality: Estimates of annual premature mortality attributable to ambient air pollution vary (GBD: ~4,000; Health Canada: ~15,000). Health Canada estimates a "$120 billion total economic cost of all health impacts, 6% of GDP".

• The lecture brings up the complexity of defining a "safe" level of air pollution and refers to: "From a public policy perspective…a… concentration-response function without a well-defined safe threshold level might be inconvenient. “As argued elsewhere, from at least one perspective, these results are good news, because they suggest that even at common levels of air pollution, further improvements in air quality are likely to result in corresponding improvements in public health.”

D. Research & Evidence:

• Methods: Various research methods are used to study air pollution's health effects, including:

• Controlled animal exposure studies.

• Human controlled exposure studies.

• Time series studies (using daily data on air pollution, mortality, and meteorology) which are described as: "Relatively simple, easy, inexpensive... 1000s of studies... Consistent associations between air pollution (PM) and mortality."

• "Chronic" exposure studies including the Harvard Six Cities Study and the American Cancer Society (ACS) study.

• Key Findings from Studies:The Harvard Six Cities Study found higher mortality rates in more polluted cities even after adjusting for confounders like smoking.

• The American Cancer Society Study showed increased risks of mortality (particularly cardiopulmonary) associated with PM2.5 exposure.

• Living near major roads is associated with increased cardiopulmonary mortality. "Risk of cardiopulmonary mortality for living near a major road relative to not living near a major road: 1.95 (1.09-3.51)".

• Specific Health Outcomes:Air pollution is now considered the most important environmental carcinogen (more important than second-hand smoke). "The IARC Working Group unanimously classified outdoor air pollution and particulate matter from outdoor air pollution as carcinogenic to humans (IARC Group 1), based on sufficient evidence of carcinogenicity in humans and experimental animals and strong mechanistic evidence."

• "The overall evidence is consistent with a causal relationship between PM2.5 exposure and cardiovascular morbidity and mortality."

• Prenatal exposure to air pollution can have lasting effects. The UGAAR study in Ulaanbaatar showed that reductions in PM exposure during pregnancy were associated with benefits like increased birth weight and higher IQ scores in children.

E. Air Quality Management:

• Significant progress has been made in reducing air pollution in some areas.

• However, progress can be eroded by factors such as wildfire smoke. "…since at least 2016, wildfire smoke has influenced trends in average annual PM2.5 concentrations in nearly three-quarters of states in the contiguous USA, eroding about 25% of previous multi-decadal progress in reducing PM2.5 concentrations on average in those states, equivalent to 4 years of air quality progress, and more than 50% in many western states.”

• Removing pollution has demonstrable benefits, e.g., "10 ug/m3 reduction in PM2.5 associated w/ average 0.6 yr increase in life expectancy."

• Air quality management is cost-effective, with benefit:cost ratios estimated at 4:1 to 30:1.

F. Household Air Pollution:

• Definition: Air pollution caused by the indoor burning of unprocessed solid fuels (charcoal, wood, crop residues, dung, coal).

• Global Prevalence: "…47% of the world’s population — almost 3.6 billion people — are still exposed to pollution from household use of solid fuels for cooking."

• Health Impacts: Affects cardiovascular, respiratory, maternal/neonatal health, and can cause cataracts.

G. Indoor Air Pollution (Wealthy Countries):

• Carbon Monoxide (CO): Colorless, odorless gas produced by combustion. Can cause headaches, dizziness, nausea, coma, and death.

• Radon: Colorless, odorless, radioactive gas from uranium in soil. "16% of lung cancer deaths among Canadians attributable to indoor radon...Responsible for > 3,000 lung cancer deaths per year." Smoking dramatically increases the risk.

II. Pesticides

A. Definition & Purpose:

• Pesticides are "Any substance or mixture of substances used for preventing, destroying, repelling, or mitigating any pest."

• Pesticides are designed to kill living things.

• Pesticides are hazardous and intentionally added to our environment

B. Categorization:

• By Target: Insecticides, herbicides, rodenticides.

• By Chemical Group: Organochlorines, organophosphates, neonicotinoids.

C. Why Use Pesticides?

• Pesticides are used to control pests that can damage crops, spread diseases, and contaminate food.

• Vector control is a major reason for pesticide use, including controlling mosquitoes (malaria, dengue), cockroaches (asthma), and rodents (food contamination).

D. Types of Pesticides:

• Herbicides: Kill weeds (e.g., Atrazine, 2,4-D, Glyphosate).

• Insecticides: Most important group for acute toxicity in humans; many are neurotoxic (e.g., Organochlorines, Organophosphates, Carbamates, Pyrethroids, Neonicotinoids).

E. Specific Pesticide Classes:

• Organochlorines (e.g., DDT): Persistent in the environment, bioaccumulate. Use restricted in wealthy countries but still used in some low- and middle-income countries for vector control. "The properties that made these chemicals such effective insecticides also brought about their demise because of their persistence, bioconcentration and biomagnification in food chains, and the acquisition of biologically active body burdens at higher trophic levels.”

• DDT and Rachel Carson: DDT was first widely used in WW2 to combat typhus and malaria. However, DDT usage came with environmental and ecological concerns. Rachel Carson's "Silent Spring" raised awareness of the dangers of DDT leading to restrictions. However, she remains a polarizing figure, with some criticizing the DDT ban for contributing to malaria deaths.

• Organophosphates (OPs): Largely replaced organochlorines. Responsible for most pesticide poisonings and deaths. Neurotoxic, inhibiting acetylcholinesterase.

• Neonicotinoids ("Neonics"): Relatively new class, systemic insecticides. Fastest growing group of insecticides.

F. Exposure Routes:

• Dietary ingestion (residues on food).

• Inhalation (occupational exposures, "spray drift").

• Dermal (occupational exposures, "spray drift").

G. Residues on Food:

• Health Canada sets Maximum Residue Limits (MRLs) for pesticides on food.

• Organic diets are associated with lower concentrations of pesticide residues in the body. "An organic diet was associated with significant reductions in urinary excretion of several pesticide metabolites and parent compounds. This study adds to a growing body of literature indicating that an organic diet may reduce exposure to a range of pesticides in children and adults.”

H. Acute Effects:

• Most often associated with organophosphates.

• Global annual estimates: 3-5 million unintentional poisonings, ~20,000 deaths, and 2 million intentional poisonings, ~150,000 pesticide suicide deaths annually.

I. Pesticides and Cancer:

• Some pesticides are classified as probable or possible carcinogens by IARC (International Agency for Research on Cancer). Examples: DDT, Diazinon, Malathion, Glyphosate, 2,4-D.

J. Integrated Pest Management (IPM):

• "A comprehensive approach to pest control that uses combined means to reduce the status of pests to tolerable levels while maintaining a quality environment."

• Includes physical, mechanical, biological, and chemical control methods.

K. Origins of Pesticides:

• The lecture gives an overview of the history of pesticides including early approaches, the use of Lead Arsenate and the usage of DDT.

L. Impact of Pesticides:

• The lecture gives examples of the negative impacts of pesticide exposure including an increased risk of preterm birth, reduced childhood survival, feminization of African clawed frogs, and the increase in the development of ADHD in children.

M. Public Opinion:

• There is a growing distrust in pesticides.

• There is a growing demand for organic food.

N. Conclusion:

• Pesticides have both benefits and risks.

• Organic food popularity is growing, although scientists are more skeptical of its claimed benefits.

• Further research, including RCTs of organic diets, is needed to quantify the benefits of organic food

Here's a comprehensive response to your query, drawing from the provided sources:

• Why are exposure assessments conducted? Exposure assessments aim to determine who is exposed to what, in what amounts, when, where, and how frequently.

• How is exposure information used? Exposure information is used in epidemiology, risk assessment/impact assessment, surveillance, evaluation of exposure trends, identification of sources/determinants of exposure, and comparison with regulations/guidelines.

• What are the three main routes of exposure? The three main routes of exposure are dermal, inhalation, and ingestion. Also, mother to fetus.

• What is an exposure pathway? An exposure pathway is the physical course a pollutant takes from its source to a subject. It includes pollutant emissions and movement.

• What is an exposure biomarker? An exposure biomarker measures a pollutant or its metabolite in a biological material such as exhaled breath, urine, blood, teeth, or hair. It estimates dose and incorporates multiple routes of exposure.

• What is the exposure control hierarchy? The exposure control hierarchy prioritizes interventions to reduce exposure, starting with the most effective. In non-occupational settings, interventions can occur at the source, along the exposure pathway, or at the household or individual level.

• Why are exposure controls at the source generally more preferable than controls at the level of the individual? Controlling exposure at the source reduces the hazard for everyone, preventing exposure before it occurs. The best way to reduce exposure to a hazard is to produce less of that hazard.

• Why are randomized controlled trials relatively uncommon in environmental epidemiology? Random assignment to different environmental exposures is often impractical or unethical. Environmental epidemiology consists nearly exclusively of non-experimental epidemiology.

• Why is it important to assess exposure carefully? What "price" do we pay if exposure is assessed poorly?Careful exposure assessment is important to accurately determine the relationship between exposure and health outcomes. Poor exposure assessment can lead to exposure misclassification and wrong effect estimates.

• What information does a dose-response (or exposure-response) curve provide? A dose-response curve provides information on the relationship between the dose of a substance and its effect.

• How do dose-response (or exposure-response) curves for essential nutrients and non-nutritive toxicants differ? Essential nutrients have a U-shaped dose-response curve, indicating that they can be beneficial at lower doses but toxic at higher doses. Non-nutritive toxicants generally have a curve where the effect increases with dose.

• What are the four major components of a risk assessment? The four major components of a risk assessment are hazard identification, dose-response assessment, exposure assessment, and risk characterization.

• How does traditional risk assessment differ between carcinogens and non-carcinogens? Traditional risk assessment for non-carcinogens uses a threshold-based approach, while for carcinogens, it uses a linear no-threshold (LNT) assumption. However, this has changed in recent years to consider the carcinogenic mode of action.

• What are the key air pollutants affecting public health? Key air pollutants affecting public health include particulate matter, ozone, sulfur dioxide, nitrogen oxides, and carbon monoxide.

• What are the major sources of these pollutants? Major sources of these pollutants include industrial processes, vehicle emissions, and burning of fossil fuels.

• What is PM2.5? PM2.5 refers to particulate matter with a diameter of 2.5 micrometers or less.

• For particulate matter air pollution, why is particle size important? Particle size affects where the particles can penetrate in the respiratory system and their potential health effects.

• What is the "energy ladder"? The "energy ladder" refers to the progression of fuel use from unprocessed solid fuels to cleaner energy sources as economic development increases.

• What is the main source of radon, and why is radon a problem primarily indoors? The main source of radon is uranium in the soil. Radon is primarily an indoor problem because it is a radioactive gas that can accumulate in enclosed spaces with limited ventilation.

• Why do we use pesticides? What benefits do they provide? Pesticides are used to prevent, destroy, repel, or mitigate pests. They help control vectors of disease and protect crops.

• Why were organochlorine insecticides largely phased out in favor of organophosphate insecticides?Organochlorine insecticides were phased out due to their persistence in the environment and bioaccumulation.

• What were some of Rachel Carson's concerns with the widespread use of chemicals, including persistent pesticides? Why does Rachel Carson remain a polarizing figure decades after the publication of Silent Spring? Rachel Carson raised concerns about the ecological and human health impacts of widespread pesticide use. Carson remains a polarizing figure due to debates over the restrictions on DDT and the impact on malaria control.

• How are different populations exposed to pesticides? Populations are exposed to pesticides through dietary ingestion, inhalation, and dermal contact.

• What chemical class of pesticides accounts for the majority of poisonings? Organophosphate pesticides account for the majority of poisonings.

• What is glyphosate? Why has it been in the news over the past few years? Glyphosate, also known as Roundup, is a commonly used herbicide. It has been in the news due to concerns about its potential carcinogenicity.

• What is "regrettable substitution"? When you replace a hazardous chemical with another one and it has an equally bad or worse outcome.

Here's a summary of environmental exposure assessments, routes of exposure, exposure control hierarchy, issues related to exposure misclassification, epidemiologic study designs, exposure prevalence, shifting the curve, and the prevention paradox, based on the provided sources:

1. Reasons for Environmental Exposure Assessments

   • To determine who is exposed to what, in what amounts, when, where, and how frequently.

   • To use the exposure information in:

     • Epidemiology.

     • Risk assessment/impact assessment.

     • Surveillance and evaluation of exposure trends.

     • Identification of sources/determinants of exposure.

     • Comparison with regulations/guidelines.

     • Health Impact Assessment.

2. Routes of Exposure for Environmental Hazards

   • The three main routes of exposure are:

     • Dermal.

     • Inhalation.

     • Ingestion.

   • Also, mother to fetus.

3. Exposure Control Hierarchy

   • The exposure control hierarchy prioritizes interventions to reduce exposure.

   • In non-occupational settings, interventions can occur:

     • At the source.

     • Along the exposure pathway.

     • At the household or individual level.

   • It is generally preferable to control exposures at the source. The best way to reduce exposure to a hazard is to produce less of that hazard.

4. Problems Caused by Exposure Misclassification

   • Careful exposure assessment is important to accurately determine the relationship between exposure and health outcomes.

   • Poor exposure assessment can lead to exposure misclassification and wrong effect estimates.

5. Role of Exposure Prevalence in Population-Level Impacts

   • In the context of environmental health, the ubiquity of exposures is relevant.

   • For some hazards and populations, 100% of the population may be exposed.

6. Concepts of Shifting the Curve and the Prevention Paradox

   • Shifting the curve: Aims to reduce exposure of entire populations to environmental hazards. If exposure prevalence is high, we can "shift the curve".

   • Prevention paradox: A large number of people at a small risk may give rise to more cases of disease than the small number who are at a high risk.