Environmental Health



Environmental Health

  • General Topics
  • Exposure
  • Epidemiology topics
  • Toxicology
  • Risk assessment
  • Specific examples

General Topics

Definition

  • Study of factors in environment that affect human health
  • physical, biological, social, psychosocial factors
  • theory and practice of assessing, correcting, controlling, and preventing factors that adversely affect health
  • chemical, biological, and physical hazards as they interact with genetic traits / social or behavior hazards

Vulnerability vs. Susceptibility

  • Vulnerability = external factors
  • Differences in how a person is exposed
  • ex.) a factory site makes a person vulnerable.  His poor socioeconomic conditions makes him vulnerable.
  • Susceptibility = internal factors
  • How a person / group responds to an exposure
  • ex.) a person’s genetics / malnutrition makes him susceptible to the disease.
  • innate susceptibility = genetic (usually)
  • acquired susceptibility = disease, age, socioeconomic status, etc.

Millennium development goals

  • eradicate extreme poverty and hunger
    • by 2015 half the proportion of people without sustainable access to safe drinking water / basic sanitation
    • by 2020 significantly improved lives of 100 million slum dwellers
  • achieve universal primary education
  • promote gender equality and enpower women
  • reduce child mortality
  • improve maternal health
  • combat HIV/AIDS, malaria, and other diseases
  • ensure environmental sustainability
    • prevent loss of biodiversity
  • global partnership for development

Intervention model

US government / policies

  • EPA = Environmental Protection Agency
    • TSCA = Toxic Substance Control Act
    • “Innocent before proven guilty” – can use new chemical until studies shown that chemical is dangerous
    • In Europe, is other way around (REACH)
  • online sites: ATSDR, IRIS
    • ATSDR is more user-friendly
    • IRIS is for specialists

Policy-driving

  • Exposure-driven
    • Don’t know health effect, but see high exposure
  • Outcome-driven
    • Community can see the effects
    • ex.) Woburn – children at school getting sick.  School built on top of toxic waste dump
  • Clinical intervention vs. public health intervention vs. environmental health intervention
    • Clinical => cut off link between disease and death
    • PH => cut off link between public/environment and disease
    • EH => cut off link between public and environment

Exposure

General

  • exposure = toxicant contact with human envelope
  • human envelope = oundary that separates interior of human body from exterior
  • Apportionment = how exposure is proportioned (what is greatest source?)
  • three major pathways: inhalation, ingestion, dermal
  • Units
    • air – ppm (parts per million = X molecules of gas in 1 million molecules of air = microgram / liter)
    • solids (soil) – ppb (parts per billion = microgram / kg)
    • liquids – ppb (microgram / liter)
  • transport = movement of contaminants with/between environmental media
  • fate = chemical / physical transformations and final destination of contaminants in environment

Exposure disease model

  • Each of these components must be present
    • if arsenic gets into toilet water, it isn’t an exposure because unlikely to come into contact / ingest toilet water
  • External
    • Source/Emissions
      • where exposure coming from
    • Media
      • way exposure is transmitted (air, water, etc.)
      • source => media – measure in: quantity / concentration / intensity
    • Micro-environments
      • local environment, near person
      • media => micro – measure in: air, water, soil, food
    • Exposure
      • inhalation, ingestion, dermal
      • not considered an “exposure” if person not exposed
      • micro => exposure – measure in: air (vapor, particulate), skin (hand wipes, dermal patches), dietary (food measurements, questionnaires)
  • Internal
    • (all of internal parts rely on victim’s susceptibility)
    • Absorbed dose
      • portion of exposure is absorbed into person
    • Biologically effective dose
      • quantity of toxicant available to interact with vulnerable tissue
      • the dose that “overcame the threshold”
    • Altered structure / function
      • symptoms
      • measure internal part by biomarkers
        • indicator of event in biological system
        • urine, breath, blood, hair, saliva, nails
        • noninvasive
        • which ones to use can be found on ATSDR
    • Disease

Chemical properties

  • physical-chemical properties are important
    • determine how transported and where stored in body
    • ex.) Zinc and Cadmium are similar.  Body needs Zn, will absorb, but Cd has greater affinity to body.  Body will absorb Cd.
  • Terms
    • volatile = high vapor pressure (want to liquid => air)
    • solublility (want solid => liquid)
    • density (will sink/float in water?)
    • half-life
    • lipophilic – able to enter living tissue through cell membrane
      • liver takes lipophilic and makes it soluble (by making hydrophilic) so can be urinated out
      • bioconcentrate = accumulation of chemical in organs
      • bioaccumulate = buildup of chemical in individual
      • biomagnification = greater accumulation as go up in food chain
    • affinity for soil vs. water
      • pesticides – if like water, end up in groundwater; if like soil, stay in soil
    • partitioning
      • Kp = concentration in octanol (binding to carbon) / concentration in water
      • if < 10, hydrophilic/high water solubility / won’t concentrate in living tissue
      • if > 10^4, very hydrophobic
        • ex.) ethanol has very low K.  Benzopyrene has very high K.

Epidemiology

Prevalence

  • proportion of people with disease at given point in time
  • for chronic diseases – not know when develop

Incidence

  • number of new cases that develop in population over specified period of time
  • when state, must state time period
  • disease that suddenly develops – ex.) flu

Absolute/relative measure

  • change in disease frequency
  • absolute = difference (risk difference)
    • the additional risk of __ for those exposed was ___ more than those unexposed.
  • relative = ratio (risk ratio, odds ratio)
    • those exposed have ___ times the risk for __ compared to those unexposed

Odds ratio

  • Odds = number of cases / number not-cases
  • Odds ratio = odds exposed / odds unexposed
  • those exposed have ___ times the odds for __ compared to those unexposed

Standardized Rate Ratio

  • weigh the rates for population by an external population
  • ex.) Miami rates * US population, Alaska rates * US population; now can compare Miami and Alaska rates

SIR/SMR

  • SIR = standardized incidence ratio
    • cases observed / cases expected * 100
  • SMR = standardized mortality ratio (use mortality rather than incidence)
  • Cannot use to compare between populations
  • Calculate ‘expected’ by using another population’s rates.  ex.) if calculating Woburn’s cases, expected = population distribution in Woburn * rates of MA as whole
  • __% more cases observed in __ than is expected.  (Remember to subtract number by 100)

Sources of error

  • Random error – lower = more precise
    • always present
    • amount sample estimate off from “true parameter” of population
    • influence by study size
    • represent by p-value and confidence interval
      • CI = range that we are ___% confidenct contain the true value of the measure of interest in overall population
  • Systematic error – lower = more valid / more accurate
    • internal
      • selection bias (how choose controls / subjects)
      • confounding (another 3rd factor affects relationship between results and disease)
      • information bias (misclassification)
    • external = generalizability

  • if think of bullseye, precision = how closely clustered the shots are / validity = how close shots are to red center
  • always check if values are adjusted; if not, confounding may be present
    • ex.) breast cancer rates are high; but this isn’t surprising when population is mostly elderly women.  Would be surprising if talking about students.

Types of studies

  • experimental = exposure assigned by investigator (not common in EH)
  • observational = exposure not assigned
  • observational study design:
  • cohort study
    • prospective = take exposed and unexposed and look at who develop disease
    • retrospective = take disease and not disease and look at whether was exposed or not
    • look at two (or more) groups (entire populations) and compare disease incidence
    • unwieldy for rare diseases, expensive follow-up, long follow-up.
  • case-control study
    • mostly same as cohort study, but choose controls (choose who belongs in comparison population)
    • use all participants with disease
    • best for rare disease, long latency period disease, and expensive assessment methods
    • subject to bias, cannot compute incidence (because not all of population used)
  • cross-sectional study
    • single point in time – measure both exposure and disease
    • always look at prevalence, not incidence
    • cheaper, hypothesis generating, generalizability
    • not sure whether exposure come first or disease (temporality unclear)
  • ecological study
    • looking at study at group level
    • ecologic fallacy – relationships existing at aggregate level may not exist at individual level
  • disease cluster
    • elevated number of cases in limited area and time
    • difficult define people at risk
    • not enough cases for epi study, but good for hypothesis generating
    • SIR

EH-specific problems

  • exposure
    • ubiquitous, chronic, complex
  • assessment
    • expensive on large scale, burdensome / impractical
    • ex.) short half-life of measurable markers.  noisy / energy-consuming measurement method
  • effect
    • long latent periods or rare disease
    • modest relative risk
    • effect is nonspecific
  • design
    • unethical to expose individuals to hazards

Toxicology

Definition

  • toxicology = study of effect of toxic substances in organisms and fate/transport in body
  • toxicant = anything producing adverse biological effect
  • toxin = any toxicant produced by a living organism
  • toxicity = degree to which substance harm humans/animals
    • acute = harmful effect at short, 1-time exposure
    • sub-chronic = causes effect for more than 1 year but less than lifetime
    • chronic = causes long-period effect and is repeated / long-term exposure
  • toxicokinetics = how chemical moves through body
    • exposure => absorbed dose => biologically effective dose => symptoms
    • absorption = process by which toxicant enters organism
      • cell membrane is hydrophobic – only hydrophobic / lipophilic substances enter easily
    • distribution = how toxicant moves after entering organism / where stored
    • metabolism = process that changes substances to aid elimination
      • bioconversion = reduce (add proton) to make hydrophilic so can’t enter cell membrane
      • conjugation = attach parts (make bigger) and reduce (add proton) to keep from entering
      • try encourage body get rid of toxic
      • may bioactivate – biotransformed metabolite is more toxic than original
    • excretion
      • urinary, fecal, respiration, saliva, hair, nail, sweat
  • toxicodynamics = how body respond to chemical (focused on end result / disease)
    • biologically effective dose => symptoms => disease
    • what is critical target organ?  what is cause of toxicity / mechanism?
  • dose = amount of agent actually deposited in body
  • response = biological effect of agent
  • LD = lethal dose = concentration at which 50% animals die through oral consumption
    • “It is the dose that makes the poison.”

Studies

  • often animal studies / experimental
  • well-defined conditions, biological plausibility
  • but only test high doses, short exposure times, and on non-human animals
  • as opposed to epidemiology / observational
  • on humans, relevant levels of exposure, realistic scenarios
  • poor exposure assessment, multiple exposures at once, low power, and many confounders
  • toxicology gives biological plausibility
  • epidemiology gives epi evidence
  • best = have both

Dose-response

  • dose = amount of substance administered
  • dosage = amount per unit weight of exposed individual
  • exposure = # of doses * frequency of doses * total period of time
  • dose-response curve = S-shaped
    • steeper slope = stronger effect of toxicant
    • no slope = no toxic effect / below threshold
    • slope appears, but slow slope – body can still metabolize / deal with toxicant
    • steep slope – body’s capacity being overwhelmed
    • no slope – body’s capacity completely overwhelmed (any more chemical would not show difference in effect)
  • before curve starts = no observable adverse effect level = NOAEL = last dose at which see no AE
  • curve starts = when start seeing effect (toxin overpowers body’s functions)
    • threshold; if = 0, then no safe dose
  • after curve starts = lowest observable adverse effect level = LOAEL = lowest dose at which see toxicity
  • special curve: essential nutrient – see AE if too low since body needs it; but also see AE if too much
  • special curve: carcinogen – assume no threshold (because isn’t threshold-based; is chance-based)
    • no matter dose, chance of harmful effect happening
    • usually, severity of response = function of dose

  • When look at dose-response curve of animal, need to extrapolate
  • animals exposed at high dose.  humans usually exposed at lower dose
  • need make assumption how humans react to doses


Risk Assessment

Definition

  • Exposure assessment – quantification of human contact with chemical agent over time/space
  • risk assessment = characterization of potential AE resulting from exposure
  • risk management = actions taken to control environmental risks based on policy
  • risk communication = communicate to experts and those affected about risks
  • hazard = dangerous, but not exposed
  • exposure = dangerous and come in contact

Risk Assessment (different depending on if carcinogen or not)

  • Hazard identification – description of potential health effects
    • literature search
    • if cancer, look at weight-of-evidence classification
  • Dose-response assessment
    • literature search – at what does does AE occur?
    • if noncancer, reference dose
    • if cancer, cancer slope factor (risk per unit dose in mg/kg*day)
  • Exposure assessment
    • who may be exposed and for how long?  how much?
    • (frequency, duration, intensity)
  • Risk characterization
    • how does exposure assessment compare with what is acceptable based off dose-response?
    • if noncancer, hazard quotient
    • if cancer, incremental lifetime cancer risk

Hazard Identification

  • what does chemical do?  what are its effects?
  • what studies have been done on it already?  (animal, human, and quality of studies)
  • weight of evidence
    • classify if strong/weak human evidence, animal evidence, evidence for or against carcinogenicity

Dose-response assessment

  • find RfD on IRIS
  • what compare people’s exposure to?
  • is not looking at what current dose is
  • Reference dose (RfD) – estimateof daily exposure to human population that is likely to be without a risk of AE
    • units = mg/kg*day
    • given on IRIS and Toxnet – also gives uncertainty factor
    • calculated by NOAEL / uncertainty factor
  • Uncertainty roughly = product of all the factors
    • 10 for human variability
    • 10 for animals => human extrapolation
    • 10 for use of not-chronic data
    • 10 for using LOAEL, not NOAEl
    • etc.
    • such a large number chosen because is more conservative
    • often try to set to more sensitive populations (pregnant women and children)
  • cancer slope factor (CSF) = incremental risk (probability) per unit increase in dose
  • cancer risk = additional risk of cancer (on top of all other factors) due to agent (is not IR!)
    • dose * CSF = risk

Exposure Assessment

  • diagram realistic scenarios based on properties
  • how were people exposed?
  • how measure?  what biomarkers use?

Risk characterization

  • calculate ADD and compare to RfD
  • why should the audience care?
  • LADD = lifetime average daily dose
    • concentration * amount * frequency
  • ADI = average daily intake
    • LADD / human weight
  • HQ or HI = hazard quotient / index
    • ADI / RfD
    • unitless number
    • because of all the arbitrarily chosen uncertainty factors, just care if greater or less than 1; don’t care how much
      • >1 – harmful effects expected
      • =1 – contaminant alone not likely cause risk
      • <1 = harmful effects not expected
    • when interpreting, don’t say “risk”

Risk Communication

  • exercise
  • helps public respond to situation and informs
  • helps experts / policy makers provide info, obtain consent, and maintain trust
  • important:
    • try connect to audience – contextualize
    • who is audience?  language and concerns will be different
    • what are common misconceptions?
    • what do people know already?
    • what is important to them?
    • stay away from jargon
    • keep concise
    • give behaviorally realistic advice
    • give doable / performable advice
    • don’t give too many details
    • keep numbers simple (and if inverse or fraction, explain.  ex.) 1/mil > 1/bil)
    • avoid inciting panic
  • in general:
    • what is current policy?
    • what is new implemented policy (if applicable)?
    • AE list (and how rare)
    • symptoms
    • how may be exposed
    • how prevent exposure (precise steps)
    • when should be alert (ie, be careful is your home is near a factory, etc.)
    • RfD
    • name, department, and contact information, if have questions

Precautionary principle

  • make sure is safe before use
  • is what EU (European Union) uses

Specific Examples

Phthalates

  • added to children / baby products to make them soft

Arsenic

  • Built tubular wells in Southern Asia to funnel water supply and avoid diseases
  • easy to build, convenient, avoid waterborne diseases
  • people showing kerotosis – sign of arsenic
  • arsenic is natural occuring.  well concentrated the water and the arsenic
  • problematic because arsenic = tasteless and colorless, so it’s hard to convince people not to use the wells

Lead (Pb)

  • Stored in bones – biomarker; can also use blood (less invasive)
  • History
    • Adverse effects known hundreds of years ago
      • lead cosmetics
        • Venetian cerruse
  • Why still in use?
    • Economic reasons
    • science vs. policy
    • hard to change
      • Not just because of low socioeconomic conditions
      • low exposure also lead to health effects
      • people thought had degree of control over exposure
      • finally realized that exposure had lasting effect that can’t be changed by policy
    • lead does work – still used on bridges
      • durable, long-lasting, dry faster, reduce mold
      • in engines, prevent “knock”
  • Exposure
    • batteries, ceramics, paint, glass, jewelry
    • for children:
      • drinking water
      • ingesting paint chips / putting things in mouth
    • ex.) Nigerian gold mining
      • for every half-penny of gold, need crush 50kg of rock
      • for every penny of gold, baseball of lead
      • women bring work home – lead dust in air
      • increased child mortality rate
      • policies: improved crushing tools, wet grinding, sluicing, amalgamate, retort, sell tailings, reprocess tailings, manage waste, remediate old sites
        • aim for health benefits, sustainability, keep away from women and children, and profitability
        • how children get exposed?
        • addressing use of ore wastes as play materials for young children
        • contribution of lead-contaminated house bricks to blood Pb levels
        • child labor
        • alternate processing methods
  • Adverse effects
    • neurotoxicity
      • ADHD, reduction in IQ
      • doesn’t seem that big a decrease until look at overall population (shift in bell curve)
    • EPM limit set at 10, but don’t seem to be threshold for effects

Mercury (Hg)

  • method of exposure important.  chemical form important
  • elemental Hg: when inhaled, high absorption.  When ingested, very low absorption
  • bacteria convert elemental Hg => methylHg (among other forms)
  • organic Hg: when ingest, high absorption
    • bioaccumulate in animals, and then bioconcentrate
    • especially in larger fish
  • after absorbed, transforms into inorganic Hg which cannot be metabolized or pass through cell membrane

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