Chapter 1:  Introduction
Dealing with exposures
1. determine risks we are exposed to
2. understand how to manage those risks
Key environmental chemicals of greatest concern
1. anthropogenic organic compounds
2. unsuspecting environmental contaminants
anthropogenic organic compounds
1. pesticides
2. solvents
3. fuel products
4. by-products of various industrial products
unsuspecting environmental contaminants
1. reproductive hormones
2. birth control pills, steroids, antibiotics, metabolites
Arsenic
–naturally occurring (released into water bodies)
–Uses: insecticides, alloying agents, wood preservatives
–Health effects: GI effects, cardiovascular disease, diabetes, reproductive effects, carcinogenic
Asbestos
–known human carcinogen
–Uses: cigarette filters, wine filters, hair dryers, brake linings, cement pipes, floor tiles
–Health effects: all related to inhalation of microscopic fibers, asbestosis, mesothelioma
Lead
–Uses: water systems, gasoline, automobile batteries, paints
–Health effects: nausea and irritability (at low levels), brain damage (at high levels)
–Major routes of exposure: inhalation and ingestion
Mercury
–Nervous system toxin
–Uses: thermometers, manometers, medicines, fungicides, combustion of fossil fuels, waste incineration, industrial processes
–present in both organic and inorganic forms
–the form of mercury and the manner of human exposure determine the nature of health effects
Organochlorine compounds
–chlorinated hydrocarbons (PCBs, DDT)
–Uses: electric transformers, pesticides, insecticides
–lipophilic and persistent
–endocrine disruptors, carcinogens, reproductive and developmental disorders
Degree of hazards posed by the contacted substance will generally be dependent upon
–physical form and chemical composition
–quantities contacted
–reactivity
–toxicity effects
–local conditions and environmental settings (temperature, humidity, light)
Chemical mixtures
–have biological effects that are different in nature and degree when compared to those of individual substances acting alone
–additive (sum of individual effects)
–synergistic (the fact is greater than the sum of individual effects)
–antagonistic (active substance decreases the effect of another active substance)
–potentiation (inactive or neutral substance enhances the action of an active substance)
classification of chemical toxicity
–acute vs. chronic
–local vs. symptomatic
–immediate vs. delayed
acute toxicity
involves the sudden onset of symptoms that lasts for a short period of time
chronic toxicity
results in symptoms that are of long continuous duration
local toxicity
occurs when the symptoms resulting from exposure to a toxicant are restricted or limited to the site of initial exposure
systematic toxicity
occurs when the adverse effects occur at sites far removed from the initial site of exposure
immediate toxicity
results when symptoms occur rapidly following the exposure of an organism to a toxicant
–delayed toxicity generally results long after exposure and therefore sometimes adds to the difficulty in establishing a cause-and-effect relationship
time depenent toxicant behavior
time dependent behavior of the toxicant is related to its absorption, distribution, storage, biotransformation, and elimination
–toxicokinetics and toxicokinetics are important areas of study in this respect
Factors influencing chemical toxicity to humans
–nature of toxic chemical (physical and chemical properties, mechanism of action)
–exposure characteristics (dose, route of exposure)
–individual susceptibility (age, gender)
–hazard controls (safe work practices, source reduction)
–medical intervention (screening, treatment)
distribution and storage of toxicants in the human body
exposure –> absorption –> distribution –> storage
Factors affecting the distribution of toxicants to tissues in the human body
–physical/chemical properties/characteristics of the toxicant
–concentration gradient (blood/tissue)
–volume of blood flowing through a specific tissue or organ
–affinity of the toxicants for specific tissues
–structural barriers to slow down the entrance of the toxicant
Scope of chemical hazard problems
potency + exposure = toxicity
“The dose makes the poison”
Ex: Metals
–essential for many cellular functions and evolutionary development
–concentrations that are too high or too low can cause problems
–distinctions between therapeutic and toxic properties (i.e. concentrations)
Need for public health risk assessment
–some risks are tolerable
–we need a tool to systematically manage risks and develop policy
–clean-up levels
–acceptable risk/non-acceptable risks
General objectives of risk management programs
1. Does a hazard exist and can humans contact it?
2. Estimate the potential threat to public health
3. Is immediate response needed?
4. Determine remedies and/or corrective action
5. Informational needs of community at risk (health, safety, reduced exposure, etc.)
Legislative Issues
–Differences in policy (regional, national, global)
–Many times risk assessment is carried out as part of a legislative process (Potential problems with this: motives, extent of risk reduction, parties affected)
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