Chapter 19.1 Toxicology and Chemical Hazards

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Chapter 19.1Toxicology and Chemical Hazards

• toxicology
• study of harmful effects of chemicals on human
  and environmental health
• acute effectsmight occur upon ingestion or
  contact with skin
• chronic exposureoccurs over years
• carcinogenic potential
• data on toxic chemicals
• http//ntp.niehs.nih.gov/ (National Toxicology
  Program)
• http//ntp.niehs.nih.gov/ntp/roc/toc11.html
  (Report on Carcinogens)
• http//cfpub.epa.gov/ncea/iris/index.cfm (EPA
  Integrated Risk Information System)
• http//www.scorecard.org/ (Environmental Defense)

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dose response and threshold

• in investigating a suspect chemical, a
  toxicologist would conduct tests on animals,
  investigate human involvement with the chemical,
  and present information linking the dose with the
  response
• dose level of exposure multiplied by the length
  of time over which exposure occurs
• response acute or chronic effect, or the
  development of tumors
• LDL0 lowest dose at which death occurred in
  animal testing

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threshold level

• in dose-response relationship, there is usually a
  threshold
• organisms are able to deal with certain levels of
  many substances without suffering ill effects
• threshold level level below which no ill effects
  are observed
• above this level, effect of a substance depends
  on concentration and duration of exposure
• for carcinogens, EPA generally takes a zero-dose,
  zero-response approach
• however, the lower the dose, the more likely it
  is that the response cannot be distinguished from
  the background level of cancers in a population

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HAZMATs

• HAZMAT hazardous material
• categorized based on the following hazardous
  properties
• ignitabilitycatch fire readily
• corrosivitycorrode storage tanks and equipment
• reactivitychemically unstable and may explode or
  create toxic fumes when mixed with water
• toxicityinjurious to health when they are
  ingested or inhaled

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sources of chemicals entering the environment

• materials making up almost everything we use,
  from shampoo to toothpaste to TVs, are products
  of chemical technology
• our use constitutes only one step in the total
  product life cycle
• life cycle begins with obtaining raw materials
  and ends in the final disposal of the product
• chemical wastes and by-products are inevitable in
  any production process, as is the potential for
  accidents and spills
• when these steps are multiplied by the hundreds
  of thousands of products used by billions of
  people, the magnitude of hazardous materials
  becomes clear

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toxics release inventory

• introduction of chemicals into the environment
  may occur in every sector, from major industrial
  plants to small shops and individual homes
• some idea of quantities of chemicals released can
  be obtained from Toxics Release Inventory (TRI)
• since TRI has been in effect, total releases have
  decreased by 68
• Emergency Planning and Community Right-to-Know
  Act (EPCRA) of 1986 requires industries to report
  releases of toxic chemicals to the environment
• Pollution Prevention Act of 1990 mandates
  collection of data on toxic chemicals that are
  treated on-site, recycled, or combusted for
  energy
• TRI does not cover small businesses such as dry
  cleaners and gas stations (facilities do not need
  to report yearly releases under 500 lb), or
  household hazardous waste

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threat from toxic chemicals

• fortunately, a large portion of chemicals
  introduced into the environment are gradually
  broken down and assimilated by natural processes
• once these chemicals are diluted, they pose no
  long-term human or environmental risk, although
  they may be toxic in acute doses
• two major classes of chemicals do not readily
  degrade in the environment
• heavy metals
• synthetic organics

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heavy metals

• most dangerous include lead, mercury, arsenic,
  zinc, cadmium, tin, chromium, and copper
• common in metalworking or metal-plating shops,
  electronics, pesticides, and some medicines
• once common in paint pigments, glazes, inks, and
  dyes due to brilliant colors
• extremely toxic because, as ions in certain
  compounds, they are soluble in water and may be
  readily absorbed by the body (usually inhibit the
  function of enzymes)

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organic compounds

• chemical basis for all plastics, synthetic
  fibers, pesticides, wood preservatives, and
  hundreds of other products
• because of their chemical structure, many are
  resistant to biodegradation (which is part of
  what makes them useful)
• compounds are toxic because they are often
  readily absorbed into the body, where they
  interact with specific enzymes
• high dose ? acute poisoning and death
• low doses over long periods ? effects can be
  mutagenic, carcinogenic, or teratogenic (birth
  defect-causing)

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dirty dozen

• particularly troublesome class of synthetic
  organics is halogenated hydrocarbons
• organic compounds in which one or more hydrogen
  atoms have been replaced by Cl, Br, F, or I
• all are toxic to varying extents and most are
  known animal carcinogens
• many are also suspected endocrine disruptors at
  very low levels
• chlorinated hydrocarbons are most common
• used in plastics (polyvinyl chloride), pesticides
  (DDT), solvents, electrical insulation (PCBs),
  and many other products

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PERC

• tetrachloroethylene, also called
  perchloroetheylene (PERC)
• major substance in dry cleaning fluid effective
  solvent found in many industrial cleaners
• evaporates readily when exposed to air, but can
  enter groundwater easily because it does not bind
  to soil particles
• enters body most readily when breathed in with
  contaminated air
• breathing PERC for short periods can bring on
  dizziness, fatigue, headaches, and
  unconsciousness
• over long periods, can cause liver and kidney
  damage
• Report on Carcinogens reasonably anticipated to
  be a carcinogen
• studies have shown higher risk of cancer along
  with neurological impairment in dry cleaner
  employees
• EPA issued ruling to phase out PERC by 2020

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Minamata

• tragic episode in early 1970s revealed potential
  for biomagnification of mercury and other heavy
  metals
• in the mid-1950s, cats in the small fishing
  village of Minamata, Japan began to show spastic
  movements, followed by partial paralysis, coma,
  and death
• at first, most thought the syndrome was specific
  to felines
• however, same symptoms began to appear in humans
• chemical company near the village was discharging
  wastes containing mercury into a river that
  flowed into a bay where villagers fished
• mercury settled with detritus, then absorbed and
  bioaccumulated by bacteria, then biomagnifed up
  the food chain
• in the end, 50 died and 150 suffered bone and
  nerve damage