Environmental Science ENVS 1401 402

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Environmental ScienceENVS 1401 402
404Instructor Don Thieme

• 3rd Lecture
• Risk Assessment

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Risk

• probability of incurring harm or loss
• harm from the environment could include
• injury
• disease
• death
• probability calculated as a fraction
• 0 (certain not to occur)
• 1 (certain to occur)

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Risk Assessment

• using statistical methods to quantify the risks
  involved in a particular action
• risks are compared and contrasted before deciding
  how to act
• risks are evaluated in order to identify the
  causes of a medical condition or an environmental
  problem

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Toxicology Model

• Dose the amount of a toxic substance that enters
  the body of an exposed individual
• Response the type and amount of damage caused by
  exposure to a particular dose of a toxic
  substance

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Toxicity

• Acute effects range from dizziness and nausea to
  death and occur immediately to within several
  days following a single exposure.
• Chronic damage to vital organs, such as the
  kidneys or liver, occurring after long-term,
  low-level exposure.

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Dose

• the amount of a substance that enters the body of
  an exposed organism
• usually expressed in milligrams per kilogram of
  body weight
• Lethal - dose which causes death.
• Sublethal - causes harm but not death.

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LD50

• the dose that is lethal to 50 of a population of
  test animals
• inversely related to the acute toxicity (negative
  correlation)
• the smaller the LD50, the more toxic
• the larger the LD50, the less toxic

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ED50

• effective dose - 50
• the dose that causes 50 of a population to
  exhibit a particular effect or response
• Dose-response curves are used to show the
  increase in frequency with dose within a test
  population

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• biological response increases as the dose is
  increased.
• threshold level exists below which there is no
  response.

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• Toxicant A has a lower effective dose-50 (ED50)
  than Toxicant B.
• Toxicant B is more toxic at lower doses than
  Toxicant A.

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Steps of Risk Assessment

• Hazard identification Does the substance cause
  an adverse health effect?
• Dose-response assessment What dose is necessary
  to cause the adverse effect?
• Exposure assessment How much, how often, and
  how long are people exposed?
• Risk characterization What is the probability
  of the adverse effect?

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Risk Management

• Use the results of a risk assessment to determine
  whether a particular risk should be reduced or
  eliminated.
• Consider the interaction between toxicants or
  hazardous substances
• additive
• synergistic
• antagonistic
• Develop and implement laws to regulate hazardous
  substances.

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Ecological Risk Assessment

• toxicant or hazardous substance is distributed
  among many organisms in a natural ecosystem
• environmental stressors - changes to the
  environment caused by people
• ecological effects range from good to bad, from
  acceptable to unacceptable
• ecological effects are incompletely understood

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Ecological Case Studies

• The Snake River ecosystem in southern Idaho
• hydroelectric dams cause stress by
• reducing river flow
• elevating water temperature
• pools support biota that contribute "nutrients"
  (N,P)
• Lake Washington (east of Seattle)
• sewage effluent increased between 1941 and 1954

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Snake River Ecosystem

• Snake River rises in the Grand Tetons and joins
  the Columbia River in eastern Washington state

• 25 dams interrupt the flow over its 1,056 mile
  length

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Snake River Dam Removal

• 4 large dams on the lower Snake River
• removal would improve the migration of salmon and
  other anadromous fish on both the Columbia and
  the Snake Rivers
• water quality would improve downstream, but...
• farmers would lose much of their irrigation water
• barge transportation would be blocked by shoals

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Cost-Benefit Analysis

• compare estimated cost of each regulation with
  its potential benefits to determine whether
  society is willing to adopt it.
• Problems
• estimates of the cost are often higher than the
  actual cost
• health and environmental benefits of regulations
  are hard to estimate
• small risk assessment errors may result in large
  errors in cost-benefit analyses

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• Lake
• Washington
• (east of
• Seattle)
• 86 km2
• freshwater
• 10 sewage treatment plants operating between
  1941 and 1954

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Eutrophication

• proliferation of organisms at the lowest level of
  the food pyramid
• growth of filamentous cyanobacteria (algae) in
  Lake Washington studied by W. T. Edmondson and
  his students
• algal blooms are caused by overabundance or
  enrichment of the lake waters in particular
  "nutrients" needed by the algae, primarily -
• nitrogen
• phosphorous

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Algal "bloom" of Oscillatoria rubescens
Photomicrograph of Oscillatoria rubescens
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Lake Washington regional plan

• passed on September 9, 1958 as a result of
  popular dissemination of scientific results by
  Edmondon and his students
• 2 per month in additional taxes paid by each
  household for trunk sewer ringing the lake
• treated sewage is now discharged into Puget Sound
• eutrophication increased between groundbreaking
  for the sewer (1961) and the final diversion of
  effluent (1968)

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The condition of Lake Washington began to improve
after 1964, by which point most of the sewage
effluent had been diverted into Puget Sound.
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Few cyanobacteria were present in the waters of
Lake Washington by 1970, as measured by the depth
at which a "Seochi" disk was visible.
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Addressing Environmental Problems

• initial assessment will typically require a
  formal model of the problem's causes (oversupply
  of nutrients).
• several remediation options should be considered
  and presented to the public.
• regulation and action should be monitored to
  corroborate the model.