Risk Assessment and Decision Analysis

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Risk Assessment and Decision Analysis

Gestión Ambiental Tema 11
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Risk Evaluation

• Risk Probability of a specific undesired
  consequence.
• Each activity produces a risk. Total risk in life
  is 1.
• Risk evaluation offers a starting point in the
  balance between acceptable risk increase vs cost
  of controlling the risk.
• When several kinds or magnitudes of injury or
  loss may occur, risk can be defined as
• Risk (Probability of an undesired consequence)
  x (size of the loss)

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Risk Assessment Methodology

• Hazard Assessment
• Dose-Response Assessment
• Exposure Assessment
• Risk Characterization

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Acute Toxicity

• Short term exposure from a single incident or
  event.
• Effect is described by means of the compound dose
  (mg/kg) needed to kill an organism. To take into
  account the different condition of the members of
  the community is used the LD50
• LD50 Dose that produce the death of the 50
  of the population

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Acute Toxicity
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Chronic toxicity

• Long-term exposure to a toxic compound
• Risk versus dose (mg/kg d)
• For non-carcinogenic chemicals the existence of a
  dosage threshold is assumed, below which there is
  no increase in adverse effects above natural
  background rates.
• A security factor for human is introduced.

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Exposure factors
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Dose-response assessment relationship for a
non-carcinogenic chemicals

• There is a threshold value
• Lower dose with observable adverse effect level
  (LOAELs)
• Non observable adverse effect level (NOAELs)
• Reference Dose (RfD) Acceptable daily intake

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Dose-response assessment relationship for a
non-carcinogenic chemicals

• RfD NOAEL/ Security factor (10)
• Dose (mg/kg d) is compared versus RfD
• Hazard quotient (HQ) Dose/RfD
• Acceptable risk for a non carcinogen HQ lt 1
• Where several chemicals are present at the same
  time, the HZ are summed to yield a Hazard index
  (HI)
• Hazard Index (HI) S (HQ)i

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Reference Dose
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Reference Dose
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Sources of uncertainty in risk assessment
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Potency factor (Carcinogens)

• Chronic Daily Intake (CDI) is the average daily
  dose of a chemical over the lifetime of an
  individual
• CDI (mg/kg d) Daily Dose (mg/d)/Weight (kg)
• Potency Factor based on the dose-response curve
• PF Incremental cancer risk for a chronic daily
  intake of 1 mg/kg d
• Incremental Risk, based on a lineal response
• Incremental lifetime cancer risk CDI x PF

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Potency factor (Carcinogens)
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Acceptable risk ?

• EPA considers acceptable a risk of 10-6
• Values higher than 10-3 are considered important
  and need an attention
• Risk between 10-4 and 10-6 can be accepted,
  although require a specific study

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Bioconcentration

• Accumulation of pollutants

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Risk Management

• Risk management Process to define the acceptable
  risk in a specific situation and decide on the
  best course of action to reduce, control or
  eliminate the risk
• There are four options to manage a risk
• Reduce or eliminate the source (removal of
  contaminated soil, reduction of gas emissions)
• Modify exposure (to avoid spread of by means of
  barriers)
• Reduce or eliminate human exposure (prohibit
  access, evacuate the population)
• Treat or compensate the effects (Less favorable
  option)

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Exposure Mechanisms
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Contaminated Sites

• There is a great experience in environmental risk
  assessment related with contaminated sites.
• It is necessary to reach an equilibrium between
  environment and health protection and the need of
  economical and technological resources.
• Risk assessment can lead to that the solution can
  be no treat the site (when the risk is acceptable)

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• Steps in the risk assessment and risk management
  for a contaminated site

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Decision Analysis

• A la hora de tomar decisiones sobre una zona
  contaminada puede existir un número importante de
  opciones diferentes (desde no hacer nada a
  diferentes respuestas tecnológicas o
  institucionales)
• A veces la identificación de los factores que
  afectan una decisión puede ser complicada
• El análisis de decisiones es una herramienta útil
  para la toma de decisiones y para estructurar e
  identificar información relevante para decidir

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Influence Diagrams

• Is a way of visualizing the important connections
  among different elements of a problem.
• In its simple form the diagram consist of a
  series of ovals representing the key variables
  that influence a decision
• Influence of factors
• over final grade in
• Environmental Management

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Interaction among the factors
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Simbols
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Global Warming (example)
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Decision trees

• Herramienta gráfica útil para el análisis de
  decisiones.
• Muestra las ramificaciones o decisiones
  alternativas e incertidumbres (Forma de árbol)
• Se construye a partir de 2 tipos de nodos
• Decisión (?). Debe elegirse una rama
• Posibilidad (o). Existen diferentes posibilidades
  que cubren todo el espectro

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Example

• Your company wants to buy and develop a site to
  build a new assembly plant for its production.
  Two available properties would serve equally
  well. The main difference is cost
• Site A costing 1,000,000 . Site A is known to be
  uncontaminated
• Site B costing 600,000 . Site B may require
  cleanup
• A consulting firm has done a preliminary
  assessment and developed a mathematical model to
  predict the likelihood of environmental risk and
  potential cleanup cost, with the following
  results
• 80 chance the property is clean
• 15 chance the land is partially contaminated
  (Cleanup effort costing 500,000 )
• 5 chance the land is highly contaminated
  (Cleanup effort costing 2,500,000 )
• Draw a decision tree for this problem based on
  the information given

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Example. Part 2

• Suppose that the consulting firm offers you the
  option of a more detailed site investigation with
  a cost of 100,000 . This procedure will yield
• 85 chance of knowing conclusively whether the
  site is safe or in need of either partial or
  major cleanup
• 15 chancethat the deeper investigation will be
  no more conclusively than the preliminary study
• Draw a decision tree for this problem based on
  the information given

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