Project Scope Review
• What’s your product/process?
• What are your important limiting assumptions?
• What impact categories will you focus on?
LCA Process (review)
Define
Scope
Inventory
Analysis
Impact
Analysis
Feedback
Manufacture
Improvement
Analysis
RERP
Where RERP is the “Environmentally Responsible
Product Rating”
LCA Impact Assessment
Impact Analysis
• A very challenging step
• Relates system outputs to impacts on the
external world
• Based extensively on Risk Assessment
• The metric for “impact” is necessarily complex
because these impacts are neither co-linear nor
orthogonal
Impact Assessment:
Prioritizing Options
• An interesting Canadian study of paper vs.
polystyrene foam drinking cups
– Martin Hocking, Univ. of British Columbia: “Paper vs.
Styrene: A complex choice”. Science, 251 (1991): 504-505
and 252 (1991): 1361-1362.
• A later study says both are better than ceramic!
– Ministry of Housing, Physical Planning, and Environment.
Integrated Substance Chain Management, Pub. VROM
91387/b/4-92. ‘s-Gravenhage, the Netherlands, 1991.
Matrix Concept for Materials and
Process Audits
• In IE we often compare alternative designs
• This requires the comprehension of large amounts of
information
• An industrial ecology matrix template can help
• Four “Primary Matrices” are prepared:
– Manufacturing: Manufacturing activity itself
– Environmental: Traditional issues, but not single-media
focused
– Toxicity/Exposure: Health related issues
– Social/Political: Non-technical aspects of produce/process
• Matrix for each design shows Life Stages vs. Issues
Categories
Matrix Concept (continued)
• Special symbols are used to label each cell
• A summary table can be developed to compare
various options on each of the four
dimensions: manufacturing, environmental,
toxicity/exposure, and social/political
Auditing by Life Stage
• Using checklists
• For each life stage, one uses these checklists to
complete ellipses where
– Four-level scale for comparison to ideal product
(excellent, good, fair, poor)
– Texture indicates degree of confidence (black =
high confidence, shade = medium, blank = low)
• Then density of “blackness” indicates degree
of environmental quality (darker is worse)
Impact Analysis => Risk
Assessment
• In order to evaluate the impact of aspects of a
product or process lifecycle, we have to be
able to assess risk
Risk Assessment Methodology
• Typically decomposed into four steps:
–
–
–
–
Hazard Identification
Dose-Response Assessment
Exposure Assessment
Risk Characterization
Hazard Identification
• Determine the nature of the hazard:
– Exposure pathways of concern, e.g.
•
•
•
•
Ingestion
Inhalation
Dermal contact
Puncture
– Toxic endpoints, e.g.
• Lethal vs. non-lethal
• Chronic vs. Acute
Acute Toxicity
• Acute toxins result in observed endpoints after
few exposures, in short timeframe
• For lethal endpoints, toxicity is a measure of
the amount of exposure required to produce
death
– Example endpoints: chemical poisoning, radiation
sickness
Chronic Toxicity
• Chronic toxins produce observed endpoints
only after repeated exposures and/or
considerable elapsed time
• Like acute toxicity, may be lethal or non-lethal
• Toxicity may be cumulative or not (e.g.
mercury vs. carbon monoxide)
– Example endpoints: cancer, birth defects
Measuring Toxicity
• Need measures of dose which causes toxic
endpoint
• Measurements for ingested toxins ordinarily
normalized for body weight (e.g. mg/kg)
• Must generalize from populations of
experimental subjects
• For lethal endpoints can use LD50
But LD50 is limited!
e.g.: here A is always more toxic than B
but A can be less toxic than C, even with
lower LD50
Toxicology vs. Epidemiology
• Toxicology answers the wrong question well
• Epidemiology answers the right question
poorly
Toxicology
• Controlled laboratory experimental conditions
but
• Surrogate subjects (usually animals)
• Exaggerated doses
Extrapolating High to Low Dose
• Experimental studies produce minimum
detectable responses on order of a percent
• Desire information on order of 10-6
• It’s virtually impossible to perform lab studies
with N large enough (e.g. megarat)
•  We need a mathematical model to perform
extrapolation
Designing Toxicology Experiments
• Selection of subject species
• Control design
• Multiple dose levels (at high levels to produce
observable effect in relatively small number of
subjects)
Epidemiology
• Human subjects
• Realistic doses
but
• Uncontrolled experimental conditions
Dose-Response Assessment
• Relating Dose to (adverse) response
• “Response” typically described as a
probability (unitless fraction or percent)
• Dose-Response Curve
– Dose on the abscissa
– Response on the ordinate
– Intercept with abscissa is “threshold dose”
Potency Factors
(a.k.a. Slope Factors)
• For chronic chemical toxicity (e.g. cancer),
Potency Factor  slope of the low dose DR curve
Incrementa l Lifetime Cancer Risk
PF 
Chronic Daily Intake
where Chronic Daily Intake (CDI) is
measured in units of mg/kg/day
Potency Factors (cont’d)
• Re-arranging,
Incremental Lifetime Cancer Risk = CDI  PF
• Potency Factors are available from EPA’s
Integrated Risk Information System (IRIS):
http://www.epa.gov/iris
Exposure Assessment
• Risk has two components:
– Toxicity of the substance
– Exposure of humans to substance
• Exposure often forgotten (see, for example, the
Scientific American article comparing indoor
pollution to outdoor pollution)
Exposure Pathways
• The route by which a toxin or hazard reaches
the human influences its impact
• Internal factors would include the human
contact route (e.g. inhalation, ingestion, &c)
• External factors would include the physical
transport (e.g. distance and travel time in air or
water, &c)
Exposure Routes and Effects
• Principle routes for chemicals:
– Ingestion
– Dermal
– Inhalation
• Other routes for hazard exposure:
– Puncture
– Eyes
– Ears
Gastrointestinal Exposures
• Chemicals gain direct access to mucous
membranes in stomach and intestines, allowing
transfer of chemical to bloodstream
• Digestive processes can transform chemicals
into others
• Physical hazard endpoints can apply (e.g. with
ingested acids)
Dermal Exposure
• Epidermis consists of former living cells
– Removed from blood vessels to some extent
– Acts as barrier to loss of fluids and entry of
contaminants
• Some materials are able to pass this barrier
– Solvents which can be absorbed into the skin
– Pores and hair follicles
Inhalation
• Rapid route of entry to bloodstream
• Alveoli designed to facilitate transfer of gases
(oxygen and carbon dioxide)
– Effectively transfer other materials too
Distribution of Toxicants
• Two factors govern transport:
– Protein binding • Toxicants can bind to proteins in the blood, thus
preventing their access to surrounding cells through
capillary walls
• But access to kidneys (for removal) is also inhibited
– Polarity • Polar toxicants obstructed by non-polar membranes
• Nonpolar toxicants dissolve through readily and can be
stored in body fat
Metabolism
• Conversion of materials through reaction
• For toxicants, tendency is to increase
polarization (and therefore reduce bio-uptake)
• In some cases chemicals can be converted into
more toxic materials
Pollution Control in the Body
• Kidneys
• Liver
Kidney Function
• Blood flowing through kidneys is exposed to
porous membrane
– the (relatively) small molecules of toxins pass
– substantial quantities of water also pass
• Aqueous solution passes along tubes which
selectively retrieve desirable nutrients, water
&c
• Concentrated aqueous toxins expelled as urine
Liver Function
• Metabolize toxicants into more polar structures
• Some substances removed from blood and
transformed into bile, stored in gall bladder
• Gall bladder sends bile into small intestine to
assist with digestion
• Toxins therefore eliminated with feces (unless
resorbed by intestinal walls)
Lifetime Exposure
Average Daily Dose
CDI 
Body Weigh t
Concentrat ion  Intake Rate
CDI 
Body Weigh t
where a 70-year lifetime is assumed
Risk Characterization
• Bring Dose-Response together with Exposure
assessment to estimate risk
Example: Chloroform in Drinking
Water
• Suppose your drinking water has 0.10 mg/L
concentration of chloroform (CHCl3)
• From IRIS, PF = 6.1x10-3 (mg/kg/day)-1
0.10 mg/L  2 L/day
CDI 
 0.00286 mg/kg/day
70 kg
• So incremental lifetime cancer risk is
CDI  PF  0.00286 mg/kg/day  6.110 3 (mg/kg/day ) 1
CDI  PF  17.4 10 6
Chloroform Example (cont’d)
• In a city of 500,000 people:
17.4 cancers
1
500,000 people  6

 0.12 cancers/yr
10 people 70 yr
General Exposure
Conc  Intake Rate  Exposure (days)
CDI 
Body Weigh t  Lifespan (yrs)  365 days/yr
Example: Occupational Exposure
• A 60 kg person works 5 days/week, 50
weeks/yr, for 25 years
• Each workday they breath 20 m3 of air
containing 0.05 mg/m3 of toxin
mg
m3
days
weeks
0.05 3  20
5
 50
 25 yrs
m
day
week
year
CDI 
60 kg  70 years  365 days/yr
CDI  0.0041 mg/kg/day
Example (cont’d)
• If the Potency Factor is 0.02 (mg/kg/day)-1:
Incr Risk  CDI  PF
Incr Risk  0.0041 mg/kg/day  0.02 (mg/kg/day )
Incr Risk  8110 6
1
Non-carcinogenic Doses
• Metrics from toxicity experiments include
–
–
–
–
Lowest Observed Effect Level (LOEL)
Lowest Observed Adverse Effect Level (LOAEL)
No Observed Effect Level (NOEL)
No Observed Adverse Effect Level (NOAEL)
• Note: NOEL and NOAEL are the highest
experimental doses at which no (adverse)
effect was seen
Reference Dose
• The Reference Dose (RfD) is taken from the
NOAEL:
NOAEL
RfD 
Uncertaint y Factors
• Where Uncertainty Factors are 10 each for
differences across population
using animal data to estimate human endpoints
using only a single species of animal
Hazard Quotient
• Compares exposure to Reference Dose:
Average Daily Dose During Exposure
HQ 
Reference Dose
• HQ < 1 should be free if significant risk of
toxicity
Hazard Index
• Considers multiple risks (e.g. from multiple
chemical toxins)
• The sum of the Hazard Quotients:
HI   HQ
Other Factors in Risk Characterization
• Also consider
– Statistical uncertainties
– Biological uncertainties
– Selection of applicable dose-response and
exposure data
– Selection of population groups toward which the
risk assessment should be targeted
Occupational Standards revisited
• The standards set by OSHA (and ACGIH and
NIOSH) are based upon such risk assessment
analyses
Occupational Standards: TWA
• The Time-Weighted Average (TWA) assumes
an 8-hour day and 40-hour week
Ct

TWA 
t
i
i i
i i
TWA Example
Exposure
(ppm)
2
Time (hr)
10
Product
(ppm*hr)
20
3
20
60
4
10
40
40
120
So TWA = 120 ppm / 40 hours = 3 ppm
Occupational Standards: STEL
• Short Term Exposure Level
• Calculated as a 15-minute TWA
• Allowed no more than four such exposure
periods per day, separated by at least 1 hour
Occupational Standards: Ceiling
• Concentration which must not be exceeded,
regardless of duration of exposure.