EVALUATING EXPOSURES

1
CHAPTER 5

• EVALUATING EXPOSURES

2
General Overview
Exposure and Risk - What consequences do the
different substances have on the environment and
people? Examples of Some Regulations - Are there
regulations concerning the different
substances? Safer Chemical Design
3
Estimating Exposure
4
Types of Exposure
OCCUPATIONAL Worker exposure in the
industry. COMMUNITY Population exposure in the
industrys surrounding area due to the waste
streams.
5
Occupational and Community Exposure
Three steps related to exposures 1) Recognition
all sources and potential sources 2) Evaluation
level and duration of exposure 3) Control (and
Elimination) based on source, pathway, and
worker/population exposure information
6
Occupational Exposure Recognition

• Uses schematic and written descriptions to
  indentify
• - Potential sources of exposure (i.e. specific
  unit operations).
• - Mechanisms that reduce worker exposure
• (i.e. ventilation systems).
• Exposure pathways
• - Inhalation
• - Dermal contact
• - Ingestion

7
Occupational Exposure Evaluation

• Monitoring worker exposure objetives include
• - Baseline
• - Diagnostic
• - Compliance
• - Types of Monitoring
• - Personal (i.e. Breathing zone measurement)
• - Area ( i.e. General monitoring to control
  long-term exposures)
• Evaluation of occupational exposure include
• Inhalation assessment and Dermal assessment

8
Evaluation Inhalation Assessment
Monitoring Techniques Include - Breathing
Simulator - Static Sampler Controlling
Techniques Include - Respirators and other
devices - Alternate process or modifications to
equipment Models used in place of monitoring to
assess inhalation are Mass Balance Model and
Dispersion Model.
9
Mass Balance or Box Model Contaminant is
dispersed evenly in the area (box)
(5.1)
Where C concentration of airborne contaminant
in the work area (mass/length3), V volume of
the work area (length3), T time during which
the contaminant has been emitted, G emission
rate of the contaminant to the air (mass/time), Q
ventilation rate in the work area
(length3/time), k a mixing factor to account
for incomplete mixing in the work area (unit
less), Co concentration of the airborne
contaminant entering the work area
(mass/length3).



10
Mass Balance or Box Model (continued)
At Steady State (ss) equation 5.1 becomes the
following
(5.2)
With constant ventilation a new contamination
source can be estimated using
(5.3)
Where
(5.4)
11
Dispersion ModelVariation of the concentration
(from the source) in a given area


Where U is the wind velocity in the x
direction (length/time) C is the concentration of
airborne contaminant (mass/length3) D is the
diffusion coefficient (lenght2/time) x is the
distance downwind from the source (length) r is
the distance from the source to the sampling
point (length)

G is the contaminant emission rate from the
source (mass/time)
(5.5)
(5.6)
12
Evaluation Dermal Exposure Assessment
The mechanisms of dermal exposure are - Direct
contact between skin and substance. - Transfer of
substance from contaminated surface to skin. -
Deposition or impaction onto skin. Monitoring
techniques include - Absorbent Pads. - Wipe
Samples. - Computerized Techniques . Controlling
techniques include - Wearing protective
clothing and aparel. - Substitution of a less
toxic chemical (that will not impact ingestion or
inhalation).
13
Dermal Exposure AssessmentModeling
(5.7)
Where DAR dermal absorbed dose rate
of the chemical (mass/time), S surface area of
the skin contacted by the chemical (length2), Q
quantity deposited on the skin per event
(mass/length2/event), N number of exposure
events per day (event/time), WF weight fraction
of the chemical of concern in the mixture
(dimensionless), ABS fraction of the applied
dose absorbed during the event (dimensionless).
14
Dermal Exposure Assessment Modeling (continued)
(5.8)
Where DA dermal absorbed dose of the
chemical (mass), S surface area of the skin
contacted by the chemical (lenght2), Kp
permeability coefficient for the chemical of
concern in the mixture (length/time), ED
exposure duration (time), WF weight fraction
of the chemical of concern in the mixture
(dimensionless), ? density of the mixture
(mass/lenght3).
15
Community ExposureRecognition
Air Contaminants Recognition - Main
substances and by-products that can cause harm. -
Main weather patterns and communities potentially
affected by discharges. - Phase changes (into
water stream or land).
16
Community Exposure Recognition (continued)

• Water Contaminants Recognition
• - Main substances and by-products that can cause
  harm.
• - Water flows and stream uses (water treatment
  plant, fishing, etc).
• Phase changes (volatilization, ab/adsorption into
  solid particles, etc).
• Solid Contaminants Recognition
• - Main substances and by-products that can cause
  harm.
• - Potential leachate and volatilization of
  substances.

17
Description Sources Standards or Guidelines
Volatile organic chemicals (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by a wide array of products numbering in the thousands. Examples include paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions. No standards have been set for VOCs in non industrial settings. OSHA regulates formaldehyde, a specific VOC, as a carcinogen. OSHA has adopted a Permissible Exposure Level (PEL) of .75 ppm, and an action level of 0.5 ppm. HUD has established a level of .4 ppm for mobile homes. Based upon current information, it is advisable to mitigate formaldehyde that is present at levels higher than 0.1 ppm.
18
Description Sources Standards or Guidelines
Lead is a highly toxic metal. Sources of lead include drinking water, food, contaminated soil and dust, and air. Lead-based paint is a common source of lead dust. The Consumer Product Safety Commission has banned lead in paint.
Health Effects Control Measures Control Measures
Lead can cause serious damage to the brain kidneys, nervous system, and red blood cells. Children are particularly vulnerable. Lead exposure in children can result in delays in physical development, lower IQ levels, shorten attention spans, and increase behavioral problems. Preventive measures to reduce lead exposure include cleaning play areas mopping floors and wiping window ledges and other smooth flat areas with damp cloths frequently keeping children away from areas where paint is chipped, peeling, or chalking preventing children from chewing on window sills and other painted areas and ensuring that toys are cleaned frequently and hands are washed before meals. Preventive measures to reduce lead exposure include cleaning play areas mopping floors and wiping window ledges and other smooth flat areas with damp cloths frequently keeping children away from areas where paint is chipped, peeling, or chalking preventing children from chewing on window sills and other painted areas and ensuring that toys are cleaned frequently and hands are washed before meals.
19
Community Exposure Evaluation

• Air Exposures
• - What chemicals (toxic or harmful substances).
• - What quantities and from where (area, point,
  mobile).
• - Estimate concentration in specific location
  (exposure location).
• Dispersion models include Gaussian models (based
  on many factors).
• - Estimate the number of people affected by
  contamination .
• Dermal Exposures
• - Frequency and duration of potential exposure
  (swimming only).
• - Concentration of given substance.

20
Community Exposure Evaluation (continued)
Surface Water - What quantity of a given toxin
remains after the wastewater. treatment process
and the actual concentration in the given
stream. - Analyze the fate of the given substance
using models. - What impact do the contaminants
have on aquatic organisms. Ground Water
Contamination - Occurs from leachates (landfills)
and rainwater runoffs. - Can be transported for
long distances (and into different phases) and
last for long periods of time.
21
Regulations
22
Persistant, Bioaccumulating and Toxic (PBT)
Substances

• The top 12
• Aldrin/Dieldrin,
• Benzo(a)pyrene,
• Chlordane,
• DDT
• Hexachlorobenzene,
• Alkyl-lead,
• Mercury and Compounds,
• Mirex,
• Octachlorostyrene,
• PCBs,
• Dioxins and Furans, and
• Toxaphene.

• References
• Binational Toxics Strategy
• http//www.epa.gov/bns/index.html
• Environment Canadas ARET program
• http//www.ec.gc.ca/nopp/aret/en/el2.cfm
• EPAs PBT Chemical Program
• http//www.epa.gov/pbt/index.htm

23
Source http//epa.gov/air/criteria.html
24
Air Pollution in the Workplace
References OSHA regulations of emissions in
workplace http//www.osha.gov/pls/oshaweb/owadisp.
show_document?p_tableFEDERAL_REGISTERp_id13306
CCOSH general website http//www.ccohs.ca/
25
Example of Emission Standards

• Water and Wastewater
• - Effluent guidelines
• On a continuous basis pH between 6.0 and 9.5
• On a monthly average basis

Total Suspended Solids (TSS) 25 mg/L
Chemical Oxygen Demand (COD) 200 mg/L
Oil and Grease 10 mg/L
Cadmium 0.1 mg/L
Chromium (total) 0.5 mg/L
Lead 0.2 mg/L
Mercury 0.01 mg/L
Nickel (total) 0.5 mg/L
Zinc 0.5 mg/L
Toxicity No more then 50 mortality in 100 effluent
Source http//www.ec.gc.ca/nopp/docs/cp/1mm8/en/
c4.cfm
26
Safer Chemical Design
27
Safer Chemical Design

• Key goals of designing safer chemicals are
  minimizing
• - Persistence and Dispersion in the environment
  (and therefore reducing exposure).
• - Bioaccumulation and reducing dose (thereby
  reducing the uptake by the body).
• - Toxicity.
• Safer Chemical Design include
• - Dose minimization.
• - Toxicity minimization.

28
Safer Chemical Design Dose Reduction

• Information needed to calculate doses
• - Mass of the chemical transfered across a
  certain membrane.
• - Depending of the different membranes, chemical
  and physical properties are needed
• Lung water solubility, particle size.
• Gastrointestinal tract lipid solubility, water
  solubility, dissociation constant and molecular
  size.
• Skin lipid solubility.

29
The lung also provides a relatively large surface
area for uptake of chemicals. The lung is a
relatively thin membrane and because the membrane
is so thin, lipid solubility plays less of a
role in chemical uptake than for the
gastrointestinal tract. High water solubility
will promote uptake through the lung, as will the
delivery of the compound on fine particles.
30
The skin presents a formidable barrier to
chemicals transport. For a chemical to be taken
up through the skin, it must pass through
multiple layers. As with the gastrointestinal
tract, moderate lipophilicity promotes absorption
through the skin because transport must occur
through both largely lipid and largely aqueous
layers.
High water solubility enhances uptake trough the
gastrointestinal tract because water soluble
materials are more easily mobilized in the large
and small intestine and the materials therefore
experience less mass transfer resistance in
migrating to the intestine wall. High lipid
solubility enhances uptake and transport across
the membrane.
31
Safer Chemical Design Toxicity Reduction

• Important information is obtained by
• - Examining mechanisms.
• - Identifying structural mechanisms.

32
Toxicity Reduction Evaluations (TREs)
TREs use toxicity tests, detailed chemical
analyses, and process evaluations to determine
the cause of effluent toxicity. These
evaluations explore treatment options to reduce
toxicity to acceptable levels or identify changes
within a facility to alter the type, quantity, or
character of the discharge. We then identify the
type and source of toxins and then make an
evaluation of treatment alternatives. When the
TRE is complete, we prepare a final report which
contains recommendations for toxicity reduction
or elimination that will bring a facility back
into compliance.