SOURCES OF AIR POLLUTION
Two main categories
Stationary sources such as power stations, oil refineries
Mobile sources such as motor vehicles
STRATEGIES TO CONTROL AIR
POLLUTION
Stationary sources
Siting of industries
Should be sited far away from residential areas
Install pollution control equipment and have tall stacks for dispersion of air pollutants
Fuel quality
Control type and quality of fuel
E.g. Use fuel with sulphur content not exceeding 2% by weight
Pollution control equipment
Equipment/processes which give rise to emissions are designed to be able to comply with emission standards
Industries encouraged to adopt cleaner technologies
Wet & Dry collectors (scrubbers)
Cyclones
Fabric filters
Electrostatic Precipitators
Tax incentives
Enforcement
Regular inspections to ensure that pollution control equipment and facilities are properly maintained
Mobile sources
Fuel quality
Use of unleaded petrol
Sulphur content of diesel is 0.05% by weight
Fitted with catalytic converters
Emission standards
Inspection and enforcement
Mandatory periodic inspections
Air pollution
Air Pollution
is the presence of any chemical, physical (e.g. particulate matter), or biological agent that modifies the natural characteristics of the atmosphere.
The atmosphere is a complex, dynamic natural gaseous system that is essential to support life on planet earth.
Worldwide air pollution is responsible for large numbers of deaths and cases of respiratory diseases
Types of air pollutants
Main gaseous pollutants
Sulphur dioxide (SO2)
Oxides of nitrogen (NO and NO2)
Carbon monoxide (CO)
Hydrocarbons (HC)
Ozone (O3)
Main non-gaseous pollutants
Suspended particulate matter
Lead
Sources of air pollution
Stationary sources
any fixed emitter of air pollutants
Fossil fuel burning power stations
Petroleum/Oil refineries
Petrochemical plants
Food processing plants
Heavy Industrial sources
Mobile sources
non-stationary source of air pollutants
automobiles, buses, trucks, ships, trains, aircraft and various other vehicles
tobacco smokers
Sources of air pollution
Sulphur dioxide
Largest single source of SO2 is the combustion of sulphur – containing fossil fuel both for electric power generation and for process heat
Some important industrial emitters
Nonferrous smelters
Except iron and aluminum, metal ores are suphur compounds
When ore is reduced to pure metal, sulphur in the ore is oxidized to SO2
Oil refining
Sulphur and hydrogen are constituents of crude oil
Hydrogen sulphide is released as gas during catalytic cracking
Hydrogen sulphide is more toxic then sulphur dioxide
It is flared to sulphur dioxide before release into air
Pulp and paper manufacture
Sulphite process for wood pulping use hot sulphiric acid
Thus emits sulphur dioxide into air
Kraft pulping process produces hydrogen sulphide, that is flared to sulphur dioxide
Natural sources
Volcanic eruptions
Sulphur containing geothermal sources – hot springs
Oxides of nitrogen
formed by the combustion of nitrogen - containing compounds
and thermal fixation by atmospheric nitrogen
NOx is created when nitrogen and oxygen in combustion air are heated to high temperature
The equilibrium constant for the reaction: N2 + O2 2NO
All high temp processes produce NO, that is oxidized to NO2 in the ambient air
Carbon monoxide
Product of incomplete combustion of carbon-containing compounds
Most of the CO in ambient air comes from vehicle exhaust
Internal combustion engines do not burn fuel completely to CO2 and water
Some unburned fuel will always be exhausted, with CO as a component
Tobacco smoke
Hydrocarbons
Major source
vehicles
Stationary sources
Petrochemical manufacture
Oil refining
Incomplete incineration
Paint manufacture and use
Dry cleaning
Particulate matter
Every industrial process is a potential source of dust, smoke 0r aerosol emissions
Waste incineration
Coal combustion
Petrochemical industry
Smelting
Agricultural operations
major source of dust – dry farming
Demolition and construction
Great quantities of dust
Fires
Major sources of airborne particulate matter, HC, CO
Tobacco smoke
CO, organic tars, metal oxides particles
Wood – burning stoves and fireplaces
Produce smoke that contains partly burned HC, tars, dioxins
Airborne lead
Vehicle exhaust
Leaded paint
Wednesday, November 11, 2009
ENV 382 cont...
Spectroscopic Methods
Spectroscopy
is the study of matter by investigating light, sound, or particles that are emitted, absorbed or scattered by the matter under investigation
Spectroscopy may also be defined as the study of the interaction between light and matter
Physical quantity measured
The type of spectroscopy depends on the physical quantity measured.
Normally, the quantity that is measured is an amount or intensity of something
Three main types of spectroscopy
Absorption spectroscopy uses the range
of electromagnetic spectra in which a
substance absorbs.
commonly used in atomic absorption spectroscopy, the sample is atomized and then light of a particular frequency is passed through the vapour
the amount of absorption can be related to the concentrations of various metal ions through the Beer-Lambert law
widely used to measure concentrations of ions such as sodium and calcium
Other types of spectroscopy may not require sample atomization
For example, ultraviolet/visible (UV/ Vis) absorption spectroscopy is most often performed on liquid samples to detect molecular content
Emission spectroscopy uses the range of
electromagnetic spectra in which a
substance radiates
The substance first absorbs energy and then radiates this energy as light
This energy can be from a variety of sources, including chemical reactions
Scattering spectroscopy
measures certain physical properties by measuring the amount of light that a substance scatters at certain wavelengths
Common types of spectroscopy
Flame Spectroscopy
Liquid solution samples are aspirated into a burner or nebulizer/burner combination, desolated, atomized, and sometimes excited to a higher energy electronic state
The use of a flame during analysis requires fuel and oxidant, typically in the form of gases
Common fuel gases used are acetylene or hydrogen
Common oxidant gases used are oxygen, air, or nitrous oxide
methods are often capable of analyzing metallic element analytes in the part per million, billion, or possibly lower concentration ranges
Atomic Emission Spectroscopy
uses flame excitation; atoms are excited from the heat of the flame to emit light
commonly uses a total consumption burner with a round burning outlet
A higher temperature flame than atomic absorption spectroscopy (AA) is typically used to produce excitation of analyze atoms
Since analyte atoms are excited by the heat of the flame, no special elemental lamps to shine into the flame are needed
Atomic Fluorescence Spectroscopy
This method commonly uses a burner with a round burning outlet
The flame is used to solvate and atomize the sample, but a lamp shines light at a specific wavelength into the flame to excite the analyte atoms in the flame
The atoms of certain elements can then fluoresce emitting light in a different direction. The intensity of this fluorescing light is used for quantifying the amount of analyte element in the sample.
A graphite furnace can also be used for atomic fluorescence spectroscopy. This method is not as commonly used as atomic absorption or plasma emission spectroscopy.
Alternatively, a monochromator can be set at one wavelength to concentrate on analysis of a single element at a certain emission line
Plasma emission spectroscopy is a more modern version of this method.
Atomic Absorption Spectroscopy (often called AAS)
commonly uses a pre-burner nebulizer (or nebulizing chamber) to create a sample mist and a slot-shaped burner which gives a longer path-length flame
The temperature of the flame is low enough that the flame itself does not excite sample atoms from their ground state
The nebulizer and flame are used to desolvate and atomize the sample, but the excitation of the analyte atoms is done by the use of lamps shining through the flame at various wavelengths for each type of analyte
In AA, the amount of light absorbed after going through the flame determines the amount of analyte in the sample
A graphite furnace for heating the sample to desolvate and atomize is commonly used for greater sensitivity
The graphite furnace method can also analyze some solid or slurry samples.
Because of its good sensitivity and selectivity, it is still a commonly used method of analysis for certain trace elements in aqueous (and other liquid) samples.
Spark or arc (emission) spectroscopy
can be used for the analysis of metallic elements in solid samples
An electric arc or spark is passed through the sample, heating the sample to a high temperature to excite the atoms in it
The excited analyte atoms glow emitting light at various wavelengths which could be detected by common spectroscopic methods
Since the conditions producing the arc emission typically are not controlled quantitatively, the analysis for the elements is qualitative.
Visible spectroscopy
Many atoms emit or absorb visible light. In order to obtain a fine line spectrum, the atoms must be in a gas phase. This means that the substance has to be vaporized.
Spectrum is studied in absorption or emission.
UV spectroscopy
All atoms absorb in the UV region because photons are energetic enough to excite outer electrons. If the frequency is high enough, photoionisation takes place.
Infra-red spectroscopy
In organic chemistry different types of interatomic bond vibrate at different frequencies in the infra-red part of the spectrum.
The analysis of IR absorption spectra shows what type of bonds are present in the sample.
Nuclear Magnetic Resonance (NMR)
spectroscopy
NMR spectroscopy analyzes certain atomic nuclei to determine different local environments of hydrogen, carbon, or other atoms in the molecule of an organic compound or other compound. This is used to help determine the structure of the compound.
Use of Atomic Absorption (AA) Spectroscopic methods
Metals
Significance
Effects of metals in water and wastewater range from beneficial to dangerously toxic
Some metals are essential
Fe – blood
Cu, Zn – physical performance
Others may adversely affect water consumers, wastewater treatment systems, and receiving waters
Arsenic- cancer, toxic to aquatic spp
Asbestos – asbestosis ( ‘black' lung cancer)
Cadmium, chromium, copper – liver and kidney damage
Methods
Atomic absorption (AA)
Colorimetric methods
Sampling and sample preservation
What fraction to be analyzed
Dissolved
Suspended
Total
Acid-extractable
Preservation
Acidify with 1.5 ml (5ml for alkaline samples) HNO3 /L sample to pH < 2
Filter samples for dissolved metals before preserving
Store in fridge at 4oC
Stable for 6 months
Pre-treatment of samples
Total metals – all metals inorganically and organically bound, both dissolved and particulate
Colorless, odorless water - < I NTU – acidify with HNO3 to pH <2 and analyze directly
Dissolved metals
filter sample (0.45 micrometer membrane filter)
acidify filtrate with HNO3 to pH < 2
And analyze directly
Suspended metals
Filter sample (0.45 micrometer membrane filter)
Digest filter
And analyze
Acid-extractable metals
Extract metals
And analyze extract
Pre-treatment for Acid-extractable metals
extractable metals – lightly absorbed on particulate matter
At collection acidify sample with 5 ml HNO3/L sample
To prepare sample
Mix well
Transfer 100 ml to flask
Add 5 ml HCl
Heat 15 min on a steam bath
Filter thorough 0.45 micrometer membrane filter)
Adjust filtrate volume to 100 ml with water and analyze
Pre-digestion of metals
Reduce interference by organic matter and to convert metal associated with particulates to a form that can be determined by AA
HNO3 – digestion is adequate for clean samples or easily oxidized materials
HNO3-H2SO4 or HNO3-HCl – digestion is adequate for readily oxidizable organic matter
HNO3-HClO4 or HNO3-HClO4-HF – is for the difficult to oxidize organic matter or minerals
Nitric Acid Digestion
Mix sample
Transfer 50 to 100ml to 125 ml conical flask
Add 5 ml conc. HNO3 and few boiling chips
Boil and evaporate on hot plate to lowest volume (10 to 20 ml) before precipitation occurs
Continue heating and adding HNO3 until digestion is complete (light-coloured, clear solution)
Wash down flask walls with water and then filter
Transfer filtrate to 100 ml flask , cool, dilute to mark, mix and analyze.
Direct Air-Acetylene Flame Method
Applicable for Ca, Cd, Cr, Co, Cu, Fe, Mg, Mn, Ni, Zn, etc
Principle
The technique of flame atomic absorption spectroscopy (AA) requires a liquid sample to be aspirated, aerosolized, and mixed with combustible gases, such as acetylene and air or acetylene and nitrous oxide
The mixture is ignited in a flame whose temperature ranges from 2100 to 2800 oC
During combustion, atoms of the element of interest in the sample are reduced to free, unexcited ground state atoms, which absorb light at characteristic wavelengths
RISK ASSESSMENT
Environmental Engineer
objective
Reduce risk from hazards to the environment and public health
Estimate future risks, then use science to prevent or mitigate them
To determine the comparative risks from various environmental pollutants and which risks it is most important to decrease or eliminate
risk analysis
Risks associated with various hazards must evaluated and quantified
Risk
1970s – environmental laws were enacted to protect public heath
E.g. US Clean Air Act
No mention of risk in US Clean Air and Clean Water Acts
Acts required that pollution standards be set that would allow adequate margins of safety to protect public health
Assumption was that pollutants have thresholds and exposure to concentrations below these thresholds would produce no harm
Problems of toxic waste were finally recognized
Toxic substances are suspected carcinogens
Even smallest exposures creates a risk
If any exposure to a substance causes some risk, how can air quality and water quality standards be set
Emergence of the field of environmental risk assessment
1980s - environmental policy - was acceptance of the role of risk assessment and risk management in environmental decision making
Risk assessment
Is a system of analysis that includes four tasks
Identification of substance (toxicant) that may have adverse health effects
Scenarios for exposure to toxicant
Characterization of health effects
As estimate of the probability (risk) of occurrence of these health effects
Is the gathering of data that are used to relate response to dose
Such dose-response data can then be combined with estimates of the likely human exposure to produce overall assessment of risk
Risk management
is the process of deciding what to do
It is the decision making, about how to allocate national resources to protect public health and the environment
Is a one-in-a-million lifetime risk of getting cancer acceptable and, if it is, how do we go about trying to achieve it?
Hazardous substances
Hazardous and toxic substances are
defined as those chemicals present in the
environment which are capable of causing harm
Risk
is the possibility of loss or
injury to people and property
Hazard
a chemical, physical, or biological agent or a set of conditions that has the potential to cause harm
Risk Assessment
Hazard identification
Is the process of determine whether or not a particular chemical is causally linked to a particular health effects, such as cancer on birth effects
Dose-response assessment
Is the process of characterizing the relationship between the dose of an agent administered or received and the incidence of an adverse effect
Dose-Response Assessment
Characteristic features of the Dose- Response
relationship:
Threshold
Is the lowest dose at which there is an observable effect
Curve A – illustrate threshold response i.e. there is no observed effect until a particular concentration is reached
Curve B - linear response with no threshold i.e. the intensity of the effect is directly proportionally to the pollutant dose, and the effect is observed for any detectable concentration of the pollutant in question
Curve C –sublinear dose-response curve and is characteristic of many pollutant dose-response relationships.
It has no clearly defined threshold, the lowest dose at which a response can be detected is called threshold limit value (TLV)
Curve D – supralinear relationship, which is found when low doses of a pollutant appear to provoke a disproportionately large response
Total body burden
An organism or a person can be exposed to simultaneously to several sources of a given pollutant
Example
inhale about 50g/day lead from ambient air and
ingest 300g/day in food and water
The concentration of lead in the body is sum of what is inhaled and ingested and what remains in the body fro prior exposure, less what has been eliminated from the body
Physiological half-life
Is the time needed for the organism to eliminate half of the internal concentration of the pollutant, through metabolism or other normal physiological functions
Bioaccumulation and bioconcentation
Bioaccumulation occurs when a substance is concentrated in one organ or the of tissue of an organism
E.g. Iodine - bioaccumulates in the thyroid gland
The organ dose of a pollutant can thus be considerably greater than what the total body burden would predict
Bioconcentation occurs with a movement up the food chain
E.g. A study of Lake Michigan ecosystem (Hickey et al. 1966) found bioconcentation of DDT as follows:
0.014 ppm (wet weight) in bottom sediments
0.41 ppm in bottom-feeding crustacea
3-6 ppm in fish
2 400 ppm in fish –eating birds
Exposure time and time vs. dosage
Most pollutant need time to react; the exposure time is thus as important as the level of exposure
Synergism
Occurs when two or more substances enhance each other’s effects, and when the resulting effect of the combination on the organism is greater than the additive effects of the substances separately
E.g. black lung disease in miners – occurs more often in miners who smoke than in those who do not
LC50 and LD50
LD50 is the dose that is lethal for 50% of the experimental animals
LC50 refers to lethal concentration rather than lethal dose
LD50 values are most useful in comparing toxicities for pesticides and agricultural chemicals
Population responses
Differ from one individual to another
Depends on age, sex, and general state of physical and emotional health
Exposure and Latency
Characterization of some health risks can take a very time
E.g.. Cancers are noticed many years or decades after exposure to potentially responsible carcinogen
Cancer in adults have a latency period between 10 – 40 years
Latency period – length of time between exposure to a risk factor and expression of adverse effect
Relative risk
Is the ratio of the probabilities that an adverse effect will occur in two different populations
E.g. relative risk of lung cancer in smokers
Ps/Pn = (Xs/Ns)/(Xn/Nn)
where
Ps = probability of fatal lung cancer in smoker
Pn = probability of fatal lung cancer in non-smokers
Xs = number of fatal lung cancer among smokers
Xn = number of fatal lung cancer among non- smokers
Ns = total number of smokers
Nn= total number on non-smoker
Relative risk of death is also called standard mortality ratio (SMR)
SMR = Ds/Dn= Ps/Pn
where
Ds = observed lung cancer deaths in a population of habitual smokers
Dn = expected lung cancer deaths in a non-smoking population of the same size
Exposure assessment
Involves determining the size and nature of the population that has been exposed to the toxicant under consideration, and the length of time and toxicant concentration to which they have been exposed
Risk characterization
Is the integration of the foregoing three steps, which results in an estimate of the magnitude of the public-health problem
Spectroscopy
is the study of matter by investigating light, sound, or particles that are emitted, absorbed or scattered by the matter under investigation
Spectroscopy may also be defined as the study of the interaction between light and matter
Physical quantity measured
The type of spectroscopy depends on the physical quantity measured.
Normally, the quantity that is measured is an amount or intensity of something
Three main types of spectroscopy
Absorption spectroscopy uses the range
of electromagnetic spectra in which a
substance absorbs.
commonly used in atomic absorption spectroscopy, the sample is atomized and then light of a particular frequency is passed through the vapour
the amount of absorption can be related to the concentrations of various metal ions through the Beer-Lambert law
widely used to measure concentrations of ions such as sodium and calcium
Other types of spectroscopy may not require sample atomization
For example, ultraviolet/visible (UV/ Vis) absorption spectroscopy is most often performed on liquid samples to detect molecular content
Emission spectroscopy uses the range of
electromagnetic spectra in which a
substance radiates
The substance first absorbs energy and then radiates this energy as light
This energy can be from a variety of sources, including chemical reactions
Scattering spectroscopy
measures certain physical properties by measuring the amount of light that a substance scatters at certain wavelengths
Common types of spectroscopy
Flame Spectroscopy
Liquid solution samples are aspirated into a burner or nebulizer/burner combination, desolated, atomized, and sometimes excited to a higher energy electronic state
The use of a flame during analysis requires fuel and oxidant, typically in the form of gases
Common fuel gases used are acetylene or hydrogen
Common oxidant gases used are oxygen, air, or nitrous oxide
methods are often capable of analyzing metallic element analytes in the part per million, billion, or possibly lower concentration ranges
Atomic Emission Spectroscopy
uses flame excitation; atoms are excited from the heat of the flame to emit light
commonly uses a total consumption burner with a round burning outlet
A higher temperature flame than atomic absorption spectroscopy (AA) is typically used to produce excitation of analyze atoms
Since analyte atoms are excited by the heat of the flame, no special elemental lamps to shine into the flame are needed
Atomic Fluorescence Spectroscopy
This method commonly uses a burner with a round burning outlet
The flame is used to solvate and atomize the sample, but a lamp shines light at a specific wavelength into the flame to excite the analyte atoms in the flame
The atoms of certain elements can then fluoresce emitting light in a different direction. The intensity of this fluorescing light is used for quantifying the amount of analyte element in the sample.
A graphite furnace can also be used for atomic fluorescence spectroscopy. This method is not as commonly used as atomic absorption or plasma emission spectroscopy.
Alternatively, a monochromator can be set at one wavelength to concentrate on analysis of a single element at a certain emission line
Plasma emission spectroscopy is a more modern version of this method.
Atomic Absorption Spectroscopy (often called AAS)
commonly uses a pre-burner nebulizer (or nebulizing chamber) to create a sample mist and a slot-shaped burner which gives a longer path-length flame
The temperature of the flame is low enough that the flame itself does not excite sample atoms from their ground state
The nebulizer and flame are used to desolvate and atomize the sample, but the excitation of the analyte atoms is done by the use of lamps shining through the flame at various wavelengths for each type of analyte
In AA, the amount of light absorbed after going through the flame determines the amount of analyte in the sample
A graphite furnace for heating the sample to desolvate and atomize is commonly used for greater sensitivity
The graphite furnace method can also analyze some solid or slurry samples.
Because of its good sensitivity and selectivity, it is still a commonly used method of analysis for certain trace elements in aqueous (and other liquid) samples.
Spark or arc (emission) spectroscopy
can be used for the analysis of metallic elements in solid samples
An electric arc or spark is passed through the sample, heating the sample to a high temperature to excite the atoms in it
The excited analyte atoms glow emitting light at various wavelengths which could be detected by common spectroscopic methods
Since the conditions producing the arc emission typically are not controlled quantitatively, the analysis for the elements is qualitative.
Visible spectroscopy
Many atoms emit or absorb visible light. In order to obtain a fine line spectrum, the atoms must be in a gas phase. This means that the substance has to be vaporized.
Spectrum is studied in absorption or emission.
UV spectroscopy
All atoms absorb in the UV region because photons are energetic enough to excite outer electrons. If the frequency is high enough, photoionisation takes place.
Infra-red spectroscopy
In organic chemistry different types of interatomic bond vibrate at different frequencies in the infra-red part of the spectrum.
The analysis of IR absorption spectra shows what type of bonds are present in the sample.
Nuclear Magnetic Resonance (NMR)
spectroscopy
NMR spectroscopy analyzes certain atomic nuclei to determine different local environments of hydrogen, carbon, or other atoms in the molecule of an organic compound or other compound. This is used to help determine the structure of the compound.
Use of Atomic Absorption (AA) Spectroscopic methods
Metals
Significance
Effects of metals in water and wastewater range from beneficial to dangerously toxic
Some metals are essential
Fe – blood
Cu, Zn – physical performance
Others may adversely affect water consumers, wastewater treatment systems, and receiving waters
Arsenic- cancer, toxic to aquatic spp
Asbestos – asbestosis ( ‘black' lung cancer)
Cadmium, chromium, copper – liver and kidney damage
Methods
Atomic absorption (AA)
Colorimetric methods
Sampling and sample preservation
What fraction to be analyzed
Dissolved
Suspended
Total
Acid-extractable
Preservation
Acidify with 1.5 ml (5ml for alkaline samples) HNO3 /L sample to pH < 2
Filter samples for dissolved metals before preserving
Store in fridge at 4oC
Stable for 6 months
Pre-treatment of samples
Total metals – all metals inorganically and organically bound, both dissolved and particulate
Colorless, odorless water - < I NTU – acidify with HNO3 to pH <2 and analyze directly
Dissolved metals
filter sample (0.45 micrometer membrane filter)
acidify filtrate with HNO3 to pH < 2
And analyze directly
Suspended metals
Filter sample (0.45 micrometer membrane filter)
Digest filter
And analyze
Acid-extractable metals
Extract metals
And analyze extract
Pre-treatment for Acid-extractable metals
extractable metals – lightly absorbed on particulate matter
At collection acidify sample with 5 ml HNO3/L sample
To prepare sample
Mix well
Transfer 100 ml to flask
Add 5 ml HCl
Heat 15 min on a steam bath
Filter thorough 0.45 micrometer membrane filter)
Adjust filtrate volume to 100 ml with water and analyze
Pre-digestion of metals
Reduce interference by organic matter and to convert metal associated with particulates to a form that can be determined by AA
HNO3 – digestion is adequate for clean samples or easily oxidized materials
HNO3-H2SO4 or HNO3-HCl – digestion is adequate for readily oxidizable organic matter
HNO3-HClO4 or HNO3-HClO4-HF – is for the difficult to oxidize organic matter or minerals
Nitric Acid Digestion
Mix sample
Transfer 50 to 100ml to 125 ml conical flask
Add 5 ml conc. HNO3 and few boiling chips
Boil and evaporate on hot plate to lowest volume (10 to 20 ml) before precipitation occurs
Continue heating and adding HNO3 until digestion is complete (light-coloured, clear solution)
Wash down flask walls with water and then filter
Transfer filtrate to 100 ml flask , cool, dilute to mark, mix and analyze.
Direct Air-Acetylene Flame Method
Applicable for Ca, Cd, Cr, Co, Cu, Fe, Mg, Mn, Ni, Zn, etc
Principle
The technique of flame atomic absorption spectroscopy (AA) requires a liquid sample to be aspirated, aerosolized, and mixed with combustible gases, such as acetylene and air or acetylene and nitrous oxide
The mixture is ignited in a flame whose temperature ranges from 2100 to 2800 oC
During combustion, atoms of the element of interest in the sample are reduced to free, unexcited ground state atoms, which absorb light at characteristic wavelengths
RISK ASSESSMENT
Environmental Engineer
objective
Reduce risk from hazards to the environment and public health
Estimate future risks, then use science to prevent or mitigate them
To determine the comparative risks from various environmental pollutants and which risks it is most important to decrease or eliminate
risk analysis
Risks associated with various hazards must evaluated and quantified
Risk
1970s – environmental laws were enacted to protect public heath
E.g. US Clean Air Act
No mention of risk in US Clean Air and Clean Water Acts
Acts required that pollution standards be set that would allow adequate margins of safety to protect public health
Assumption was that pollutants have thresholds and exposure to concentrations below these thresholds would produce no harm
Problems of toxic waste were finally recognized
Toxic substances are suspected carcinogens
Even smallest exposures creates a risk
If any exposure to a substance causes some risk, how can air quality and water quality standards be set
Emergence of the field of environmental risk assessment
1980s - environmental policy - was acceptance of the role of risk assessment and risk management in environmental decision making
Risk assessment
Is a system of analysis that includes four tasks
Identification of substance (toxicant) that may have adverse health effects
Scenarios for exposure to toxicant
Characterization of health effects
As estimate of the probability (risk) of occurrence of these health effects
Is the gathering of data that are used to relate response to dose
Such dose-response data can then be combined with estimates of the likely human exposure to produce overall assessment of risk
Risk management
is the process of deciding what to do
It is the decision making, about how to allocate national resources to protect public health and the environment
Is a one-in-a-million lifetime risk of getting cancer acceptable and, if it is, how do we go about trying to achieve it?
Hazardous substances
Hazardous and toxic substances are
defined as those chemicals present in the
environment which are capable of causing harm
Risk
is the possibility of loss or
injury to people and property
Hazard
a chemical, physical, or biological agent or a set of conditions that has the potential to cause harm
Risk Assessment
Hazard identification
Is the process of determine whether or not a particular chemical is causally linked to a particular health effects, such as cancer on birth effects
Dose-response assessment
Is the process of characterizing the relationship between the dose of an agent administered or received and the incidence of an adverse effect
Dose-Response Assessment
Characteristic features of the Dose- Response
relationship:
Threshold
Is the lowest dose at which there is an observable effect
Curve A – illustrate threshold response i.e. there is no observed effect until a particular concentration is reached
Curve B - linear response with no threshold i.e. the intensity of the effect is directly proportionally to the pollutant dose, and the effect is observed for any detectable concentration of the pollutant in question
Curve C –sublinear dose-response curve and is characteristic of many pollutant dose-response relationships.
It has no clearly defined threshold, the lowest dose at which a response can be detected is called threshold limit value (TLV)
Curve D – supralinear relationship, which is found when low doses of a pollutant appear to provoke a disproportionately large response
Total body burden
An organism or a person can be exposed to simultaneously to several sources of a given pollutant
Example
inhale about 50g/day lead from ambient air and
ingest 300g/day in food and water
The concentration of lead in the body is sum of what is inhaled and ingested and what remains in the body fro prior exposure, less what has been eliminated from the body
Physiological half-life
Is the time needed for the organism to eliminate half of the internal concentration of the pollutant, through metabolism or other normal physiological functions
Bioaccumulation and bioconcentation
Bioaccumulation occurs when a substance is concentrated in one organ or the of tissue of an organism
E.g. Iodine - bioaccumulates in the thyroid gland
The organ dose of a pollutant can thus be considerably greater than what the total body burden would predict
Bioconcentation occurs with a movement up the food chain
E.g. A study of Lake Michigan ecosystem (Hickey et al. 1966) found bioconcentation of DDT as follows:
0.014 ppm (wet weight) in bottom sediments
0.41 ppm in bottom-feeding crustacea
3-6 ppm in fish
2 400 ppm in fish –eating birds
Exposure time and time vs. dosage
Most pollutant need time to react; the exposure time is thus as important as the level of exposure
Synergism
Occurs when two or more substances enhance each other’s effects, and when the resulting effect of the combination on the organism is greater than the additive effects of the substances separately
E.g. black lung disease in miners – occurs more often in miners who smoke than in those who do not
LC50 and LD50
LD50 is the dose that is lethal for 50% of the experimental animals
LC50 refers to lethal concentration rather than lethal dose
LD50 values are most useful in comparing toxicities for pesticides and agricultural chemicals
Population responses
Differ from one individual to another
Depends on age, sex, and general state of physical and emotional health
Exposure and Latency
Characterization of some health risks can take a very time
E.g.. Cancers are noticed many years or decades after exposure to potentially responsible carcinogen
Cancer in adults have a latency period between 10 – 40 years
Latency period – length of time between exposure to a risk factor and expression of adverse effect
Relative risk
Is the ratio of the probabilities that an adverse effect will occur in two different populations
E.g. relative risk of lung cancer in smokers
Ps/Pn = (Xs/Ns)/(Xn/Nn)
where
Ps = probability of fatal lung cancer in smoker
Pn = probability of fatal lung cancer in non-smokers
Xs = number of fatal lung cancer among smokers
Xn = number of fatal lung cancer among non- smokers
Ns = total number of smokers
Nn= total number on non-smoker
Relative risk of death is also called standard mortality ratio (SMR)
SMR = Ds/Dn= Ps/Pn
where
Ds = observed lung cancer deaths in a population of habitual smokers
Dn = expected lung cancer deaths in a non-smoking population of the same size
Exposure assessment
Involves determining the size and nature of the population that has been exposed to the toxicant under consideration, and the length of time and toxicant concentration to which they have been exposed
Risk characterization
Is the integration of the foregoing three steps, which results in an estimate of the magnitude of the public-health problem
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