Pollution Flashcards
(135 cards)
1
Q
What are the properties of pollutants? How do they affect their impact?
A
- State of matter, can affect how pollutants are dispersed
- Energy form, changes the impact
- Density, changes dispersal rate and radius
- Persistence, how long the impact lasts for
- Toxicity, how badly the pollutant effects organisms
- Specificity, what organisms will be affected by the pollutant
- Reactivity, how bad the pollution will be in tandem with others
- Secondary Pollutants, further effects of pollution
- Adsorption, how easily the pollutant can be captured
- Solubility in water/lipids, how easily the pollutant spreads
- Bioaccumulation, how easily the pollutant can build up
- Biomagnification, how easily pollutants can be passed up the food chain
- Mutagenic Action, how easily pollutant changes DNA
- Teratogenic Action, how easily a pollutant can affect offspring
- Mobility, how easily a pollutant can spread
2
Q
What environmental features can affect Persistance?
A
- light
- temperature
-oxygen level - pH
- Presence of Bacteria
3
Q
What ways can pollutants chemically degrade?
A
- Biodegradation, caused by living organisms
- Photodegradation, caused by light
- Thermal degradation, cause by heat
4
Q
How do we measure the persistence of a pollutant?
A
Environmental half-life
5
Q
How do toxic substances usually cause harm?
A
Damage to proteins, especially enzymes
6
Q
What is the difference between Biomagnification and Bioaccumulation?
A
Bioaccumulation is the build up of a pollutant within a single organism. Biomagnification is the successive build up in a food chain
7
Q
What are common effects of Mutagenic Action?
A
- Gondiac effects on sperm, eggs or embryos resulting in birth deformities
- Somatic effects that are changes in bodily cells including cancer
- Carcinogenic action, which causes cancer
8
Q
What is the difference between Mutagenic and Teratogenic action?
A
Mutagenic affects the DNA of anything, not just unborn offspring while Teratogenic affects the proteins and enzymes that control gene expression. Both can result in birth defects
9
Q
What environmental features can affect dispersal?
A
- Wind and Water currents
- Temperature Inversion
- Adsorbent Materials like clay
10
Q
What is a temperature Inversion?
A
Where cold air is trapped under warm air usually in a valley thanks to low wind velocities
11
Q
What strategies can help to control pollution?
A
- Critical Pathway Analysis
- Critical Group Monitoring
- Control of Emission location
- Control of Emission timing
12
Q
What is Critical Pathway Analysis?
A
A method of predicting the path of dispersal a pollutant would take to see if it warrants further action to prevent, of it it will have minimal effects
13
Q
What is Critical Group Analysis?
A
A way of assessing public risk of pollutants by monitoring the most at risk group in a community
14
Q
What is environmental monitoring?
A
The process of monitoring places where pollutants, especially radioactive ones, are likely to build up and assuming if they are fine, then everywhere else is too
15
Q
What are the 4 principles of Pollution Control?
A
- “Polluter Pays”, the one responsible for the pollution should pay for the prevention and cleaning up
- “Precautionary”, always assume something will cause pollution unless research shows it won’t
- “Selection”, always select the correct method of control
- “Efficiency”, Emissions should be “As Low As Reasonably Achievable” (ALARA) using the “Best Available Technology, Not Entailing Excessive Cost” (BATNEEC)
16
Q
What categories of pollution control are there? Give example of each
A
- Production prevention, such as pre-combustion desulfurization
- Release Prevention, such as Catalytic Convertors
- Post-release Remediation, such as oil clean-up methods
- Alternatives, such as electric vehicles or renewables energy
17
Q
What are the categories of smoke?
A
PM10: particulate matter less than 10 microns in diameter
PM5: particulate matter less than 5 microns in diameter
PM1: particulate matter less than 1 micron in diameter
18
Q
What are the main sources of smoke?
A
- Combustion of fossil fuels
- Combustion of biofuels
19
Q
What effects can smoke pollution have on humans and animals?
A
- respiratory diseases
- destruction of lung tissues
- Increased infection risks
- Some carcinogenic chemicals
20
Q
What effects can smoke pollution have on plants?
A
- reduced photosynthesis
- heavy metal pollution
21
Q
What effects can smoke pollution have on non-living objects and the environment?
A
- Building damage from acids
- Temperature reduction (due to albedo decrease)
- Nuclear Winter
- Ozone layer depletion
22
Q
What is smog? Why is it dangerous?
A
Smog is a combination of fog and smoke that is more easily breathed in the smoke, leading to increased impacts.
23
Q
How can smoke pollution be controlled?
A
- Legislation such as the Clean Air Act
- Domestic use of electricity over wood
- Diesel particulate filters on cars
- Electrostatic precipitators that remove airborne smoke particles
- Scrubber, that uses a fine water spray to remove smoke particles
- Coal treatment, which produces smoke-less coal and tar
- More efficient combustion technology
24
Q
What is photochemical smog?
A
Neither smoke or fog despite the name. It is nitrogen monoxide from combustion combining with ozone and unburnt hydrocarbons
25
How and where are most Oxides of Nitrogen released?
From exhausts where nitrogen and oxygen from the air are drawn in and react under high temperatures
26
Where are unburnt hydrocarbons released?
Usually engine exhausts, fuel evaporation or spilling
27
What negative effects can photochemical smogs have?
- Individual pollutants are either toxic or increase risk of respiratory diseases
- Toxic
- Cause eye irritation
- Difficulty breathing and worsening of respiratory diseases
28
Where are photochemical smogs common?
Areas in valleys where temperature inversions can form with high vehicle use
29
How can photochemical smogs be contolled?
- NOx can be controlled using catalytic convertors in vehicles
- Unburnt hydrocarbons can be prevented by being collected by activated carbon filters
30
What pH is acid rain?
Higher than 5.6
31
What can be the main components of acid rain?
- sulphur dioxide or trioxide
- oxides of nitrogen
- ozone
- hydrogen chloride
32
What effects can acid rain have on non-living things and the environment?
- Corroding metal
- damage to porous rock structures
- metal ion leaching from soil
- mobilisation of toxic ions
33
What effects can acid rain have on living organisms?
- Acids can denature proteins and enzymes
- damage exposed tissues
- dissolve exoskeletons
- change lichen pH
- cause breathing issues
34
What environmental factors can affect acid rain severity and how?
- High soil lime content can neutralise acids
- Fog can increase damage done if acid rain becomes acid fog
- Snow may build up as acidic snow which creates major acidic meltwater flows
35
What methods of desulfurization exist?
- Natural gas desulfurization using iron particle reactions
- Coal can be desulfurized by washing and streaming
- Dry flue-gas desulfurization happens by passing the gases through crushed calcium carbonate
- Wet flue-gas desulfurization bubbles the gases through sodium sulphite
36
How can oxides of nitrogen be controlled?
- Low temperature combustion
- Catalytic convertors
- Urea sprays
37
Why is tropospheric ozone bad?
It is toxic to living organisms and can:
- reduce plant growth
- cause difficultly breathing
- contributes to other pollutants like acid rain
38
What negative effects does carbon monoxide have?
It binds to haemoglobin and prevents it from carry oxygen through the body. It also worsens heart disease
39
How can carbon monoxide be controlled?
Catalytic convertor
40
How can natural processes affect water pollution?
The water cycle naturally removes and purifies water containing pollutants through evaporation
41
What factors can affect the dilution/concentration of pollutants in water?
- The volume of water
- Water residence time
- The amount of pollutant
42
What factors affect the degradation of waterborne pollutants?
- High sunlight or UV levels
- Higher dissolved oxygen speeds up bacterial breakdown of sewage
- Increased temperatures
43
Why can pollution dispersal be both a boon and an issue?
It can spread the pollution to such a degree it becomes harmless, but also makes it harder to control and should it re-amass it can cause damage
44
What are the harmful effects of Thermal pollution?
- Reduction in possible dissolved oxygen
- Denaturing aquatic organism enzymes
- Increased metabolic rates of organisms
- Colonisation and thriving of invasive species
45
What is the main source of thermal pollution and how can it be controlled?
Cooling water used by factories or other industry.
It can be controlled by
- Implementing cooling towers
- Taking only from large water bodies so that temp increase will be spread thin
46
What effects can oil pollution have?
- Toxicity
- asphyxiation and photosynthesis denial
- Drown birds
- Reduction of oxygen able to dissolve into water
- Sense of smell for aquatic organisms effected
47
What operation methods can be used to prevent oil pollution?
- Recycling of waste oil
- Safter and further out shipping routes to prevent beaching
- Better navigation to avoid ship collision
- Filling oil tankers with exhaust not oxygen to prevent explosions
- Tank washing
- Oily waste water disposal
48
What designs can be used to prevent oil pollution?
- Double hulls that protect the oil tanks
- Twin engines to prevent helplessness if one dies
- Separate oil and ballast tanks to prevent contamination
- Oil interceptors that split oil from drainage water
- Bund walls to prevent overflowing of oil containers
49
What methods of treating oil spills are there?
- Booms, which are long floating tubes with a skirt below that prevent oil movement unless the current is too strong
- Skimmers, which rotate to pick up oil
- Absorbent materials
- Dispersants, which break up oil and cause it to split into small biodegradable parts
- Steam washing which can remove oil from beaches by spraying it with hot steam
- Bioremediation, where bacteria break down the hydrocarbons
50
What is MDAF and MDNF for pesticides?
MDNF is the minimum dose that can be used without killing any of a population.
MDAF is the minimum dose that is fatal to the entire population.
51
What effects can pesticides have?
- Inhibiting metabolic processes
- Illness
- Other toxicity effects like sterilisation
52
What are the 4 groups of pesticides?
- Organochlorines
- Organophosphates
- Pyrethroids
- Neonicotinoids
53
What are the properties of Organochlorines? Name an example
- High toxicity to insects
- Low toxicity to vertebrates
- High persistence
- High liposolubility
- Low Water solubility
DDT
54
What are the properties of Organophosphates?
- Neurotoxic
- Low persistence
- Low liposolubility
- Low specificity
- High toxicity to mammals
- Possible carcinogen
55
What are the properties of Pyrethroids?
- High insect toxicity
- Low mammal toxicity
- Low persistence
- High fish toxicity
56
What are the properties of Neonicotinoids?
- Neurotoxic
- High insect toxicity
- Low vertebrate toxicity
- High persistence
- High water solubility
- Especially toxic to bees
57
How can pesticide pollution be reduced?
- Restrictions on use
- Non-persistent pesticides
- Specific pesticides
- Application timing
- Use of alternative pest control
58
What are examples of inorganic nutrients?
- Phosphates in sewage
- Nitrates from fertiliser
59
What effects can inorganic nutrients have on living organisms?
- May be toxic
- May react with haemoglobin
- May be carcinogens
60
What effects can inorganic nutrients have on the environment? What is the name for this?
Cultural Eutrophication, is the process of providing too many nutrients to an aquatic habitat depleting oxygen by growing too many plants or algae that can have negative consequences
61
How can inorganic nutrients be controlled?
- Reduced nitrate fertiliser use
- Reduced ploughing before heavy rain
- fast-release fertilisers
- reduce cultivation of high nitrogen plants
- reduce reliance on inorganic fertilisers
62
What is organic nutrient pollution?
Process involving animals and plant products producing organic nutrients that are then released
63
What effects can organic nutrient pollution have?
- Eutrophication or similar process
- Spread of pathogens
64
How can the effects of organic nutrient pollution be reduced?
- Banning of sewage discharge
- Sewage treatment
65
What are the 5 groups of sewage treatment?
- pre-treatment
- primary treatment
- secondary treatment
- tertiary treatment
- sludge treatment
66
What does pre-treatment do? Give an example
Removes large solid objects like paper or grit.
Examples:
- Metal grill or sieve 'screens' that trap suspended objects
- Grit traps
67
What does primary treatment do? How does it work?
Separates organic matter from the sewage by sedimentation tanks
68
What is sludge treatment?
It is the process of dealing with the sediment built up in sewage work sedimentation tanks by:
- Adding it to landfill
- Dispersing it into the sea
- Incineration
- Agricultural use as fertiliser
69
What does secondary treatment do? What methods are used?
Removes and destroys the remaining organic matter.
- Aeration tanks that allow bacteria to break down the organic matter by mixing in oxygen using paddles
- Secondary Sedimentation tanks, self explanatory
- Trickling filter beds that spray the sewage through lumps of solid material allowing for bacteria, algae and fungi to digest the organic matter
70
What is tertiary treatment?
Additional removal of phosphates and bacteria for release into ecologically sensitive discharge points.
- Phosphates are removed by iron(III) reactions
- Micro-strainers remove most bacteria and UV is used to remove the rest
71
How is acid mine drainage produced?
Sulphides in spoil heaps undergo reactions with oxygen to produce metal oxides and oxides of sulphur, which combine with drainage water to produce sulphuric acid
72
How can acid mine drainage be prevented?
passing the drainage water through limestone beds to neutralise the acids
73
How does BOD monitoring work?
Biological oxygen demand monitoring works by monitoring the oxygen levels of water to see how much deoxygenation has been caused by pollutants
74
How does Coliform count monitoring work?
E.coli can be tested for in water as evidence of faecal contamination as it is the most common gut bacteria
75
How do Biotic Indices work? What features do they have?
Biotic indices are organisms that can be used to indicate the quality of an environment
- Range of sensitivity to pollution
- Easy to identify
- Easy to find
- Common
- well distributed
76
What are the largest sources of lead pollution?
Lead acid batteries of lead construction materials
77
What are the effects of acute lead exposure?
- brain damage
- paralysis
- death
- liver and kidney failure
78
How can lead pollution be controlled?
- Replacing lead water pipes
- Replacing lead petrol additives
- Replacing lead paint
- Replacing lead fishing weights
- Replacing lead shotgun pellets
79
What are the sources of mercury pollution?
- Disposal of mercury batteries, lights or thermometers
- Chemical production plants that use mercury to make chlorine
- Combustion of coal
80
What are the effects of mercury? How do they vary with chemical form?
- Liquid is not easily absorbed through the skin or gut
- Inorganic compounds can be absorbed in the gut
- organic compounds are easily absorbed by skin or gut
- gaseous mercury can easily be inhaled
All are very toxic
81
How can mercury pollution be controlled?
- Replacing mercury equipment
- Removed using activated carbon filters
- Ion exchangers
82
What are sources of Cadmium pollution?
- Old cadmium batteries
- incineration of cadmium paints or plastics
- drainage water from cadmium mines
83
What effects can cadmium have?
- Brain death
- Paralysis
- Lung cancer
- Kidney failure
- Skeletal collapse
84
How is cadmium pollution controlled?
- banning
- responsible disposal into hazardous waste sites
85
What is the source of tin pollution? How has it been stopped?
TBT was an active chemical in a paint used to prevent marine life growing on boats, this practice is now prohibited
86
What effects can tin pollution have?
TBT is toxic to marine life and can alter the growth and reproductive physiology of marine animals
87
What effects can Iron pollution have?
Iron is toxic and can cause deoxygenation of water
88
How can iron pollution be controlled?
Implementation of mesh screens around spoil heaps to filter out iron
89
What are some sources of solid waste?
- Mine overburden and spoil heaps
- Demolition waste
- packaging thrown away
- old appliances
- thrown away clothes
- large amounts of sewage waste
- industrial waste
90
What industrial practices increase solid waste production?
- Built-in obsolescence
- Disposable products
- Over-packaging
91
What factors affect the disposal of solid waste?
- population density
- mass of the waste
- properties of the waste (flammability, toxicity, etc)#- - land availability
- recycling technology
- environmental awareness
- legislation
- waste processing costs
92
What are features of responsible landfill management?
- Separation of waste type
- Polymer lining to prevent fluid escape
- Fence to trap litter being blown away
- Covering with soil
- Collection of products such as leachate and methane
- Deodorising spray to control smell
- Dispersal of flammable materials
93
What are the disadvantages of landfill?
- potential loss of resources
- Large land use
- Release of greenhouse gases
- Toxic leachate
- Transport of waste
94
What are spoil heaps?
Large quantities of non-toxic waste produced by industrial activities
95
How can spoil heaps be managed?
- Stability to prevent slips
- Drainage
- Addition of topsoil and nutrients
- pH reduction
- Landscaping
- Toxic leachate and metal leaking prevention
- Reduce airflow to flammable wastes
96
What are the advantages of incineration?
- Ash has low volume
- Heat can be used for energy
- No sorting is needed
97
What are the disadvantages of incineration?
- Resource value lost
- Toxic gas release
- Expensive fuels
- Treatment of pollutants raises costs
98
What is encapsulation?
Hazardous wastes containing heavy metals and intermediate radioactive waste are mixed with cement slurry and poured into unreactive containers
99
What is vitrification?
Highly radioactive wastes are mixed with molten glass and poured into steel containers which are sealed and put inside a concrete building
100
What is the worst part of this unit?
Noise pollution
101
What scale is used to measure human hearing? Why is it special?
The Bel, it is special because it is a lotharithmic scale and does not start at no sound, instead starting at the lowest sound a human can here
102
What is the typical human hearing range?
20-20000 Hz
103
What effects can noise pollution have on non-living objects?
- Acoustic fatigue: when a noise hits a frequency that causes an object to vibrate (the natural resonant frequency), it can potentially crack
- Vibrational damage: similar to above, but due to repeated exposure to general vibrations
- Shock Impacts: sudden loud noises (like sonic booms) can cause damage
104
What effects can noise pollution have on humans?
- Hearing damage
- Increase in stress and stress-related health problems
- Behavioural changes due to lack of sleep or increased stress
- Communication interruption or other issues
105
What effects can noise pollution have on non-human organisms?
- Livestock can become panicked leading to injuries or breeding failure
- Disturbance of breeding bird song
- Birds may be scared leading to abandoning nests or knocking eggs out
- Reduced feeding success for animals that rely on hearing to find prey
- Whales and dolphins may be harmed by loud noises such as sonar
106
How can noise pollution from loud military aircraft be reduced?
- Keep airfields away from urban areas
- Avoidance areas (for urban and ecological areas)
- Vary flight paths
- Low-flying stop requests
- Flight timetables published
- Compensation
107
How can noise pollution from civil aircraft, which are typically located closer to urban areas, be reduced?
- High cruise altitudes to reduce noise reaching the ground
- Aircraft scheduling to minimise number and times of flights to ideal levels
- Include acoustic insulation
- Prevent urban development around airports
- Baffle mounds and acoustic barriers
- Multiple runways reduce fast landing need and therefore break noise levels
108
How can aircraft engine design be changed to lower noise pollution?
- High bypass-ratio engines which have a second cowling to allow bypass air that smooths the flow of exhaust air and reduces noise
- Chevron Nozzles which have a serrated trailing to mix the bypass air more smoothly
- Engine acoustic liners to absorb noise
109
How can aircraft body design reduce noise pollution?
- Blended wing aircraft, which have top engines that use the body as a noise buffer
- Aerodynamic can be increased using fairings that reduce turbulence around hinges and wheels
- Lighter aircraft made of carbon fibre for example reduce the engine thrust needed therefore reducing engine noise
110
How can aircraft operation be used to reduce noise pollution?
- Take-off angle being steeper means less time close to the ground
- Flight path planning to avoid densely populated areas
- Constant descent angle makes engine noise less intrusive
- Night flight restriction to prevent sleep disruption
111
How can noisier aircraft be controlled?
- Noise limits that categorise planes into increasing strict groups based on level of noise which are slowly being phased out starting with the noisiest
- Increased charges for noisier planes to use airports and for night flights
- Restricted flight times
- Quota count system that adds points to airlines depending on the noise of their planes and total points cannot exceed a threshold
- Ban of supersonic flight
112
How can railway noise be controlled?
- Wheel vibration can be reduced by sound absorbing ballasts and track polishing
- Engine noise can be reduced by sound absorbing suspension
- Pantograph turbulence can be reduced by aerodynamic improvements
- Wheel squeak on corners can be reduced by lubrication of tracks
- Breaking squeal can be reduced by composite material brakes
- Wheel noise can be reduced by good carriage suspension
113
How can road traffic noise be controlled
- Wheel noise can be reduced by sound absorbing road materials like porous or rubber asphalt
- Vehicles air turbulence can be reduced by aerodynamic designs
- Engine noise can be reduced by acoustic insulation and quieter exhaust pipes
- General road vehicle noise can be reduced by rerouting traffic, producing free-flow traffic, creating fences wall or dense trees and by acoustic insulating buildings near to roads
114
What are the sources and controls of industrial noise?
- Air compressors and pumps can be fitted with silencers
- Stamping machines can be replaced with quieter techniques like pressing
- Metal conveyors can include wheels, rollers or bearings
- Mine blasting can be timed and reduced by baffle mounds
115
What general methods of industrial noise reduction?
- Sound absorbing surfaces
- Acoustic curtains around machinery
- Machinery made of sound absorbent materials
- Remote machine operation
- Worker ear protection
116
How can domestic noise be controlled?
- Domestic appliances can be fitted with acoustic absorbers
- Ear defenders when power tools are used
- Volume limiters of music equipment
- Quieter domestic appliances
- Control of loud pets (e.g. dogs)
117
How are road traffic noise levels measured?
- LA10, measuring noise level exceeded for 10% in a set period
- LA90, measures noise level exceeded for 90% in a set period
- LA10(18h), assumes traffic noise is only a problem between 6 to 12, measures noise exceeded for 10% of each hour and then averages
- Traffic Noise Index, uses both LA10 and LA90 to produce a representative measure
118
How are aircraft noise levels measured?
- Effective Perceived Noise levels. the estimate of relative loudness of a plane during take-off flight and landing
- Noise and Number Index, combines number of flights with aircraft noise levels above 80dB. Replaced by Leq 57dB
- Leq 57dB, average sound over a particular period, usually 57dB in UK airports
119
What are the issues with assessing risk of ionising radiation?
- symptoms may take a long time to develop
- effects may have alternative causes
- accurate data on impacts is not usually available
- accurate data on who and how badly exposed is not usually available
120
What are the natural sources of radiation exposure and the % average dose
- Cosmic sun radiation, 10%
- Gamma rays from lithosphere, 14%
- Internal body sources, 11%
- Ground Radon, 50%
121
What are the human sources of radiation exposure and the % average dose
- Medicinal exposure, 14%
- Occupational exposure, 0.3%
- Weapons fallout, 0.2%
- Consumer products, <0.1%
- Industrial discharge, <0.1%
122
What is the measure of comparative effects of different types of ionising radiation on living tissues?
Relative Biological Effectiveness (RBE)
123
What is the ease of absorption, RBE and health risks of Alpha radiation?
Very easily absorbed, travels short distances
RBE: 20
Ingested alpha emitters will cause large damage to internal body structure
124
What is the ease of absorption, RBE and health risks of Beta radiation?
Moderately easily absorbed, travels medium distances
RBE: 1
Moderate danger when sources is close by
125
What is the ease of absorption, RBE and health risks of Gamma and X rays?
Not easily absorbed, travels long distances
RBE: 1
Low danger, sources have a larger range of risk
126
What is the ease of absorption, RBE and health risks of Neutrons?
Moderately easily absorbed, travels medium distance
RBE: 2-10
Very dangerous, can pose a risk even after being absorbed, and can cause a stable nucleus to decay and release radiation
127
What effects can ionising radiation have on living tissue?
- Damage to cell nucleus, causing changes in DNA called mutations
- Damage to other cell parts which can cause cell death
- Somatic effects, general damage to body cells and organs
- Gondiac effects, damage to ovary or testes cells
- Chronic effects, which appear slowly in proportion to exposure
- Acute effects, which are rapid and often dangerous health effects like damage to bone marrow and the immune system
128
What is the difference between exposure and contamination?
Exposure is the absorption of ionising radiation. Contamination refers to carrying radioactive material which can release radiation and cause exposure
129
What are the two principles of ionising radiation control?
ALARA: exposure should be "As Low As Reasonably Achievable"
BATNEEC: Low exposure can be achieved by using the "Best Available Technology Not Entailing Excessive Cost"
130
What strategies can be used to reduce radiation exposure?
- Closed sources prevent workers from coming into direct contact by enclosing it in a container, pretty obvious honestly
- Absorbent materials used for barriers
- Protective clothing
- Distance from the source
- Reducing exposure period
- Decontamination after exposure and potential contamination
131
How is dosage of radiation calculated using distance from source? What is this called?
1/Distance^2. The Inverse square law
132
How are high level wastes managed?
Vitrification (encasing powdered wastes in molten glass inside stainless steel box inside concrete)
133
How are intermediate level wastes managed?
Mixed with cement and stored in stainless steel drums
134
How are low level wastes managed depending on their state?
- Solids are sealed in thick polythene bags, inside steel drums inside truck containers in concrete-lined landfills
- Liquids are filtered including ion exchange and then discharged
- Gases are filtered and then released
135
What 3 measures are there for radiation? When is each used?
- Becquerels measure activity of a source
- Grays measure absorbed dose
- Sieverts measure the effective dose that produces differing effects
