Toxicology: Nlom: Dose-Response Assessment (Test I)

Front 1

The dose-response assessment step quantitates what?

Back 1

The dose-response assessment step quantitates the hazards which were identified in the hazard evaluation phase.

Front 2

Dose-response assessment determines the relationship between what?

Back 2

It determines the relationship between dose and incidence of effects in humans.

Front 3

Dose-response assessment normally requires two major what? Explain.

Back 3

There are normally two major extrapolations required. The first is from high experimental doses to low environmental doses and the second from animal to human doses.

Front 4

The procedures used to extrapolate from high to low doses are different between what?

Back 4

The procedures used to extrapolate from high to low doses are different for assessment of carcinogenic effects and non-carcinogenic effects.

Front 5

The procedures used to extrapolate from high to low doses are different for assessment of carcinogenic effects and non-carcinogenic effects. Explain?

Back 5

Carcinogenic effects are not considered to have a threshold and mathematical models are generally used to provide estimates of carcinogenic risk at very low dose levels.

Noncarcinogenic effects (e.g. neurotoxicity) are considered to have dose thresholds below which the effect does not occur. The lowest dose with an effect in animal or human studies is divided by Safety Factors to provide a margin of safety.

Front 6

Cancer risk assessment involves how many steps. What are they?

Back 6

Cancer risk assessment involves two steps.

Front 7

The first step of cancer risk assessment is a qualitative evaluation of what?

Back 7

The first step is a qualitative evaluation of all epidemiology studies, animal bioassay data, and biological activity (e.g., mutagenicity).

Front 8

A substance is classified as a carcinogenic risk to humans based what? If the evidence is sufficient, the substance may be classified as a what?

Back 8

The substance is classified as to carcinogenic risk to humans based on the weight of evidence. If the evidence is sufficient, the substance may be classified as a definite, probable or possible human carcinogen.

Front 9

What is the second step of cancer risk assessment?

Back 9

The second step is to quantitate the risk for those substances classified as definite or probable human carcinogens.

Front 10

In cancer risk assessment mathematical models are used to extrapolate what?

Back 10

Mathematical models are used to extrapolate from the high experimental doses to the lower environmental doses.

Front 11

What are the two primary cancer classification schemes?

Back 11

The two primary cancer classification schemes are those of the Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC). The EPA and IARC classification systems are quite similar.

Front 12

The EPA's cancer assessment procedures have been used by whom?

Back 12

The EPA's cancer assessment procedures have been used by several Federal and State agencies.

Front 13

What is the ATSDR?

Back 13

The Agency for Toxic Substances and Disease Registry (ATSDR) relies on EPA's carcinogen assessments.

Front 14

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of ?categories.

Back 14

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories.

Front 15

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories. List the 6 groups.

Back 15

1. Group A

2. Group B1

3. Group B2

4. Group C

5. Group D

6. Group E

Front 16

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories. Describe Group A.

Back 16

Human Carcinogen. Sufficient human evidence for causal association between exposure and cancer.

Front 17

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories. Describe Group B1.

Back 17

Probable Human Carcinogen. Limited evidence in humans.

Front 18

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories. Describe Group B2.

Back 18

Probable Human Carcinogen. Inadequate evidence in humans and sufficient evidence in animals.

Front 19

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories. Describe Group C.

Back 19

Possible Human Carcinogen. Limited evidence in animals.

Front 20

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories. Describe Group D.

Back 20

Not classifiable as to human carcinogenicity. Inadequate evidence in animals.

Front 21

The EPA's cancer assessment procedures have been used by several Federal and State agencies. A substance is assigned to one of six categories. Describe Group E.

Back 21

No evidence of Carcinogenicity in Humans. At least two adequate animal tests or both negative epidemiology and animal studies.

Front 22

The basis for sufficient human evidence for a carcinogen is what?

Back 22

The basis for sufficient human evidence is an epidemiology study that clearly demonstrates a causal relationship between exposure to the substance and cancer in humans.

Front 23

Carcinogen data is determined to be limited evidence in humans if there are what?

Back 23

data are determined to be limited evidence in humans if there are alternative explanations for the observed effect

Front 24

Carcinogen data is considered to be inadequate evidence in humans if no what
exist?

Back 24

data are considered to be inadequate evidence in humans if no satisfactory epidemiology studies exist.

Front 25

For a carcinogen what is considered sufficient evidence in animals?

Back 25

An increase in cancer in more than one species or strain of laboratory animals or in more than one experiment is considered sufficient evidence in animals. Data from a single experiment can also be considered sufficient animal evidence if there is a high incidence or unusual type of tumor induced.

Front 26

Normally, what is considered as only limited evidence in animals?

Back 26

Normally, however, a carcinogenic response in only one species, strain, or study, is considered as only limited evidence in animals.

Front 27

When is something subjected to a quantitative risk assessment?

Back 27

When an agent is classified as a Human or Probable Human Carcinogen, it is then subjected to a quantitative risk assessment

Front 28

What is the cancer slope factor?

Back 28

The key risk assessment parameter derived from the EPA carcinogen risk assessment is the cancer slope factor.This is a toxicity value that quantitatively defines the relationship between dose and response. The cancer slope factor is a plausible upper-bound estimate of the probability that an individual will develop cancer if exposed to a chemical for a lifetime of 70 years. The cancer slope factor is expressed as mg/kg/day.

Front 29

Mathematical models are used to extrapolate what? Most assume what?

Back 29

Mathematical models are used to extrapolate from animal bioassay or epidemiology data to predict low dose risk. Most assume linearity with a zero threshold dose.

Front 30

EPA uses the what Model to conduct its cancer risk assessments?

Back 30

EPA uses the Linearized Multistage Model (LMS) to conduct its cancer risk assessments.

Front 31

EPA uses the Linearized Multistage Model (LMS) to conduct its cancer risk assessments. What does it yield? What does it assume?

Back 31

EPA uses the Linearized Multistage Model (LMS) to conduct its cancer risk assessments. It yields a cancer slope factor, known as the q1* (pronounced Q1-star) which can be used to predict cancer risk at a specific dose. It assumes linear extrapolation with a zero dose threshold from the upper confidence level of the lowest dose that produced cancer in an animal test or in a human epidemiology study.

Front 32

List 5 models that have been used for cancer assessments.

Back 32

1. Linearized Multistage Model (LMS)

2. One hit model

3. Multi hit model

4. Probit model

5. Physiologically Based Pharmacokinetic Models (PB-PK models).

Front 33

Describe the One hit model used for cancer assessment.

Back 33

This is a very conservative model. It assumes that there is a single stage for cancer and that one molecular event induces a cell transformation.

Front 34

Describe the Multi hit model used for cancer assessment.

Back 34

This model is one of the least conservative models. It assumes several interactions are needed before a cell can be transformed.

Front 35

Describe the Probit model used for cancer assessment.

Back 35

This model assumes log normal distribution (probit) for tolerances of exposed population. While sometimes used, it is generally considered inappropriate for the assessment of cancer.

Front 36

Describe the Physiologically Based Pharmacokinetic Models (PB-PK models) used for cancer assessment.

Back 36

This model incorporates pharmacokinetic and mechanistic data into the extrapolation process. It requires extensive data and is becomingly commonly used.

Front 37

PB-PK models are relatively ? and are being employed when?

Back 37

PB-PK models are relatively new and are being employed when biological data are available.

Front 38

PB-PK models quantitate what?

Back 38

They quantitate the absorption of a foreign substance, its distribution, metabolism, tissue compartments, and elimination

Front 39

How are compartments involved in PB-PK models? What are these parameters used to derive?

Back 39

Some compartments store the chemical (bone and adipose tissue) whereas others biotransform or eliminate it (liver or kidney). All these biological parameters are used to derive the target dose and comparable human doses.

Front 40

Historically, the Acceptable Daily Intake (ADI) procedure has been used to calculate what?

Back 40

Historically, the Acceptable Daily Intake (ADI) procedure has been used to calculate permissible chronic exposure levels for humans based on non-carcinogenic effects.

Front 41

What is an ADI?

Back 41

The ADI is the amount of a chemical to which a person can be exposed each day for a long time (usually lifetime) without suffering harmful effects.

Front 42

How is an ADI determined?

Back 42

It is determined by applying safety factors (to account for the uncertainty in the data) to the highest dose in human or animal studies which has been demonstrated not to cause toxicity (NOAEL).

Front 43

The EPA has slightly modified the ADI approach. Explain.

Back 43

The EPA has slightly modified the ADI approach and calculates a Reference Dose (RfD) as the acceptable safety level for chronic non-carcinogenic and developmental effects.

Front 44

The ATSDR calculates what for noncancer end points?

Back 44

The ATSDR calculates Minimal Risk Levels (MRLs) for noncancer end points

Front 45

What is the critical toxic effect?

Back 45

The critical toxic effect used in the calculation of an ADI, RfD, or MRL is the serious adverse effect which occurs at the lowest exposure level. It may range from lethality to minor toxic effects. It is assumed that humans are as sensitive as the animal species unless evidence indicates otherwise.

Front 46

In determining the ADIs, RfDs or MRLs, the NOAEL is divided what? Why?

Back 46

In determining the ADIs, RfDs or MRLs, the NOAEL is divided by safety factors (uncertainty factors) in order to provide a margin of safety for allowable human exposure

Front 47

What is the equation for an ADI as it relates to NOAEL?

Back 47

ADI (human dose) = NOAEL (experimental dose) / Safety Factor(s).

Front 48

When a NOAEL is not available, a ? can be used to calculate the RfD. What is included if this is done?

Back 48

When a NOAEL is not available, a LOAEL can be used to calculate the RfD. An additional safety factor is included if an LOAEL is used.

Front 49

A Modifying Factor of 0.1-10 allows risk assessors to do what? Give an example.

Back 49

A Modifying Factor of 0.1-10 allows risk assessors to use scientific judgment in upgrading or downgrading the total uncertainty factor based on the reliability and quality of the data. For example, if a particularly good study is the basis for the risk assessment, a modifying factor of < 1 may be used. If a poor study is used, a factor of >1 can be incorporated to compensate for the uncertainty associated with the quality of the study.

Front 50

List the 5 Uncertainty Factors or Safety Factors used to derive an ADI or RfD.

Back 50

1. 10X (human variability)

2. 10X (extrapolation from animals to humans)

3. 10X (use of less than chronic data)

4. 10X (use of LOAEL instead of NOAEL)

5. 0.1 - 10X (modifying factor)

Front 51

The modifying factor is used only in deriving what?

Back 51

The modifying factor is used only in deriving EPA Reference Doses.

Front 52

The number of factors included in calculating the ADI or RfD depend upon what?

Back 52

The number of factors included in calculating the ADI or RfD depend upon the study used to provide the appropriate NOAEL or LOAEL.

Front 53

What is the general formula for deriving the RfD?

Back 53

RfD = (NOAEL or LOAEL)/(UF1 x UF2 x ...)

Front 54

The more uncertain or unreliable the data becomes, the ? will be the total uncertainty factor that is applied.

Back 54

The more uncertain or unreliable the data becomes, the higher will be the total uncertainty factor that is applied.

Front 55

A subchronic animal study with a LOAEL of 50 mg/kg/day was used. What are the uncertainty factors?

Back 55

10 for human variability, 10 for an animal study, 10 for less than chronic exposure, and 10 for use of an LOAEL instead of a NOAEL.


RfD = (50mg/kg/day)/(10 X 10 X 10 X 10) = 0.005mg/kg/day

Front 56

In addition to chronic effects, RfDs can also be derived for what?

Back 56

In addition to chronic effects, RfDs can also be derived for other long term toxic effects, including developmental toxicity.

Front 57

While ATSDR does not conduct cancer risk assessments, it does derive Minimal Risk Levels (MRLs) what?

Back 57

While ATSDR does not conduct cancer risk assessments, it does derive Minimal Risk Levels (MRLs) for noncancer toxicity effects (such as birth defects or liver damage).

Front 58

Define Minimal Risk Levels?

Back 58

The MRL is defined as an estimate of daily human exposure to a substance that is likely to be without an appreciable risk of adverse effects over a specified duration of exposure.

Front 59

For inhalation or oral routes, MRLs are derived for what?

Back 59

For inhalation or oral routes, MRLs are derived for acute (14 days or less), intermediate (15-364 days), and chronic (365 days or more) durations of exposures

Front 60

The method used to derive MRLs is a modification of what?

Back 60

The method used to derive MRLs is a modification of the EPA's RfD methodology.

Front 61

The method used to derive MRLs is a modification of the EPA's RfD methodology. What is the primary modification?

Back 61

The primary modification is that the uncertainty factors of 10 may be lower, either 1 or 3, based on scientific judgment. These uncertainty factors are applied for human variability, interspecies variability (extrapolation from animals to humans), and use of a LOAEL instead of NOAEL. As in the case of RfDs, the product of uncertainty factors multiplied together is divided into the NOAEL or LOAEL to derive the MRL.

Front 62

What are also conducted to derive permissible exposure levels for acute or short term exposures to chemicals.

Back 62

Risk assessments are also conducted to derive permissible exposure levels for acute or short term exposures to chemicals.

Front 63

Health Advisories (HAs) are determined for chemicals in drinking water. What are HAs?

Back 63

Health Advisories (HAs) are determined for chemicals in drinking water. HAs are the allowable human exposures for one day, ten days, longer-term, and lifetime durations.

Front 64

What is the method used to calculate HAs?

Back 64

The method used to calculate HAs is similar to that for the RfD's using uncertainty factors. Data from toxicity studies with durations of length appropriate to the HA are being developed.

Front 65

For occupational exposures, what are developed?

Back 65

For occupational exposures, Permissible Exposure Levels (PELs), Threshold Limit Values (TLVs), and NIOSH Recommended Exposure Levels (RELs) are developed.

Front 66

For occupational exposures, Permissible Exposure Levels (PELs), Threshold Limit Values (TLVs), and NIOSH Recommended Exposure Levels (RELs) are developed. They represent dose levels that will not produce adverse health effects from repeated daily exposures in the workplace. What are the methods used to derive these?

Back 66

For occupational exposures, Permissible Exposure Levels (PELs), Threshold Limit Values (TLVs), and NIOSH Recommended Exposure Levels (RELs) are developed. They represent dose levels that will not produce adverse health effects from repeated daily exposures in the workplace. The method used to derive is conceptually the same. Safety factors are used to derive the PELs, TLVs, and RELs.

Front 67

Animal doses must be converted to what? This is based on what assumption?

Back 67

Animal doses must be converted to human dose equivalents. The human dose equivalent is based on the assumption that different species are equally sensitive to the effects of a substance per unit of body weight or body surface area.

Front 68

Historically, the FDA has used what as a ratio of what to calculate the human dose equivalent?

Back 68

Historically, FDA used a ratio of body weights of humans to animals to calculate the human dose equivalent. The animal dose was multiplied by the ratio of human to animal body weight raised to the 2/3rd power (to convert from body weight to surface area). FDA and EPA have agreed to use body weight raised to the 3/4th power to calculate human dose equivalents in the future.

Front 69

The last step in risk assessment is to express the risk in terms of what? Give an example?

Back 69

The last step in risk assessment is to express the risk in terms of allowable exposure to a contaminated source. Risk is expressed in terms of the concentration of the substance in the environment where human contact occurs. For example, the unit risk in air is risk per mg/m3 whereas the unit risk in drinking water is risk per mg/L.

Front 70

For carcinogens, the media risk estimates are calculated by doing what?

Back 70

For carcinogens, the media risk estimates are calculated by dividing cancer slope factors by 70 kg (average weight of man) and multiplying by 20 m3/day (average inhalation rate of an adult) or 2 liters/day (average water consumption rate of an adult).

Front 71

The primary toxic effect which determines the type of procedure to be used in conducting a risk assessment is:





lethality in laboratory animals




evidence that the chemical is carcinogenic




the ability of the chemical to cause eye irritation

Back 71

The primary toxic effect which determines the type of procedure to be used in conducting a risk assessment is evidence that the chemical is carcinogenic. The risk assessment for carcinogens is quite different from that of noncarcinogens. Carcinogenic effects are viewed as non-threshold effects and non-carcinogenic effects are considered to have dose thresholds.

Front 72

The EPA classification of a substance as a "Probable Human Carcinogen" requires that the substance meets the following criteria:





inadequate evidence of cancer in humans and sufficient evidence of cancer in animals




limited evidence of cancer in animals




sufficient human evidence for a causal association between exposure and cancer

Back 72

Inadequate evidence in humans means that no satisfactory epidemiology study exists. With sufficient evidence in animals (positive test results in more than one species or study), the substance can be considered as a Possible Human Carcinogen.

Front 73

The primary cancer assessment model used by the EPA is known as the:





Probit model




Multi hit model




Linearized multistage model

Back 73

The primary cancer assessment model used by the EPA is known as the linearized multistage model. It is a very conservative model and assumes linear extrapolation with a zero dose threshold from the upper confidence level of the lowest dose that produced cancer in an animal test or in a human epidemiology study.

Front 74

The ADI is calculated by the following procedure:





dividing the NOAEL by safety factors




linear extrapolation from the LOAEL to the zero intercept




multiplying the RfD by a modifying factor

Back 74

The ADI is determined by applying safety factors (to account for the uncertainty in the data) to the highest dose in human or animal studies which has been demonstrated not to cause toxicity (NOAEL). ADI (human dose) = NOAEL (experimental dose) / Safety Factor(s).

Front 75

Which of the following statements best describes the derivation of Minimal Risk Levels?





The method used to derive MRLs is similar to that for the RfD, except that the uncertainty factors of 10 may be lower.




MRLs for dermal exposure are derived by multiplying the dermal penetration by the NOAEL.




The MRL is derived by multiplying the cancer slope factor by the lowest exposure dose.

Back 75

The method used to derive MRLs is similar to that for the RfD, except that the uncertainty factors of 10 may be lower. The ATSDR applies uncertainty factors of 1, 3, or 10 for human variability, interspecies variability, and use of a LOAEL instead of NOAEL

Front 76

For risk assessment, it is necessary to convert animal doses to human dose equivalents. The current conversion procedure consists of:





Multiplying the animal dose by the human to animal body weight ratio.




Multiplying the animal dose by the human to animal body weight ratio raised to the 2/3rds power.




Multiplying the animal dose by the human to animal body weight ratio raised to the 3/4ths power.

Back 76

For risk assessment, it is necessary to convert animal doses to human dose equivalents. The current conversion procedure consists of multiplying the animal dose by the human to animal body weight ratio raised to the 3/4ths power. FDA and EPA have recently agreed to use body weight raised to the 3/4th power to calculate human dose equivalents

Front 77

What is Exposure Assessment?

Back 77

Exposure assessment is a key phase in the risk assessment process since without an exposure, even the most toxic chemical does not present a threat. All potential exposure pathways are carefully considered. Contaminant releases, their movement and fate in the environment, and the exposed populations are analyzed.

Front 78

List the 3 steps of exposure assessment. Give examples.

Back 78

Exposure assessment includes three steps:


1. characterization of the exposure setting (e.g., point source)



2. identification of exposure pathways (e.g., groundwater)



3. quantification of the exposure (e.g., µg/L water)

Front 79

List the 5 main variables of exposure assessment.

Back 79

The main variables in the exposure assessment are:


1. exposed populations (general public or selected groups)



2. types of substances (pharmaceuticals, occupational chemicals, or environmental pollutants)



3. single substance or mixture of substances



4. duration of exposure (brief, intermittent, or protracted)



5. pathways and media (ingestion, inhalation, and dermal exposure)

Front 80

All possible types of exposure are considered in order to assess what?

Back 80

All possible types of exposure are considered in order to assess the toxicity and risk that might occur due to these variables.

Front 81

The risk assessor first looks at the physical environment and the potentially exposed populations. The physical environment may include what?

Back 81

The risk assessor first looks at the physical environment and the potentially exposed populations. The physical environment may include considerations of climate, vegetation, soil type, ground-water and surface water. Populations that may be exposed as the result of chemicals that migrate from the site of pollution are also considered.

Front 82

Subpopulations may be at greater risk due to what? Give examples of subpopulations.

Back 82

Subpopulations may be at greater risk due to a higher level of exposure or because they have increased sensitivity (infants, elderly, pregnant women, and those with chronic illness).

Front 83

Pollutants may be transported away from the source. They may be physically, chemically or biologically transformed. They may also accumulate in various media. Assessment of the chemical fate requires knowledge of many factors including what?

Back 83

1. organic carbon and water partitioning at equilibrium (Koc)



2. chemical partitioning between soil and water (Kd)



3. partitioning between air and water (Henry's Law Constant)



4. solubility constants



5. vapor pressures



6. partitioning between water and octanol (Kow)



7. bioconcentration factors

Front 84

Pollutants may be transported away from the source. They may be physically, chemically or biologically transformed. They may also accumulate in various media. Assessment of the chemical fate requires knowledge of many factors including:


organic carbon and water partitioning at equilibrium (Koc)



chemical partitioning between soil and water (Kd)



partitioning between air and water (Henry's Law Constant)



solubility constants



vapor pressures



partitioning between water and octanol (Kow)



bioconcentration factors



These factors are integrated with the data on sources, releases and routes of the pollutants to determine what?

Back 84

The exposure pathways of importance.

Front 85

Exposure pathways may include what?

Back 85

1. groundwater



2. surface water



3. air



4. soil



5. food



6. breast-milk

Front 86

Since actual measurements of exposures are often not available, what may be used? Give an example.

Back 86

Since actual measurements of exposures are often not available, exposure models may be used.For example, in air quality studies, chemical emission and air dispersion models are used to predict the air concentrations to downwind residents. Residential wells downgradient from a site may not currently show signs of contamination. They may become contaminated in the future as chemicals in the groundwater migrate to the well site. In these situations, groundwater transport models may estimate when chemicals of potential concern will reach the wells.

Front 87

A major aspect of the exposure assessment is to:





determine the amount of exposure that must be reduced in order to comply with the acceptable risk level




identify the exposure pathways




measure the amount of a substance that is metabolized in the body

Back 87

A major aspect of the exposure assessment is to identify the exposure pathways. All potential exposure pathways are carefully considered as well as contaminant releases, movement and fate in the environment and the exposed populations.

Front 88

The primary method used to predict movement of substances in environmental media is:





actual measurements of air and water pollutants at various places in the environment




by use of exposure models




tagging pollutants with radioactive tracers and measuring the radioactivity at various times and locations within the environmental media

Back 88

Exposure models are the primary method used to predict movement of substances in environmental media. Because actual measurements of environmental chemical exposure are often unavailable, exposure models are used. Models can predict future movement into areas that are currently free from contamination.

Front 89

What is Risk Characterization?

Back 89

This final stage in the risk assessment process involves prediction of the frequency and severity of effects in exposed populations. Conclusions reached concerning hazard identification and exposure assessment are integrated to yield probabilities of effects likely to occur in humans exposed under similar conditions.

Front 90

Since most risk assessments include major uncertainties, it is important that biological and statistical uncertainties are what? The assessment should identify what?

Back 90

Since most risk assessments include major uncertainties, it is important that biological and statistical uncertainties are described in the risk characterization. The assessment should identify which components of the risk assessment process involve the greatest degree of uncertainty.

Front 91

Potential human carcinogenic risks associated with chemical exposure are expressed in terms of what? Give an example.

Back 91

Potential human carcinogenic risks associated with chemical exposure are expressed in terms of an increased probability of developing cancer during a person's lifetime. For example, a 10-6 increased cancer risk represents an increased lifetime risk of 1 in 1,000,000 for developing cancer. For carcinogenicity, the probability of an individual developing cancer over a lifetime is estimated by multiplying the cancer slope factor (mg/kg/day) for the substance by the chronic (70-year average) daily intake (mg/kg-day).

Front 92

For non-carcinogenic effects, the exposure level is compared with an ?, ? or ?derived for similar exposure periods. Three exposure durations are considered: ?, ?, or ?.

Back 92

For non-carcinogenic effects, the exposure level is compared with an ADI, RfD or MRL derived for similar exposure periods. Three exposure durations are considered: acute, intermediate, or chronic.

Front 93

For humans, acute effects are considered those that arise when? Intermediate effects? Chronic effects?

Back 93

For humans, acute effects are considered those that arise within days to a few weeks, intermediate effects are those evident in weeks to a year, and chronic effects are those that become manifest in a year or more.

Front 94

In some complex risk assessments such as for hazardous waste sites, the risk characterization must consider what? Why?

Back 94

In some complex risk assessments such as for hazardous waste sites, the risk characterization must consider multiple chemical exposures and multiple exposure pathways. Simultaneous exposures to several chemicals, each at a subthreshold level, can often cause adverse effects by simple summation of injuries.

Front 95

The assumption of dose additivity is most acceptable when?

Back 95

The assumption of dose additivity is most acceptable when substances induce the same toxic effect by the same mechanism. When available, information on mechanisms of action and chemical interactions are considered and are useful in deriving more scientific risk assessments.

Front 96

Individuals are often exposed to substances by what? In such situations, the total exposure will usually equal what?

Back 96

Individuals are often exposed to substances by more than one exposure pathway (e.g., drinking of contaminated water, inhaling contaminated dust). In such situations, the total exposure will usually equal the sum of the exposures by all pathways.

Front 97

The process in which the dose-response assessment and exposure assessments are integrated to predict risk to specific populations is known as:





risk management




hazard identification




risk characterization

Back 97

Risk characterization is the process in which the dose-response assessment and exposure assessments are integrated to predict risk to specific populations. It is the final stage in the risk assessment process and involves the prediction of the frequency and severity of effects in exposed populations.

Front 98

An increased cancer risk of 2.0 X 10-6 means that:





it is likely that 2 persons in one million will develop the specific type of cancer in their lifetime due to exposure to the chemical.




the xenobiotic for which the cancer risk assessment was performed is likely to cause cancer in 200 persons on a yearly basis.




it is probable that 2 million persons will develop cancer if they are continuously exposed to the chemical for life.

Back 98

An increased cancer risk of 2.0 X 10-6 means that it is likely that 2 persons in one million will develop the specific type of cancer in their lifetime due to exposure to the chemical. For many years, a one in one million acceptable risk level has been used by the FDA and EPA.