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Noncancer Toxicity Assessment Flashcards

1
Q

The toxicity assessment is usually divided into two parts, what are the parts?

A

Non-cancer effects and cancer effects

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2
Q

What is the key parameter of non-cancer effects?

A

Threshold dose- dose at which an adverse effect first becomes evidence

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3
Q

Describe the threshold of carcinogens. How is it determined?

A

No threshold, mathematical models are used to provide estimates of carcinogenic risk at very low dose levels

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4
Q

Describe the threshold of non-carcinogenic chemicals. How is it determined?

A

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

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5
Q

How do we determine the threshold dose? What two measurements does it lie between?

A

Threshold dose typically estimated from toxicological data (derived from studies of humans and /or animals) by determining the highest dose that does not produce an effect. It lies between the NOAEL and LOAEL.

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6
Q

How do you calculate the reference dose?

A

NOAEL or LOAEL / safety factors OR see slide for BMD calculation

*Conservative

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7
Q

What is the position of the EPA on sensitivity of humans to toxins?

A

humans are as sensitive as the most sensitive species unless other data available

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8
Q

What is the purpose of dividing the NOAEL or LOAEL by uncertainty factors?

A

To ensure that the RfD is not higher than the true threshold for adverse effects; it gives a margin of safety

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9
Q

What is POD?

A

Point of departure- point on a dose-response curve that corresponds to an estimated low effect or no effect level.

It marks the beginning of extrapolation to toxicological RfD or RfC

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10
Q

Draw a dose response with NOAEL, LOAEL, BMD, and POD

A

See slide

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11
Q

What are the uncertainty factors that are considered? And modifying factors? What are modifying factors?

A
  • 10: human variability
  • 10 : extrapolation from animals to humans
  • 10 use of less than chronic data
  • 10: use of LOAEL instead of NOAEL
  • 10 incomplete database
  • 0.1 to 10 MF

Modifying factors account for additional uncertainty factors such as data quality, confidence in a data set

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12
Q

Describe the benchmark dose appraoch

A
  • Newest approach to estimating noncarcinogenic toxicty
  • general value for BMD=dose that adversely affects 10% of test population (ED10)
  • may be better because NOAEL and LOAEL are subject to exp design, but BMD consistently defined
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13
Q

What is the conservative estimate of the BMD?

A

*Lower 95% confidence limit for estimate

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14
Q

Describe why the benchmark dose may be a better approach

A

experiments to measure NOAEL/ LOAEL may be too high or too low of a dose to measure threshold, choosing standard benchmark (ED10) is not a function of chosen doses and it estimates the proper value from all the data, not just a single point

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15
Q

Are uncertainty factors still required for the BMD?

A

they may still be applied so BMD/ product (UF)*MF

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16
Q

What are the common measurements for non-carcinogenic effects for possible chronic exposure?

A

*Acceptable daily intake (ADI)
Allowable daily intake
Minimum Risk Levels (ATSDR)

17
Q

What organizations use the ADI?

A

US Food and Drug Administration, World Health Organization, and Consumer Product Safety Commission

18
Q

What is the ADI?

A

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

19
Q

What measurement calculation is used to determine the ADI?

A

RfD

20
Q

What are Minimum Risk Levels (MRLs)?

A

Estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure

measurement of ATSDR

Similar to RfD/ RfC

21
Q

What is ATSDR? What is their mission?

A

Agency for Toxic Substances and Disease Registry- 1985- national public health agency for chemical safety with a goal to prevent and mitigate harmful exposure to toxic substances and related diseases

22
Q

What are the two components of toxicity assessment for cancer effects

A

*A qualitative evaluation based on weight of evidence (WOE) that the chemical does or does not cause cancer in humans

Quantitative evaluation- describe the carcinogenic potency of the chemical, done by quantifying how the number of cancers observed in exposed animals or humans increases as the dose increases

23
Q

Draw a sample graph of a cancer dose curve and extrapolation

A

see slide

24
Q

Does cancer have a threshold? how about NOAEL, LOAEL, or RfD?

A

No, No, No

25
Q

What is another name for slope factor?

A

Carcinogen potency factor/ cancer slope factor/ potency factor

26
Q

What does the slope factor depend on?

A

The medium under consideration (ie oral ingestion versus inhalation)

27
Q

Draw a dose response curve with a slope factor

A

See slide

28
Q

What is the slope factor?

A

upper-bound estimate of the probability that an individual will develop cancer if exposed to a chemical for lifetime of 70 years

29
Q

What is dose measurement of the slope factor?

A

The lifetime average daily dose or chronic daily intake (CDI)

30
Q

What are the units of the slope factor?

A

1/(mg/kg/day)

31
Q

What is the equation for the lifetime risk of cancer?

A

if linear= CDI*PF

see slide for equation

32
Q

What is the integrated risk information system? IRIS

A

-internal database of human health assessments for chemical found in the environment

33
Q

Who is IRIS intended for?

A

those without extensive training in toxicology but with some knowledge of health sciences

34
Q

What information does IRIS contain?

A

chronic noncarcinogenic health effects: oral RfD, inhalation RfC for
*carcinogenic effects: hazard ID, oral slope factors, and oral and inhalation unit risks

35
Q

What is used in IRIS to describe human carcinogenicity?

A

Weight of Evidence Characterization

36
Q

What are the groups in the weight of evidence characterization?

A 
A- human carcinogen
B- Probable carcinogen
B1: Linked human data
B2: no human evidence, animals only
C: Possible carcinogen
D: No classification
E: No evidence
37
Q

What are the two cancer descriptors?

A

OSF and IUR

38
Q

What is OSF

A

Estimate of the increased cancer risk from oral exposure to a dose of 1 mg/kg-day for a lifetime. The OSF can be multiplied by an estimate of the lifetime exposure in mg/kg/day to estimate the lifetime cancer risk

39
Q

What is IUR?

A

Estimate of the increased cancer risk from inhalation exposure to a concentration of 1 mg/m3 for a lifetime. The IUR can be multipled by an estimate of lifetime exposure (in mg/m3) to estimate the lifetime cancer risk

Risk Assessment (3 decks)

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