EESA10H3 Chapter Notes - Chapter L#10: Reference Dose, Blood Lead Level, Precautionary Principle

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LECTURE 10 NOTES (52-66)
2.2 RESPONDING TO ENVIRONMENTAL HAZARDS TO HUMAN HEALTH
- Scientific understanding of env. Health hazards is translated into real world outcomes
through 3 major activities
o1. Risk assessment (regulatory science)
o2. Risk management (where the assessment is translated into action)
o3. Risk Communication, a 2 way sharing of understanding between experts and
communities
Risk Assessment
- gov. agencies that have to regulate hazards can’t wait for scientific certainty all the time
have to make decisions/policy actions earlier this is risk management; regulators
need working answers for scientific questions that scientists have not fully answered yet
orisk assessment bridges this gap: operate in the boundary between science and
policy, it is an agreed upon
set of procedures for
integrating and
interpreting scientific data
for the practical purpose
of making a decision
is a formal process
for estimating the
human health risk
of a toxicant or a site by bringing together information on exposure and
toxicity
use a 4 step framework:
exposure assessment: estimate how much exposure the
populations of concern have to the chemical(s) of concern
hazard identification: qualitative evaluation of toxicity with the
purpose of establishing the scope of a chemical’s health effects
( or the presence of multiple chemicals, in the case of site-risk
assessment)
dose response assessment quantifies the relationship between
dose and effect (eg. Characterizes the dose response curve for
specific toxic effects of the chemical or chemicals of concern)
risk characterization (final step) brings together information on
exposure w/ information on toxicity at diff. exposures includes
an estimates of the uncertainties that are built into it
all these steps are done together
Risk assessment framework for a chemical
- not all toxic chemicals are carcinogenic, so, in a given chemical, risk assessors integrate
what is known about the actual mechanisms of toxicity
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a) Risk Assessment for the Non-cancer effects of a chemical
- Objective of exposure assessment is first to identify pop. Exposed to the chemical of
concern
- In assessing the noncancer health effect, the objective of exposure assessment is first to
identify the populations exposed to the chemical of concern, and then to estimate
their exposures assessment considers all important sources of exposures w/ their
associated pathways and routes of exposure, (while taking into account the physical-
chemical properties of the chemical)
oExposures are quantified in dose units (eg. Mg/(kg * day)
- The qualitative step in toxicity assessment (hazard identification) establishes the range
of noncancer health effects of a chemical  eg. Review human case report,
epidemiological studies of acute/chronic health effects, bioassays etc.
- The dose-response assessment (quantitative assessment) are shaped by the assumption
that non-cancer effects have a threshold implies that there is a safe dose thus: the
dose-response assessment is directed at defining the reference rose (RfD) (units:
mg/kg*day)
oReference dose is expected to have no adverse effects in people
oMost literature on a chemical does not have epidemiological information on it
so: the RfD is derived from some other dose available in the literature, and then
adjusted downward to ensure that it is protected of vulnerable humans (eg. The
old, young etc.)
Eg. If the RfD is derived from the NOAEL in a chronic rodent bioassay, the
NOAEL is adjusted downward to account for people who might be more
sensitive than rodents and then adjusted downward again to account for
the more sensitive people out of the people you adjusted down for
- If starting value is a LOAEL rather than LOAEL, then make additional downward
adjustments
- The procedure for these downward adjustments is to divide the starting value (eg. A
chronic rodent LOAeL) by one or more uncertainty factors, each of which is a hedge
against the effects of a specific limitation in the available toxicity data
o2 main decision in this process
1. Selection of the dose to be used as the starting value
2. The assignment of values of the specific uncertainty factors by which
the starting value is reduced in deriving the dose (eg. Should the starting
value be reduced by a factor of 3 to account for study limitations, of by
10?)
olengthy process  so: EPA only has this published for 370 chemicals
- b/c the D-R assessment for noncancer effects is a dose, the risk characterization step is
a simple comparison of the actual or estimate dose to the reference dose (that you have
just derived)
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Document Summary

2. 2 responding to environmental hazards to human health. Health hazards is translated into real world outcomes through 3 major activities: 1. Risk management (where the assessment is translated into action: 3. Risk communication, a 2 way sharing of understanding between experts and communities. Risk assessment gov. agencies that have to regulate hazards can"t wait for scientific certainty all the time. Objective of exposure assessment is first to identify pop. The qualitative step in toxicity assessment (hazard identification) establishes the range of noncancer health effects of a chemical eg. review human case report, epidemiological studies of acute/chronic health effects, bioassays etc. If the rfd is derived from the noael in a chronic rodent bioassay, the. Noael is adjusted downward to account for people who might be more sensitive than rodents and then adjusted downward again to account for the more sensitive people out of the people you adjusted down for.

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