Environmental Engineering Reference
In-Depth Information
table 12.1
Terms Used in National Research Council's (1983, 1993) Formal Human Health Risk Assessment (HRA),
as Well as Other Risk Evaluation Paradigms
NRC's risk assessment paradigm for humans
Hazard identifi cation: Specifi cation of the hazards (or stressors) that potentially can cause adverse effects).
Dose-response assessment: Establishing a relationship (through laboratory, fi eld, or epidemiologic studies) between
dose and the magnitude of adverse effects.
Exposure assessment: Assessing the contaminant levels in various media and biota, including in target organs, as well
as pathways from contaminants to target species (and organs).
Risk characterization: Estimating the probability of an adverse outcome, or the threshold below which the probability
of an adverse outcome is negligible.
Additional terms used for both human and ecologic risk assessment to broaden it to include stakeholders and
public policy
Data acquisition, verifi cation, and monitoring: Collecting fi eld data on either contaminant levels or exposures,
verifying the accuracy of the data, and monitoring (media or biota) to determine the potential for continued risk.
Problem-formulation (or scoping): Defi ning the problem that requires examining the potential risk to humans and
the environment (including specifi c ecoreceptors or ecosystem processes.
Risk management: Discussion between risk assessors, risk managers, and scientists (health professionals, ecologists)
about how to reduce or manage the potential risk to humans or the environment.
Stakeholder identifi cation: Identifying the interested and affected parties (includes government agencies,
nongovernmental organizations, and the interested public).
note: Also see Burger and Gochfeld (1997b), and Gochfeld and Burger (2007). These methods are used for assessing risk for any stressor,
including mercury pollution.
of the need for evaluating the effects of new chemicals,
especially beginning in the 1960s. Agencies and compa-
nies used various methods. However, in, 1983, the National
Research Council (NRC, 1983, 1993) formalized the human
health risk assessment (HRA) paradigm to include four
parts: hazard identifi cation, dose-response assessment,
exposure assessment, and risk characterization (Table 12.1,
Figure 12.1). HRA has also been called “environmental risk
assessment,” but the term human risk assessment is more use-
ful to distinguish it from ecological risk assessment (ERA).
Hazard identifi cation is identifying any agent (or con-
dition) that has the potential to cause harm (Rasmussen,
1981). This includes determining whether a substance is a
carcinogen. Dose-response assessment evaluates the toxico-
logic (and in some cases, epidemiologic or pharmacologic)
literature to estimate the parameters of the dose-response
curve, including a threshold (if any can be determined).
It examines the relationship between the amount of the
chemical and the response. Exposure assessment is deter-
mining the pathways and routes of exposure and estimat-
ing dose, both to the receptor (plants, animals, or humans)
and to target organs (liver, kidney, muscle). Finally, risk
characterization combines the results of the dose-response
and exposure assessment to assign probabilities for certain
outcomes to certain doses, or to determine a “safe” level
below which no harm is anticipated.
Most risk assessments are deterministic, and consider
one point in time when examining exposure and toxic-
ity inputs, but more recently probabilistic risk assessment
has moved to the fore. Probabilistic risk assessments use
probability distributions of toxicity and exposure variables
and can consider several points in time and an array of
exposure scenarios to provide more realistic exposure esti-
mates. These often use Monte Carlo simulations in com-
bination with various shaped distributions (e.g. normal,
log-normal, triangular). Probabilistic risk assessment is
designed to capture the distribution or range of exposures and
environmental conditions, and can be used for both HRA
and ERA (Constantinou et al., 1995; Barron et al., 2004;
Tran et al., 2004; Rumbold, 2005; Brain et al., 2006; USEPA
2010). Distributions, rather than point values, can also be
useful for identifying benchmark levels, allowing the user
to select a tissue concentration that is associated with the
protection of a specifi c percentage of organisms (Steevens
et al., 2005). Probabilistic assessments can be used for
determining mercury dose from a range of samples (Stern,
2005) and for determining environmental dynamics and
regional mercury cycles as well. This approach encompasses
the variability in environmental characteristics, as well as
dose-related variables (Seigneur et al., 2006).
HRA thus involves identifying hazardous agents (such as
mercury), establishing the effects of the hazardous agent
 
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