Alceon has pioneered the use of Monte Carlo simulations
and other probabilistic techniques in human health risk assessments. These
techniques overcome important limitations in older, deterministic risk
assessment methods. Deterministic risk assessments combine a set of average,
conservative, high, and worst-case assumptions to derive "conservative"
point estimates for exposure and risk. The major drawback of this approach
is that no one can say how conservative these estimates are. Risk managers
have no way of knowing if the estimated risk represents the 90th, 99th,
99.99th, or some higher percentile of risk.
In the Monte Carlo method -- now 50 years old and widely used throughout science and engineering -- input variables are treated as random variables described by probability distributions (i.e., not as point values). With appropriate precautions to consider correlations, dependencies, and other pitfalls, Monte Carlo techniques give risk assessors the proper tools to estimate full distributions of risks in a population and, as appropriate, full distributions for cleanup targets (acceptable exposure point concentrations).
Alceon staff members have:
Completed
multi-media Monte Carlo risk assessments, reviewed existing Monte Carlo
simulation models, and published some 40 articles in refereed journals.
Derived
and published the correct method to estimate distributions for cleanup
targets.
Been instrumental
in removing an important obstacle to the use of probabilistic techniques
in health risk assessment: fitting probability distributions for exposure
variables.
Developed
and published distributions for soil ingestion by children, drinking water
intake for children and adults, height and weight for adults, body surface
area for adults, bioconcentration of lipophilic chemicals in finfish, distributions
for children's body weight, lipid intake by nursing infants, fish consumption,
and the fraction of indoor dust in single-family homes originating from
outdoor soils.
Taught dozens
of courses, workshops, and classes , especially emphasizing "2-dimensional"
simulations that separate variability and uncertainty in analyses.
Since publishing its exposure assessment guidelines in 1992, the US Environmental Protection Agency has repeatedly recognized the validity and power of Monte Carlo techniques in refining human health risk assessments. Several of the Agency's regional offices and leading states (MA, CA) now accept probabilistic techniques in risk assessments. As Monte Carlo techniques become the tool of choice in risk assessment, Alceon will work closely with private and public clients to apply these techniques and to provide formal estimation of distributions needed for such assessments.