A new perspective on human health risk assessment: development of a time dependent methodology and the effect of varying exposure durations.

We present a new Time Dependent Risk Assessment (TDRA) that stochastically considers how joint uncertainty and inter-individual variability (JUV) associated with human health risk change as a function of time. In contrast to traditional, time independent assessments of risk, this new formulation relays information on when the risk occurs, how long the duration of risk is, and how risk changes with time. Because the true exposure duration (ED) is often uncertain in a risk assessment, we also investigate how varying the magnitude of fixed size durations (ranging between 5 and 70 years) of this parameter affects the distribution of risk in both the time independent and dependent methodologies. To illustrate this new formulation and to investigate these mechanisms for sensitivity, an example of arsenic contaminated groundwater is used in conjunction with two scenarios of different environmental concentration signals resulting from rate dependencies in geochemical reactions. Cancer risk is computed and compared using environmental concentration ensembles modeled with sorption as 1) a linear equilibrium assumption (LEA) and 2) first order kinetics (Kin). Results show that the information attained in the new time dependent methodology reveals how the uncertainty in other time-dependent processes in the risk assessment may influence the uncertainty in risk. We also show that individual susceptibility also affects how risk changes in time, information that would otherwise be lost in the traditional, time independent methodology. These results are especially pertinent for forecasting risk in time, and for risk managers who are assessing the uncertainty of risk.

[1]  Reed M. Maxwell,et al.  Evaluating effective reaction rates of kinetically driven solutes in large‐scale, statistically anisotropic media: Human health risk implications , 2012 .

[2]  Charles F. Harvey,et al.  Arsenic Mobility and Groundwater Extraction in Bangladesh , 2002, Science.

[3]  B. L. Johnson,et al.  Chemical mixtures released from hazardous waste sites: implications for health risk assessment. , 1995, Toxicology.

[4]  Claire Welty,et al.  Revisiting the Cape Cod bacteria injection experiment using a stochastic modeling approach. , 2005, Environmental science & technology.

[5]  Max Henrion,et al.  Uncertainty: A Guide to Dealing with Uncertainty in Quantitative Risk and Policy Analysis , 1990 .

[6]  D. K. Smith,et al.  On the evaluation of groundwater contamination from underground nuclear tests , 2002 .

[7]  Y. Rubin,et al.  A methodology to integrate site characterization information into groundwater‐driven health risk assessment , 1999 .

[8]  Jim E. Jones,et al.  Newton–Krylov-multigrid solvers for large-scale, highly heterogeneous, variably saturated flow problems , 2001 .

[9]  Susan D. Pelmulder,et al.  On the development of a new methodology for groundwater‐Driven health risk assessment , 1998 .

[10]  Jery R. Stedinger,et al.  Probabilistic risk and uncertainty analysis for bioremediation of four chlorinated ethenes in groundwater , 2007 .

[11]  K. Brown,et al.  An estimation of the risk associated with the organic constituents of hazardous and municipal waste landfill leachates , 1988 .

[12]  R. Spear,et al.  Integrating uncertainty and interindividual variability in environmental risk assessment. , 1987, Risk analysis : an official publication of the Society for Risk Analysis.

[13]  T E McKone,et al.  Uncertainties in health-risk assessment: an integrated case study based on tetrachloroethylene in California groundwater. , 1992, Regulatory toxicology and pharmacology : RTP.

[14]  M. McBride,et al.  Health risk from heavy metals via consumption of food crops in the vicinity of Dabaoshan mine, South China. , 2009, The Science of the total environment.

[15]  Melisa F. Pollak,et al.  Research for deployment: incorporating risk, regulation, and liability for carbon capture and sequestration. , 2007, Environmental science & technology.

[16]  Steven F. Carle,et al.  Contamination, risk, and heterogeneity: on the effectiveness of aquifer remediation , 2008 .

[17]  E. Wynder,et al.  International comparisons of mortality rates for cancer of the breast, ovary, prostate, and colon, and per capita food consumption , 1986 .

[18]  T. McKone,et al.  PREDICTING THE UNCERTAINTIES IN RISK ASSESSMENT , 1991 .

[19]  A. Shraim,et al.  A global health problem caused by arsenic from natural sources. , 2003, Chemosphere.

[20]  Ying Zhang,et al.  The Impact of Ventilation Rate and Partition Layout on the VOC Emission Rate: Time‐Dependent Contaminant Removal , 1994 .

[21]  Albert J. Valocchi,et al.  Spatial moment analysis of the transport of kinetically adsorbing solutes through stratified aquifers , 1989 .

[22]  S. Ashby,et al.  A parallel multigrid preconditioned conjugate gradient algorithm for groundwater flow simulations , 1996 .

[23]  R. Maxwell,et al.  Integrated surface-groundwater flow modeling: A free-surface overland flow boundary condition in a parallel groundwater flow model , 2006 .

[24]  R. Maxwell,et al.  MOVEMENT OF RADIONUCLIDES IN TERRESTRIAL ECOSYSTEMS BY PHYSICAL PROCESSES , 2002, Health physics.

[25]  S. Tareq,et al.  Arsenic poisoning in groundwater: health risk and geochemical sources in Bangladesh. , 2002, Environment international.

[26]  R. Maxwell,et al.  Stochastic environmental risk analysis: an integrated methodology for predicting cancer risk from contaminated groundwater , 1999 .

[27]  V. Cvetkovic,et al.  Evaluation of Risk from Contaminants Migrating by Groundwater , 1996 .

[28]  James Flynn,et al.  Risk Perception, Trust, and Nuclear Waste: Lessons from Yucca Mountain , 1991 .

[29]  D. Pierce,et al.  Lung cancer in radon-exposed miners and estimation of risk from indoor exposure. , 1995, Journal of the National Cancer Institute.

[30]  B. D. Beck,et al.  The enigma of arsenic carcinogenesis: role of metabolism. , 1999, Toxicological sciences : an official journal of the Society of Toxicology.

[31]  R. Maxwell,et al.  AN IMPROVED MODEL FOR PREDICTION OF RESUSPENSION , 2011, Health physics.

[32]  S. Ferson,et al.  Propagating Uncertainty in Ecological Risk Analysis Using Interval and Fuzzy Arithmetic , 1992 .

[33]  Stefan Kollet,et al.  A serendipitous, long-term infiltration experiment: water and tritium circulation beneath the CAMBRIC trench at the Nevada Test Site. , 2008, Journal of contaminant hydrology.

[34]  Yoram Rubin,et al.  A risk‐driven approach for subsurface site characterization , 2008 .

[35]  John E. McCray,et al.  A quantitative methodology to assess the risks to human health from CO2 leakage into groundwater , 2010 .

[36]  R. V. Nicholson,et al.  Migration of contaminants in groundwater at a landfill: A case study 6. Hydrogeochemistry , 1983 .

[37]  F. O. Hoffman,et al.  Propagation of uncertainty in risk assessments: the need to distinguish between uncertainty due to lack of knowledge and uncertainty due to variability. , 1994, Risk analysis : an official publication of the Society for Risk Analysis.