Sunday, June 21, 2009

FIRESIDE CHAT: Hudson River PCB Dredging (f)

Bias in the US Environmental Protection Agency’s Baseline Health Risk Assessment Supporting the Decision to Require Dredging of PCB-Bearing Sediments from the Hudson River

Robert A. Michaels, Uriel M. Oko



This investigation adopts the methods of health risk assessment (HRA) and health impact assessment (HIA) to identify parameters used by EPA to assess baseline (non-dredging) health risks potentially posed by PCB in the Hudson River and, essentially, peer review their quantification based upon Agency documentation. Two criteria were used to determine whether effective insulation of science from politics was attained: 1. whether parameter values were estimated accurately and, 2. with respect to any parameters evaluated inaccurately, whether the direction of estimation error was mixed, or consistently overestimated or underestimated potential PCB transfer from Hudson River water to air. Overestimating the risk of transferring PCBs from sediments to water and water to air in the vicinity of Hudson River communities could contraindicate dredging, whereas the reverse error would be conducive to dredging.

The null hypothesis is absence of bias. This corresponds to finding a random distribution of errors, not to finding an absence of errors. Any finding of significant systematic error in either direction would constitute evidence of bias justifying rejection of the null hypothesis..

Statistical analysis

We determined whether each parameter examined was estimated correctly. If EPA's evaluation of a parameter was grossly inaccurate, we included it among parameters to be examined statistically to determine whether the distribution of the directions of mis-estimation was nonrandom. Each parameter that is estimated inaccurately must be overestimated or underestimated (otherwise it is accurate). If these outcomes can be assumed to be equally probable, then occurrence of each is associated with an equal expected probability of 0.5 (50 percent, or ‘fifty fifty’). If the parameters also are independent (mis-estimating one parameter does not affect estimation of another), then any two randomly selected parameters that are mis-estimated would have a 0.25 probability (P = 0.5 x 0.5 = 0.25) of being mis-estimated in a direction more permissive to dredging and, likewise, 0.25 would be the probability of the same two parameters being mis-estimated in a direction less permissive to dredging.

In general, the probability of mis-estimating all of n parameters consistently in a particular direction by chance alone is 0.5n where, for example, the probability of mis-estimating five out of five parameters in a direction permissive to dredging would be 0.03 (P = 0.55 = 0.03). When probabilities reach such low values, below the usual 0.05 criterion of scientific uncertainty, the null hypothesis of randomness is rejected. Speaking qualitatively, bias in the outcome of EPA's analysis (possibly unintentional) would be inferred.

Secondary methods

Secondary methods also were applied. They are not a priori methods, and they are not described in detail here. Rather, they are the diverse methods typical of peer review, which most essentially consists of considering the scientific merit with which numerous methods were selected for use and applied in the original analyses supporting the dredging decision. Readers can judge for themselves whether or not we applied the methods of HRA, HIA, and peer review objectively.


EPA identification of parameters used in assessing potential risks posed by PCBs

The number of parameters on which the dynamics of PCBs entering the water column from sediments and entering the air from the water column are diverse and numerous, numbering in the hundreds or thousands. The number that are visible in any scientific explication of this issue depends upon the degree of detail with which the analysis is conducted. The parameters include initial concentrations of all 209 PCB congeners, from monochlorinated to decachlorinated biphenyls, in each medium, bulk amounts, areas involved, depths of water and sediments, as well as parameters describing the physical, chemical, and environmental degradation (such as half life), transformation (such as dechlorination), and other environmental dynamics (such as solubility, boiling point, volatilization, and vapor density) of these numerous congeners. The safety issue also encompasses toxicological parameters of each PCB congener. The full list of such parameters is too long to elucidate in detail here.

Fortunately, the present analysis requires no such highly detailed elucidation. The parameters that are of greatest concern here are those that are most susceptible to being overestimated or underestimated, especially if by a wide margin, or overlooked entirely. These are the parameters (unlike, say, molecular weights, which are known to a high degree of accuracy) whose estimated values substantially may depend upon who is doing the estimating. Quantification of these parameters can vary from liberal to conservative, depending upon whether the estimator has a (conscious or unconscious) agenda other than to conduct a purely scientific analysis… in short, a bias. Nine such estimated, determinative parameters that were (or should have been) used for technical analysis in the baseline HRA supporting the dredging decision were identified, as follows:

--1. Mobilization of sediment-borne PCBs in dredging. Sediment-borne PCBs will become mobilized by dredging. The amount mobilized depends upon the dredging method. Mobilization must be considered in assessing potential public health significance of PCB dredging;

--2. PCB congeners to be included in the analysis. All 209 PCB congeners should be included;

--3. Phases of PCBs to be included in the analysis. All phases should be included, most notably including PCBs that are adsorbed onto particles, molecular PCBs that are dissolved, and particulate PCBs that are colloidal;

--4. Precipitation of PCB-bearing sediment particles from the water column.Precipitation rates should be quantified realistically, as this parameter is important in determining the rate of PCB removal (to sediments), and the resulting PCB concentration in the water column;

--5. Electrostatic charges on PCB-bearing sediment particles in the water column.Clay sediment particles resuspended in water (as by dredging) tend to exhibit negative surface charges. Such particles are maintained in suspension by electrostatic interaction of the negative surface charges with cations (positive ions) in the water. This electrostatic charge configuration inhibits agglomeration. It should be accounted for because of its potential importance in inhibiting settling of clay particles and removal of adsorbed PCB from the water column;

--6. Reflection coefficient of precipitating PCB-bearing sediment particles. The reflection coefficient quantifies the tendency of particles, once settled out of the water column, to return to the water column as a result of ‘bouncing’. The reflection coefficient should be quantified, and is especially important for particles that are of low mass, or likely to be affected by currents, as in the Hudson River;

--7. PCB codistillation. Codistillation is a chemical process well documented for PCBs. It results from molecular attraction to surfaces. For PCBs these surfaces include the air-water interface in lakes and rivers. Entry of PCBs into air from water is significantly faster and more extensive in a given interval than would be the case if the same mass of waterborne PCBs were assumed to be distributed evenly throughout the water column (as quantified by the ‘bulk concentration’). Accurate estimation of waterborne PCB entry into the air that people will breathe requires quantification of PCB codistillation;

--8. Empirical measurement of airborne PCBs over PCB-contaminated waters.Empirical measurements, to the extent available, should be used for validating modeled relationships, such as models of PCB entry into the air from Hudson River water;

--9. Warm water sources of Hudson River PCB entry into the atmosphere. Warm water occurs at near-shore locations where cooling water is discharged from industrial facilities and, before discharge, in cooling towers supplied by Hudson River water. These sources of potential entry of PCBs into the atmosphere near population centers must be accounted for assessing potential public health significance of PCBs, and the possibly increased significance to public health if PCB dredging is undertaken.


Anonymous. Great Lakes Show Signs of Exhaling Contaminants. Air & Waste Management Association, EM Magazine, page 9, December 2001;

Baker, JE; et al. PCBs in the upper Hudson River: The Science Behind the Dredging Controversy. White paper prepared for the Hudson River Foundation, 47 pages, 25 October 2001;

ATSDR. Toxicological Profile for Polychlorinated Biphenyls (PCBs). Atlanta, Georgia; US DHHS, Public Health Service, Agency for Toxic Substances and Disease Registry, 948 pages, November 2000;

Baibergenova, A.; R. Kudyakov, M. Zdeb, and D. O. Carpenter. Low birth weight and residential proximity to PCB-contaminated waste sites. Environmental Health Perspectives, 111:1352–1357, 2003;

Bernhardt, E. S.; et al. Synthesizing U. S. river restoration efforts. Science, 308:636-7, 29 April 2005;

Buckley, E. H.; and T. J. Tofflemire. Uptake of airborne PCBs by terrestrial plants near the tailwater of a dam. Proceedings of the National Conference on Environmental Engineering, ASCE Specialty Conference, pages 662-9, 6-8 July 1983;

Cappiello, D. New EPA plan dredges more PCBs. Agency raises estimate by 50 percent on new data from GE. Albany, New York; Times Union Newspaper, page B5, 6 December 2001;

Carpenter, D. O. Polychlorinated biphenyls and human health. International Journal of Occupational Medicine and Environmental Health, 11:291–303, 1998;

Carpenter, D. O. Hospitalization rates for coronary heart disease in relation to residence near areas contaminated with persistent organic pollutants and other pollutants. Environmental Health Perspectives, 113(6):756–61, June 2005;

Carpenter, D.O.; T. Nguyen, L. Le, A. Baibergenova, and R. Kudyakov. Profile of health effects related to proximity to PCB-contaminated hazardous waste sites in New York. Fresenius Environmental Bulletin, 12:173–180, 2003;

Chase, K. H.; O. Wong, D. Thomas, B. W. Berney, and R. K. Simon. Clinical and metabolic abnormalities associated with occupational exposure to polychlorinated biphenyls (PCBs). Journal of Occupational Medicine, 24:109–Chase et al. 19824, 1982;

Choi, W; S. Y. Eum, Y. W. Lee, B. Hennig, L. W. Robertson, and M. Toborek. PCB 104-induced proinflammatory reactions in human vascular endothelial cells: relationship to cancer metastasis and atherogenesis. Toxicological Science, 75:47–56, 2003;

Harza. Fort Edward Dam PCB remnant deposit containment environmental monitoring program: report of 1991 results. Chicago, Illinois; Harza Engineering Company, March 1992;

Hennig, B.; B. D. Hammock, R. Slim, M. Toborek, V. Saraswathi, and L. W. Robertson. PCB-induced oxidative stress in endothelial cells: modulation by nutrients. International Journal of Hygiene and Environmental Health 205:95–102, 2002;

IADN. Atmospheric Deposition of Toxic Substances to the Great Lakes: IADN Results to 1996.Environment Canada and the U. S. Environmental Protection Agency, US EPA report number EPA 905-R-00004, 126 pages, 2000;

Lucier, G. W. Humans are a sensitive species to some of the biochemical effects of structural analogs of dioxin. Environmental Toxicology and Chemistry, 10:727–735, 1991;

NYS DEC. New York State DAR-1: Guidelines for the control of toxic ambient air contaminants. Albany, New York; New York State Department of Environmental Conservation, 62 pages, 12 November 1997;

NYS DEC. Hudson River Sediment and Biological Survey. Albany, New York; New York State Department of Environmental Conservation, Division of Water; 19 pages, available at, November 2000;

NYS DEC. DAR-1 AGC/SGC Tables. Albany, New York; New York State Department of Environmental Conservation, 59 pages, 22 December 2003;

Oko, U., and C. Oko. Dr. Oko’s Petition for Full Party Status – Response to PSEG, in the matter of the application of PSEG Power New York, Inc. for a State Pollution Discharge Elimination System permit, State Air Facilities permit and PSD permit. Petition by Uriel M. Oko and Carol Oko with consulting assistance from Dr. Robert Michaels, RAM TRAC Corporation, 12 pages, 18 December 2001;

Paquin, J. Insights into the origin, movement, and capture of PCB DNAPL contamination at the Smithville site. Toronto, Ontario, Canada. Proceedings of the Fractured Rock 2001 International Conference, 10 pages, 25-28 March 2001;

PSEG NY, BEC Application, HRA. Multipathway Risk Assessment for Bethlehem Energy Center Project. Acton, Massachusetts; ENSR Corporation, i. p., June 2001;

Shavit, U.; S. Moltchanov, Y. Agnon. Particles resuspension in waves using visualization and PIV measurements - coherence and intermittency. International Journal of Multiphase Flow, 29:Chase et al. 198283-92, 2003;

Slim, R.; M. Toborek, L. W. Robertson, and B. Hennig. Antioxidant protection against PCB-mediated endothelial cell activation. Toxicological Science, 52:232–239, 1999;

Stehr-Green, P. A.; E. Welty, G. Steele, and K. Steinberg. Evaluation of potential health effects associated with serum polychlorinated biphenyl levels. Environmental Health Perspectives, 70:255–259, 1989;

Taylor, P. R.; J. M. Stelma, and C. E. Lawrence. The relation of polychlorinated biphenyls to birth weight and gestational age in the offspring of occupationally exposed mothers. American Journal of Epidemiology, 129:395–406, 1989;

US EPA. HRA, Mid-Hudson River. Phase 2 Report - Further Site Characterization and Analysis. Volume 2F - A Human Health Risk Assessment for the Mid-Hudson River. Hudson River PCBs Reassessment FS. Bloomfield, New Jersey, TAMS Consultants, 30 pp. plus appendices, December 1999;

US EPA. Revised HRA, Mid- and Upper Hudson River. Phase 2 Report - Further Site Characterization and Analysis. Volume 2F - A Human Health Risk Assessment; Hudson River PCBs Reassessment FS. Bloomfield, New Jersey, TAMS Consultants, 128 pp. plus appendices, November 2000a;

US EPA. Revised HRA, Mid- and Upper Hudson River, Appendix E. Hudson River PCBs Reassessment FS. Appendix E: Engineering Analysis. Section 6. Technical Memorandum: Semiquantitative Analysis of Water Quality Impacts Associated with Dredging Activities. Bloomfield, New Jersey, TAMS Consultants, pp. 33-67, November 2000b;

US EPA. Actions Prior to EPA's February 2002 Rod [Record of Decision]. Fig. 2-2, Hudson River PCB Site History. URL:, updated 15 May 2006.


or see:

Michaels, RA.; and UM Oko. Bias in the US EPA baseline health risk assessment supporting the decision to require dredging of PCB-bearing sediments from the Hudson River. Environmental Practice (Cambridge University Press), 9(2):96-111, June 2007.