FIRESIDE CHAT: Hudson River PCB Dredging (h)

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

CONTINUED FROM PREVIOUS POST

DISCUSSION AND CONCLUSIONS

Statistical significance

A parameter that is estimated inaccurately must be overestimated or underestimated; otherwise it is estimated accurately. If these two alternative directions of mis-estimation are equally probable, as they should be, then occurrence of each is associated with an expected probability of 0.5 (50 percent, or ‘fifty fifty’). If the parameters also are independent (under- or overestimating one does not cause mis-estimation of another), then any two randomly selected parameters that are mis-estimated would have a 0.25 probability 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, and 0.50 [1.0 - (0.25 + 0.25)] would be the probability of one mis-estimation being in the dredging-permissive direction and the other in the dredging-prohibitive direction. The confluence of fully nine parameters linked in a single direction, as reported above in the Findings section, would be associated with a vanishingly small probability of occurring by chance alone (0.5⁹, which is 0.0002). Qualitatively speaking, a low probability (for example, below the usual 0.05 scientific confidence level) supports the conclusion that bias (possibly unintentional) rather than chance alone, influenced EPA's analysis consistently in the direction of underestimating PCB risks in the baseline HRA for the Hudson River.

Significance for health risk assessment

The findings reported above signify that potential inhalation risks that should have been quantified in EPA's HRA were not quantified. EPA's HRA states the following:

“Risks and hazards through inhalation of volatilized PCBs were not assessed in the Mid-Hudson HHRA because calculated risks for this pathway were shown to be de minimis (insignificant) in the Human Health Risk Assessment for the Upper Hudson River. Given that concentrations of PCBs found in the sediment and river water in the Mid-Hudson are lower than concentrations in the Upper Hudson, the risks from volatilization also would be expected to be insignificant (and lower) in the Mid-Hudson” (US EPA 1999, page ES-2).

This means that EPA’s estimate of airborne PCB concentrations are below the New York State Department of Environmental Conservation (NYS DEC) de minimis AGC (Annual Guideline Concentration; NYS DEC 1997, 2003) which, if exceeded, would trigger a requirement to quantify inhalation risks potentially posed by airborne PCBs under a reasonable worst-case scenario. Accordingly, although the HRA ‘considered’ airborne PCBs, risks to public health potentially posed by transfer of PCBs from Hudson River water to the air effectively were assessed as zero. Risks posed by PCBs entering the air from cooling towers (with or without dredging) were neither quantified nor considered. Other sources of airborne PCB risks that also were unquantified, according to EPA’s HRA, were "the contribution of PCBs in air from contaminated sediment and floodplain soil" (US EPA 1999, section 2.3.4, page 20).

Regulatory Significance

If EPA had accepted empirical measurements of PCB transfer from water to air that the Agency reported, potential risks to people inhaling PCBs would have been required to be included in its HRA (Table 3). Even the lowest of the five empirical measurements of airborne PCB concentration generated by PCB at specified concentrations in water (0.03 ug/M³) exceeded NYS DEC's published AGC value for airborne PCBs of 0.002 ug/M³ by a factor of 15-fold. EPA’s use of the mean (0.15 ug/M³) or the median (0.09 ug/M³) of all five empirically measured airborne PCB concentrations would, of course, exceed these critical benchmarks even more dramatically. Most notably, the measured range of airborne PCB concentrations (0.033 to 0.53 ug/M³) reported by EPA exceeded by a factor of five-fold NYS DEC’s de minimis value of 0.1 ug/M³ that would have triggered inclusion of PCB inhalation as an exposure pathway to be quantified in the HRA. EPA's procedures, therefore, undermined public health protection by eroding safety and/or the margin of safety that should be built into Agency standards of public health protection.

EPA understatement of PCB release to air affects other projects besides the Hudson River dredging project. NYS DEC, for example, need not account for PCB emissions from cooling towers in approving permit applications for projects (such as power plants), even if those projects will use cooling towers. Indeed, citizen criticism of EPA's EIS value in NYS DEC permit review of project proposals has been rejected, not on technical grounds, but because the EPA values previously had undergone peer review. As a result, HRAs prepared by project applicants may 'account' for public health risks potentially posed by waterborne PCBs becoming airborne simply by quantifying them as zero, based upon the erroneous and apparently unreviewable assumption that PCB emissions from water to air will be “de minimis.” The potential significance is exemplified by the permit proceedings for the BEC gas-fired power plant on the Hudson River (Oko and Oko 2001, PSEG NY 2001), in which the applicant was exempted from quantifying risks potentially posed by airborne PCBs on the authority of the EPA HRA for the Mid-Hudson River (US EPA 1999, 2000a, b).

Significance to Hudson River communities

The most valuable reward for doing river restoration projects is that a river is in some sense 'fixed'. Although this reward would have to be especially large for the Hudson River to justify the enormous price of 'fixing' it, the reality seems different. Whereas sediments and water should be cleaned, EPA’s dredging program cleans only PCB 'hotspots', leaving PCBs in sediments, biota, and water elsewhere in the river; and also leaving virtually all non-PCB contaminants in sediments, biota, and water even after dredging is completed. Indeed, EPA’s dredging proposal addresses 150,000 pounds (68,000 kg) of sediment-borne PCB compared with 1.3 million pounds (591,000 kg) that GE concedes that it discharged into the Hudson from two capacitor plants. That amounts to less than 12 percent of known PCB, and an even smaller fraction of the total PCB discharged into the Hudson River.

Whereas sport fisheries should be uncontaminated and game fish caught in the river safe to consume, in fact the fish cannot become edible in the reasonably foreseeable future. Even if every PCB molecule could be removed from the river, all other Hudson River pollutants will survive PCB ‘hotspot’ dredging, including persistent chlorinated hydrocarbon pesticides, PAHs, and heavy metals such as cadmium, copper, lead, mercury, and zinc (NYS DEC 2000). Whereas air pollution arising from river water should become de minimis, in fact mobilization of PCBs by dredging will increase PCB release to the air for years, and other pollutants also will become airborne after dredging is completed. Whereas the incidence of adverse health effects that might be caused by airborne PCBs should become de minimis, in fact such health effects (if really caused by PCBs) would increase for years before they begin to diminish after dredging.

With or without dredging, purging PCB from Hudson River sediments will require decades (Bakeret al. 2001). At one extreme, remaining PCB might amount to only the 150,000 pounds to be dredged. In that case about 90 percent already has been eliminated without dredging, and the river has cleansed itself of a major fraction of PCB via processes that are ongoing and further self-cleansing would be expected. Realistically, cleansing has eliminated less than 90 percent; and multiples of 150,000 pounds must remain. In that case, if dredging occurs, a preponderance of PCB still would remain after 150,000 pounds is removed. Ultimately, the Hudson River must cleanse itself, with or without dredging.

Some people see light at the end of the tunnel, when dredging will reduce PCBs in sediment, biota, water, and air; and reduce PCB-associated human disease to de minimis incidence. Others see light at the end of a different, longer tunnel, when continued natural burial by sediment loading from runoff into the river likewise will sever the connection of sediment-borne PCB to the water, biota, and air; and reduce PCB-associated human disease to de minimis incidence. Continued natural dechlorination of buried PCBs; and further degradation via physical, chemical, and biological processes acting beneath the sediments; eventually will finish the job, with or without dredging.

The dredging argument has focused narrowly on the two tunnels described above leading to de minimis PCB levels, and whether shortening one via dredging is justified despite near-term environmental disruption. Even objective scientists cannot resolve subjective issues associated with deciding which tunnel constitutes the better route to essentially the same destination. Objective science, however, remains essential. Given the evident biases identified in Findings, objective consideration of at least three issue areas is needed:

--1. Are PCBs harming health and, if so, are effects sufficiently serious, and risks sufficiently high, to justify urgent PCB removal?

--2. If PCBs are harming human health in Hudson River communities, will dredging exacerbate harm by further mobilizing sediment-borne PCB? If PCB-mediated health effects are unacceptable now, their prolonged exacerbation by dredging would be more unacceptable. Additional measures to protect populations would have to be contemplated, short of evacuation, but expensive. Conversely, if PCB health risks are acceptable, why dredge to remove PCBs, when natural processes eventually will remove them anyway?

--3. If the benefits of eliminating PCB from 'hotspots' are deemed worth the enormous price in a hypothetical, otherwise clean Hudson River, are they also worth the price in the actual Hudson River, which has pollutants other than PCBs, and PCBs in places other than in hotspots where dredging will occur? Lost in the dredging debate seems to be the big picture: a dredged river polluted as before, but with at best 12 percent less PCB in its sediments. Is narrowly focusing on dredging hotspot PCB justified, if the river will remain toxic with other pollutants and with non-hotspot PCB?

In light of these questions, the near-term price of dredging must include potential ecological and public health impacts. The Findings and considerations addressed above justify three specific conclusions and one general conclusion. First, risks to public health potentially posed by inhalation of PCBs were grossly understated (effectively quantified as zero), and likewise would be ignored in a dredging-specific HRA if only the baseline HRA exposure routes and pathways are included in it for comparison. Second, even if all PCB could be removed from the river, or from hotspots to be dredged, all other Hudson River pollutants would remain. Their continued presence after dredging would continue to limit recreational and commercial river use for many decades. For example, they still would limit safe consumption, especially in pregnant women, young children, and other sensitive subpopulations. Third, PCB inhalation risks and their acceptability were unassessed, and remain unknown, as is the degree to which dredging would exacerbate them, and for how long. Finally, EPA’s ultimate decision to dredge or not dredge will depend upon subjective issues, whose resolution must be informed by objective science to answer the above questions, and others, credibly.

LITERATURE CITED

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 athttp://www.dec.state.ny.us/website/dow/bwam/hrsb2000.pdf, 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: http://www.epa.gov/hudson/actions.htm, updated 15 May 2006.

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.

FIRESIDE CHAT: Hudson River PCB Dredging (g)

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

CONTINUED FROM PREVIOUS POST

Mobilization of sediment-borne PCBs in dredging

PCB mobilization must be considered in assessing the potential public health significance of PCB dredging. Its consideration by EPA, however, was inadequate. PCB mobilization exacerbated by dredging depends upon three types of cause:

--1. sediment disruption, as by extreme weather events or barge sinkings,

--2. the method of dredging,

--3. and accounting in full rather than in part for PCBs that might be mobilized.

Sediment disruption by extreme weather events. Research undertaken by Joel Baker and colleagues at the Chesapeake Biological Laboratory in Maryland simulating Hudson River PCB dredging (Baker et al. 2001). revealed that EPA modeling lacked the spatial resolution high enough to predict PCB mobilization reliably. They concluded that errors, which could have gone in either direction, probably had in fact underestimated sediment and PCB mobilization from extreme weather events. The authors used this finding to argue in favor of dredging, fearing that harmful PCBs would be mobilized over years if dredging did not remove them. However, removal by dredging presumably also could exert a nearer-term effect episodically.

The method of dredging. EPA’s for the Hudson River PCB site was prepared in 1999 and 2000, when GE planned to dredge hydraulically, via the ‘suction’ method. Indeed, a television commercial campaign by GE impugned the ‘clamshell’ or ‘bucket’ method of dredging as being too dirty. Since preparation of the HRA, however, GE’s proposal has reverted to use of the clamshell method.

Accounting in full for PCBs that might be mobilized. The mass of PCB that will be mobilized may be expressed as a fraction of the inventory of PCB in Hudson River sediments. If the inventory is underestimated, mobilization will be underestimated commensurately. This source of underestimation is addressed with respect to other parameters, below.

In short, EPA’s estimate of PCB mobilization from sediments to the water column and from the water column to the air, together contributing to potential PCB inhalation risks, should not have emerged from EPA's model of the Hudson River; and it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots actually is undertaken.

PCB congeners to be included in the analysis

All PCB congeners should be included in the inventory of PCBs in Hudson River sediments (Fig. 1). Mono- and dichlorinated PCBs, however, were excluded from the inventory of PCBs in Hudson River water, thereby underestimating waterborne PCBs subject to becoming airborne. Several figures in the revised Hudson River health risk assessment (HRA; US EPA 1999, 2000a, b) depict a precipitous fall-off of“total tri+ PCB congener water column concentrations” within approximately 10 meters of the dredge site. PCB congeners can bind from one to 10 chlorine atoms. If each number of chlorines were represented equally, exclusion of the monochlorinated and dichlorinated PCBs would represent two of 10 (20 percent). The actual fraction (weight-percent) excluded is unclear because commercial PCBs were sold as Aroclors, such as Aroclor 1254, with 54 weight-percent chlorine, such that each Aroclor product sold had a distinctive distribution of mono- to deca- chlorinated PCB congeners (hence the ability to ‘fingerprint’ PCB sources). In addition, PCB degradation in sediments results in gradual dechlorination, which tends to deplete the high-chlorine congeners and enrich the low-chlorine congeners... precisely the congeners that were excluded from the figures, and which apparently were excluded from consideration in quantifying PCB release from river water to air. The fraction of total PCB represented by the monochlorinated and dichlorinated PCBs would appear to be about one third, as suggested by an EPA estimate that is described below.

The plan to dredge Hudson River sediments selected one option from among several remediation options. The option favored by environmentalists, “Alternative no. 5,” would remove 155,000 pounds of PCBs, compared with 1.3 million pounds; which equals 650 tons, or approximately 600,000 kg or 60 tonnes disposed. That is the amount that is reported to have been deposited into the Hudson River by GE from its two upriver capacitor plants before PCBs were banned from U. S. commerce by the Toxic Substances Control Act of 1976. Responding to criticism of the plan to dredge only 100,000 pounds of PCB under a less ambitious option, GE provided ‘new data’ to the EPA that showed that the actual amount of PCBs that would be dredged from the river bottom under Alternative no. 5 would be 150,000 pounds, almost identical to the amount preferred by environmental groups (Cappiello 2001):

“The U. S. EPA says it can dredge 50 percent more PCBs from the Hudson River without increasing the volume of sediment removed” (Cappiello 2001).

By way of explanation, EPA indicated that it simply had refined its PCB estimate of a year earlier. EPA did this by including previously-excluded monochlorinated and dichlorinated PCBs, on the rationale (according to EPA’s TAMS contractor) that “fish principally absorb (higher chlorinated) PCBs.”

The Agency apparently assumed that the monochlorinated and dichlorinated PCBs constituted one third of total PCB (50,000 pounds out of 150,000 pounds of total PCB). Clearly, the Agency’s HRA of 1999 (US EPA 1999) and 2000 (US EPA 2000a, b) for Hudson River dredging therefore excluded approximately one third of total PCBs from the PCB inventory. This was done, notwithstanding that the scope of the Hudson River HRA included the airborne risks, not just fish consumption risks, that might be posed by PCBs that will be resuspended and mobilized by dredging. This exclusion, however, did not stop EPA from taking credit for inclusion in its dredging plan of the extra 50,000 pounds of PCB assumed to be accounted for by the monochlorinated and dichlorinated PCBs to augment the acceptability of its dredging plan in the face of criticism in 2001.

The Agency actions described above highlight three issues relating to potential bias in the scientific analysis:

--1. whether EPA accurately inventoried the amount of PCBs that might pose risks to health,

--2. whether EPA accurately assessed risks potentially posed by PCBs in its PCB inventory (addressed in greater detail later), and

--3. whether the PCB risks that were quantified in the HRA corresponded to the PCB amounts that would be dredged, and that would be subject to mobilization with the potential to pose health risks.

The findings indicate that EPA based its risk estimates on a smaller pool of PCBs. They indicate further that the Agency did this at least in part by excluding monochlorinated and dichlorinated PCB congeners from the HRA. EPA did this, notwithstanding that the excluded congeners would necessarily be included in sediments that would be dredged, and therefore would contribute to airborne PCB concentrations and health risks that might be posed by dredging to people situated near the river. In short, EPA’s estimated PCB residue load contributing to potential PCB inhalation risks should not have emerged from EPA's model of Hudson River and, due to failure to account for mono- and dichlorinated congeners, it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

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. All PCBs in the HRA, however, were assumed to settle under Stokes Law for spherical silt particles. This assumption constitutes a continuous process of removal of PCBs from the water column, notwithstanding that molecular and dissolved PCB phases would remain because they do not settle. That is, these waterborne PCBs are subject to becoming airborne, but this is not accounted for in EPA's HRA.

The mechanical action of dredging ‘hot spots’ will cause PCBs adsorbed to silt particles to enter the water column. Whereas much if not most of the PCB in the water column will remain adsorbed to silt, a significant, possibly majority fraction will enter the water column in a dissolved (molecular) or a colloidal phase (consisting of microscopic PCB droplets). Exclusion of PCBs in these dissolved and colloidal phases from the revised Hudson River HRA is reported in Appendix E, Section 5.2, titled "TSS Plume Estimates.”In that section, only silt particles were used to estimate settling rates:

"Since data on settling rates were not available, a median value for settling velocity of 1.9 x 10-4 M/sec [16.5 M/d]was used in the transport calculations” (US EPA 2000b).

The above description of settling velocity as a ‘median value’ suggests misleadingly that settling was calculated for a heterogeneous distribution of particles whose median settling velocity is 1.9 x 10-4 M/sec [16.5 M/d]. In fact, only the 'median' value was used. This uniform settling velocity, corresponding to a 20-micron (uM) sphere, excludes dissolved and colloidal PCBs, which are smaller. Dissolved PCBs (bound to water) and colloidal PCBs (subject to Brownian motion and water turbulence) never settle. This unstated simplification overestimates the rate of PCB removal from the modeled water column by assuming that all waterborne PCB is adsorbed to particles that settle at the assumed velocity. Actually, a significant if not predominant fraction of total waterborne (resuspended) PCB will consist of free PCB present in dissolved and colloidal phases.

Inasmuch as silt has specific gravity of about 2.5, the assumed ‘median’ settling velocity corresponds to (spherical) particles of diameter exceeding 20 uM, whereas Stoke’s Law ceases to apply when the settling particles are fines that are less than about 50 uM. EPA's implicitly assumed particle size therefore, also implicitly, assumes that the vastly more numerous PCB molecules in dissolved and colloidal phases will settle at the median rate. Colloidal PCBs are commonly recognized as being 1 uM and smaller and, of course, individual PCB molecules are smaller still. These PCB molecules and colloids also would suspend in the water phase even beyond the dredge site perimeter of perhaps 20 M. Molecular and colloidal PCBs can remain in the water, suspended as globules of pure PCBs that are smaller than 20 uM, without being captured by silt curtains, and without settling at all (Paquin 2001, page 2):

“PCB in colloidal form constitutes the most mobile form of PCB in water, being affected only minimally by settling, physical retention or adsorption. Concentrations of PCB-like compounds in water can be much higher in colloidal form than in suspended solids or in dissolved form, and can be much more difficult to intercept through physico-chemical means” (Paquin 2001, page 2).

Indeed, molecular and colloidal phases of PCB together reasonably may be expected to constitute a significant, possibly the predominant fraction of total PCB in the water column, as illustrated by Table 1. Table 1 shows a site at which dissolved and colloidal PCB together amounted to 54 percent of total waterborne PCB.

An EPA review of experience of dredging PCB shows that dredging hot spots can disperse waterborne PCB beyond a 20-meter envelope ('silt curtain') around a dredge site, with observed concentrations of 0.1 to 0.2 ppm (100 to 200 ug/L, or 100,000 to 200,000 ng/L). This is approximately 3,000 to 6,000 times the PCB concentration assumed under a non-dredging scenario in the HRA prepared in support of another project (specifically, the PSEG NY proposal to site the Bethlehem Energy Center, or BEC, gas-fired power plant on the Hudson River at Bethlehem, New York; Oko and Oko 2001, PSEG NY 2001). In this higher waterborne PCB concentration range, resulting airborne PCB concentrations were reported to have exceeded safe concentrations (24). Indeed, EPA’s HRA Appendix E (US EPA 2000b) states the following:

“While these estimates of total tri+ PCB congener concentrations represent cumulative concentrations, dissolved or particulate tri+ PCB congener concentrations may be of even greater interest. In particular, the dissolved water column concentrations tend to be of greater concern because of their increased bioavailability” (US EPA 2000b, page 59, emphasis added).

In short, EPA’s estimated PCB residue load contributing to potential PCB inhalation risks should not have emerged from EPA's model of the Hudson River and, due to failure to account for dissolved and colloidal phases of PCB in the water column, it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

Precipitation of PCB-bearing sediment particles from the water column

Precipitation rates should be quantified realistically, as they in turn quantify the rate of removal from the water column of PCBs that had been resuspended and mobilized by dredging. Instead the residence time of flat, PCB-bearing clay particles in river water was quantified unrealistically, based upon the more rapid precipitation of spherically shaped particles acting in accordance with Stokes Law (Fig. 2). This procedure underestimated waterborne PCBs, and thereby also underestimated the amount of PCB that would become airborne.

Mathematical treatment is simplified when a spherical shape for fine particulates is assumed, which is the case in Stoke’s Law. This assumption, however, predicts faster than natural settling rates because, in nature, spherical particles are rare. Disk, rod shapes, and irregular random shapes are more common, and these shapes settle more slowly than spheres. Mathematical predictions of settling rates that do not account for irregular shapes can predict 100 percent faster settling rate at the >20-uM particle size range, and more than 1,000 percent faster at the <10-um> size range.

Clay is abundant in the Hudson River region, and would constitute a significant if not the preponderant fraction of PCB-contaminated sediment particles that will be resuspended and mobilized during dredging. Flat clay particles settle via a side-to-side oscillation during descent, greatly increasing their path length and residence time in the water column. That is why they settle more slowly than predicted by Stokes Law. Such delay in exiting the water column reasonably would be expected to increase the concentration of PCB-laden particles in the water column markedly, much as delays at highway exits markedly increase traffic on the highway. In short, EPA’s suspended silt cleansing rate should not have emerged from EPA's model of the Hudson River and, due to failure to account for the flatness of clay silt particles, it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

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 column. This electrostatic charge configuration inhibits agglomeration of fine silt particles resuspended by dredging. Electrostatic charges should be accounted for because of their potential importance in inhibiting settling of clay particles and removal of adsorbed PCB from the water column of the Hudson River at dredging sites.

Electrostatic charges should be modeled, but instead they were ignored. By this omission EPA fails to account for prolonged suspension in the water column of charge-separated PCB-bearing clay particles, and it thereby also underestimates waterborne PCBs subject to becoming airborne. Most fine particles, in part because of their high surface-area-to-volume ratio, tend to become electrostatically charged in water (Fig. 3). Clay sediment particles resuspended in water (as by dredging) tend to exhibit negative surface charges. The similar charges cause the particles bearing them to repel one another. The space between charge-separated negatively charged particles then is filled with cations (positive ions) already present in the water column. This configuration of charge separation increases particle residence times in the water column. Some charge-separated particles will not settle at all. Electrostatically separated PCB-bearing particles that do not settle remain in the water column, from which they are more available than settling particles to enter the atmosphere, where they may pose airborne risks.

By excluding this potentially significant factor from the analysis of settling of suspended particles in the Hudson River water column, EPA overestimates the settling velocity of PCB-laden particles to the river bottom, and thereby underestimates the likely concentration of PCBs in the water. In short, EPA’s suspended silt cleansing rate should not have emerged from EPA's model of the Hudson River and, due to failure to account for electrostatic charge separation of suspended silt particles, it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

Reflection coefficient of precipitating PCB-bearing sediment particles

The reflection coefficient should be quantified because it constitutes a potentially significant source of return to the water column of PCB-bearing silt particles that are of relatively low mass. If 20 percent of low-mass particles encountering the substrate are swept by currents back into the water column, then EPA's underestimation of the suspended particle population in the water column arising from omitting a reflection coefficient would be 20 percent. We don't know what (if any) single value of the reflection coefficient should be assumed for the Hudson River, or what multiple values might be assumed at each location in the river, under varying flow conditions. Clearly, however, EPA incorporated no reflection coefficient at all (or, equivalently, a reflection coefficient of zero was incorporated) in calculating PCB removal rates from the water column. This procedure thereby underestimated waterborne PCBs subject to becoming airborne.

The rate of free settling in water of silt particles influenced by earth’s gravity can be predicted from particle size and the specific gravity of discrete particles. At the bottom of settling columns where the particles compact, however, other mechanisms take over. One of these processes is reflection (Shavit, Moltchanov and Agnon 2003), which refers to the fact that particles of low mass may bounce off the substrate on which they land. The mass of particles that might be swept back into the water column after settling to the substrate would be expected to be greater in flowing waters, such as the Hudson River, and in laboratory wave chambers (Shavit, Moltchanov and Agnon 2003).

Similarly, colloids may remain in suspension indefinitely as a result of bouncing off water molecules with which they collide (in a well-documented phenomenon termed Brownian motion). The phenomena of reflection and bounce occur in a zone of activity termed the 'hindered zone' of settling. Failure to incorporate a reflection coefficient when calculating settling of PCB-laden particles in the Hudson River water column tends to underestimate particle and PCB concentrations in the water, just as traffic could be underestimated on a highway if the model used fails to count a high fraction of exiting vehicles that immediately reenter the highway. In short, EPA’s suspended silt cleansing rate should not have emerged from EPA's model of the Hudson River and, due to failure to account for reflection of settling silt particles, it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

PCB codistillation

Empirical measurements should be used to validate model assumptions that are made in quantifying PCB entry into the air. Instead, available empirical measurements were diluted with modeled values (see below), thereby underestimating the water-to-air transfer coefficient. Accurate estimation of waterborne PCB entry into the air requires quantification via accounting for PCB codistillation. By ignoring PCB codistillation in quantifying the water-to-air PCB transfer coefficient, EPA underestimated waterborne PCBs subject to becoming airborne. A recent news item (Anonymous 2001) based upon research conducted by the Integrated Atmospheric Deposition Network (IADN 2000) reveals that codistillation has transferred nearly two tons of PCB from Lake Ontario to the atmosphere between 1992 and 1996. According to a news report (Anonymous 2001) describing this startling finding:

"The Great Lakes have begun to 'exhale' significant quantities of chemicals, including ...PCBs..., releasing them into the atmosphere... Researchers say ... the lakes begin naturally cleansing themselves through the volatilization process (i. e., evaporating pollution off the water surface). The latest figures from the Integrated Atmospheric Deposition Network (IADN) show a net release from Lake Ontario alone of almost two tons of PCBs into the air... from 1992 through 1996..." (Anonymous 2001, page 9, emphasis added).

That's a half ton (nearly 500 kg) of PCBs each year codistilling from the surface of a cold lake.Codistillation, however, also is temperature-dependent. Thus it would occur at a greater rate, and to a greater degree, in warm water, such as in Hudson River water that is heated during industrial use as a cooling fluid, and then itself cooled in cooling towers before return to the river. EPA’s failure to account for codistillation might be explained by unfamiliarity with the phenomenon, as well as by an unwillingness to give appropriate credence to empirical data arising from credible reports. In short, EPA’s assumed water-to-air PCB transfer rate should not have emerged from EPA's model of the Hudson River, and it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

Empirical measurement of airborne PCBs over PCB-contaminated waters

The degree to which EPA was familiar with PCB codistillation cannot be inferred with certainty. However, such familiarity should have been unnecessary for enabling the Agency to quantify accurately PCB water-to-air transfer coefficients, inasmuch as empirical measurements cited by EPA had been made to quantify them. Indeed, the revised Hudson River HRA (US EPA 2000a, b) Appendix B cites nine empirical measurements of airborne PCB concentrations (Buckley and Tofflemire 1983) contributing toward estimating the transfer coefficient of PCBs from water to air (US EPA 2000b; see EPA’s Table B-1). These and possibly other measurements were used by EPA to produce PCB water-to-air transfer coefficients (summarized in 24; see EPA’s Table B-2; and also see the original data source, Harza 1992) as follows:

“These data can be used to estimate an empirical water to air transfer coefficient, representing the ratio of the PCB concentration in air divided by the PCB concentration in water. Using the detected PCB concentrations in air and water summarized in Table B-2, empirical air-water transfer coefficients range from 0.02 to 0.4 ug/M³ per ug/L, with a median value of 0.09, and an average value of 0.15 (ug/M³ per ug/L)” (US EPA 2000a, page 18).

EPA expressed surprise about the magnitude of these measured values, however, possibly because EPA was unfamiliar with codistillation. In that case the Agency would have expected the transfer coefficients to be lower than those suggested by the measurements. Further investigation could have elucidated the explanation for the higher-than-expected PCB water-to-air transfer coefficients, but further investigation apparently was not undertaken.

Instead, the measured values described above were assigned a low weighting. This EPA accomplished via adulteration of the nine empirically derived transfer coefficients with two lower transfer coefficients that were derived via two modeling approaches (Table 2). The two modeling approaches ignore codistillation, instead producing transfer coefficients consistent with Henry's Law acting on bulk PCB concentrations, that is, assuming even distribution of PCB through water. Model results expressed in units of ng/M² sec per ng/L could not be compared directly with the empirical values expressed in ug/M³ per ug/L. The units were brought into line, and the comparison made, via use of the average PCB concentration in the river (24 ng/L = 0.024 ug/L; US EPA 2000a, page 18). EPA used this concentration to produce a flux (13 ug/sec; US EPA 2000a, page 19) which, using the median empirical transfer coefficient (0.09), generated a modeled airborne concentration of 0.00012 to 0.00021 ug/M³ (US EPA 2000a, page 20, compared with 0.033 to 0.53 ug/M³ detected empirically (US EPA 2000a, page 20). This corresponds to a factor of 157 to 4,400 difference between the modeled vs. empirical data (0.53/0.00012 = 4,417; 0.033/0.00021 = 157). That is, the modeled water-to-air transport factors downwardly biased the estimated transfer of PCBs from Hudson River water to the atmosphere by a factor ranging from as little as 1/4,400^th to 1/157^th of the empirically determined values.

EPA’s preference for modeled transfer coefficient values biased the expected concentration of airborne PCBs over the river surface in a direction favorable to EPA’s dredging proposal and, in this sense, this action was self-serving. It was sufficiently self-serving to reduce airborne PCB estimates to below levels of concern to EPA, and below levels of concern to the New York State Department of Environmental Conservation (NYS DEC). Specifically, EPA’s weighting procedure diminished assumed airborne PCB concentrations from above published de minimis levels, requiring quantitative risk assessment, to concentrations below de minimis levels, not requiring quantitative assessment of risks potentially posed by inhalation of mobilized PCBs that might become airborne as a result of dredging (Table 3). Contrary to EPA’s routine procedure of validating its air models against reality via use of dyes or other markers, in this case EPA effectively invalidated empirical data based upon real-world data failing to conform to EPA’s air model. In short, EPA’s estimated water-to-air PCB transfer rate should not have emerged from EPA's model of the Hudson River and, due to failure to adequately consider empirical measurements, it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

Warm water sources of Hudson River PCB entry into the atmosphere

Potential warm-water sources of Hudson River PCB entry into the atmosphere, such as cooling towers, must be accounted for in assessing the potential public health significance of airborne PCBs under any dredging scenario. Instead, PCB concentrations resulting from water-to-air transfer were estimated based upon unheated (relatively cold) river water. According to the revised HRA for the Upper Hudson and Mid-Hudson River (US EPA 2000):

"The concentrations of PCBs in air were calculated from a combination of historical monitoring data and modeled emissions from the river…" (US EPA 2000, page ES-4; emphasis added).

The water temperature in cooling towers may be elevated to approximately 100° F (56° C)above that of the ambient river water source.

For every 10° C rise in temperature, the rate of a chemical reaction, such as the rate of PCB codistillation, may be expected roughly to double. The rate of PCB transfer from water to air occurring with a 40° C water temperature increase accordingly would be expected to undergo four doublings. Thus, the rate at which PCBs in cooling tower water might be expected to escape to the air from water at a temperature of, say, 45° C (113° F) in a cooling tower would be approximately 16 times greater than that in a source of Hudson River water at a temperature of 5° C (41° F).

If dissolved and/or colloidal PCBs rise to 10 ug/L (parts per billion by weight) during dredging, the weight of PCBs entering the cooling tower under one project proposal (the BEC power plant; Oko and Oko 2001, PSEG NY 2001), based on 4,500 gallon/minute uptake, would be 0.25 kg/d (nearly 10 tons/year). Examination of studies forming the basis for the passage quoted above pertaining to transfer of PCBs from river water to air, however, reveal no studies addressing PCB release from warm water in cooling towers. In short, EPA’s assumed low water-to-air PCB transfer rate should not have emerged from EPA's model of the Hudson River and, due to failure to consider warm water sources of PCB entry to the atmosphere, it cannot materialize in the Hudson River if dredging of PCB-bearing sediments at hotspots is indeed undertaken.

Summary of EPA quantification of parameters used in dredging decision making

As documented above, EPA evaluation of the nine subject parameters addressed in this study systematically have underestimated concentrations of PCBs that could, and presumably would, become airborne under non-dredging and dredging scenarios. Adoption of simplifying assumptions in modeling river flow, precipitation of suspended particles, and PCB dynamics can result in omission and/or unreliable quantification of important parameters contributing to overall PCB-associated risk. That this indeed has occurred is hinted at in Section 5 (Assessment of Water Quality Impacts) of Appendix E of EPA’s revised HRA for the Hudson River (US EPA 2000b):

“A complete evaluation of water quality impacts requires integrating a calibrated hydrodynamic model of the system with a water quality model capable of predicting changes due to advection, turbulent diffusion, and settling of the suspended particles. Such a model is beyond the scope of this evaluation” (US EPA 2000b, Section 5, page 12; emphasis added).

LITERATURE CITED

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 athttp://www.dec.state.ny.us/website/dow/bwam/hrsb2000.pdf, 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: http://www.epa.gov/hudson/actions.htm, updated 15 May 2006.

TO BE CONTINUED

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.