Sunday, June 21, 2009

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



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.


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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.