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Polychlorinated biphenyl (PCB) toxicology and risk assessment

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Project log

Robert A. Michaels
added 2 research items
Modern environmental regulation prioritizes pollution prevention, but persistent ‘legacy contaminants’ already have been disseminated. Examples include arsenic, lead, chlorinated dioxins, DDT (dichlorodiphenyltrichloroethane), PAHs (polycyclic aromatic hydrocarbons), PCBs (polychlorinated biphenyls), PFCs, and radioactive fallout. Risks posed by some have been recognized for decades. Concern about others is emerging. PCB risks include some of longstanding concern, and others of emerging concern, including emerging evidence of possible autism causation among exposed infants and/or pregnant women. We investigated GE's recently completed seven-year EPA-mandated clamshell dredging project for remediating PCB contamination in the Hudson River Superfund Site. Post-project PCB levels in water and fish are higher than anticipated, suggesting to some the incompleteness of dredging, and the need to extend the project to remove more PCB-bearing sediments. We found, however, that the preponderance of dredged PCB sediment was mobilized by clamshells rather than barged, and much PCB outside of dredge buckets also was mobilized. We attribute excessive PCB levels in the river to inefficiency intrinsic to clamshell dredging, rather than to incompleteness of dredging. We conclude that extension of the dredging project would prolong mobilization processes, allowing PCBs to spread more widely and pose risks in more ecosystems that include endangered fish such as sturgeon, endangered birds such as bald eagles, and people. These lessons should be applied to environmental dredging involving PCBs and other emerging contaminants. They should be embodied in remediation laws, regulations, and enforcement to assure that we leave to our descendants a more positive environmental legacy than that left to us.
Technology, where he investigated surface behavior of mine tailings water that had been contaminated with heavy metal ions: zinc, lead, copper and mercury. He has designed remediation systems for pollution abatement of aquifers, stripping systems for the removal of MTBE (methyl-tert-butyl ether) and other volatile organic compounds from water, and cathodic protection systems for underground pipelines and storage tanks. Dr. Oko has served as an expert witness in litigation of industrial accidents. Prominent cases have involved metallurgical examination of collapsed bridge sections, fugitive chlorine gas from a water treatment plant, and collapsed scaffolds, cranes and ladders. Michaels & Oko, Lessons from Hudson River PCB dredging page 3 ABSTRACT Modern environmental regulation prioritizes pollution prevention, but persistent 'legacy contaminants' already have been disseminated. Examples include arsenic, lead, chlorinated dioxins, DDT (dichlorodiphenyltrichloroethane), PAHs (polycyclic aromatic hydrocarbons), PCBs (polychlorinated biphenyls), PFCs, and radioactive fallout. Risks posed by some have been recognized for decades. Concern about others is emerging. PCB risks include some of longstanding concern, and others of emerging concern, including emerging evidence of possible autism causation among exposed infants and/or pregnant women. We investigated GE's recently completed seven-year EPA-mandated clamshell dredging project for remediating PCB contamination in the Hudson River Superfund Site. Post-project PCB levels in water and fish are higher than anticipated, suggesting to some the incompleteness of dredging, and the need to extend the project to remove more PCB-bearing sediments. We found, however, that the preponderance of dredged PCB sediment was mobilized by clamshells rather than barged, and much PCB outside of dredge buckets also was mobilized. We attribute excessive PCB levels in the river to inefficiency intrinsic to clamshell dredging, rather than to incompleteness of dredging.
Robert A. Michaels
added a research item
We have studied the proposal to dredge, and its implementation, since 2007. Our contributions regarding reasonably anticipated and actual project effectiveness were ignored in EPA’s first five-year evaluation and in its proposed second five-year review. Our studies, ignored by EPA, focused on all stages of the dredging proposal, starting with EPA's a priori assumptions. We concluded that EPA’s analysis to justify dredging was biased, based upon our findings that critical assumptions made by the Agency were erroneous, and that all identified errors were made in the dredging friendly direction rather than randomly. We then studied dredging while in progress, during Phase 1 of the project, and found critical deficiencies in the project and in monitoring programs to document it. Most recently we studied dredging during and after Phase 2. We reported negative Hudson River Superfund Site remediation effectiveness: clamshell dredging massively mobilized sediments, increasing PCB contamination rather than decreasing it. Our purpose in providing these comments is to motivate EPA to address the serious concerns that we have expressed both publicly and privately regarding the expected and the actual performance of the clamshell dredging project. Our 2007 and 2010 peer-reviewed Environmental Practice articles predicted that primitive clamshell dredging in the Hudson River would massively mobilize buried PCB sediments, and spread them to an expanding area of river ecosystems that include fish and birds. Clamshells basically are floating backhoes that are useful for navigational dredging. Our 2017 articles analyze the structure of clamshell dredge buckets used in the Hudson River, and the computerized dredge bucket data produced on each closure (the ‘bucket files’). We found that 75-80 percent of dredged sediment is returned to the river in mobile form, rather than removed to waiting barges for off-site disposal.
Robert A. Michaels
added 2 research items
Batch unialgal cultures of one resistant and one sensitive marine phytoplankter were exposed to polychlorinated biphenyls (PCB's) under a variety of culture conditions, and the effects on growth and photosynthesis were determined to detect interactions between environmental conditions and toxicity. The hypothesis was tested that varying culture regimes would alter the relative growth and PCB-resistance of the organisms studied. These were the resistant, naked green flagellate, Dunaliella tertiolecta, and two isolates of the sensitive diatom, Thalassiosira pseudonana, one of estuarine and one of oceanic (Sargasso Sea) origin. Compared with growth in a fully nutrient-enriched culture medium, low nutrient concentration inhibited growth of the estuarine isolate T. pseudonana; sensitivity to PCB increased under this nutrient stress. In contrast, low nutrient concentration enhanced growth, but not PCB resistance, of the oceanic isolate, reducing the differential in PCB resistance between these isolates. Low salinity inhibited growth of the estuarine isolate of T. pseudonana and increased resistance, enhancing growth of cells treated with PCB at low compared with normal salinity. Increased resistance with stress suggested that altered PCB distribution at low salinity reduced exposure of sensitive intracellular sites of action to the toxin. This hypothesis was refuted by adapting cells to low salinity, transferring them to normal salinity and finding resistance to PCB equal to that exhibited at low salinity. Genetic or physiological adaptation to low salinity, rather than altered PCB availability, produced the resistance. Whereas T. pseudonana gained resistance, D. tertiolecta lost resistance to PCB upon sudden exposure to low salinity. Unlike walled T. pseudonana, naked D. tertioledta responded to sudden reductions in salinity by expanding in volume. Very low salinity caused lysis. PCB did not affect this process. Induced sensitivity to PCB must have been caused physiologically by PCB gaining access to sensitive sites of action, rather than structurally by weakening the cell membrane and sensitizing the cell to osmotic damage at low salinity. To identify the factor in salinity variation most important in modifying PCB susceptibility, altered ion concentrations and ratios were investigated. Variation in Na+, H+, and in total ionic concentration modified PCB toxicity, whereas variation in K+ and Ca2+ did not. In T. pseudonana, when the nonelectrolyte glycerol was substituted for seawater salts to reduce total ion concentration while maintaining constant osmolarity, PCB-treated cells displayed reduced susceptibility as in the case of lowered salinity. Hence, the effect of ions exceeded any effect of osmolarity. Photosynthetic 14C-fixation per cell and cell density were measured simultaneously at low, normal, or high salinity. The relationship between salinity and susceptibility of T. pseudonana to PCB was identical whether the indicator of PCB effect was growth or photosynthesis per cell. At normal salinity photosynthesis per cell was inhibited up to 90% by 50 ug/l of PCB, refuting claimed independence of PCB action and photosynthesis. PCB inhibition of photosynthesis per cell diminished at low salinity, but not at high salinity, paralleling the effect of PCB on growth. Although growth of D. tertiolecta decreased at low salinity, photosynthesis per cell increased. The increase was not as great as that of controls, however, paralleling the sensitization of growth to PCB at low salinity. At normal or high salinity, photosynthesis per cell, like growth, was unaffected by PCB. The resistance of D. tertiolecta to PCB did not vary with nutrient concentration. In contrast with T. pseudonana, D. tertiolecta resistance was not conferred by release of a PCB detoxifier into the medium, nor by possession of PCB-resistant ATPase. Thus, the differential in susceptibility to PCB, athough somewhat variable, was pronounced under all culture conditions applied. In contrast, the differential between isolates of T. pseudonana depended upon culture conditions, and was not determined by habitat of origin.
To determine whether the resistance of algae to PCB contamination is dependent upon the predictability of the species' habitat, two estuarine algae were exposed to PCB at varying salinities.