PCB POP hen I first heard the words “polychlorinated biphenyl”, I thought it sounded as though chemistry had all kinds of interesting names. But this phrase was always inserted as a quick explanatory footnote to a three-letter acronym only uttered with ominous tones: P-C-B. As a schoolchild, the threat of these three letters leaking out of decrepit fluorescent lights had our classes relegated to the school library on a rotating basis over several months as workers replaced the fixtures and parents rended their proverbial garments. (The experience of hazmat-clad workers and rending was repeated in high school, but that time due to the ominous utterance of “asbestos” and a suggestion that the whole building be torn asunderswhich happened later for myriad reasons anyway). This fear of PCBs that wracked the 1980s was a response to the manufacturing bans of the 1970s. As usage was not forbidden, but surely questioned, barrels of unwanted sludge began to show up in warehouses and Superfund waterways. Prevalence studies, then egged on by legislation to scope out the threat indicated that PCBs were the epitome of persistent organic pollutants (POPs). Studies suggested some congeners are pernicious (neuro)toxicants, teratogens, and carcinogens. Chemists know that one congener does not a family paint, but the invocation of child development/cancer often trips public insistence on a precautionary approach to all related compounds. (Note: PCBs are a biphenyl backbone studded with various numbers of Cl atoms; the individual species comprising a morphological family are “congeners”, being co-genus members. Each congener can of course have different properties. This fact of congener heterogeneity is clarified in chemistry contexts but often glossed over in environmental contexts: the 2008 printing of the Oxford Dictionary of Chemistry speaks of “PCB” as “derivatives of biphenyl (C6H5C6H5)...[that] are highly toxic and are suspected to be carcinogenic; their increasing use has caused concern because [of accumulation] in the food chain”, whereas sister publication the Oxford Dictionary of Environment and Conservation states that a “PCB” is “a synthetic, organic chemical...[that] is highly toxic and a potent carcinogen, and the management of PCB wastes is tightly regulated”.) The news around PCBs drummed up rampant fear, but then the news cycle redirected attention to acid rain, followed by ozone depletion, then oil spills, Styrofoam containers, hormone-mimicry, and CO2; PCB nightmares transiently flickered to life, usually as remediation efforts literally and conceptually dredged up the 1970s. Yet the attention of environmental researchers has hardly waned, as continued contributions to ES&T attest. The complexity of the problem regarding indus-
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10.1021/es100838c
2010 American Chemical Society
Published on Web 04/13/2010
trial prevalence, environmental distribution/ accumulation, (eco)toxicodynamics, and bodily harm, captured in this Focus Issue on PCB Sources, Exposures, [and] Toxicities, is an effort to continue the path to more effective regulation via fundamental understanding. The distribution of PCBs is addressed by several articles herein. Generally for POPs, (Environ. Sci. Technol. DOI 10.1021/es9030694) considers the meaning of “remote” so the global extent of potential harm can be better quantified. This aids both pollution modeling and risk assessment, so defining “remote“ should temper regulatory/legislative efforts. Specific to PCBs, researchers herein report on the fact that airborne concentrations are not abating and seem ubiquitously similar. Both urban environs and water are indicated as sources for these levels by (Environ. Sci. Technol. DOI 10.1021/es901871e), (Environ. Sci. Technol. DOI 10.1021/es9012036), (Environ. Sci. Technol. DOI 10.1021/es901691s), and (Environ. Sci. Technol. DOI 10.1021/es902911a) (including a news summary (Environ. Sci. Technol. DOI 10.1021/es100696y). This suggests that between electrical transformers, building materials, and contaminated sediments, PCB flux to the atmosphere could continue for decades. While concern is merited for airborne levels, new research herein also indicates widespread PCB contamination in consumer products. Cereal boxes and other materials are implicated by (Environ. Sci. Technol. DOI 10.1021/es901155h) and commercial paints by (Environ. Sci. Technol. DOI 10.1021/es902413k). The widespread use of such products further spread PCB flux to the environmentsa concept captured by this issue’s cover graphic and remarked on in the news story (Environ. Sci. Technol. DOI 10.1021/es100692h). Once PCBs are in the environment, their persistence and the variety of congeners makes for a long-term ecotoxicology incubator (of risk). Boundaries on the extent of that risk are perhaps suggested by (Environ. Sci. Technol. DOI 10.1021/es902325t): those congeners swept up by passive samplers are more bioavailable than those concentrated in sediment. However, (Environ. Sci. Technol. DOI 10.1021/es902208u), (Environ. Sci. Technol. DOI 10.1021/es901781p), and (Environ. Sci. Technol. DOI 10.1021/es902227a) indicate that PCB ecotoxicodynamics are variable upon chirality and enantiomeric considerations. This seems to differ from the physicochemical selectivity that would correlate to passive sampling and geo/hydro/aero fluxing. Thus distribution parameters may not go far enough for risk modeling. To that end, (Environ. Sci. Technol. DOI 10.1021/es902109w) addresses dechlorination pathways to statistically get a handle on potential threats. April 15, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 2747
Getting to organisms themselves: (Environ. Sci. Technol. DOI 10.1021/es9023139) (spiders), (Environ. Sci. Technol. DOI 10.1021/es901632e) (benthic creatures), and (Environ. Sci. Technol. DOI 10.1021/ es902514d) (plants). By interrogating the nature of trophic transfer, ecological import, and synergistic relationships, the findings presented by this trio suggest manners of better tracking pollution’s harm to then get a handle on (bio)remediative efforts. Certainly human exposure and risk studies are quick to follow an ecotoxicological focus. Echoing the frustration of the distribution/eco-accumulation disconnect, (Environ. Sci. Technol. DOI 10.1021/ es9021427) and (Environ. Sci. Technol. DOI 10.1021/ es902149b) find little or no correlation between PCBs in humans and its presence in food/dust and geographical profile differences. Human toxicodynamics then indicates a stymieing spread of structure-activity relationships: (Environ. Sci. Technol. DOI 10.1021/ es902321a) suggests differing types of neurotoxicant harm where the number of chlorine atoms could cause overstimulation or attenuation of vital neurotransmitter GABAA; (Environ. Sci. Technol. DOI 10.1021/es9012432) considers the mechanism of PCBs metabolizing to carcinogens, yet finds the expected path involving thyroid biomolecules to be unaffected. Yet there does appear to be cause for concern as (Environ. Sci. Technol. DOI 10.1021/es901918h) implicates PCBs in cochlear development. So PCBs may or may
2748 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / April 15, 2010
not be really awful (neuro)toxicants or carcinogens or teratogens, as covered in the news summary (Environ. Sci. Technol. DOI 10.1021/es100689b). As noted in their Guest Comment (Environ. Sci. Technol. DOI 10.1021/es100801f), Keri Hornbuckle and Larry Robertson remark that this Focus Issue is part of the ongoing effort to better understand PCB harm potentials. Surely this arc of findings will aid the development of more meaningful risk modeling and result in improved regulatory/legislative actions. Being exemplary POPs, the lessons learned for PCBs would hopefully improve the prospect for all such persistent and troublesome molecules. While elucidating toxicodynamics often gives credence to more focused fear, such investigation is frequently the window to improved pharmacodynamics. Therefore, in reading of this ongoing nightmarish prospect of chemicals a generation removed from their synthesis, it is hoped that the insight herein and your pursuits may help to ultimately improve ecological and environmental health.
Darcy J. Gentleman Managing Editor
[email protected].
