A procedure to detect and identify specific chemicals of potential inhalation toxicity concern in aerosols.

OBJECTIVE: Understanding the potential inhalation toxicity of poorly characterized aerosols is challenging both because aerosols may contain numerous chemicals and because it is difficult to predict which chemicals may present significant inhalation toxicity concerns at the observed levels. We have developed a novel systematic procedure to address these challenges through non-targeted chemical analysis by two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) and assessment of the results using publicly available toxicity data to prioritize the tentatively identified detected chemicals according to potential inhalation toxicity. MATERIALS AND METHODS: The procedure involves non-targeted chemical analysis of aerosol samples utilizing GC × GC-TOFMS, which is selected because it is an effective technique for detecting chemicals in complex samples and assigning tentative identities according to the mass spectra. For data evaluation, existing toxicity data (e.g. from the U.S. Environmental Protection Agency CompTox Chemicals Dashboard) are used to calculate multiple toxicity metrics that can be compared among the tentatively identified chemicals. These metrics include hazard quotient, incremental lifetime cancer risk, and metrics analogous to hazard quotient that we designated as exposure-(toxicology endpoint) ratios. RESULTS AND DISCUSSION: We demonstrated the utility of our procedure by detecting, identifying, and prioritizing specific chemicals of potential inhalation toxicity concern in the mainstream smoke generated from the machine-smoking of marijuana blunts. CONCLUSION: By designing a systematic approach for detecting and identifying numerous chemicals in complex aerosol samples and prioritizing the chemicals in relation to different inhalation toxicology endpoints, we have developed an effective approach to elucidate the potential inhalation toxicity of aerosols.

Impacts of Nicotine and Flavoring on the Sensory Perception of E-Cigarette Aerosol.

INTRODUCTION: To examine the interaction between an added flavoring (cherry) and nicotine on the perception of electronic cigarette (e-cigarette) aerosol and how this impacts the appeal of flavored liquids for e-cigarette (e-liquids). METHODS: A total of 19 subjects (13 male, 6 female) vaped six commercially available e-liquids with varying contents of nicotine (0, 6, 12 mg/mL) and cherry flavor (4.7% or 9.3% vol/vol). For each e-liquid, subjects first rated overall liking/disliking of the aerosol using the Labeled Hedonic Scale, followed by perceived intensities of sweetness, bitterness, harshness (irritation), and cherry flavor of the aerosol using the general version of Labeled Magnitude Scale. RESULTS: The main findings were that (1) added nicotine increased perceived irritation and bitterness, and decreased the perceived sweetness of the e-cigarette aerosol; (2) cherry flavoring added a characteristic "cherry flavor" and an increase in the flavoring concentration from 4.7% to 9.3% tended to increase perceived intensities of sweetness, harshness, and bitterness; and (3) hedonic ratings of the e-cigarette aerosol decreased as nicotine level increased, but were not affected by flavor level. CONCLUSIONS: Our findings indicate that the appeal of the e-cigarette aerosol decreases as nicotine concentration increases. Conversely, perceived sweetness improved liking. An increase in the concentration of cherry flavoring did not appear to impact any of the measured attributes to a significant degree. IMPLICATIONS: This work demonstrates that the perception of specific sensory attributes of e-cigarettes and their overall appeal are affected by the e-liquid constituents. Most significantly, the results suggest that nicotine decreases the sensory appeal of e-cigarettes by contributing to the perceived irritation and bitterness of the aerosol. These data have implications for the role that nicotine plays in the sensory perception and appeal of e-cigarettes aerosol and further how these sensory factors can be modulated by sweet flavoring.

The Application of Commercially Available Mobile Cigarette Topography Devices for E-cigarette Vaping Behavior Measurements.

INTRODUCTION: The ability to reliably measure real-world vaping behavior is critical to understand exposures to potential toxins. Commercially available mobile topography devices were originally designed to measure cigarette puffing behavior. Information regarding how applicable these devices are to the measurement of electronic cigarette (e-cigarette) vaping topography is needed. METHODS: Clinical Research Support System (CReSS; Pocket) and Smoking Puff Analyzer Mobile (SPA-M) topography devices were tested against the calibrated laboratory-based smoking puff analyzer duplicator (SPA-D) device combined with an analytical smoking machine that generates programmable puffs with high precision. Puff topography of e-cigarettes was measured over a range of puff volumes (10-130 mL) at 2 and 5 s puff durations (using bell- and square-shaped puffs). "Real-world" topography data collected from 10 participants during 1 week of at-home vaping were also analyzed. Recording anomalies and limitations of the devices, such as accuracy of detection of the puff end, flow rate dropouts, unreported puffs, and abandoned vaping sessions for the CReSS, and multi-peak puffs for the SPA-M were defined. RESULTS: The accuracy of puff volumes and durations was determined for both devices. The error for SPA-M was generally within ±10%, whereas that for the CReSS varied more widely. The CReSS consistently underestimated puff duration at higher flow rates. CONCLUSIONS: CReSS and SPA-M topography devices can be used for real-world e-cigarette topography measurements, but researchers have to be aware of the limitations. Both devices can provide accurate measurements only under certain puff parameter ranges. The SPA-M provided more accurate measurements under a wider range of puffing parameters than the CReSS. Summary data reported by both devices require thorough analysis of the raw data to avoid misleading data interpretation. IMPLICATIONS: Results of this study provide researchers with valuable information about the capability of commercially available cigarette topography devices to measure real-world vaping behaviors. The differing measurement ranges of the two devices and puff recording limitations and anomalies should be taken into account during analysis and interpretation of real-world data.

Evidence of compensation among waterpipe smokers using harm reduction components.

OBJECTIVES: We examined two waterpipe tobacco smoking components advertised to reduce harm to determine if they result in lower levels of biomarkers of acute exposure. METHODS: We conducted a crossover study of 34 experienced waterpipe smokers smoking a research-grade waterpipe in three configurations ad libitum in a controlled chamber: control (quick-light charcoal), electric (electric heating) and bubble diffuser (quick-light charcoal and bubble diffuser). We collected data on smoking topography, environmental carbon monoxide (CO), subjective effects, heart rate, plasma nicotine and exhaled CO and benzene. RESULTS: Smokers' mean plasma nicotine, heart rate, and exhaled benzene and CO boost were all significantly lower for electric compared with control. However, smokers puffed more intensely and took significantly more and larger volume puffs for a larger total puffing volume (2.0 times larger, p<0.0001) when smoking electric; machine yields indicate this was likely due to lower mainstream nicotine. Smokers rated electric smoking experience less satisfying and less pleasant. For charcoal heating, the mean mass of CO emitted into the chamber was ~1 g when participants smoked for a mean of 32 minutes at a typical residential ventilation rate (2.3 hr-1). CONCLUSION: Waterpipe smokers engaged in compensation (i.e., increased and more intense puffing) to make up for decreased mainstream nicotine delivery from the same tobacco heated two ways. Waterpipe components can affect human puffing behaviours, exposures and subjective effects. Evidence reported here supports regulation of waterpipe components, smoking bans in multifamily housing and the use of human studies to evaluate modified or reduced risk claims.

Chemical characterization of marijuana blunt smoke by non-targeted chemical analysis.

Background: Marijuana blunts, which are tobacco cigar wrappers filled with marijuana, are commonly smoked in the US as a means of cannabis use. The use of marijuana blunts presents toxicity concerns because the smoke contains both marijuana-related and tobacco-related chemicals. Thus, it is important to understand the chemical composition of mainstream smoke (MSS) from marijuana blunts. This study demonstrates the ability to detect and identify chemical constituents exclusively associated with blunt MSS in contrast to tobacco cigar MSS (designated as 'new exposures') through non-targeted chemical analysis.Methods: Samples collected separately from blunt MSS and tobacco cigar MSS were analyzed using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS).Results and Discussion: Two new exposures, which likely represent only a subset of all new exposures, were identified by evaluating the data from thousands of detected signals and then confirming selected compound identities in analyses using authentic chemical standards. The two confirmed new exposures, mellein and 2-phenyl-2-oxazoline, are not cannabinoids and, to the best of our knowledge, have not been previously reported in association with cannabis, tobacco, or smoke of any kind. In addition, we detected and quantified three phenols (2-, 3-, and 4-ethylphenol) in blunt MSS. Given the toxicity of phenols, quantifying the levels of other phenols could be pursued in future research on blunt MSS.Conclusion: This study shows the power and utility of GC × GC-TOFMS as a methodology for non-targeted chemical analysis to identify new chemical exposures in blunt MSS and to provide data to guide further investigations of blunt MSS.

Effectiveness of Practices To Increase Timeliness of Providing Targeted Therapy for Inpatients with Bloodstream Infections: a Laboratory Medicine Best Practices Systematic Review and Meta-analysis.

BACKGROUND: Bloodstream infection (BSI) is a major cause of morbidity and mortality throughout the world. Rapid identification of bloodstream pathogens is a laboratory practice that supports strategies for rapid transition to direct targeted therapy by providing for timely and effective patient care. In fact, the more rapidly that appropriate antimicrobials are prescribed, the lower the mortality for patients with sepsis. Rapid identification methods may have multiple positive impacts on patient outcomes, including reductions in mortality, morbidity, hospital lengths of stay, and antibiotic use. In addition, the strategy can reduce the cost of care for patients with BSIs. OBJECTIVES: The purpose of this review is to evaluate the evidence for the effectiveness of three rapid diagnostic practices in decreasing the time to targeted therapy for hospitalized patients with BSIs. The review was performed by applying the Centers for Disease Control and Prevention's (CDC's) Laboratory Medicine Best Practices Initiative (LMBP) systematic review methods for quality improvement (QI) practices and translating the results into evidence-based guidance (R. H. Christenson et al., Clin Chem 57:816-825, 2011, http://dx.doi.org/10.1373/clinchem.2010.157131). SEARCH STRATEGY: A comprehensive literature search was conducted to identify studies with measurable outcomes. A search of three electronic bibliographic databases (PubMed, Embase, and CINAHL), databases containing "gray" literature (unpublished academic, government, or industry evidence not governed by commercial publishing) (CIHI, NIHR, SIGN, and other databases), and the Cochrane database for English-language articles published between 1990 and 2011 was conducted in July 2011. DATES OF SEARCH: The dates of our search were from 1990 to July 2011. SELECTION CRITERIA: Animal studies and non-English publications were excluded. The search contained the following medical subject headings: bacteremia; bloodstream infection; time factors; health care costs; length of stay; morbidity; mortality; antimicrobial therapy; rapid molecular techniques, polymerase chain reaction (PCR); in situ hybridization, fluorescence; treatment outcome; drug therapy; patient care team; pharmacy service, hospital; hospital information systems; Gram stain; pharmacy service; and spectrometry, mass, matrix-assisted laser desorption-ionization. Phenotypic as well as the following key words were searched: targeted therapy; rapid identification; rapid; Gram positive; Gram negative; reduce(ed); cost(s); pneumoslide; PBP2; tube coagulase; matrix-assisted laser desorption/ionization time of flight; MALDI TOF; blood culture; EMR; electronic reporting; call to provider; collaboration; pharmacy; laboratory; bacteria; yeast; ICU; and others. In addition to the electronic search being performed, a request for unpublished quality improvement data was made to the clinical laboratory community. MAIN RESULTS: Rapid molecular testing with direct communication significantly improves timeliness compared to standard testing. Rapid phenotypic techniques with direct communication likely improve the timeliness of targeted therapy. Studies show a significant and homogeneous reduction in mortality associated with rapid molecular testing combined with direct communication. AUTHORS' CONCLUSIONS: No recommendation is made for or against the use of the three assessed practices of this review due to insufficient evidence. The overall strength of evidence is suggestive; the data suggest that each of these three practices has the potential to improve the time required to initiate targeted therapy and possibly improve other patient outcomes, such as mortality. The meta-analysis results suggest that the implementation of any of the three practices may be more effective at increasing timeliness to targeted therapy than routine microbiology techniques for identification of the microorganisms causing BSIs. Based on the included studies, results for all three practices appear applicable across multiple microorganisms, including methicillin-resistant Staphylococcus aureus (MRSA), methicillin-sensitive S. aureus (MSSA), Candida species, and Enterococcus species.

Role of sweet and other flavours in liking and disliking of electronic cigarettes.

OBJECTIVE: To examine the extent to which the perception of sweet and other flavours is associated with liking and disliking of flavoured electronic cigarettes (e-cigarettes). METHODS: 31 participants (13 females/18 males; 12 sole/19 dual users) vaped 6 commercially available flavours of blu Tanks: Classic Tobacco (CT), Magnificent Menthol (MM), Cherry Crush (CC), Vivid Vanilla (VV), Piña Colada (PC) and Peach Schnapps (PS); all 'medium' strength, 12 mg/mL nicotine concentration. For each flavoured e-cigarette, participants first rated liking/disliking on the Labeled Hedonic Scale, followed by perceived intensities of sweetness, coolness, bitterness, harshness and specific flavour on the generalised version of the Labeled Magnitude Scale. The psychophysical testing was conducted individually in an environmental chamber. RESULTS: PC was perceived as sweetest and liked the most; CT was perceived as least sweet and liked the least. Across all flavours, liking was correlated with sweetness (r=0.31), coolness (r=0.25), bitterness (r=-0.25) and harshness (r=-0.29, all p<0.001). Specifically, liking was positively correlated with sweetness of PS (r=0.56, p=0.001) and PC (r=0.36, p=0.048); and with coolness of MM, CT and VV (r=0.41-0.52, p<0.05). In contrast, harshness was negatively correlated with liking for CC, PC and PS (r=0.37-0.40, p<0.05). In a multivariate model, sweetness had the greatest positive impact on liking followed by coolness; harshness had the greatest negative impact on liking. CONCLUSIONS: Our findings indicate that bitterness and harshness, most likely from nicotine, have negative impacts on the liking of e-cigarettes, but the addition of flavourants that elicit sweetness or coolness generally improves liking. The results suggest that flavours play an important role in e-cigarette preference and most likely use.

Respiratory and cardiovascular effects of metals in ambient particulate matter: a critical review.

In this review, we critically evaluated the epidemiological and toxicological evidence for the role of specific transition metals (As. Cr. Cu. Fe. Mn. Ni. Sc. Ti. V and Zn) in causing or contributing to the respiratory and cardiovascular health effects associated with ambient PM. Although the epidemiologic studies arc suggestive. and both the in vivo and in vitro laboratory studies document the toxicity of specific metals (Fe. Ni. V and Zn). the overall weight of evidence does not convincingly implicate metals as major contributors to health effects. None of the epidemiology studies that we reviewed conclusively implicated specific transition metals as having caused the respiratory and cardiovascular effects associated with ambient levels of PM. However, the studies reviewed tended to be internal ly consistent in identifying some metals (Fe, Ni, V and Zn) more frequently than others (As, Cu, Mn and Sc) as having positive associations wi th health effects. The major problem wi th which the epidemiological studies were faced was classifying and quantifying exposure. Community and population exposures to metals or other components of ambient PM were inferred from centrally- located samplers that may not accurately represent individual level exposures. Only a few authors reported findings that did not support the stated premise of the study; indeed, statistic ally significant associations are not necessarily biologically significant. It is likely that ·'negative studies" are under-represented in the published literature, making it a challenge to achieve a balanced evaluation of the role of metals in causing health effects associated with ambient PM. Both the in vivo and in vitro study results demonstrated that individual metals (Cu. Fe. Ni. V and Zn) and extracts of metals from ambient PM sources can produce acute inflammatory responses. However. the doses administered to laboratory animals were many orders of magnitude greater than what humans experience from breathing ambient air. The studies that used intratracheal instillation have the advantage of delivering a known dose to a specific anatomical location. but arc not analogous to an inhaled dose that is distributed over the surface area of the respiratory tract. Studies. in which laboratory animals or human volunteers inhaled CAPs best represent exposures to the general human population. The in vivo and in vitro studies reviewed provide indications that the probable mechanisms involved in the respiratory and cardiac effects from high metal exposures include: an inflammatory response mediated by formation of ROS, upregulation of genes coding for inflammatory cytokines, altered expression of genes involved in cell signaling pathways and maintenance of metals homeostasis.The fact that doses of metals many orders of magnitude greater than those existing in ambient air were required to produce measurable adverse effects in animals makes it doubtful that metals play any major role in respiratory and cardiovascular effects produced from human exposure to ambient PM. We suggest that future research priorities should focus on testing at more environmentally relevant exposure levels and that any new toxicological studies be written to include dosages in units that can be easily compared to human exposure levels.

Little Cigars vs 3R4F Cigarette: Physical Properties and HPHC Yields.

OBJECTIVE: Our objective was to characterize physical properties and semivolatile harmful and potentially harmful constituent yields in the mainstream smoke (MSS) of 4 popular little cigars compared to the 3R4F reference cigarette. METHODS: We used the ISO and Canadian Intense Regimen protocols to generate MSS for Cheyenne (Full Flavor and Menthol) and Swisher Sweets (Original and Sweet Cherry) little cigars; and the 3R4F. We examined physical properties such as length, tobacco filler mass, pressure drop, and ventilation for each product. Nicotine, benzo[a]pyrene, and tobacco-specific nitrosamine (TSNA) yields were determined in the MSS. RESULTS: Little cigars were longer (~15mm), contained more tobacco filler (100-200 mg), and had a higher pressure drop (~1.3X) compared to the 3R4F. Ventilation holes were found only on the filter paper of the 3R4F. Nicotine transmitted to the MSS was similar for all products under the intense smoking protocol. The highest yields of TSNAs and benzo(a)pyrene were measured for the little cigars. CONCLUSIONS: Little cigars may deliver similar levels of nicotine but higher levels of carcinogens to the MSS compared to cigarettes. Thus, previous reports on the toxicity of tobacco smoke based on cigarettes might not apply to little cigar products.

Temporal Variations in Cigarette Tobacco Bacterial Community Composition and Tobacco-Specific Nitrosamine Content Are Influenced by Brand and Storage Conditions.

Tobacco products, specifically cigarettes, are home to microbial ecosystems that may play an important role in the generation of carcinogenic tobacco-specific nitrosamines (TSNAs), as well as the onset of multiple adverse human health effects associated with the use of these products. Therefore, we conducted time-series experiments with five commercially available brands of cigarettes that were either commercially mentholated, custom-mentholated, user-mentholated, or non-mentholated. To mimic user storage conditions, the cigarettes were incubated for 14 days under three different temperatures and relative humidities (i.e., pocket, refrigerator, and room). Overall, 360 samples were collected over the course of 2 weeks and total DNA was extracted, PCR amplified for the V3V4 hypervariable region of the 16S rRNA gene and sequenced using Illumina MiSeq. A subset of samples (n = 32) was also analyzed via liquid chromatography with tandem mass spectrometry for two TSNAs: N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Comparative analyses of the five tobacco brands revealed bacterial communities dominated by Pseudomonas, Pantoea, and Bacillus, with Pseudomonas relatively stable in abundance regardless of storage condition. In addition, core bacterial operational taxonomic units (OTUs) were identified in all samples and included Bacillus pumilus, Rhizobium sp., Sphingomonas sp., unknown Enterobacteriaceae, Pantoea sp., Pseudomonas sp., Pseudomonas oryzihabitans, and P. putida. Additional OTUs were identified that significantly changed in relative abundance between day 0 and day 14, influenced by brand and storage condition. In addition, small but statistically significant increases in NNN levels were observed in user- and commercially mentholated brands between day 0 and day 14 at pocket conditions. These data suggest that manufacturing and user manipulations, such as mentholation and storage conditions, may directly impact the microbiome of cigarette tobacco as well as the levels of carcinogens.

Mentholation affects the cigarette microbiota by selecting for bacteria resistant to harsh environmental conditions and selecting against potential bacterial pathogens.

BACKGROUND: There is a paucity of data regarding the microbial constituents of tobacco products and their impacts on public health. Moreover, there has been no comparative characterization performed on the bacterial microbiota associated with the addition of menthol, an additive that has been used by tobacco manufacturers for nearly a century. To address this knowledge gap, we conducted bacterial community profiling on tobacco from user- and custom-mentholated/non-mentholated cigarette pairs, as well as a commercially-mentholated product. Total genomic DNA was extracted using a multi-step enzymatic and mechanical lysis protocol followed by PCR amplification of the V3-V4 hypervariable regions of the 16S rRNA gene from five cigarette products (18 cigarettes per product for a total of 90 samples): Camel Crush, user-mentholated Camel Crush, Camel Kings, custom-mentholated Camel Kings, and Newport Menthols. Sequencing was performed on the Illumina MiSeq platform and sequences were processed using the Quantitative Insights Into Microbial Ecology (QIIME) software package. RESULTS: In all products, Pseudomonas was the most abundant genera and included Pseudomonas oryzihabitans and Pseudomonas putida, regardless of mentholation status. However, further comparative analysis of the five products revealed significant differences in the bacterial compositions across products. Bacterial community richness was higher among non-mentholated products compared to those that were mentholated, particularly those that were custom-mentholated. In addition, mentholation appeared to be correlated with a reduction in potential human bacterial pathogens and an increase in bacterial species resistant to harsh environmental conditions. CONCLUSIONS: Taken together, these data provide preliminary evidence that the mentholation of commercially available cigarettes can impact the bacterial community of these products.

Lipoprotein Biomarkers and Risk of Cardiovascular Disease: A Laboratory Medicine Best Practices (LMBP) Systematic Review.

BACKGROUND: Controversy exists about the incremental utility of nontraditional lipid biomarkers [e.g., apolipoprotein (apo) B, apo A-I, and non-HDL-C] in improving cardiovascular disease (CVD) risk prediction when added to a conventional model of traditional risk factors (e.g., total cholesterol, LDL cholesterol, HDL cholesterol, sex, age, smoking status, and blood pressure). Here we present a systematic review that was conducted to assess the use of nontraditional lipid biomarkers including apo B, apo A-I, apo B/A-I ratio, and non-HDL-C in improving CVD risk prediction after controlling for the traditional risk factors in populations at risk for cardiovascular events. CONTENT: This systematic review used the Laboratory Medicine Best Practices (LMBP™) A-6 methods. A total of 9 relevant studies published before and including July 2015 comprised the evidence base for this review. Results from this systematic review indicated that after the adjustment for standard nonlipid and lipid CVD risk factors, nontraditional apolipoprotein biomarkers apo B (overall effect = relative risk: 1.31; 95% CI, 1.22-1.40; 4 studies) and apo B/apo A-I ratio (overall effect = relative risk: 1.31; 95% CI, 1.11-1.38; 7 studies) resulted in significant improvement in long-term CVD risk assessment. SUMMARY: Available evidence showed that nontraditional lipid biomarkers apo B and apo B/apo I ratio can improve the risk prediction for cardiovascular events after controlling for the traditional risk factors for the populations at risk. However, because of insufficient evidence, no conclusions could be made for the effectiveness of apo A-I and non-HDL-C lipid markers to predict the CVD events, indicating a need for more research in this field.

Custom Mentholation of Commercial Cigarettes for Research Purposes.

In the U.S. menthol remains the sole permitted characterizing cigarette flavor additive in part because efforts to link menthol cigarette use to increased tobacco-related disease risk have been inconclusive. To perform definitive studies, cigarettes that differ only in menthol content are required, yet these are not commercially available. We prepared research cigarettes differing only in menthol content by deposition of L-menthol vapor directly onto commercial nonmenthol cigarettes, and developed a method to measure a cigarette's menthol and nicotine content. With our custom-mentholation technique we achieved the desired moderately high menthol content (as compared to commercial brands) of 6.7 ± 1.0 mg/g (n = 25) without perturbing the cigarettes' nicotine content (17.7 ± 0.7 mg/g [n = 25]). We also characterized other pertinent attributes of our custom-mentholated cigarettes, including percent transmission of menthol and nicotine to mainstream smoke and the rate of loss of menthol over time during storage at room temperature. We are currently using this simple mentholation technique to investigate the differences in human exposure to selected chemicals in cigarette smoke due only to the presence of the added menthol. Our cigarettes will also aid in the elucidation of the effects of menthol on the toxicity of tobacco smoke.

Gas-phase polychlorinated biphenyl and hexachlorocyclohexane concentrations near the Great Lakes: a historical perspective.

The Integrated Atmospheric Deposition Network (IADN) has been measuring gas-phase, polychlorinated biphenyl (PCB) concentrations at sites near Lakes Michigan and Superior for over a decade. Data through 2000 were used in this study to investigate PCB temporal trends in the Great Lakes atmosphere. Decreasing trends were found at both sites, and half-lives of approximately 20 yr were calculated using IADN data. However, when these data were supplemented by historical data for Lakes Michigan and Superior dating back to 1977, half-lives dropped to 10 and 6 yr, respectively. These latter half-lives agreed well with half-lives in other environmental compartments. Exponential curves fitted to the historical and IADN data indicated little decline in PCB concentrations in the basin since the mid-1990s. A similar historical analysis of alpha-and gamma-hexachlorocyclohexane (HCH) data indicated that IADN data were the best predictor of trends, resulting in half-lives of around 4 yr for both compounds. Gamma-HCH concentrations, however, have shown little decline in recent years, most likely because of its continuing use. PCB and alpha-HCH temporal trends indicated that bans on these substances have helped to remove them from the atmosphere. This work also showed that decades of data may be necessary to properly interpret long-term temporal trends in gas-phase organochlorine concentrations.

Causes of variability in pesticide and PCB concentrations in air near the Great Lakes.

Data through 2001 from the Integrated Atmospheric Deposition Network (IADN) were used to investigate the causes of variability in gas-phase polychlorinated biphenyl (PCB) and pesticide concentrations measured near Lakes Michigan, Erie, and Superior. A multiple linear regression model that incorporates temperature and time was used explain the variability in the concentrations. Our approach used autocorrelation analyses of the residuals to help us determine the effectiveness of the regression. Autocorrelation plots forthe in-use pesticide lindane indicated that an agricultural application cycle was also present in the regression residual data at all sites. The addition of parameters for this effect to the regression equation accounted for, on average, 16% more of the variability in the data. Similar analyses forthe in-use pesticide endosulfan did not show an agricultural application effect. The banned compounds DDT and chlordane showed that temperature and time correctly accounted for the variability in the atmospheric concentrations of these compounds at all sites. In contrast to the other compounds, PCBs and hexachlorobenzene showed strong residual autocorrelation patterns near Lake Michigan of an unknown origin.