A Statistical Approach for Left-Censored Data: Distributions of Atmospheric Polychlorinated Biphenyl Concentrations near the Great Lakes as a Case Study

Polychlorinated biphenyl (PCB) congener concentrations were measured in atmospheric samples collected once every 12 days at six sites on the shores of the North American Great Lakes. These data have been obtained as part of the Integrated Atmospheric Deposition Network (IADN), which began in 1991. This data set now consists of ∼2900 samples, each of which has been measured for ∼80 PCB congeners. Some of these congeners are present at levels sufficiently high to be quantitated in almost every sample, while others are detected in fewer than two-thirds of the samples. These latter congeners represent an example of left-censored environmental measurements. This paper offers a simple approach to dealing with uncensored and censored atmospheric PCB concentration data based on a careful examination of the distribution function of the data and using the curve fitting power of the Solver feature of Excel

Atmospheric Concentrations of PCB-11 Near the Great Lakes Have Not Decreased Since 2004

3,3′-Dichlorobiphenyl (PCB-11) is thought to be a byproduct of the production of yellow pigments, and thus, it has sources to the environment that differ both in type and magnitude compared to the PCBs that made up the, now banned, Aroclor commercial products. To assess these differences, the temporal trends of atmospheric concentrations of PCB-11 relative to those of 31 specific Aroclor-related congeners and relative to those of total Aroclor-PCBs at six sites near the North American Great Lakes were investigated. About 1800 atmospheric samples were collected over the period of 2004–2015 (inclusive). A multiple linear regression approach was used to isolate the variations in the atmospheric concentrations due to the human population near the sampling sites, seasonal effects, and long-term temporal changes. The atmospheric concentrations of the Aroclor-PCBs are decreasing with halving times of about 12 years, but the atmospheric concentrations of PCB-11 have not changed significantly over this time period. These results suggest that PCB-11 is still leaking into the environment, while at the same time sources of Aroclor-PCBs are coming under control. This effect is particularly notable at the most remote site on Lake Superior, where PCB-11 levels are, on average, 11% of those of total Aroclor-PCBs; this is a not insignificant abundance of a single PCB congener

Brominated and Chlorinated Flame Retardants in Tree Bark from Around the Globe

Brominated and chlorinated flame retardants were measured in about 40 samples of tree bark from 12 locations around the globe. The analytes were polybrominated diphenyl ethers (PBDE), Dechlorane Plus (DP), decabromodiphenylethane (DBDPE), hexabromocyclododecane (HBCD), hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), pentabromobenzene (PBBz), and tetrabromo-<i>p</i>-xylene (pTBX). The highest concentrations of these compounds were detected at an urban site in Downsview, Ontario, Canada. Total PBDE and DP concentrations ranged from 2.1 to 190 ng/g lipid weight and from 0.89 to 48 ng/g lipid weight, respectively. Relatively high levels of DP (46 ± 4 ng/g lipid weight) were found at a remote site at Bukit Kototabang in Indonesia. The concentrations of total PBDE, DP, PBEB, and HBCD in the tree bark samples were significantly associated with human population in the nearby areas (<i>r</i>² = 0.21–0.56; <i>P</i> < 0.05). In addition, the concentrations of total PBDE and DP were significantly associated (<i>r</i>² = 0.40–0.64; <i>P</i> < 0.05). with the corresponding atmospheric concentrations of these compounds over a concentration range of 2–3 orders of magnitude

Bromobenzene Flame Retardants in the Great Lakes Atmosphere

Seven bromobenzene flame retardants were measured in vapor-phase samples collected at five sites, all near the shores of the North American Great Lakes during 2008–2009, inclusive. The target compounds were hexabromobenzene (HBB), pentabromobenzene (PBBz), pentabromotoluene (PBT), pentabromobenzylacrylate (PBBA), pentabromobenzyl bromide (PBBB), tetrabromo-<i>p</i>-xylene (pTBX), and pentabromoethyl benzene (PBEB). Detection frequencies were, on average, higher than 50% for all of the compounds, with the exception of PBBA, which was detected only in 22% of all the samples. Considering all the sampling sites together, HBB showed the highest average concentration (4.6 ± 1.0 pg/m³), followed by PBBB (3.3 ± 0.5 pg/m³) and PBEB (1.0 ± 0.1 pg/m³). The concentrations of these compounds were generally significantly correlated with one another, with the exception of PBBA, which was correlated only to PBBB. The atmospheric concentrations of PBT, pTBX, PBBB, and PBBA tracked local human population density, suggesting that these compounds are or were used in a variety of commercial products. Unexpectedly, the concentration of PBEB was highest at the remote site of Eagle Harbor in northern Michigan, whereas that of HBB was highest at Sturgeon Point, ∼25 km southwest of Buffalo, New York. The lack of dependence of these two compounds’ concentrations on human population suggests local point sources

Revised Temporal Trends of Persistent Organic Pollutant Concentrations in Air around the Great Lakes

The concentrations of polychlorinated biphenyls, polycyclic aromatic hydrocarbons (PAH), and several chlorinated insecticides in air have been measured every 12 days since 1991 at several sites on the shores of the North American Great Lakes. We give here the geometric mean concentrations for each of these compounds for each year and at each site. In most cases, these concentrations have been measured in both the vapor and particle phases; if concentrations were available for both phases, the two concentrations were summed, and those data are presented here. Assuming a first-order rate model for these data, we have calculated the time it takes for the concentrations to decrease by half. For most compounds, the halving times are the same for the vapor phase and for the vapor and particle phase concentrations summed together. The halving times are generally not distinguishable among the sites. Overall, the observed halving times are 8–15 years, except for that of lindane, which is disappearing with a halving time of ∼4 years

Tribromophenoxy Flame Retardants in the Great Lakes Atmosphere

The 2,4,6-tribromophenoxy moiety is a common structural feature of several brominated flame retardants, and we have previously reported on the environmental concentrations of one such compound, 1,2-<i>bis</i>(2,4,6-tribromophenoxy) ethane (TBE). Here we report the atmospheric concentrations of TBE and three other tribromophenoxy compounds: allyl 2,4,6-tribromophenyl ether (ATE), 2-bromoallyl 2,4,6-tribromophenyl ether (BATE), and 2,3-dibromopropyl 2,4,6-tribromophenyl ether (DPTE). The samples were collected at five sites near the shores of the Great Lakes during the period 2008–2009, inclusive. Of these four compounds, TBE and ATE are currently used as flame retardants, and DPTE was formerly used as a flame retardant until its production ceased in the mid-1980s. The total concentrations of ATE, BATE, and DPTE were ∼2 pg/m³ in the cities of Chicago and Cleveland and 0.1–0.4 pg/m³ at the rural and remote sites. The concentrations of TBE were ∼1 pg/m³ in these cities and 0.2–0.8 pg/m³ at the rural and remote sites. In both cases, this was a very significant urban effect. The concentrations of ATE, BATE, and DPTE did not change significantly over the two-year study, but the concentrations of TBE decreased by about a factor of 2 during this time. This temporal change was statistically significant but not strong compared to the urban effect

Air is Still Contaminated 40 Years after the Michigan Chemical Plant Disaster in St. Louis, Michigan

The Michigan Chemical (also known as Velsicol Chemical) plant located in St. Louis, Michigan operated from 1936–1978. During this time, the plant manufactured polybrominated biphenyls (PBBs), hexabromobenzene (HBB), 1,1,1-trichloro-2,2-<i>bis</i>(4-chlorophenyl) ethane (DDT), and <i>tris</i>(2,3-dibromopropyl) phosphate (TDBPP), among other products. Due to widespread PBB contamination of Michigan, the plant eventually became a Superfund site, and despite years of cleanup activities, many of the compounds can still be found in the local ecosystem. To investigate the current atmospheric levels and to determine their spatial distributions, we collected tree bark samples from around Michigan and measured the concentrations of these pollutants. For comparison, other organic pollutants, such as polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs), which were not manufactured at the Michigan Chemical plant, were also measured in the same tree bark samples. Our results show levels of PBBs, DDT, and HBB in tree bark collected within 10 km of the Velsicol Superfund site (43, 477, and 108 ng/g lipid wgt., respectively) are 1–2 orders of magnitude higher than at sites located more than 10 km from the site (0.36, 28, and 0.36 ng/g lipid wgt., respectively). Levels of PBDEs and OPEs did not depend on distance from St. Louis. This is the first study on the atmospheric distribution of these chemicals around the Superfund site

Interstudy and Intrastudy Temporal Trends of Polychlorinated Biphenyl, Pesticide, and Polycyclic Aromatic Hydrocarbon Concentrations in Air and Precipitation at a Rural Site in Ontario

Polychlorinated biphenyl (PCB), organochlorine pesticide, and polycyclic aromatic hydrocarbon (PAH) concentrations were measured in air (in the vapor and particle phases) and in precipitation samples collected at Point Petre on the northeastern shore of Lake Ontario as a part of the Integrated Atmospheric Deposition Network. These data were measured in two separate studies, one running from 1992 to 2003 (inclusive) and the other from 1998 to 2011 (inclusive). Having these two independent studies is a direct way of measuring changes in atmospheric concentrations and comparing interstudy changes to intrastudy changes. The concentrations of almost all pesticides declined between the two studies with halving times of 3–6 years; the concentrations of PAHs and PCBs did not change much between the two studies. This suggests that there are continuing sources of PAHs and PCBs to the Great Lakes atmosphere. PAH concentrations were elevated in the winter when space heating consumes greater amounts of fuel and emits larger amounts of PAHs. Pesticide and PCB concentrations were elevated in the summer because of enhanced volatilization from terrestrial or aquatic surfaces during hot summer days. Although there were a few exceptions (notably lindane), in general, the data from the two study periods gave similar results

Halogenated Flame Retardants in Baby Food from the United States and from China and the Estimated Dietary Intakes by Infants

Three categories of baby food (formula, cereal, and puree) were bought from United States and Chinese stores in 2013 and analyzed for polybrominated diphenyl ethers (PBDEs) and related flame retardants. The primary goal of this project was to investigate whether there were differences in the levels of flame retardants between these two nations’ baby foods. The median concentrations of total PBDEs (sum of BDE-17, -28, -47, -49, -99, -100, -153, -183, and -209) were 21 and 36 pg/g fresh weight for the Unites States and Chinese baby foods, respectively. Among non-PBDE flame retardants, hexabromobenzene, Dechlorane Plus (DP), and decabromodiphenylethane were frequently detected (22–57%) with median concentrations of 1.6, 8.7, and 17 pg/g fresh weight for United States samples, and 1.3, 13, and 20 pg/g fresh weight for Chinese samples. In general, the flame retardant concentrations in the United States and Chinese samples were not statistically different, but very high DP concentrations were observed in one Chinese formula sample (4000 pg/g) and in one United States cereal sample (430 pg/g), possibly suggesting contamination of the raw materials or contamination during production of these two samples. A comparison of median estimated daily dietary intake rates of BDE-47, -99, and -153 with existing reference doses for neurodevelopmental toxicity and other existing criteria suggested no concerns for the consumption of these baby foods

Organophosphate and Halogenated Flame Retardants in Atmospheric Particles from a European Arctic Site

Levels of 13 organophosphate esters (OPEs) and 45 brominated and chlorinated flame retardants (BFRs) were measured in particle phase atmospheric samples collected at Longyearbyen on Svalbard in the European Arctic from September 2012 to May 2013. Total OPE (ΣOPEs) concentrations ranged from 33 to 1450 pg/m³, with the mean ΣOPE concentration of 430 ± 57 pg/m³. The nonchlorinated tri-<i>n</i>-butyl phosphate (TnBP) and 2-ethylhexyl-diphenyl phosphate (EHDPP) were the most abundant OPE congeners measured, and the sum of all nonchlorinated OPE concentrations comprised ∼75% of the ΣOPE concentrations. The most abundant chlorinated OPE was <i>tris</i>(1-chloro-2-propyl) phosphate (TCPP). Total BFR concentrations (ΣBFRs) were in the range of 3–77 pg/m³, with a mean concentration of 15 ± 3 pg/m³. 2-Ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB) and <i>bis</i>(2-ethylhexyl)­tetrabromophthalate (TBPH) were among the relatively abundant BFRs measured in these samples and comprised ∼46% and 17% of ΣBFR concentrations, respectively. Total PBDE (ΣPBDE) concentrations constituted ∼37% of ΣBFR concentrations on average and ranged from 1 to 31 pg/m³. The most abundant PBDE congener was BDE-209, which contributed 24% to ΣPBDE concentrations. Dechlorane Plus (DP) was detected in all of the samples, and ΣDP concentrations (<i>syn</i>- + <i>anti</i>-DP concentrations) ranged from 0.05 to 5 pg/m³. Overall, ΣOPE concentrations were 1–2 orders of magnitude higher than the ΣBFR concentrations