Michael S. Milligan

Formation of dioxins: Competing rates between chemically similar precursors and de novo reactions

Abstract The formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) on fly ash was investigated using polychlorinated phenols (principally 2,3,4,6-tetrachlorophenol) in competition with the de novo synthesis reaction (e.g., synthesis from native, nonextractable carbon in the fly ash). At the relatively high gas-phase concentrations employed, 38–370 ng ml −1 , the chlorophenol pathway was up to 100 times faster than the de novo pathway. For short reaction times (t ≤5 min) chlorophenols do not yield PCDF, suggesting that the formation of PCDF in incinerators is not controlled by this reaction over short time scales.

Polybrominated diphenyl ethers (PBDEs): turning the corner in Great Lakes trout 1980-2009.

Lake trout and walleye composites were collected between 2004 and 2009 as part of the Great Lakes Fish Monitoring and Surveillance Program (GLFMSP) and analyzed for polybrominated diphenyl ethers (PBDEs). Yearly mean total PBDE concentrations (sum of congeners BDE-47, BDE-99, BDE-100, BDE-153, BDE-154) ranged from 44-192, 28-113, 50-107, 37-111, and 11-22 ng/g wet wt. for Lakes Michigan, Huron, Ontario, and Superior lake trout, and Lake Erie walleye, respectively. A 1980-2009 temporal record of PBDE concentrations in the Great Lakes top predator fish (lake trout and walleye) was assembled by integrating previous GLFMSP data (1980-2003) with current results (2004-2009). Temporal profiles show obvious breakpoints between periods of PBDE accumulation and decline in trout for Lakes Huron, Michigan and Ontario with a significant (p < 0.0001 and r = 0.55, 0.72, and 0.51, respectively) decrease in concentration after 2000-2001. A similar transition was observed in Lake Superior for the nearshore site accompanied by a less significant decreasing trend (p = 0.016, r = 0.33), suggesting concentrations are declining very slowly or have leveled off. In contrast, Lake Erie walleye concentrations began leveling off in the late 1990s and no statistically significant trend (increasing or decreasing) has been observed in recent years. A decrease in the BDE-47/BDE-153 ratio was also recently observed, suggesting a transition to more highly brominated PBDEs is occurring in Great Lakes trout. This study provides region-wide evidence that PBDE concentrations are generally declining in Great Lakes trout, although there are clear exceptions to this trend. Results from this study reflect the positive impact of the 2004 PentaBDE ban on macro-scale aquatic freshwater ecosystems.

The role of precursors in formation of polychloro-dibenzo-p-dioxins and polychloro-dibenzofurans during heterogeneous combustion

Abstract Although by now literature reports suggest that compounds containing almost any combination of C, H, O, and Cl can form PCDD/PCDFs under suitable conditions, questions of the relevancy of such findings to the formation of these compounds in MSW-incinerators remain. To address these questions the formation and destruction of plausible precursors (intermediates) over time/temperature scales found in incinerators must be better understood. In our laboratory we have attempted to simulate MSW-incineration using a systems approach, i.e., a spouted bed combustor coupled to two post-combustion stages. In this system, formation of PCDD/PCDFs and potential precursors has been investigated in the bed (pre-flame), the post flame regions, and over fly ash (post flame combustion gases). From the lean combustion of chlorobenzenes (mono, 1,2-di-, and 1,2,4-tri-) hexachlorobenzene (HCB) and pentachlorophenol (PCP) are major PICs (products of incomplete combustion) formed in characteristic times 1, recent results suggest that this ratio may be very sensitive to local conditions. These two compounds are certainly possible precursors on the relevant time/temperature scales, but it has not been proven that they are required intermediates. In these combustions OCDD is the major dioxin congener, lower chlorinated congeners are only formed at longer residence times or over fly ash (at ∼300°C). A mechanism accommodating these observations will be proposed and the relevancy of the findings to recent measurements from incinerators will be discussed.

Temporal trends of polychlorinated biphenyls and organochlorine pesticides in Great Lakes fish, 1999-2009.

Temporal trend analysis of the latest Great Lake Fish Monitoring and Surveillance Program (GLFMSP) data showed statistically significant decreases in persistent bioaccumulative and toxic (PBT) contaminant (polychlorinated biphenyls (PCBs), dichloro-diphenyl-trichlorethane and its metabolites (DDTs), dieldrin, cis-chlordane, oxychlordane, cis-nonachlor) concentrations in Lakes Huron, Ontario, and Michigan lake trout over the period of 1999 to 2009. In contrast, for most contaminants, no statistically significant concentration trends were found in top predator fish in Lakes Superior and Erie during the same period. For Lakes Huron, Ontario, and Michigan 5.0 ± 2.6% average annual concentration decreases were found for PCBs, DDTs, dieldrin, and other organochlorine pesticides (OCs) decreased at a faster rate, ranging from 10 ± 4.3% to 20 ± 7.1% per year. For these three lakes, with the exception of PCBs, these current decreases are greater than were shown by an earlier trend analysis that estimated an annual contaminant decrease of about 2-5% for the period of 1980 to 2003. For Lakes Superior and Erie, the finding of no statistically significant trend is in agreement with previously reported results for these lakes.

Mechanistic aspects of the de novo synthesis of polychlorinated dibenzo-p-dioxins and furans in fly ash from experiments using isotopically labeled reagents

13 C-activated carbon mixed with MSW incinerator fly ash and reacted with gas-phase oxygen at 300-350 o C resulted in the formation of 13 C-labeled chlorobenzene and PCDDJF products. Unlabeled chlorobenzene and PCDD/F derived from native carbon were also detected, but no scrambling of the added 13 C or native 12 C in the resultant products was evident. The [ 13 C]PCDD/F and [ 12 C]PCDD/F yields were both observed to have an optimum formation temperature around 325 o C, suggesting that the added 13 C-activated carbon was subject to the same fly ash-catalyzed formation and destruction mechanisms as the native carbon. 13 C-activated carbon added to otherfly ashes had PCDD/F formation rates reflective of their respective rates from the native carbon already present. Experiments with 13 C-labeled CO and CD, reacted with fly ash at 300 o C in the presence of gas-phase oxygen showed that neither is an effective precursor to PCDD/F

Rapid formation of polychlorinated dioxins/furans in the post combustion region during heterogeneous combustion

Abstract The formation of chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) downstream from the combustion zone of a heterogeneous combustor occurred within seconds in the temperature range of 430-380°C, but not at substantially lower temperatures. A spouted bed reactor was used with sand as the heterogeneous medium and a fuel mixture of 1,2-dichlorobenzene/heptane. Total PCDD/F-concentrations were in the range of 100 ng m −3 ; chlorobenzenes other than the starting compound and chlorophenols were formed. The formation of PCDD/F may be mediated by high surface area particles originating from the bed due to attrition. Homogeneous gas phase mechanisms cannot account readily for the levels observed.

Measured summertime concentrations of particulate components, Hg0, and speciated polycyclic aromatic hydrocarbons at rural sites in New York State

Daily PM2.5 samples, Hg0 and speciated polycyclic aromatic hydrocarbon (PAH) were simultaneously collected at Potsdam and Stockton site in NY during the summers of 2000 and 2001. Samples for determination of the mass concentration and chemical composition of the PM2.5 were obtained with a speciation network PM2.5 sampler. Chemical composition including trace elemental composition, water-soluble ions, and elemental carbon were analyzed. Elemental mercury and PAHs were sampled separately. Daily PM2.5 concentrations ranged from 0.47 to 53.7 microg m(-3) at the Potsdam site, and from 0.82 to 47.23 microg m(-3) at the Stockton site with large daily differences between the two sites. Potsdam consistently had lower mass values than Stockton. The greatest contributors to the PM2.5 mass (generally >0.1 microg/m(3)) were sulfate, nitrate, ammonium, and BC at both sites. Seventeen PAHs were identified at each site in 2000 and the average total concentrations were 3.2 ng/m(3) and 2.9 ng/m(3) at the Potsdam and Stockton sites, respectively. The mean vapor phase mercury concentration at the Potsdam site (2.4 +/-1.2 ng m(-3), n=93) was higher than that at the Stockton site (1.2 +/- 1.0 ng m(-3), n=60) in 2000, whereas in 2001, the average concentrations were 1.1 ng m(-3) and 1.6 ng m(-3) at the Potsdam and Stockton sites, respectively. In general, vapor phase mercury concentrations increased with increasing ambient temperature at the Stockton site in 2000. These differences in values between 2000 and 2001 can be largely explained by distinct differences in the meteorological regimes that dominated in the different years.

Formation of precursors to chlorinated dioxin/furans under heterogeneous conditions

In our laboratory, we have attempted to simulate MSW-incineration with a spouted bed combustion system. Our studies show that the combustion of simple chlorinated compounds can lead to some potentially important precursors to PCDDIF. This paper presents results from the lean combustion of 1,2·dichlorobenzene. The effect of equivalence ratio and the chlorine to carbon ratio in the fuel are investigated. Maxima in CE, ORE and PICs are observed as a function of equivalence ratio. The carbon to chlorine ratio influences the chtcrobcnzcne (CB) to chlorophenols (CP) ratio in the products. Measurements in MSW (municipal solid waste) incinerators have shown that polychlorinated dioxins/furans (hereafter PCDD/F) can form heterogeneously in the colder «4500C) portion of the post combustion regions. However, controversies continue to exist about the rates of these processes and the precursors involved. Quantitative knowledge of potential precursor concentrations as well as their rates of formation and reaction is re...

The catalytic gasification of carbon in incinerator fly ash

Four fly ashes collected from electrostatic precipitators—three from municipal solid waste incinerators and one from a coal-fired power plant—were studied for their potential to catalyze carbon gasification reactions. A fixed-bed tubular reactor employing mixtures of oxygen and nitrogen was used to measure CO and CO2 evolved from native carbon in fly ash in the temperature range 275–350°C. Experiments using pure carbon were also run for comparison. MSWI fly ash was discovered to accelerate carbon gasification rates by at least an order of magnitude. At 300°C, gasification rates of native carbon in the different MSWI fly ash ranged from 1–8 mg-C/g-min, compared to pure carbon gasification rates of 0.03–0.2 mg-C/g-min. Activated carbon, having a high internal surface area, mixed to MSWI fly ash also showed an accelerated gasification rate, suggesting that the catalytic action was long-range. No catalytic activity was observed with coal fly ash. Apparent activation energies for gasification of native carbon in MSWI fly ash ranged from 25–34 kcal/mole, while those for pure carbon ranged from 10–20 kcal/mole. The apparent activation energy of gasification in coal fly ash was 14 kcal/mole. The oxygen concentration dependence on gasification rate in fly ash was determined to be 0.54; that for pure carbon was 0.71.

Toxaphene analysis in Great Lakes fish: a comparison of GC-EI/MS/MS and GC-ECNI-MS, individual congener standard and technical mixture for quantification of toxaphene

Toxaphene is considered to be a problematic organochlorine pollutant because of its bioaccumulation potential and persistence in aquatic environments. In this study, whole lake trout and walleye composites were used to evaluate two analytical techniques for total toxaphene and selected congener analysis. The efficacy of using gas chromatography electron ionization tandem mass spectrometry (GC-EI/MS/MS) and electron capture negative ionization mass spectrometry (GC-ECNI-MS) were compared. Although the sensitivity using GC-ECNI-MS was approximately five times greater than GC-EI/MS/MS, the latter provided more consistent inter-Parlar relative response factors (RRF). When using technical calibration mixtures, these results suggest a more accurate total toxaphene measurement was obtained using the GC-EI/MS/MS method. Total toxaphene concentrations in lake trout composites from both methods were highly correlated (R2u2009=u20090.985) with the MS/MS concentrations approximately half of those determined by ECNI, suggesting systematic high bias in toxaphene concentrations when measured using GC-ECNI.