Thor Halldorson

Biomagnification of α- and γ-Hexabromocyclododecane Isomers in a Lake Ontario Food Web

The extent of bioaccumulation of hexabromocyclododecane (HBCD) isomers (α, β, and γ) was determined in the Lake Ontario pelagic food web using liquid chromatography tandem mass spectrometry (LC/MS/MS). Concentrations of the α-isomer were consistently higher than that of the γ-isomer. The β-isomer was below method detection limits in all samples. Whole body concentrations (ng/g, wet wt) of α- and γ-HBCD were highest in the top predator lake trout samples ranging from 0.4 to 3.8 ng/g for the α-isomer and 0.1 to 0.8 ng/g for the γ-isomer. For the prey fish species, the trends in α- and γ-HBCD levels were slimy sculpin > smelt > alewife. Mean concentrations of total (Σ) HBCD (sum of α- and γ-isomers) in the macrozooplankter Mysis relicta (0.14 ± 0.02 ng/g wet wt) and in the benthic invertebrate Diporeia hoyi (0.16 ± 0.02 ng/g, wet wt) were similar and approximately twice as high as in plankton (0.06 ± 0.02 ng/g, wet wt). A strong positive linear relationship was found between ΣHBCD concentrations (wet wt) and...

Dietary accumulation of hexabromocyclododecane diastereoisomers in juvenile rainbow trout (Oncorhynchus mykiss) I: bioaccumulation parameters and evidence of bioisomerization.

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to three diastereoisomers (alpha, beta, gamma) of hexabromocyclododecane (C12H18Br6) via their diet for 56 d followed by 112 d of untreated food to examine bioaccumulation parameters and test the hypothesis of in vivo bioisomerization. Four groups of 70 fish were used in the study. Three groups were exposed to food fortified with known concentrations of an individual diastereoisomer, while a fourth group were fed unfortified food. Bioaccumulation of the gamma-diastereoisomer was linear during the uptake phase, while the alpha- and beta-diastereoisomers were found to increase exponentially with respective doubling times of 8.2 and 17.1 d. Both the beta- and the gamma-diastereoisomers followed a first-order depuration kinetics with calculated half-lives of 157 +/- 71 and 144 +/- 60 d (+/-1 x standard error), respectively. The biomagnification factor (BMF) for the alpha-diastereoisomer (BMF = 9.2) was two times greater than the beta-diastereoisomer (BMF = 4.3); the large BMF for the beta-diastereoisomer is consistent with this diastereoisomer dominating higher-trophic-level organisms. Although the BMF of the beta-diastereoisomer suggests that it will biomagnify, it is rarely detected in environmental samples because it is present in small quantities in commercial mixtures. Results from these studies also provide evidence of bioisomerization of the beta- and gamma-diastereoisomers. Most importantly, the alpha-diastereoisomer that was recalcitrant to bioisomerization by juvenile rainbow trout in this study and known to be the dominant diastereosiomer in fish was bioformed from both the beta- and the gamma-diastereoisomers. To our knowledge, this is the first report of bioisomerization of a halogenated organic pollutant in biota.

Kinetics of tris (1-chloro-2-propyl) phosphate (TCIPP) metabolism in human liver microsomes and serum

Tris(1-chloro-2-propyl) phosphate (TCIPP) is an emerging contaminant which is ubiquitous in the indoor and outdoor environment. Moreover, its presence in human body fluids and biota has been evidenced. Since no quantitative data exist on the biotransformation or stability of TCIPP in the human body, we performed an in vitro incubation of TCIPP with human liver microsomes (HLM) and human serum (HS). Two metabolites, namely bis(2-chloro-isopropyl) phosphate (BCIPP) and bis(1-chloro-2-propyl) 1-hydroxy-2-propyl phosphate (BCIPHIPP), were quantified in a kinetic study using HLM or HS (only BCIPP, the hydrolysis product) and LC-MS. The Michaelis-Menten model fitted best the NADPH-dependent formation of BCIPHIPP and BCIPP in HLM, with respective V(MAX) of 154 ± 4 and 1470 ± 110 pmol/min/mg protein and respective apparent K(m) of 80.2 ± 4.4 and 96.1 ± 14.5 μM. Hydrolases, which are naturally present in HLM, were also involved in the production of BCIPP. A HS paraoxonase assay could not detect any BCIPP formation above 38.6 ± 10.8 pmol/min/μL serum. Our data indicate that BCIPP is the major metabolite of TCIPP formed in the liver. To our knowledge, this is the first quantitative assessment of the stability of TCIPP in tissues of humans or any other species. Further research is needed to confirm whether these biotransformation reactions are associated with a decrease or increase in toxicity.

Determination of 4(5)-methylimidazole in carbonated beverages by isotope-dilution liquid chromatography-tandem mass spectrometry

The purpose of this study was to develop a method to quantify 4(5)-methylimidazole (4-MEI), a suspected carcinogen, in carbonated beverages by simple sample dilution and isotope-dilution reverse-phase LC-MS/MS. Isotope dilution using hexa-deuterated methylimidazole (d6-4-MEI) was used to quantify native 4-MEI and to assess matrix effects quantitatively. The accuracy of the method was assessed by intentionally fortifying a negative control sample at three doses: low, medium and high (replicates of n = 5 each) with a known amount of 4-MEI. The respective absolute error in each case was 18.7 ± 0.7%, 14.6 ± 2.8% and 21.1 ± 9.7%. Within-day (intra-) and day-to-day (inter-) repeatability, determined as the relative standard deviation by fortifying a negative control sample (n = 5), were 9.5% and 15.4%, respectively. Average ion suppression of d6-4-MEI in beer was 63.9 ± 3.2%, while no suppression or enhancement was seen in non-alcoholic samples. The instrument and method limit of detection were calculated as 0.6 and 5.8 ng ml–1, respectively. 4(5)-Methylimidazole was quantified in a variety of store-bought consumer beverages and it was found that in many of the samples tested consuming a single can of beer would result in intake levels of 4-MEI that exceed the no significant risk guideline of 29 µg day–1. Conversely, 4-MEI in the samples was orders of magnitude smaller than the European Food Safety Authority acceptable daily intake threshold value of 100 mg kg–1 bw day–1. Graphical Abstract

Polycyclic aromatic hydrocarbon metabolites in Arctic cod (Boreogadus saida) from the Beaufort Sea and associative fish health effects.

In 2012, Arctic cod (Boreogadus saida) were collected from offshore regions of the Beaufort Sea to determine the concentrations of CYP1A1 phase I metabolites of polycyclic aromatic hydrocarbons (OH-PAHs) in liver and to correlate measured concentrations with (i) morphometric measurements that are known to be indicative of fish health and, (ii) biochemical end points of health including vitamin A/E and metabolites and hepatic deiodinase activity (DI). Four ring OH-PAHs were detected in 90% of our samples with a mean liver concentration of 1829.2 ± 159.2 ng/g (ww). Total (∑) concentrations of 5/6-membered ring OH-PAHs in liver were smaller [mean of 931.6 ± 104.3 ng/g, (ww)] and detected less frequently (75%) than the 4-ring OH-PAHs. Fish length and liver weight were both negatively correlated to ∑ concentrations of 4-ringed OH-PAHs (p < 0.001). Liver somatic index was also negatively correlated to ∑4-OH-PAHs (p < 0.05) but not for ∑5/6-OH-PAHs (p > 0.1). There was a significant positive relationship between DI and 4-ring OH-PAHs (p < 0.05) in liver, suggesting an induction of this enzyme. No such correlation was observed for the 5/6-ring OH-PAHs. Retinyl palmitate (RP) was the only vitamin that could be measured in liver ranging from 0.230 to 26.3 ug/g (ww). No associations between RP and levels of the 4- or 5/6-ringed OH-PAHs were observed. Continued baseline studies are clearly warranted to further understand effects of OH-PAHs on fish health before planned exploration activities begin in this region.

Laboratory study of the particle-size distribution of Decabromodiphenyl ether (BDE-209) in ambient air.

Laboratory measurements for particle-size distribution of Decabromodiphenyl ether (BDE-209) were performed in a 0.5 m(3) sealed room at 25 °C. BDE-209 was manually bounded to ambient particles. An electrostatic field-sampler was employed to collect particles. The number of collected particles (n(i,j), i and j was the class of particle diameter and applied voltage on electrostatic field-sampler sampler, respectively) and the corresponding mass of BDE-209 in collected particles (m(∑i,j)) were determined in a series of 6 experiments. The particle-size distribution coefficient (ki) was calculated through equations related to n(i,j) and m(∑i,j), and the particle-size distribution of BDE-209 was determined by ki·n(i,j). Results revealed that BDE-209 distributed in particles of all size and were not affiliated with fine particles as in field measurements. The particle size-fraction should be taken into account when discussing the particle-size distribution of BDE-209 in ambient air due to the normalized coefficients (normalized to k1) and were approximately in the same order of magnitude for each diameter class. The method described in the present study was deemed feasible in determining the particle-size distribution of BDE-209 from vaporization sources and helpful to understanding the instinct rule of particle-size distribution of BDE-209, and potentially feasible for other SVOCs.