Biomedical subjects

Sierra Rayne

Publications and source records attributed to Sierra Rayne.

8 recordsLinked to original sources

PubMed2003

Rapidly increasing polybrominated diphenyl ether concentrations in the Columbia River system from 1992 to 2000.

Concentrations and congener patterns of 32 individual PBDE congeners from mono- through hexa-brominated were investigated in two fish species occupying similar habitats--but having different diets and trophic levels--and surficial sediments from several locations on the major river system of western North America, the Columbia River, in southeastern British Columbia, Canada. Total PBDE concentrations have increased by up to 12-fold over the period from 1992 to 2000 in mountain whitefish from the Columbia River, with a doubling period of 1.6 years. The rate at which PBDE concentrations are increasing in whitefish is greater than has been previously reported worldwide. At the current rate of increase, sigmaPBDE will surpass those of sigmaPCB by 2003 to become the most prevalent organo-halogen contaminant in this region. SigmaPBDE in whitefish from the mainstem of the Columbia River range up to 72 ng/g wet weight, concentrations that are 20-50-fold higher than in a nearby pristine watershed affected only by atmospheric contaminant transport. Conversely, sigmaPBDE in largescale suckers were approximately an order of magnitude lower than in whitefish, demonstrating the influence of biomagnification and feeding habits. Congener patterns in whitefish from the Columbia River directly correlated with the two major commercial penta-BDE mixtures in use and represent the first time free-swimming aquatic biota such as fish have been found to contain PBDE congener patterns so similar to commercial mixtures. PBDE concentrations in sediments were not linked to a variety of investigated point sources but were instead inversely correlated with the ratio of organic carbon:organic nitrogen in surficial sediments with a pattern suggesting the dominant influence of septic field inputs from the primarily rural population.

Animals↗

PubMed2003

Development of a multiple-class high-resolution gas chromatographic relative retention time model for halogenated environmental contaminants.

A predictive model for the relative gas chromatographic retention times (GC-RRTs) of the following nine classes of halogenated environmental contaminants was developed: polybrominated diphenyl ethers (PBDEs); polychlorinated diphenyl ethers (PCDEs); polychlorinated biphenyls (PCBs); polychlorinated naphthalenes (PCNs); polychlorinated dibenzo-p-dioxins (PCDDs); polychlorinated dibenzofurans (PCDFs); polybrominated dibenzo-p-dioxins (PBDDs); polybrominated dibenzofurans (PBDFs); and organochlorine pesticides. MOPAC calculated physicochemical properties and structural descriptors in the model include molecular weight, square root of the number of halogen substituents, ionization potential, dipole moment, and the number of ortho, meta, and para halogen substituents. Using these variables, individual models for each of the contaminant classes were combined into a multiple class model incorporating the GC-RRTs of the 375 compounds of interest. The individual and multiclass GC-RRT models had acceptable fits between observed and predicted GC-RRTs (r2 = 0.9741-0.9990 for PBDEs, PCDEs, PCBs, PCNs, PCDD/Fs, and PBDD/Fs; r2 = 0.9250 for pesticides; and r2 = 0.9631 for the multiclass model) over a wide range of retention times and molecular structures. The combined model was tested on known GC-RRTs of hydroxylated PCBs and chlorinated phenoxyphenols and provided satisfactory results, demonstrating the strength of the model in predicting GC-RRT windows for contaminant classes not used in constructing the model. Such models will be useful in predicting the GC retention characteristics of novel environmental contaminants and their degradation products, for which analytical standards may not be available.

Journal Article↗

PubMed2003

Anaerobic microbial and photochemical degradation of 4,4'-dibromodiphenyl ether.

The anaerobic microbial and photochemical degradation pathways of 4,4'-dibromodiphenyl ether (BDE15) were examined. BDE15 was reductively debrominated within a fixed-film plug-flow biological reactor at hydraulic retention times of 3.4 and 6.8 h, leading to exclusive production of 4-bromodiphenyl ether (BDE3) and diphenyl ether (DE). A suite of potential BDE15 metabolites arising from reductive debromination, hydroxylation, and methoxylation of the aromatic C-Br and C-H bonds were not observed. Following initial debromination of BDE15, degradation of BDE3 to DE readily occurs, suggesting the rate-limiting step for anaerobic BDE15 degradation is conversion of BDE15 to BDE3. The photochemical degradation of BDE15 was also examined in organic (CH3CN and CH3OH) and aqueous (H2O:CH3CN; 1:1 v/v) solvent systems at 300 nm. Only photochemically induced reductive debromination was found to occur via homolytic C-Br bond cleavage, with no evidence of C-O bond cleavage or products arising from heterolytic bond cleavage.

Bacteria, Anaerobic↗

PubMed2002

Chromatographic and ionization properties of polybrominated diphenyl ethers using GC/high-resolution MS with metastable atom bombardment and electron impact ionization.

The chromatographic and ionization properties of 35 polybrominated diphenyl ether (PBDE) congeners were investigated using GC/HRMS with metastable atom bombardment (MAB) and electron impact (EI) ionization. A multiple linear regression model based on bromine substitution patterns and MOPAC calculated physical properties was developed to predict relative GC retention times of individual PBDE congeners. Although five different sources of metastable rare gas atoms (He, N2, Ar, Xe, and Kr) were investigated with MAB ionization, only MAB-N2 provided adequate ionization efficiency and predictability. Because of reduced background noise to the MS detector, MAB-N2 had a lower limit of detection for tetra- and penta-BDEs than EI, despite having a lower sensitivity. Using MAB-N2, the molecular ion was always the base peak, with little fragmentation taking place. Conversely, using EI ionization, the [M - nBr]+ peak (where n = 1-4, depending on the number of Br substituents) was the dominant ion for all PBDE congeners. Multiple linear regression models representing the molecular ion response of PBDE congeners analyzed by GC/ HRMS with MAB-N2 and EI ionization were also developed using the number and type of Br substituents and ionization potentials. A significantly higher level of predictability was obtained for the MAB-N2 response model than for EI.

Electrons↗

PubMed2002

Photochemical mass balance of 2,3,7,8-TeCDD in aqueous solution under UV light shows formation of chlorinated dihydroxybiphenyls, phenoxyphenols, and dechlorination products.

Polychlorinated dibenzo-p-dioxins (PCDDs) are a class of halogenated diaryl compounds that are environmentally important because of their high toxicity and bioaccumulatory properties. There is an incomplete understanding of their photochemistry because the majority of photoproducts, as indicated by incomplete mass balances, have not been identified. We studied the photochemical transformation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TeCDD) in aqueous solution using 302 nm light. Our results allow for the first photochemical mass balance (92-99%) for this compound and confirm the operation of a novel photochemical pathway, which gives rise to 2,2'-dihydroxy-4,4',5,5'-tetrachlorobiphenyl (4,4',5,5'-TeCDHBP) at >50% conversion from the starting material. Rearrangement from 2,3,7,8-TeCDD to 4,4',5,5'-TeCDHBP takes place following preferential homolytic C-O bond cleavage via a proposed mechanism analogous to the parent dibenzo-p-dioxin system. Photochemical conversion from the starting material to dechlorinated PCDDs or chlorinated phenoxyphenols are minor pathways, although the exact contribution of the strictly dechlorination pathways remains uncertain because of the complexity of the system. The results suggest that the photochemical conversion of PCDDs to chlorinated dihydroxybiphenyls, which are also polychlorinated biphenyl (PCB) metabolites, may be an important part of their environmental fate.

Biphenyl Compounds↗

PubMed2002

Exponential increases of the brominated flame retardants, polybrominated diphenyl ethers, in the Canadian Arctic from 1981 to 2000.

A suite of 37 polybrominated diphenyl ether (PBDE) congeners and all of the homologue groups from mono- to deca-brominated were determined in ringed seal (Phoca hispida) blubber collected from subsistence hunts in the Canadian Arctic in 1981, 1991, 1996, and 2000. Total PBDE (sum(PBDE)) concentrations have increased exponentially over this period in male ringed seals aged 0-15 years. Penta- and hexa-BDEs are increasing at approximately the same rate (t2 = 4.7 and 4.3 years, respectively) and more rapidly than tetra-BDEs (t2 = 8.6 years) and tri-BDEs (t2 = infinity) in this age/sex grouping. In contrast to declining PBDE concentrations since 1997 in human milk from Sweden, sum(PBDE) concentrations in arctic ringed seals continue to increase exponentially similar to worldwide commercial penta-BDE production. PBDE congener profiles in male ringed seals aged 0-15 years from 1991 to 2000 also differ significantly from other aquatic organisms and semipermeable membrane devices collected from temperate coastal regions of British Columbia. While PBDE concentrations are 50 times lower than those of mono-ortho and non-ortho PCBs, and approxiamately 500 times higher than PCDD/Fs, our data indicate that, at current rates of bioaccumulation, PBDEs will surpass PCBs to become the most prevalent organohalogen compound in Canadian arctic ringed seals by 2050.

Adipose Tissue↗

PubMed2002

Occurrence and congener profiles of polybrominated diphenyl ethers (PBDEs) in environmental samples from coastal British Columbia, Canada.

Environmental levels and detailed congener profiles (31 congeners and 3 coeluting congener groups) of polybrominated diphenyl ethers (PBDEs) were assessed in a number of biota samples taken over a large geographic range covering harbours and industrial sites on Canada's West Coast. Additionally, PBDE congener profiles were determined using semipermeable membrane devices (SPMDs) deployed in the Fraser River, the river in Western Canada with the largest industrial activity. PBDE levels detected in biota were between 4 and 2300 ng/g lipid and these levels were compared with those reported in selected European biota to provide a wider perspective on PBDE contamination on Canada's West Coast. Thirteen-congener PBDE patterns in the environmental samples were examined using principal component analysis (PCA), and additionally, comparisons were made between the PBDE profiles in the sample groups and commercially used PBDE technical mixtures (e.g., Bromkals) on a percent composition basis. PCA on congener specific data revealed that PBDE patterns are remarkably similar over a wide geographical range in Western Canada, however, the general pattern in environmental samples varies significantly from those of the predominant technical mixtures. Finally, correlations between PBDE and other persistent and toxic co-occurring contaminants found in Dungeness crab were determined.

Animals↗

PubMed2002

Reconstructing source polybrominated diphenyl ether congener patterns from semipermeable membrane devices in the Fraser River, British Columbia, Canada: comparison to commercial mixtures.

Semipermeable membrane devices (SPMDs) were placed in the Fraser River near Vancouver, British Columbia, Canada, between August 6 and September 30, 1996. This location is near a large urban and industrial region (population 2,000,000) and is expected to be representative of other large, modern cities. After exposure to the ambient water column, SPMD samples were analyzed for a suite of 36 polybrominated diphenyl ether (PBDE) congeners plus all homologue groups from mono- through hexa-brominated. Observed congener patterns differed significantly from that of the commercial penta- and octa-BDE mixtures. A reconstruction approach was developed based on an aquatic transport model and utilizing published octanol-water partition coefficients, calculated SPMD uptake rates, and predicted water concentrations by using the EcoFate multimedia mass balance aquatic simulation model for the 13 major PBDE congeners. In combination, composite technical mixtures were created by combining commercial penta-BDE mixtures (Bromkal 70-SDE and Great Lakes Chemicals DE-71) with commercial octa-BDE mixtures (Bromkal 79-8DE and Great Lakes Chemicals DE-79) in their relative 2000 North American production volumes. The reconstructed SPMD patterns more closely approximated the composite technical mixtures and suggest that PBDEs in such an industrial region arise primarily from penta- and octa-BDE source mixtures.

British Columbia↗