Biomedical subjects

Heather M Stapleton

Publications and source records attributed to Heather M Stapleton.

10 recordsLinked to original sources

PubMed2007

Determination of polybrominated diphenyl ethers in environmental standard reference materials.

Standard reference materials (SRMs) are valuable tools in developing and validating analytical methods to improve quality assurance standards. The National Institute of Standards and Technology (NIST) has a long history of providing environmental SRMs with certified concentrations of organic and inorganic contaminants. Here we report on new certified and reference concentrations for 27 polybrominated diphenyl ether (PBDE) congeners in seven different SRMs: cod-liver oil, whale blubber, fish tissue (two materials), mussel tissue and sediment (two materials). PBDEs were measured in these SRMs, with the lowest concentrations measured in mussel tissue (SRM 1974b) and the highest in sediment collected from the New York/New Jersey Waterway (SRM 1944). Comparing the relative PBDE congener concentrations within the samples, we found the biota SRMs contained primarily tetrabrominated and pentabrominated diphenyl ethers, whereas the sediment SRMs contained primarily decabromodiphenyl ether (BDE 209). The cod-liver oil (SRM 1588b) and whale blubber (SRM 1945) materials were also found to contain measurable concentrations of two methoxylated PBDEs (MeO-BDEs). Certified and reference concentrations are reported for 12 PBDE congeners measured in the biota SRMs and reference values are available for two MeO-BDEs. Results from a sediment interlaboratory comparison PBDE exercise are available for the two sediment SRMs (1941b and 1944).

Journal Article↗

PubMed2006

In vivo and in vitro debromination of decabromodiphenyl ether (BDE 209) by juvenile rainbow trout and common carp.

Decabromodiphenyl ether (BDE 209), the major congener in the high volume industrial flame retardant mixture "DecaBDE", has recently been shown to be metabolized by carp. To further explore this phenomenon, juvenile rainbow trout were exposed to BDE 209 via the diet for a five month period. Analysis of the whole body homogenate, liver, serum, and intestinal tissues revealed that BDE 209 accumulated in rainbow trout tissues and was most concentrated in the liver. In addition to BDE 209, several hepta-, octa-, and nonaBDE congeners also accumulated in rainbow trout tissues over the same period as a result of BDE 209 debromination. Based on the total body burden of the hepta- through decaBDE congeners, uptake of BDE 209 was estimated at 3.2%. Congener profiles were different among whole body homogenate, liver, and serum, with the whole body homogenates having a greater contribution of the debrominated biotransformation products. Extracts of the rainbow trout whole body homogenates were compared with extracts from a previous experiment with common carp. This comparison revealed that BDE 202 (2,2',3,3',5,5',6,6'-octabromodiphenyl ether) was a dominant debromination product in both studies. To determine whether the observed debromination was metabolically driven, liver microsomal fractions were prepared from both common carp and rainbow trout. Analysis of the microsomal fractions following incubation with BDE 209 revealed that rainbow trout biotransformed as much as 22% of the BDE 209 mass, primarily to octa- and nonaBDE congeners. In contrast, carp liver microsomes biotransformed up to 65% of the BDE 209 mass, primarily down to hexaBDE congeners. These microsomal incubations confirm a metabolic pathway for BDE 209 debromination.

Animals↗

PubMed2006

Instrumental methods and challenges in quantifying polybrominated diphenyl ethers in environmental extracts: a review.

Increased interest in the fate, transport and toxicity of polybrominated diphenyl ethers (PBDEs) over the past few years has led to a variety of studies reporting different methods of analysis for these persistent organic pollutants. Because PBDEs encompass a range of vapor pressures, molecular weights and degrees of bromine substitution, various analytical methods can lead to discrimination of some PBDE congeners. Recent improvements in injection techniques and mass spectrometer ionization methods have led to a variety of options to determine PBDEs in environmental samples. The purpose of this paper is therefore to review the available literature describing the advantages and disadvantages in choosing an injection technique, gas chromatography column and detector. Additional discussion is given to the challenges in measuring PBDEs, including potential chromatographic interferences and the lack of commercial standards for higher brominated congeners, which provides difficulties in examining degradation and debromination of BDE congeners, particularly for BDE 209.

Journal Article↗

PubMed2005

Determination of polybrominated diphenyl ethers in indoor dust standard reference materials.

Polybrominated diphenyl ethers (PBDEs) have been measured for the first time in three different indoor dust Standard Reference Materials (SRMs) prepared by the National Institute of Standards and Technology (NIST). Two of these, SRM 2583 (Trace Elements in Indoor Dust) and SRM 2584 (Trace Elements in Indoor Dust), have been certified previously for lead and other inorganic constituents. A third, SRM 2585 (Organics in Indoor Dust), is a new indoor dust reference material prepared by NIST which will be certified for various organic compounds (polycyclic aromatic hydrocarbons, pesticides and polychlorinated biphenyls) in 2005 including certified concentrations for 16 individual PBDE congeners and reference values for an additional three PBDE congeners. Dust SRMs were analyzed for 30 PBDE congeners using high-resolution gas chromatography combined with low-resolution mass spectrometry operated in both negative chemical ionization (GC/ECNI-MS) and electron impact ionization (GC/EI-MS) modes. Sensitivity was an order of magnitude higher using GC/ECNI-MS relative to GC/EI-MS. These SRMs have been characterized and compared to the three PBDE commercial products (pentaBDE, octaBDE and decaBDE). PentaBDE and DecaBDE were present in all three SRMs and were the dominant commercial products, making up approximately 33% and 58%, respectively. Recent studies suggest that house dust may be a leading source of human exposure to PBDEs. These SRMs are the first reference materials with certified concentrations for PBDEs, which will aid in validating future measurements of PBDEs in house dust and other similar matrices.

Chromatography, High Pressure Liquid↗

PubMed2005

Polybrominated diphenyl ethers in house dust and clothes dryer lint.

Few studies have measured the flame retardants polybrominated diphenyl ethers (PBDEs) in the indoor environment. Here, we report measurements of PBDEs in house dust samples collected from the Washington, D.C. metropolitan area in the United States. Dust samples were analyzed for 22 individual PBDE congeners and our results found PBDEs present in every sample. Concentrations of total PBDEs ranged from 780 ng/g dry mass to 30 100 ng/g dry mass. The dominant congeners observed in the dust samples were congeners associated with the pentaBDE and decaBDE commercial mixtures. Ancillary data were collected on the homes and examined for any correlations with total PBDE concentrations. No correlations were observed with year of house construction, type of flooring (i.e., hardwood vs carpet) or the number of television sets or personal computers in the home. However, a significant inverse correlation (p < 0.05) was observed between the area of the home and the contribution of BDE 209 to the total PBDE concentration in dust. Using estimates of inadvertent dust ingestion (0.02-0.2 g/day) by young children (ages 1-4), we estimate ingestion of total PBDEs to range from 120 to 6000 ng/day. Clothes dryer lint was also sampled and analyzed for PBDEs from five of the homes and were present in all five samples ranging from 480 to 3080 ng/g dry mass. This study demonstrates that PBDEs are prevalent at relatively high concentrations within homes where people, and particularly young children, may be susceptible to exposure.

Age Factors↗

PubMed2005

Persistent organic pollutants in two dolphin species with focus on toxaphene and polybrominated diphenyl ethers.

Assessing trends of persistent organic pollutants (POPs) in marine mammals is difficult due to age, gender, and metabolism influences on accumulation. To help elucidate these effects in dolphins, POP concentrations were determined in the Atlantic white-sided dolphin, Lagenorhynchus acutus, a pelagic delphinid inhabiting North Atlantic waters, and in the rough-toothed dolphin, Steno bredanensis, a pelagic delphinid inhabiting tropical and subtropical waters. The specific objectives of this study were to determine baseline POP concentrations in L. acutus and S. bredanensis blubber samples and to examine the effects of age, gender, and metabolism on POP concentrations in dolphin blubber. Focus was aimed at contaminants of emerging concern, specifically, toxaphene and polybrominated diphenyl ethers (PBDEs). Samples collected from L. acutus (n = 47) stranding events in Massachusetts (1993--2000) and S. bredanensis samples (n = 15) were analyzed for PCBs, toxaphene, and other organic pesticides by gas chromatography/mass spectrometry (GC/MS). Age and gender influences were similar between the two species, with adult females having significantly lower POP concentrations as compared to adult males and juveniles. Mean sigma toxaphene concentrations were highest in juvenile L. acutus, 13.0 (6.7) microg/g wet mass (1 SD), and lowest in adult female S. bredanensis, 1.49 (1.4) microg/g wet mass. sigma PBDE (sum of congeners 47, 99, 100, 153, and 154) concentrations were highest in juvenile L. acutus, 2.41 (1.2) microg/g wet mass, and lowest in adult female S. bredanensis, 0.51 (0.6) microg/g wet mass. POP concentrations did not significantly differ between adult males and juveniles, suggesting metabolism of congeners and/or dilution with growth. PBDE concentrations in juvenile white-sided dolphins were not significantly related to collection year, suggesting that there may be a lag period for higher concentrations to be detected in pelagic marine mammals such as L. acutus or that concentrations have already peaked in this species prior to the first collection in 1993.

Adipose Tissue↗

PubMed2004

Debromination of polybrominated diphenyl ether congeners BDE 99 and BDE 183 in the intestinal tract of the common carp (Cyprinus carpio).

Polybrominated diphenyl ether (PBDE) congener patterns in biota are often enriched in tetra-, penta-, and hexabrominated diphenyl ethers, which is believed to result from the use of the commercial "pentaBDE" formulation. However, our evidence suggests that debromination of PBDEs occurs within fish tissues leading to appreciable accumulation of less brominated congeners. This suggests that PBDE body burdens can reflect both direct uptake from exposure and debromination of more highly brominated congeners. We conducted two independent dietary exposure studies using the common carp (Cyprinus carpio) to trace the fate of 2,2',4,4',5-pentabromodiphenyl ether (BDE 99) and 2,2',3,4,4',5',6-heptabromodiphenyl ether (BDE 183) in fish tissues. Carp were fed food spiked with individual BDE congeners for 62 d, and depuration was monitored during the following 37 d. Significant debromination was observed, converting BDE 99 to 2,2',4,4'-tetrabromodiphenyl ether (BDE47) and BDE 183 to 2,2',4,4',5,6-hexabromodiphenyl ether (BDE 154) and another as yet unidentified hexa-BDE congener. The BDE 99 concentration rapidly declined from 400 +/- 40 ng/g ww in the food to 53 +/- 12 ng/g ww in the gut content material sampled 2.5 +/- 1 h following feeding. At least 9.5 +/- 0.8% of the BDE 99 mass in the gut was debrominated to BDE 47 and assimilated in carp tissues. In the BDE 183 exposure, approximately 17% of the BDE 183 mass was debrominated and accumulated in carp tissues in the form of two hexa-BDE congeners. In both exposure studies, the concentration of the exposure compound decreased significantly in the gut within 2.5 +/- 1 h following ingestion. This rapid decrease in the concentration of the BDE congeners could not be explained entirely by debromination to quantified products or fecal egestion. Reactions occurring within the gut transform BDE congeners to other products that may accumulate or be excreted. Further studies are needed to identify and determine the effects of these BDE metabolites.

Animals↗

PubMed2004

Debromination of the flame retardant decabromodiphenyl ether by juvenile carp (Cyprinus carpio) following dietary exposure.

The congener 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE 209) is the primary component in a commonly used flame retardant known as decaBDE. This flame retardant constitutes approximately 80% of the world market demand for polybrominated diphenyl ethers (PBDEs). Because this compound is very hydrophobic (log K(ow) approximately 10), it has been suggested that BDE 209 has very low bioavailability, although debromination to more bioavailable metabolites has also been suggested to occur in fish tissues. In the present study, juvenile carp were exposed to BDE 209 amended food on a daily basis for 60 days, followed by a 40-day depuration period in which the fate of BDE 209 was monitored in whole fish and liver tissues separately. No net accumulation of BDE 209 was observed throughout the experiment despite an exposure concentration of 940 ng/day/fish. However, seven apparent debrominated products of BDE 209 accumulated in whole fish and liver tissues over the exposure period. These debrominated metabolites of BDE 209 were identified as penta- to octaBDEs using both GC/ECNI-MS and GC/HRMS. Using estimation methods for relative retention times of phenyl substitution patterns, we have identified possible structures for the hexa- and heptabromodiphenyl ethers identified in the carp tissues. Although exposure of carp to BDE 209 did not result in the accumulation of BDE 209 in carp tissues, our results indicate evidence of limited BDE 209 bioavailability from food in the form of lower brominated metabolites.

Administration, Oral↗

PubMed2004

Dietary accumulation and metabolism of polybrominated diphenyl ethers by juvenile carp (Cyprinus carpio).

Polybrominated diphenyl ethers (PBDEs) are hydrophobic organic contaminants with properties and nomenclature similar to polychlorinated biphenyls (PCBs). While much information is available on the bioaccumulation and pharamcokinetics of PCBs, little information is available on PBDEs. In this study, juvenile carp were exposed to a diet spiked with a cocktail of four BDE congeners (2,4,4'-tribromoDE [BDE 28], 2,2',4,4'-tetrabromoDE [BDE 47], 2,2',4,4',5-pentabromoDE [BDE 99], and 2,2',4,4',5,5'hexabromoDE [BDE 153]) for 60 d followed by a 40-d depuration period. As a positive control, three PCB congeners with similar log K(ow), values (2,2',5,5'-tetrachlorobiphenyl [PCB 52], 2,2',4,4', 5,5'-hexachlorobiphenyl [PCB 153], and 2,2',3,4,4',5,5'-heptachlorobiphenyl [PCB 180]) were included in the cocktail to compare their assimilation and fate with the model BDE congeners. Concentrations of BDEs and PCBs were monitored in whole-fish tissues and liver tissues over the duration of the experiment. In addition, blood serum samples were taken and pooled among replicates to determine if any phenolic metabolites of BDE and PCBs were formed. Rapid assimilation of BDE 47 was observed relative to all other BDE and PCB congeners, whereas apparently no accumulation of BDE 99 occurred over the course of the experiment. Assimilation efficiencies for BDE 47 suggest that approximately 100% of the BDE 47 exposure was absorbed by carp tissues after 60 d. However, based on the time course of BDE 47 assimilation, it is improbable that all BDE 47 was assimilated; more likely, production of BDE 47 in carp tissues occurred as a result of debromination of higher-brominated compounds, possibly BDE 99. The net assimilation efficiencies of BDE 28 and BDE 153 were also apparently low (20 and 4%, respectively) relative to the three PCBs (40% assimilated) examined in this study. The low assimilation efficiency and high depuration rates for BDEs suggest a higher potential for biotransformation. While all three PCB compounds displayed very similar assimilation and depuration rates, three of the four BDE compounds displayed significantly different assimilation rates among BDE congeners and relative to the PCBs. This study suggests that BDEs have significantly different fate dynamics relative to PCBs in wild carp and likely other species of fish.

Animals↗

PubMed2003

Polybrominated diphenyl ether flame retardants in the North American environment.

North America consumes over half of the world's production of polybrominated diphenyl ether (PBDE) flame retardants. About 98% of global demand for the Penta-BDE mixture, the constituents of which are the most bioaccumulative and environmentally widespread, resides here. However, research on the environmental distribution of PBDEs in North America has lagged behind that in Northern Europe. Examination of available governmentally maintained release data suggests that Deca-BDE use in the US substantially exceeds that in Canada. Penta-BDE use probably follows a similar pattern. PBDE demand in Mexico is uncertain, but is assumed to be comparatively modest. Recent research examining air, water, sediment, sewage sludge and aquatic biota suggests that Penta-BDE constituents are present in geographically disparate locations in the US and Canada. The less brominated congeners have been observed in areas distant from their known use or production, e.g. the Arctic. PBDEs have been detected in low concentrations in North American air, water and sediment, but much higher levels in aquatic biota. Increased burdens as a function of position in the food web have been noted. PBDE concentrations in US and Canadian sewage sludges appear to be at least 10-fold greater than European levels and may be a useful barometer of release. In general, PBDE concentrations in environmental media reported in North America are comparable or exceed those observed elsewhere in the world. In contrast to Europe, environmental burdens are increasing over time here, consistent with the greater consumption of the commercial mixtures. However, data remain relatively scarce. Deca-BDE in the North American environment appears largely restricted to points of release, e.g. urban areas and those where PBDE-containing sewage sludges have been applied. This lack of redistribution is likely due to its extremely low volatility and water solubility. Penta-BDE and Deca-BDE products are used in different applications and this may also be a factor controlling their environmental release.

Environment↗