PubMed Health⌕ Search

Biomedical subjects

Deborah L Swackhamer

Publications and source records attributed to Deborah L Swackhamer.

10 recordsLinked to original sources
PubMed2006

Partitioning and bioaccumulation of PBDEs and PCBs in Lake Michigan.

Water from Lake Michigan and fish from all five Great Lakes have been sampled and analyzed for a suite of six polybrominated diphenyl ether (PBDE) congeners and 110 polychlorinated biphenyl congeners (PCBs). The Lake Michigan dissolved phase PBDE congener concentrations (0.2 to 10 pg/L) are similar to dissolved phase PCB congener concentrations (nondetected to 13 pg/L). Partitioning of PBDEs between the particulate and dissolved phases exhibits behavior similar to that of PCBs. Organic-carbon-normalized water-particle partition coefficients (log K(OC)s) ranged from 6.2 to 6.5. Lake trout are depleted in BDE-99 relative to dissolved phase concentrations, and in contrast to what is expected from the PCB congener patterns. This reflects suspected debromination of BDE-99 in the food web of Lake Michigan. A regression of the log of the bioaccumulation factor (BAF) and the log of the octanol-water partition coefficent (K(OW)) indicated a positive relationship for both PCB congeners and PBDE congeners. BDE-99 does not appear to followthe same trend, a further indication that it is subject to biotransformation. Using the PBDE BAFs for Lake Michigan and the PBDE fish concentrations from the other Great Lakes it is expected that the dissolved phase concentrations of congeners in the other lakes would range from 0.04 to approximately 3 pg/L.

Animals↗
PubMed2006

Changes in antibacterial activity of triclosan and sulfa drugs due to photochemical transformations.

Sulfa drugs and triclosan represent two classes of antibacterials that have been found in natural waters and for which photodegradation is anticipated to be a significant loss process. Parent antibacterial compounds and the products of photolysis reactions were compared for three sulfa drugs and triclosan to determine the extent to which photolysis affects their antibacterial potency on Escherichia coli DH5alpha. Sulfathiazole (median effective concentration [EC50] = 20.0 microM), sulfamethoxazole (EC50 = 12.3 microM), and sulfachloropyridazine (EC50 = 6.9 microM) inhibited bacterial growth but did not affect respiratory activity. Photolysis products of these sulfa drugs did not retain any measurable ability to inhibit growth. Triclosan inhibited both the growth (EC50 = 0.24 microM) and respiratory activity of E. coli DH5alpha. Triclosan photolysis products also exhibited no measurable effect on growth or respiratory activity. These experiments indicate that the products of triclosan and sulfa drug photolysis are unlikely to possess antibacterial activity in natural waters. The rapid screening method used for these two classes of compounds will be useful for helping to identify photolabile antibacterial compounds, for which photoproducts could require further investigation.

Anti-Bacterial Agents↗
PubMed2005

Effect of microbes on contaminant transfer in the Lake Superior food web.

The partitioning of PCBs to natural populations of aquatic heterotrophic bacteria from Lake Superior was measured in both field and laboratory studies to better understand the role of bacteria and the microbial food web in persistent, bioaccumulative, toxic organic contaminant (PBT) transfer. A filtration method that separated material >1 microm from that <1 microm was used to collect and measure PCB concentrations in the bacterial fraction. We used bacterial biovolume and a conversion factor to calculate bacterial carbon, which was used to normalize PCB concentrations. The range of total PCB concentrations in the bacterial fraction (61-337 ng/g organic carbon; OC) was similar, but generally higher than that of the total particulate fraction (36-324 ng/g OC). Measured log bioaccumulation factors (BAFoc, bacterial fraction; Koc, total particulate) were significantly greater in the bacterial fraction than in the total particulate fraction (bacterial range 6.7-7.3, total particulate range 5.8-7.0). Laboratory experiments demonstrated that a hexachlorobiphenyl reached steady state with a natural community of Lake Superior bacteria within 48 h and had a mean log BAFoc of 7.5 +/- 1.9. The octanol/ water partition coefficient (Kow) consistently under-predicted BAFoc, however, the magnitude of the under-prediction was still within the range of uncertainty in food web modeling (factors of 3-9). Food web modeling and risk assessment of PBT bioaccumulation in aquatic systems could be improved by considering the microbial food web (bacteria and its protozoan grazers) as a previously unaccounted for pathway of contaminant transfer.

Animals↗
PubMed2005

Partitioning of polychlorinated biphenyls in octanol/water, triolein/water, and membrane/water systems.

The use of the octanol/water partition constant (Kow) as a surrogate parameter for lipid/water partitioning of persistent organic pollutants (POPs) was reassessed by comparing the measured Kow of 12 selected polychlorinated biphenyl congeners (PCBs) with partition constants in triolein/water (Ktw) and membrane/water (Kmw) systems. Kow and Ktw were measured by the slow-stirring method. Kmw was measured by an adaptation of the slow-stirring method using suspensions of phosphatidylcholine and phosphatidylserine liposomes. Partitioning of POPs to octanol, triolein, and liposomes is similar but not equal. The log-log correlation for Kow and Ktw is excellent (r2 = 0.982) and that for Kow and Kmw is somewhat weaker (r2 = 0.856). Ktw values are greater than Kow by a factor of 1.6. Kmw of some PCB congeners exceed both Kow and Ktw by an order of magnitude. The differences are attributed to different PCB activity coefficients in the different lipid phases. The results imply that Kow can be used as a reasonable conservative estimate of lipid/water partitioning. But the observed differences between Kow and Kmw also indicate that using Kow to predict accumulation of POPs, particularly highly hydrophobic ones, in the polar lipids of organisms will underestimate their concentrations at equilibrium.

Animals↗
PubMed2004

Subcellular accumulation of polychlorinated biphenyls in the green alga Chlamydomonas reinhardtii.

In this study, the subcellular accumulation of 13 polychlorinated biphenyl (PCB) congeners was investigated in the green alga Chlamydomonas reinhardtii. Two main arguments pertaining to the mechanism of bioaccumulation of persistent bioaccumulative toxic chemicals (PBTs) in phytoplankton were evaluated, including the controversy of whether the limitation of uptake of ultra-hydrophobic pollutants is kinetic or due to a physical barrier presented by the membrane that prevents transfer into the internal parts of the cell, and second, the role of surface adsorption for the bioaccumulation process. The first argument was addressed by studying the time-dependent subcellular uptake of PCBs into thylakoids (photosynthetic membranes) as representative internal membranes. The second issue was addressed by investigating the role of the algal cell wall as a potential extracellular sorbate. Accumulation of PCBs in thylakoids was found to be limited kinetically and slow compared to total accumulation in the alga. Super-hydrophobic PCBs with Kow > 6 were not restricted from entering the cell. Sorption to the cell wall was found to be less than 10% and insignificant compared to total bioaccumulation in C. reinhardtii. To our knowledge, this is the first study in which the subcellular uptake of a class of PBTs was investigated directly. The results offer a mechanistic framework for improving kinetic modeling of PBT bioaccumulation in phytoplankton.

Adsorption↗
PubMed2003

Influence of suspended solids on acute toxicity of carbofuran to Daphnia magna: II. An evaluation of potential interactive mechanisms.

It has been demonstrated that simultaneous exposure of Daphnia magna to suspended solids and a carbamate pesticide potentiates the toxic response to the pesticide. The toxicodynamics between these stressors were investigated to determine possible mechanisms of interaction. Three experimental series were conducted with D. magna to determine: the effect of food availability on carbofuran toxicity; the effect of food availability on jointly administered carbofuran and suspended solids; and changes in the magnitude of effects which can occur with suspended solids of different composition. These experiments demonstrated that both carbofuran toxicity and the joint toxicity of carbofuran and suspended solids to D. magna can be modulated by food availability. While it is clear that food dilution could contribute to energy stress, it appears likely that additional interactive processes also contribute to the observed synergism between carbofuran and suspended solids. Additionally, decomposed peat was shown to be less of a stressor to these pelagic invertebrates than inorganic subsoil.

Animals↗
PubMed2003

Influence of suspended solids on acute toxicity of carbofuran to Daphnia magna: I. Interactive effects.

This study explored the effects on Daphnia magna from exposure to the pesticide carbofuran in combination with stress from suspended solids exposure. Our objective was to assess whether suspended solids affects the toxicodynamic response of D. magna to carbofuran. A series of laboratory experiments was performed where animals were exposed to carbofuran concentrations ranging from 0 to 160 microg/l in combination with suspended solids concentrations ranging from 0 to 10000 mg/l. In the absence of suspended solids, effects of carbofuran were dose dependent and resulted in an EC(50) of 92 microg/l. Exposure to suspended solids, up to extreme levels that may be encountered in the environment and in the absence of carbofuran, showed no measurable toxicity. When D. magna were exposed to a constant carbofuran concentration, the numbers of affected organisms increased with increasing suspended solids concentrations. At a suspended solids concentration of 1000 mg/l, the EC(50) for carbofuran was reduced by half to 45 microg/l. The relationship between the toxicity of carbofuran (microg/l) and the concentration of suspended solids (mg/l) can be described with the following equation: carbofuran EC(50)=72 exp(-0.00014 [suspended solids]). An analysis of the data indicates that this relationship is consistent with a potentiated toxicity mechanism rather than an additive model.

Animals↗
PubMed2002

Preferential biomagnification of aryl hydrocarbon hydroxylase-inducing polychlorinated biphenyl congeners in the Lake Michigan, USA, lower food web.

Preferential biomagnification of 14 dioxin-like polychlorinated biphenyls (PCBs) was determined in lower-trophic-level organisms of the Lake Michigan, USA, food web. Bioaccumulation of these coplanar, aryl hydrocarbon hydroxylase (AHH)-inducing PCB congeners and total PCBs in phytoplankton, zooplankton, Mysis relicta, and Diporeia sp. were studied for two locations in Lake Michigan over time. The results indicate that both total PCB and AHH-inducing PCBs biomagnify with increasing food web trophic level, with biomagnification of the AHH-inducing PCBs occurring to a greater degree. The biomagnification factors (BMFs) of the AHH-inducing PCBs suggest that they are highly conserved relative to other PCB congeners. The concentrations expressed as dioxin toxic equivalencies (TEQ concentrations) indicate that the biomagnification of AHH PCBs causes greater concentrations, and thus greater toxicity risk, with increasing trophic level.

Animals↗