Biomedical subjects

Jason M Conder

Publications and source records attributed to Jason M Conder.

6 recordsLinked to original sources

PubMed2005

Solid phase microextraction of aminodinitrotoluenes in tissue.

Tubifex tubifex metabolizes 2,4,6-trinitrotoluene (TNT) to 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT). Elimination rates of metabolically-generated ADNTs are low compared to ADNTs absorbed directly from water, suggesting that metabolically-generated ADNTs may be bound or sequestered within tissue and therefore less available for elimination. A solid phase microextraction (SPME) technique was used to extract ADNTs from T. tubifex tissue to investigate the recalcitrance of metabolically-generated ADNTs. As SPME is a gentle, non-depletive, equilibrium sampling technique useful for measuring "available" organic compounds, we hypothesized that metabolically-generated ADNTs would be less extractable than absorbed ADNTs. T. tubifex were exposed to two scenarios to generate tissues containing absorbed ADNTs and metabolically-generated ADNTs. Tissue was then homogenized in a neutral buffer solution. Polyacrylate-coated (PA) SPME fibers were deployed and agitated in tissue homogenates to measure available ADNTs. Extractability of ADNTs from tissue containing metabolically-generated ADNTs was significantly less than expected: 50-60% based on the theoretical fiber-water partition ratio. Extractability of absorbed ADNTs was significantly higher (81-90%), and not significantly different than expected. The lower SPME extractability of metabolically-generated ADNTs may stem from the unavailability of metabolically-generated ADNTs sequestered in tissue or bound to tissue macromolecules during metabolism of TNT to ADNT. Tissue extractions using SPMEs may be able to estimate bound organic residues in tissue and serve to indicate the toxicological bioavailability of tissue-associated organic compounds.

Aniline Compounds↗

PubMed2005

Solid-phase microextraction for predicting the bioavailability of 2,4,6-trinitrotoluene and its primary transformation products in sediment and water.

Disposable solid-phase microextraction fibers (SPMEs) were used to measure the availability of 2,4,6-trinitrotoluene (TNT) and its two primary transformation products, 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT). The SPMEs (85-microm polyacrylate) and sediment-dwelling oligochaetes (Tubifex tubifex) were exposed to TNT-spiked sediment, to TNT-spiked sediment amended with activated carbon, and to TNT-, 2ADNT-, and 4ADNT-spiked water. Sediment concentration was a poor predictor of bioavailability in unamended and carbon-amended sediments (r2 = 0.14-0.73) The activated carbon amendment reduced the bioavailability of compounds in carbon-amended sediment, causing the relationships between Tubifex concentrations and sediment concentrations to differ significantly between unamended and carbon-amended sediment for all compounds. In contrast, SPME TNT concentrations predicted Tubifex TNT concentrations (r2 = 0.54-0.79). and regression models did not differ significantly among the three TNT-spiked matrices. The SPME 2ADNT and 4ADNT concentrations also were predictive of Tubifex 2ADNT and 4ADNT concentrations (r2 = 0.44-0.90). Relationships between Tubifex concentrations and SPME concentrations were the same between unamended and carbon-amended TNT-spiked sediments for 2ADNT and 4ADNT; however, the relationship in sediment (pooled data) differed from the relationship found in 2ADNT- and 4-ADNT-spiked water. The SPMEs provided carbon amendment-independent measures of ADNT availability in sediment and matrix-independent measures of TNT availability among the three matrices. The SPMEs show promise for predicting bioavailable organic compounds in sediment and water.

Animals↗

PubMed2004

Preliminary kinetics and metabolism of 2,4,6-trinitrotoluene and its reduced metabolites in an aquatic oligochaete.

We examined the toxicokinetics and metabolism of 2,4,6-trinitirotoluene (TNT) and four of its major reduced metabolites (2-amino-4,6-dinitrotoluene (2ADNT), 4-amino-2,6-dinitrotoluene (4ADNT), and 2,4-diamino-6-nitrotoluene (2,4DANT)) in the freshwater, aquatic oligochaete Tubifex tubifex exposed to spiked, reconstituted water. In uptake experiments with each compound, steady state concentrations were reached within 1h, and all absorbed compounds were completely eliminated in 0-3 h. The appearance of 2ADNT and 4ADNT (from metabolism of absorbed TNT) was five times slower, reaching 95% of steady state in 14.2-16.1h. Approximately, 82% of absorbed TNT was metabolized to ADNTs; metabolism to 4ADNT was favored over 2ADNT by a factor of 3. No further metabolism of ADNTs to DANTs was detected. After a loss of 29-50% of metabolically-generated ADNTs during the first hour of the TNT depuration experiment, Tubifex ADNT concentrations remained constant throughout the 53h depuration period. This suggests differences between the toxicokinetics of absorbed ADNTs and the toxicokinetics of metabolically-generated ADNTs. Experiments using radiolabeled (14C) TNT revealed that only 15-47% of 14C-TNT equivalents were identified as TNT, 2ADNT, or 4ADNT, indicating significant metabolism and/or binding to biomolecules. Of unidentified 14C-TNT equivalents, 28-38% remained unextractable. Both unextractable and extractable unidentified substances increased throughout the 54 h 14C-TNT uptake experiment. The unidentified portions of the radiolabel were not eliminated during a 53-h depuration experiment. Bioconcentration factors (BCFs) for HPLC-detectable compounds were found to be linearly related to log K(OW) (r2 = 0.9963). BCFs for 2ADNT, 4ADNT, and 2,4DANT were 10.22, 12.41, and 2.75, respectively. The BCF for TNT was 12.25, based on a molar sum of total TNT and its metabolites (SigmaTNT + 2ADNT + 4ADNT), and 2.53 based on TNT only. Compound hydrophobicity predicted the toxicokinetics and bioconcentration of compounds absorbed from water, however, the large discrepancy between the toxicokinetics of absorbed versus metabolically-generated ADNTs and the bioconcentration and toxicokinetics of the unidentified substances warrant further investigation.

Analysis of Variance↗

PubMed2004

Recommendations for the assessment of TNT toxicity in sediment.

Previous investigations of the ecotoxicity of TNT in spiked sediments noted the rapid degradation and disappearance of the toxicant, yet little is understood regarding the effects of this process on toxicity and subsequent derivation of toxicity reference values. We conducted environmental fate studies and 28-d sediment toxicity tests with benthic oligochaete worms (Tubifex tubifex) with sediments spiked at three different TNT concentrations (440, 1,409, and 4,403 nmol/g dry wt) aged for 1, 8, and 29 d. Because of rapid degradation of TNT, disappearance of degradation products, and partitioning to overlying water, only 25 to 40% of the added nitroaromatic mass balance was associated with sediment immediately after spiking. Lethal toxicity decreased with aging time and was best described by measured sediment nitroaromatic concentrations (sum of TNT and degradation products) at the beginning of exposure, with a median lethal concentration of nitroaromatic compounds of 184 nmol/g dry weight. To accurately describe the ephemeral exposure doses of TNT and its degradation products during toxicity tests with spiked sediments, we suggest that sediments should be aged at least 8 to 14 d after spiking, exposure should be based on measured sediment concentrations or chemical measures of availability, exchange of overlying water should be avoided or minimized, and short-term toxicity tests should be considered.

Animals↗

PubMed2003

Nondestructive, minimal-disturbance, direct-burial solid-phase microextraction fiber technique for measuring TNT in sediment.

We explored a novel technique to deploy solid-phase microextraction (SPME) fibers to nondestructively measure the explosive compound 2,4,6-trinitrotoluene (TNT) and its nitroaromatic (NA) degradation products in laboratory sediment toxicity tests and field sediments in situ. SPME fibers within steel mesh envelopes were exposed statically via direct burial within sediment. Six fiber types (polymer coatings) were tested. Polyacrylate (PA) SPME fiber was sufficiently durable for this application, yielded the lowest detection limits, and exhibited a linear uptake relationship across toxicologically relevant sediment NA concentrations (100-2000 nmol/g dw (20-500 microg/g dw)). Temperature greatly influenced SPME absorption kinetics. Via evaluation of absorption at different temperatures, recommended sampling times needed to achieve steady-state equilibrium were 48 h for room temperatures (23-25 degrees C) and up to 7 d for cold (5 degrees C) temperatures. Although a comparison of TNT residues by SPMEs and TNT bioavailability and toxicity in sediments has not been completed, differences in SPME availability of TNT and its degradation products were found between two different TNT-spiked sediments. Our disposable SPME technique was slightly less expensive and as precise as the conventional extraction for total NAs and may prove to be a powerful exposure evaluation tool for assessing the ecological risk of these compounds.

Absorption↗

PubMed2002

Method for determining toxicologically relevant cadmium residues in the earthworm Eisenia fetida.

We investigated a method to isolate toxicologically relevant Cd in earthworms (Eisenia fetida) exposed in a 14-d Cd bioaccumulation study. A procedure involving acid insoluble ash (AIA) content was combined with homogenization and centrifugation techniques to divide total earthworm Cd burdens into supernatant (metallothionein-bound), pellet (toxicologically active), and soil-associated Cd fractions. Whereas the supernatant fraction of the earthworm digests increased linearly throughout the exposure period (from approximately 0 to 3.59 mmol/kg), the pellet fraction reached a steady-state concentration (95% CI) of 1.2 (0.9-1.4) mmol/kg, suggesting the ability of the metallothionein detoxification system to sequester incoming Cd. The AIA method was useful for correcting earthworm Cd concentrations for ingested soil-associated Cd and observing soil ingestion, which was suppressed in Cd-spiked artificial soil (1.06 (0.57-1.55)%) compared to controls (17.25 (14.36-20.15)%). These methods may be useful in investigating soil ingestion and Cd uptake and detoxification in earthworms.

Animals↗