In the interest of reducing animal use, in vitro alternatives for skin sensitization testing are under development. One unifying characteristic of chemical allergens is the requirement that they react with proteins for the effective induction of skin sensitization. The majority of chemical allergens are electrophilic and react with nucleophilic amino acids. To determine whether and to what extent reactivity correlates with skin sensitization potential, 82 chemicals comprising allergens of different potencies and nonallergenic chemicals were evaluated for their ability to react with reduced glutathione (GSH) or with two synthetic peptides containing either a single cysteine or lysine. Following a 15-min reaction time with GSH, or a 24-h reaction time with the two synthetic peptides, the samples were analyzed by high-performance liquid chromatography. UV detection was used to monitor the depletion of GSH or the peptides. The peptide reactivity data were compared with existing local lymph node assay data using recursive partitioning methodology to build a classification tree that allowed a ranking of reactivity as minimal, low, moderate, and high. Generally, nonallergens and weak allergens demonstrated minimal to low peptide reactivity, whereas moderate to extremely potent allergens displayed moderate to high peptide reactivity. Classifying minimal reactivity as nonsensitizers and low, moderate, and high reactivity as sensitizers, it was determined that a model based on cysteine and lysine gave a prediction accuracy of 89%. The results of these investigations reveal that measurement of peptide reactivity has considerable potential utility as a screening approach for skin sensitization testing, and thereby for reducing reliance on animal-based test methods.
Recent concern that the increased use of triclosan (TCS) in consumer products may contribute to the emergence of antibiotic resistance has led us to examine the effects of TCS dosing on domestic-drain biofilm microcosms. TCS-containing domestic detergent (TCSD) markedly lowered biofouling at 50% (wt/vol) but was poorly effective at use levels. Long-term microcosms were established and stabilized for 6 months before one was subjected to successive 3-month exposures to TCSD at sublethal concentrations (0.2 and 0.4% [wt/vol]). Culturable bacteria were identified by 16S rDNA sequence analysis, and their susceptibilities to four biocides and six antibiotics were determined. Microcosms harbored ca. 10 log 10 CFU/g of biofilm, representing at least 27 species, mainly gamma proteobacteria, and maintained dynamic stability. Viable cell counts were largely unaffected by TCSD exposure, but species diversity was decreased, as corroborated by denaturing gradient gel electrophoresis analysis. TCS susceptibilities ranged widely within bacterial groups, and TCS-tolerant strains (including aeromonads, pseudomonads, stenotrophomonads, and Alcaligenes spp.) were isolated before and after TCSD exposure. Several TCS-tolerant bacteria related to Achromobacter xylosoxidans became clonally expanded during dosing. TCSD addition did not significantly affect the community profiles of susceptibility to the test biocides or antibiotics. Several microcosm isolates, as well as reference bacteria, caused clearing of particulate TCS in solid media. Incubations of consortia and isolates with particulate TCS in liquid led to putative TCS degradation by the consortia and TCS solubilization by the reference strains. Our results support the view that low-level exposure of environmental microcosms to TCS does not affect antimicrobial susceptibility and that TCS is degradable by common domestic biofilms.
An extensive monitoring program was conducted to
determine the occurrence of polydimethylsiloxane (PDMS)
in environmental compartments impacted by consumer
waste disposal practices. Eight wastewater treatment
plants,
representative of those found in North America, were
monitored to determine PDMS removal during wastewater
treatment. Surface waters, sediments, and sludge-amended soils impacted by wastewater treatment plant
effluents and sludges were also monitored for a more
complete
assessment of the environmental fate of PDMS. Newly
developed GPC−ICP and/or HPLC−ICP analytical
techniques
were used to provide insight into the environmental fate
of PDMS and anticipated PDMS degradation products.
PDMS
was found to be highly removed during wastewater treat
ment with effluent concentrations, in most cases, below
the quantitation limit of the analytical technique (<5
μg/L).
PDMS sludge concentrations ranged from 290 to 5155 mg/kg and varied as a function of influent concentration and
sludge processing method. Sediment levels of <6 mg/kg were measured near the outfall of the wastewater
treatment
plants sampled. Measured sludge-amended agricultural
soil concentrations ranged from <0.41 to 10.4 mg/kg and
were
lower than expected in most cases based on calculated
PDMS loadings via historical sludge application. The
lower
than expected PDMS concentrations in sludge-amended
soil combined with detection of dimethylsilane-1,1-diol,
an
expected PDMS breakdown product, suggest degradation
of PDMS in the soil environment.
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