Daniel P.Y. Chang

In Vitro Biologic Activities of the Antimicrobials Triclocarban, Its Analogs, and Triclosan in Bioassay Screens : Receptor-Based Bioassay Screens

Background Concerns have been raised about the biological and toxicologic effects of the antimicrobials triclocarban (TCC) and triclosan (TCS) in personal care products. Few studies have evaluated their biological activities in mammalian cells to assess their potential for adverse effects. Objectives In this study, we assessed the activity of TCC, its analogs, and TCS in in vitro nuclear-receptor–responsive and calcium signaling bioassays. Materials and methods We determined the biological activities of the compounds in in vitro, cell-based, and nuclear-receptor–responsive bioassays for receptors for aryl hydrocarbon (AhR), estrogen (ER), androgen (AR), and ryanodine (RyR1). Results Some carbanilide compounds, including TCC (1–10 μM), enhanced estradiol (E2)-dependent or testosterone-dependent activation of ER- and AR-responsive gene expression up to 2.5-fold but exhibited little or no agonistic activity alone. Some carbanilides and TCS exhibited weak agonistic and/or antagonistic activity in the AhR-responsive bioassay. TCS exhibited antagonistic activity in both ER- and AR-responsive bioassays. TCS (0.1–10 μM) significantly enhanced the binding of [3H]ryanodine to RyR1 and caused elevation of resting cytosolic [Ca2+] in primary skeletal myotubes, but carbanilides had no effect. Conclusions Carbanilides, including TCC, enhanced hormone-dependent induction of ER- and AR-dependent gene expression but had little agonist activity, suggesting a new mechanism of action of endocrine-disrupting compounds. TCS, structurally similar to noncoplanar ortho-substituted poly-chlorinated biphenyls, exhibited weak AhR activity but interacted with RyR1 and stimulated Ca2+ mobilization. These observations have potential implications for human and animal health. Further investigations are needed into the biological and toxicologic effects of TCC, its analogs, and TCS.

Denitrification and nitric oxide reduction in an aerobic toluene-treating biofilter

The presence of significant denitrification activity in an aerobic toluene-treating biofilter was demonstrated under batch and flow-through conditions. N2O concentrations of 9.2 ppmv were produced by denitrifying bacteria in the presence of 15% acetylene, in a flow-through system with a bulk gas phase O2 concentration of >17%. The carbon source for denitrification was not toluene but a byproduct or metabolite of toluene catabolism. Denitrification conditions were successfully used for the reduction of 60 ppmv nitric oxide to 15 ppmv at a flow rate of 3 L min-1 (EBRT of 3 min) in a fully aerated, 17% v/v O2 (superficially aerobic) biofilter. Higher NO removal efficiency (97%) was obtained by increasing the toluene supply to the biofilter.

Highly sensitive dioxin immunoassay and its application to soil and biota samples

Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known highly toxic compound that is present in nearly all components of the global ecosystem, including air, soil, sediment, fish and humans. Dioxin analysis is equipment intensive and expensive requiring low ppt or even ppq levels of detection. A simple, rapid, cost-effective method of analysis is desired to enable researchers to explore issues involving dioxin more quickly and to make more rational regulatory decisions. A sensitive immunoassay for TCDD has been developed in this laboratory. In the present study, this assay is further optimized using a new coating antigen system and validated with biota samples by HRGC-HRMS. The I50 of current assay to 2,3,7-trichloro, 8-methyldibenzo-p-dioxin (TMDD), a surrogate standard for TCDD, is 36 ± 6.0 ppt, and the lower detection limit (LDL) is 4 ppt in the buffer. A good agreement between immunoassay and GC/MS was achieved for fish and egg samples. To interface with the immunoassay, a rapid sample preparation method was developed for soil samples. Without any further cleanup, the soil extracts can be directly used in the ELISA with a detection limit at the low ppt level. It can be used as an on-site tool for environmental monitoring.

Toxic combustion by-products from the incineration of chlorinated hydrocarbons and plastics

Abstract Polyvinylidene chloride and polyvinyl chloride were pyrolyzed in a thermal gravimetric analyzer and by-products were collected for chemical analysis and bioassay. Trichloroethylene was also burned in a laminar diffusion flame of methane with varying concentrations of the chlorinated compound. Soot particulates collected on filters and post-flame gases collected on sorbent tubes were extracted and analyzed using gas chromatography-mass spectrometry. Extracts were evaluated for potential toxicity using an in vitro hyperkeratinization bioassay that is sensitive to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Chemical analyses identified polycyclic aromatic hydrocarbons and chlorinated PAHs as the major pyrolysis products. Products generated from the pyrolysis of both polymers yielded definite positive bioassay responses. Most of the products obtained from the trichloroethylene flame were associated with soot particles emitted from the flame. A series of chlorinated aromatic compounds, including hexachlorocyclopentadiene and chlorinated benzenes, polycyclic aromatics, and fulvalenes were identified as major products. Dichloromethane extracts of the soots elicited a positive bioassay response.

The fate of arsenic in a laminar diffusion flame

Abstract An arsenic compound (cacodylic acid) has been added to laminar diffusion flames burning in a co-flowing stream of air. Two fuels were used viz. ethene (C2H4) and a mixture of hydrogen and nitrogen. Samples of aerosols and gaseous species were collected within the flames and above the flames with filters and sorbent tubes. The hydrogen flame showed the conversion of arsenite to arsenate with increased residence time through the flame. The conversion of arsenite to arsenate in the ethene flames was inhibited by the emission of soot, which apparently competed with the arsenic for oxygen in the postflame gas. Arsenic was not found to be incorporated into soot particles. The carbon and arsenic were present in the posflame gases as two distinct aerosol phases. The addition of arsenic did not have a significant effect on the formation and oxidation of soot. The addition of arsenic did not lead to the production of organoarsenic species; only common polycyclic aromatics were found in the sooting flames.

Investigation of polychlorinated biphenyl removal from contaminated soil using microwave-generated steam

ABSTRACT A feasibility study of polychlorinated biphenyl (PCB) removal from contaminated soils using microwave-generated steam (MGS) was performed. Initial experimental results show that MGS effectively removed PCBs from contaminated soil with an overall removal efficiency of greater than 98% at a steam-to-soil mass ratio of 3:1. Removal efficiency was found to be dependent upon the amount of steam employed, expressed as a mass ratio of steam applied to soil mass. Evaporation was identified as a major mechanism in removing PCBs from the soil. Rapid expansion and evaporation of pore water by microwave dielectric heating accelerated evaporation rates of PCB molecules. Increased solubility of PCBs into the heated aqueous phase is also hypothesized. Together these effects increase mass-transfer rates, thus enhancing removal of PCBs from the soil.

An experimental investigation of the incineration and incinerability of chlorinated alkane droplets

An experimental investigation has been conducted on the vaporization, combustion, and extinction of droplets of pure chlorinated alkanes and their mixtures with n-alkanes in “inert” and oxidizing environments. From results on the droplet vaporization/combustion rates, the state of extinction, and temporal changes in the droplet composition, it is shown that droplets of lightly chlorinated alkanes as represented by monochloroalkanes burn almost as vigorously as normal alkanes, that heavily chlorinated alkanes as represented by 1, 1, 2, 2-tetrachloroethane (TECA) burn weakly if at all, that TECA can be rendered to burn vigorously with the addition of only 25 volume percent of an equal-volatility alkane, and that this enhancement can be further improved by decreasing the volatility of the additive. Implications on hazardous waste incineration are discussed.

Microwave Plasma Conversion of Volatile Organic Compounds

Abstract A microwave-induced, steam/Ar/O2 , plasma “torch” was operated at atmospheric pressure to determine the feasibility of destroying volatile organic compounds (VOCs) of concern. The plasma process can be coupled with adsorbent technology by providing steam as the fluid carrier for desorbing the VOCs from an adsorbent. Hence, N2 can be excluded by using a relatively inexpensive carrier gas, and thermal formation of oxides of nitrogen (NOx ) is avoided in the plasma. The objectives of the study were to evaluate the technical feasibility of destroying VOCs from gas streams by using a commercially available microwave plasma torch and to examine whether significant byproducts were produced. Trichloroethene (TCE) and toluene (TOL) were added as representative VOCs of interest to a flow that contained Ar as a carrier gas in addition to O2 and steam.The O2 was necessary to ensure that undesirable byproducts were not formed in the process. Microwave power applied at 500–600 W was found to be sufficient to achieve the destruction of the test compounds, down to the detection limits of the gas chromatograph that was used in the analysis. Samples of the postmicrowave gases were collected on sorbent tubes for the analysis of dioxins and other byproducts. No hazardous byproducts were detected when sufficient O2 was added to the flow. The destruction efficiency at a fixed microwave power improved with the addition of steam to the flow that passed through the torch.

BIODEGRADATION OF RECALICTRANT COMPONENTS OF ORGANIC MIXTURES

Biodegradation of two recalcitrant compounds, dichloromethane and methyl tert-butyl ether was investigated individually and in combination with toluene and benzene. A vapor phase biofilter operating at an air flux of 1 m3/m2·min and an empty bed residence time of 1 minute was used as the reaction system. Inlet recalcitrant contaminant concentrations were typically 35 ppm on a volume basis while the aromatic compound concentrations were varied from 8 ppm to 150 ppm. Dichloromethane removals were not impacted by the introduction of toluene. However, a rapid decrease in methyl tert-butyl ether removal resulted from the initial introduction of toluene. Complete removal of both methyl tert-butyl ether and toluene was achieved within a week of operation.

The transformation of chromium in a laminar premixed hydrogen-air flame

The transformation of chromium was studied numerically and experimentally in a simple laminar premixed hydrogen-air flame. Chromium was added to the flame as a vapor of chromium hexacarbonyl that provided a source of zero-oxidation-state pure elemental chromium through its rapid pyrolysis. The flame was operated over a range of equivalence ratios. The metal aerosol and vapors that were created in the flame were sampled at different heights with a dilution sampling probe. Aerosol was collected on a filter and vapors in a liquid nitrogen trap. Analysis of the samples showed an initial increase in the amount of hexavalent chromium with increasing distance from the burner, followed by a drop to about 5% far from the burner. The modeling of detailed chromium kinetics showed a similar behavior. The observations highlighted the importance of finite-rate kinetics in controlling the ultimate state of the metal oxide. Aerosol samples were analyzed with an electrical mobility analyzer and condensation nuclei counter. Mean diameters were of the order of 40 nm. The numerical model of the chromium aerosol showed qualitatively good agreement between measured and predicted aerosol size distributions.