Characterization and Biological Potency of Mono- to Tetra-Halogenated Carbazoles.

This paper deals with the characterization and aryl hydrocarbon receptor (AhR) agonist activities of a series of chlorinated, brominated, and mixed bromo/chlorocarbazoles, some of which have been identified in various environmental samples. Attention is directed here to the possibility that halogenated carbazoles may currently be emitted into the environment as a result of the production of carbazole-containing polymers present in a wide variety of electronic devices. We have found that any carbazole that is not substituted in the 1,3,6,8 positions may be lost during cleanup of environmental extracts if a multilayer column is utilized, as is common practice for polychlorinated dibenzo-p-dioxin (dioxin) and related compounds. In the present study, (1)H NMR spectral shift data for 11 relevant halogenated carbazoles are reported, along with their gas chromatographic separation and analysis by mass spectrometry. These characterization data allow for confident structural assignments and the derivation of possible correlations between structure and toxicity based on the halogenation patterns of the isomers investigated. Some halogenated carbazoles exhibit characteristics of persistent organic pollutants and their potential dioxin-like activity was further investigated. The structure-dependent induction of CYP1A1 and CYP1B1 gene expression in Ah-responsive MDA-MB-468 breast cancer cells by these carbazoles was similar to that observed for other dioxin-like compounds, and the magnitude of the fold induction responses for the most active halogenated carbazoles was similar to that observed for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). 2,3,6,7-Tetrachlorocarbazole was one of the most active halogenated carbazoles and, like TCDD, contains 4 lateral substituents; however, the estimated relative effect potency for this compound (compared to TCDD) was 0.0001 and 0.0032, based on induction of CYP1A1 and CYP1B1 mRNA, respectively.

Reconstruction of historical 2,3,7,8-tetrachlorodibenzo-p-dioxin discharges from a former pesticide manufacturing plant to the Lower Passaic River.

Based on chemical fingerprinting and other lines of scientific evidence, a former pesticide manufacturing plant in Newark, New Jersey (U.S.A.) has been implicated in numerous journal articles as the major source of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the sediments of the Lower Passaic River (LPR). Although the site has been extensively studied for over three decades, no previous study has identified a pathway capable of discharging an amount of 2,3,7,8-TCDD comparable to the mass estimates made for 2,3,7,8-TCDD in the sediments of the LPR and Newark Bay, or examined the timing of specific manufacturing processes at the site in relation to 2,3,7,8-TCDD concentrations in dated sediment cores. A reconstruction of the historical operations at this site was performed, supporting it as the major source of 2,3,7,8-TCDD to the LPR. A 2,4,5-trichlorophenol purification process, utilized prior to September 1954, was specifically identified as a significant source of 2,3,7,8-TCDD to the LPR. This purification process generated a dioxin-rich sludge that was discharged to the river prior to September 1954. Annual 2,4,5-trichlorophenol production, coupled with modeling to predict concentrations of 2,3,7,8-TCDD, indicate that 2,3,7,8-TCDD discharges to the LPR from this one process (20-80 kg) are consistent with mass estimates of 2,3,7,8-TCDD in the river (30-50 kg). 2,3,7,8-TCDD and cesium-137 data from nearby sediment cores support this purification process as a major pathway by which 2,3,7,8-TCDD entered the river.

Arsenic removal by iron-modified activated carbon.

Iron-impregnated activated carbons have been found to be very effective in arsenic removal. Oxyanionic arsenic species such as arsenate and arsenite adsorb at the iron oxyhydroxide surface by forming complexes with the surface sites. Our goal has been to load as much iron within the carbon pores as possible while also rendering as much of the iron to be available for sorbing arsenic. Surface oxidation of carbon by HNO3/H2SO4 or by HNO3/KMnO4 increased the amount of iron that could be loaded to 7.6-8.0%; arsenic stayed below 10 ppb until 12,000 bed volumes during rapid small-scale tests (RSSCTs) using Rutland, MA groundwater (40-60 ppb arsenic, and pH of 7.6-8.0). Boehm titrations showed that surface oxidation greatly increased the concentration of carboxylic and phenolic surface groups. Iron impregnation by precipitation or iron salt evaporation was also evaluated. Iron content was increased to 9-17% with internal iron-loading, and to 33.6% with both internal and external iron loading. These iron-tailored carbons reached 25,000-34,000 bed volumes to 10 ppb arsenic breakthrough during RSSCTs. With the 33.6% iron loading, some iron peeled off.

The removal of perchlorate from groundwater by activated carbon tailored with cationic surfactants.

In rapid small-scale column tests, cationic surfactant-tailored activated carbons (ACs) effectively removed perchlorate to below detection levels for up to 30 times longer than virgin AC. By pre-loading bituminous AC with dicocodimethylammonium chloride, tallowtrimethylammonium chloride, cetyltrimethylammonium chloride, or cetylpyridinium chloride, 75 ppb perchlorate was removed for 27,000-35,000 bed volumes before the effluent perchlorate rose above 1 ppb. These tests employed a natural groundwater that also contained 30 mg/L sulfate, 26 mg/L nitrate (as NO3-), and other ions. By the time of 25 ppb perchlorate breakthrough, 7.3-10.1% of quaternary ammonium sites had perchlorate associated with them. Although some of the surfactants leached out of the tailored carbon beds (0.6-21.2% of the amount loaded), the leached surfactant could be removed to below detectable limits with a virgin AC polishing bed that chased the tailored bed.

Removing low ppb level perchlorate, RDX, and HMX from groundwater with cetyltrimethylammonium chloride (CTAC) pre-loaded activated carbon.

Perchlorate contaminates vast amounts of groundwater throughout the United States which could potentially be used as potable water. Activated carbon pre-loaded with cetyltrimethylammonium chloride has been shown in this research to be an effective adsorbent for removing perchlorate from three low conductivity (50-66 microS/cm) groundwaters containing perchlorate (ClO(4)(-)) concentrations of 0.85, 1.0, and 5.6 parts per billion (ppb), respectively. In rapid small-scale column tests (RSSCTs), the virgin granular activated carbon (GAC) (used as a control) treated between 20,000 and 40,000 bed volumes (BV) of water. In contrast, the activated carbon that was pre-loaded with CTAC processed 170,000-270,000 BV before perchlorate was detected above 0.25 ppb in the effluent. Though this pre-loading significantly increased the capacity for perchlorate, it also diminished the GAC's capacity to remove organics. The groundwater containing 1 ppb ClO(4)(-) also contained the nitro-organics HMX (0.6 ppb) and RDX (5.5-6.6 ppb). RDX was detected in the effluent from the CTAC-pre-loaded bed after only 8000 BV had been processed whereas 308,000 BV could be processed through the virgin bed before RDX was detected. Likewise, HMX breakthrough was observed after 116,000 BV in the CTAC-pre-loaded bed while the virgin RSSCT exhibited no breakthrough of HMX during a test that was operated for 309,000 BV. However, by combining a CTAC-pre-loaded bed followed by a virgin GAC bed in series, both perchlorate and RDX could be removed for the same length of time.

Halogenated indigo dyes: a likely source of 1,3,6,8-tetrabromocarbazole and some other halogenated carbazoles in the environment.

In recent years, a number of halogenated carbazoles have been detected in environmental samples. These emerging contaminants have been shown to be persistent and possess dioxin-like toxicological potential. The goal of this research was to examine the literature to determine likely anthropogenic origin(s) of halogenated carbazoles in the environment. The scientific literature indicated a number of pathways by which 1,3,6,8-tetrabromocarbazole could form in the manufacture of 5,5',7,7'-tetrabromoindigo. The U.S. production history of 5,5',7,7'-tetrabromoindigo correlates well with the concentration rise, decline, and disappearance of 1,3,6,8-tetrabromocarbazole in dated Lake Michigan sediments. Additionally, other halogenated carbazoles that have been found in environmental sediments can be explained by the production of other halogenated indigo dyes. 1,8-dibromo-3,6-dichlorocarbazole can be accounted for by the manufacture of 7,7'-dibromo-5,5'-dichloroindigo, while 1,3,6,8-tetrachlorocarbazole was found at relatively high concentration near the outfall of a U.S. manufacturer of 5,5',7,7'-tetrachloroindigo. Carbazoles containing an iodo-substituent can be explained by the use of iodine as a catalyst in the manufacture of halogenated indigo dyes. 3,6-Dichlorocarbazole measured in soils and dibromocarbazoles measured in more recently deposited sediments are not easily rationalized on the basis of an indigo related source and may be related to other anthropogenic sources or natural origins.

2,4,6,8-Tetrachlorodibenzothiophene in the Newark Bay Estuary: the likely source and reaction pathways.

Historic industrial activity along the Newark Bay Estuary has resulted in pollution from a number of contaminants; one of which is 2,4,6,8-tetrachlorodibenzothiophene (2,4,6,8-TCDT), a unique chemical contaminant whose origins have not been adequately explained. This research demonstrates that the probable source of 2,4,6,8-TCDT was the chlorination of phenol produced via the sulfonation method. Thiophenol, the major impurity in this type of phenol, was likely converted to 2,4,6,8-TCDT through one or more pathways during the production of 2,4-dichlorophenol, 2,4-dichlorophenoxyacetic acid (2,4-D), or 2,4,6-trichlorophenol. From a mass balance standpoint, production of these chemicals at an industrial plant along the Passaic River could account for the 2,4,6,8-TCDT in the Newark Bay Estuary.

Combined hydrous ferric oxide and quaternary ammonium surfactant tailoring of granular activated carbon for concurrent arsenate and perchlorate removal.

Activated carbon was tailored with both iron and quaternary ammonium surfactants so as to concurrently remove both arsenate and perchlorate from groundwater. The iron (hydr)oxide preferentially removed the arsenate oxyanion but not perchlorate; while the quaternary ammonium preferentially removed the perchlorate oxyanion, but not the arsenate. The co-sorption of two anionic oxyanions via distinct mechanisms has yielded intriguing phenomena. Rapid small-scale column tests (RSSCTs) with these dually prepared media employed synthetic waters that were concurrently spiked with arsenate and perchlorate; and these trial results showed that the quaternary ammonium surfactants enhanced arsenate removal bed life by 25-50% when compared to activated carbon media that had been preloaded merely with iron (hydr)oxide; and the surfactant also enhanced the diffusion rate of arsenate per the Donnan effect. The authors also employed natural groundwater from Rutland, MA which contained 60 microg/L As and traces of silica, and sulfate; and the authors spiked this with 40 microg/L perchlorate. When processing this water, activated carbon that had been tailored with iron and cationic surfactant could treat 12,500 bed volumes before 10 microg/L arsenic breakthrough, and 4500 bed volumes before 6 microg/L perchlorate breakthrough. Although the quaternary ammonium surfactants exhibited only a slight capacity for removing arsenate, these surfactants did facilitate a more favorably positively charged avenue for the arsenate to diffuse through the media to the iron sorption site (i.e. via the Donnan effect).