TCBTs

Recently van Haelst et al. [241, 242] have determined the bioconcentration factors of single TCBT isomers in zebra mussels Dreissena polymorpha ) and in adult female guppies (Poecilia reticulata). The bioconcentration factors on a wet weight basis (BCF ) and on a lipid basis (BCFl) of eight tetrachlorobenzyltoluenes (TCBTs) isomers in mussels are compiled in Table 14. The melting points, water solubilities, and the n-octanol/water partition coefficients (log... 

Kq ) of the investigated TCBTs are presented also in Table 14. The BCF values of TCBTs isomers in the mussels ranged from ca. 27,000 to 154,900 and the BCFl values ranged from ca. 620,000 to 3,560,000. 

Fig. 15. Predicted metabolites of some tetrachlorobenzyltoluene (TCBT) isomers with supposed estrogenic and/or other endocrine-disrupting effects in fish and mammals including human...

Tetrachlorobenzyltoluenes (TCBT) manufactured by Prodelec, France have been patented as substitutes for PCBs in dielectric and cooling materials of capacitors and transformers and in hydraulic fluids [78-82]. An important application of 100% TCBT mixture (Ugilec 141) was for hydraulic linkages in... 

There are 96 possible isomers (congeners) of TCBTs. Based on analogy to PCBs, Ehmann and Ballschmiter have developed a systematic numbering for the isomers [84]. Structures and numbers of the six major components of Ugileg 141 are shown below. 

Because 3,5-dichlorotoluene was formed only in very small amounts in the first step of technical TCBT synthesis, the number of relevant isomers in the final Ugilec 141 product was 70. Structures of these congeners were identified by syntheses of defined TCBT reference mixtures and using GC with three phases of differing polarity [84]. 

TCBTs are relatively persistent and non-flammable (and therefore useful in hydraulic oils). Pyrolysis in a closed system for two days in the presence of hydrogen peroxide at 300 °C produced as main components chlorinated benzo-phenones, fluorenes, fluorenones, xanthenes, and xanthones. Polychlorodiben-zofurans (PCDF) and polychlorodibenzo-p-dioxins (PCDD) were formed in much lower concentrations than from PCB product Pyralene T1 under identical conditions [84]. In pyrolysis at 450-700 °C with excess oxygen TCBTs produce more PCDFs and PCDDs. In parallel with the behavior of PCBs, PCDFs are formed in significantly higher amounts than PCDDs from PCBTs [86],... 

TCBTs are coextracted with PCBs and other lipophilic substances in standard methods of analyses from different environmental matrixes. Waste oil samples were homogenized by ultrasonic shaking, water removed, sample dried by filtration over anhydrous sodium sulfate, and diluted with n-hexane [85]. Water samples (1000 ml) were mixed with 50 ml hexane by Turrax (11,000 rpm). The hexane phase was then dried with anhydrous sodium sulfate [86]. Laboratory water sample (1000 ml) was extracted with three portions of hexane (100 ml, 60 ml, and 60 ml) [87]. Another water sample (50 ml) from laboratory exposure experiments was liquid-liquid extracted with 9 ml of hexane [88]. 

For water, rat tissue, and fish samples, cleanup with deactivated Florisil (magnesium silicate containing 5% water) was performed. Column length was 300 mm and inner diameter 30 mm. A maximum of 0.6 g of lipidic sample per 20 g of Florisil was applied. The upper portion of column was packed with anhydrous sodium sulfate. TCBTs were eluted with 150 ml of hexane. A second elution with 100 ml of hexane/dichloromethane (85/15) was performed to determine whether any TCBT had been retained in the column. Both eluates were concentrated prior to chromatographic analyses [87]. 

In analyses of extract from freeze-dried fish [89] gel chromatography on Bio-Beads S-X3 with cyclohexane/ethyl acetate (1/1) was used for removal of neutral fat. Then adsorption column chromatography on silica gel (1.5% water) according to the multi-residue procedure of Specht and Tillkes [93] was applied. Elution with n-hexane separated TCBTs and PCBs from the main portion of organochlorine pesticides and other more polar compounds. The hexane extract was evaporated to 0.5 ml for GC-MS determination [89,90]. 

Capillary gas chromatography must be used to achieve sufficient separation for TCBTs in product, waste, and environmental samples. Coatings DB-1701 (85% dimethyl, 15% cyanopropylsilyl) and CP-Sil 88 (100% cyanopropyl) gave better separation than DB-5 (95% dimethyl, 5% phenyl) [84]. Retention indices of twelve TCBT isomers are listed in Table 5 together with melting points, solubilities in water, and log Kows of nine pure compounds. 

EC-detection was useful for analysis of TCBT formulation or samples from laboratory bioaccumulation experiments [87, 88, 92-94]. However, ECD appeared to be unsuitable for environmental analyses because its responses varied greatly [84], interference with PCBs was difficult to avoid, and sensitivity of... 

ECD to TCBT isomers was a factor of two lower than for the corresponding tetra- and higher chlorinated PCB congeners [85]. Therefore, most practically successful TCBT analyses were done by GC-MS, especially with SIM mode [84-86,89-91]. The most useful EI-MS ions of TCBT are those of (high resolution) m/z (Int%) values 319.9508(46.5), 317.9537(60.0), 284.9819(97.1), and 282.9848(100), two M+ and two (M-C1)+ peaks, respectively. Model electron impact mass spectrum (upper part) of a TCBT isomer is presented in Fig. 7. 

Fig. 7. Simulated (high resolution m/z values calculated, intensity ratios of the highest peaks taken from [89]) upper part of mass spectrum of a TCBT isomer...

There the intensity ratios between ion clusters were taken from experimental measurement of low resolution MS [89], but intensity ratios within each isotope cluster was calculated as the sum of binary distributions of the natural abundance of each isotope involved. High resolution m/z values of major peaks (for HRMS) were calculated as sums of exact masses of isotopes. This simulation method (ISOCLUST) developed by the present author (J. Paasivirta) is operable with a desk computer. Low resolution electron impact MS is suitable for TCBT determinations, especially by selected ion monitoring (SIM). In this mode, focusing to four ions, m/z 213.0,283.0,285.0, and 320.0, which are not interfered with by PCBs is recommended. In a TCBT study, quantitative results were based on their sum intensity for better signal to noise ratio [91]. 

Immunotoxicity of TCBTs to mammals has been established. The tetanus antibody response was reduced in male rats after six weeks feeding with 200 ppm of TCBT, and in both males and females fed with 1000 ppm [92]. 

Enzyme induction experiments in male and female Wistar rats with administration of TCBT (Ugilec 141) produced a weak increase of total Cytochrome P-450 (< 1.9-fold). Benzhepthamine-AT-demethylase rose up to 3.5-fold, but benzo(a)pyrene hydroxylase (AHH) and ethoxyresorufin-O-deethylase (EROD) inductions were very low. Instead, the latter two inductions were markedly high with TCBT pyrolysate. TCBTs were concluded to be the pheno-barbital (PB) type of inducer, while pyrolysis products contained 3-methyl-colanthrene (3-MC) inducers of the dioxin type. The authors recommended use of TCBTs only in sealed systems [101]. 

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