Comparative toxicity of 1,2,3,4-, 1,2,4,5-, and 1,2,3,5-tetrachlorobenzene in the rat: results of acute and subacute studies

A continuous in silico learning strategy to identify safety liabilities in compounds used in the leather and textile industry

There is a widely recognized need to reduce human activity's impact on the environment. Many industries of the leather and textile sector (LTI), being aware of producing a significant amount of residues (Keßler et al. 2021; Liu et al. 2021), are adopting measures to reduce the impact of their processes on the environment, starting with a more comprehensive characterization of the chemical risk associated with the substances commonly used in LTI. The present work contributes to these efforts by compiling and toxicologically annotating the substances used in LTI, supporting a continuous learning strategy for characterizing their chemical safety. This strategy combines data collection from public sources, experimental methods and in silico predictions for characterizing four different endpoints: CMR, ED, PBT, and vPvB. We present the results of a prospective validation exercise in which we confirm that in silico methods can produce reasonably good hazard estimations and fill knowledge gaps in the LTI chemical space. The proposed protocol can speed the process and optimize the use of resources including the lives of experimental animals, contributing to identifying potentially harmful substances and their possible replacement by safer alternatives, thus reducing the environmental footprint and impact on human health.

Trapping analytes into dynamic hot spots using Tyramine-medicated crosslinking chemistry for designing versatile sensor

HYPOTHESIS

Due to the intrinsic nature of the surface-enhanced Raman scattering (SERS), the detection of molecules with weak binding affinities toward metal substrates is critical for development of a universal SERS sensing platform. We hypothesized the physical trapping of small pesticide molecules for active hot spot generation using tyramine-mediated crosslinking chemistry and silver nanoparticles (Ag NPs) enhances SERS detection sensitivity.

EXPERIMENTS

Tyramine-mediated crosslinking chemistry for sensor application was validated by ultraviolet-visible absorption spectroscopy, scanning electron microscopy, dynamic light scattering, and Raman spectroscopy. SERS sensing platform using tyramine-mediated crosslinking reaction was systematically studied for detection of 1,4-dyethylnylbenzene as a model analyte. This sensor system was applied to detect two other pesticides, thiabendazole and 1,2,3,5-tetrachlorobenzene, which have different binding affinities toward metal surfaces.

FINDINGS

The SERS signal of 1,4-dyethylnylbenzene obtained using this sensor system was 3.6 times stronger than that obtained using the Ag colloidal due to the nanogap of approximately 1.3 nm within the generated hot spots. This sensor system based on tyramine-mediated crosslinked Ag NPs was evaluated as a promising tool to achieve a solution based sensitive detection of various pesticide molecules that cannot be adsorbed on the surfaces of typical SERS substrates such as metal nanoparticles.

Cross-Reactivity between Chemical Antibodies Formed to Serum Proteins and Thyroid Axis Target Sites

In some instances, when chemicals bind to proteins, they have the potential to induce a conformational change in the macromolecule that may misfold in such a way that makes it similar to the various target sites or act as a neoantigen without conformational change. Cross-reactivity then can occur if epitopes of the protein share surface topology to similar binding sites. Alteration of peptides that share topological equivalence with alternating side chains can lead to the formation of binding surfaces that may mimic the antigenic structure of a variant peptide or protein. We investigated how antibodies made against thyroid target sites may bind to various chemical–albumin compounds where binding of the chemical has induced human serum albumin (HSA) misfolding. We found that specific monoclonal or polyclonal antibodies developed against thyroid-stimulating hormone (TSH) receptor, 5′-deiodinase, thyroid peroxidase, thyroglobulin, thyroxine-binding globulin (TBG), thyroxine (T4), and triiodothyronine (T3) bound to various chemical HSA compounds. Our study identified a new mechanism through which chemicals bound to circulating serum proteins lead to structural protein misfolding that creates neoantigens, resulting in the development of antibodies that bind to key target proteins of the thyroid axis through protein misfolding. For demonstration of specificity of thyroid antibody binding to various haptenic chemicals bound to HSA, both serial dilution and inhibition studies were performed and proportioned to the dilution. A significant decline in these reactions was observed. This laboratory analysis of immune reactivity between thyroid target sites and chemicals bound to HSA antibodies identifies a new mechanism by which chemicals can disrupt thyroid function.

Differential acute toxicity of tetrachlorobenzene isomers to oligochaetes in soil and water: application of the critical body residue concept

The acute, lethal potency of the 1,2,3,4-, 1,2,4,5- and 1,2,3,5-tetrachlorobenzene isomers was compared in the terrestrial and aquatic oligochaetes Eisenia andrei and Tubifex tubifex. 1,2,4,5-TeCB was neither lethal, nor produced any perceptible adverse effects, at lipid normalized concentrations predicted to be lethal according to the well-established critical body residue concept. If a narcotic is defined as a substance capable of inducing narcosis, rather than a substance displaying certain physical or chemical properties (e.g., log K(ow)), then we do not believe these findings challenge the critical body residue because by the former definition, 1,2,4,5-tetrachlorobenzene is not a narcotic.

Use of a medium-term liver focus bioassay to assess the hepatocarcinogenicity of 1,2,4,5-tetrachlorobenzene and 1,4-dichlorobenzene

1,2,4,5-Tetrachlorobenzene (TeCB) and 1,4-dichlorobenzene (DCB) are important environmental contaminants that have been used extensively for a variety of industrial applications. Limited data are available in the literature regarding the carcinogenicity of TeCB. DCB has been shown to cause renal adenocarcinomas in rats and hepatic adenomas and carcinomas in mice at high doses in a 2-year study. In the studies presented here, we report that TeCB can promote the formation of preneoplastic foci and DCB cannot in a medium-term initiation/promotion assay. These results suggest that TeCB is a liver tumor promoter and that DCB is not at fairly low doses (0.1 and 0.4 mmol/kg per day).

Body distribution and endocrine toxicity of hexachlorobenzene (HCB) in the female rat

Hexachlorobenzene (HCB) residue levels in dosed rats (50.0 mg kg-1 body wt.day-1, n = 9) were significantly (P < 0.05) greater in the periovarian fat compared to the thyroid gland. Hexachlorobenzene residue levels were significantly (P < 0.05) greater in the thyroid versus the adrenal and ovary. Ovarian HCB residue levels were greater than those found in the thymus, liver and lung. Serum thyroxin (T4) and the free T4 index (FTI) were significantly (P < 0.05) suppressed in HCB-treated rats compared to the control group (n = 8). In contrast, no significant differences in serum concentrations of oestradiol (E2), progesterone (P4) or percentage triiodothyronine uptake (%T3) were observed, thus suggesting an HCB-induced hypothyroid-like state. In a second experiment, adult female Sprague Dawley rats (n = 16) were dosed as above and superovulated with pregnant mare serum gonadotrophin (PMSG, 10 IU s.c.) and human chorionic gonadotrophin (hCG, 20 IU s.c.). Circulating levels of P4 were significantly (P < 0.05) elevated compared to the control group (n = 8). The %T3 uptake and serum T4 levels were significantly (P = 0.05) suppressed compared to controls. Hexachlorobenzene treatment had no effect on circulating levels of E2 or on the FTI. These results suggest that HCB-induced changes found in the spontaneously cycling rat are augmented by ovulation induction strategies. We also conclude that HCB concentrates in the endocrine tissues in addition to the fat.

Oral toxicity of trichlorobenzyl chloride and its acid derivative

The acute rat oral LD50 of 2,4,6-Trichlorobenzyl chloride (TCBC) was determined to be 3075 mg/kg. When male and female rats were administered 1500 and 3000 ppm TCBC in the diet for 3 weeks, marked retardation in weight gain was observed. Reductions in food consumption were noted in both groups of treated male, but not female, rats. All blood chemistry and urinalysis parameters including those indicative of liver injury, were within the range of normal limits. Gross necropsy revealed pale livers in all high-dose rats and the majority of low-dose animals. Gross observations correlated with observation of degenerative hepatic changes (irregularity of cell and nuclear size, cord pattern, edema and cytoplasmic alterations) following microscopic evaluation. Rats and dogs administered up to 100 ppm trichlorobenzoic acid (TCBA) in the diet for 90 days exhibited no effects considered related to treatment.

Metabolism of 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetrachlorobenzene in the rat

Adult male rats were given orally single doses of 14C-labeled 1,2,3,4-, 1,2,3,5-, or 1,2,4,5-tetrachlorobenzene (TCB) at 10 mg/kg body weight, and were housed in individual metabolism cages to collect urine and feces for radioassay. For 1,2,3,4- and 1,2,3,5-TCB, approximately 46-51% of the doses were excreted in urine and feces within 48 h after administration. During the same period only 8% of the administered 1,2,4,5-tetrachlorobenzene was excreted. Analysis of urine indicted that the tetrachlorobenzenes were biotransformed to a number of polar compounds. The metabolites for each of the three TCBs in decreasing order of quantities were as follows: 1,2,3,4-TCB, to 2,3,4,5- and 2,3,4,6-tetrachlorophenol and a trace of tetrachlorothiophenol and 2,3,4-trichlorophenol; 1,2,3,5-TCB, to 2,3,4,6-tetrachlorophenol, isomeric hydroxythrichlorothiophenols, and a trichlorophenol; 1,2,4,5-TCB, to 2,3,5,6-tetrachlorophenol, tetrachloroquinol, and a trichlorophenol.

Toxicity of 1,2,3,4-, 1,2,3,5- and 1,2,4,5-tetrachlorobenzene in the rat: results of a 90-day feeding study

Tetrachlorobenzenes (TCB) are industrial chemicals which have been used as intermediates for chemical synthesis and for electrical insulation. Recently TCB residues have been found in Great Lakes fish. The present study was designed to determine the subchronic toxicity of these compounds. Groups of 15 male and 15 female rats were fed diets containing 0, 0.5, 5.0, 50 or 500 ppm of each of 1,2,3,4-, 1,2,3,5- and 1,2,4,5-TCB for 13 weeks. Rats fed 500 ppm 1,2,4,5-TCB exhibited significant increases in liver and kidney weight. 1,2,4,5-TCB at the highest dose level caused a significant increase in serum cholesterol levels. Hepatic microsomal aminopyrine demethylase and aniline hydroxylase activities were induced by this compound at 50 and 500 ppm in the males, and 500 ppm in the females. Moderate to severe histological changes occurred in the liver and kidney of rats fed the three TCB isomers but the 1,2,4,5-isomer caused the most severe lesions. 1,2,4,5-TCB accumulated in fat and liver in a dose-dependent manner. Results indicate that 1,2,4,5-TCB is the most toxic isomer of the three and accumulates in liver and fat in a dose-dependent manner.