An evaluation of the capability of organic chemicals to mineralize is an important factor to consider when assessing their fate in the environment. Microbial degradation can convert a toxic chemical into an innocuous one, and vice versa, or alter the toxicity of a chemical. Moreover, primary biodegradation can convert chemicals into stable products that can be difficult to mineralize. In this paper, we present some new results obtained on the basis of a recently developed probabilistic approach to modeling biodegradation based on microbial transformation pathways. The metabolic transformations and their hierarchy were calibrated by making use of the ready biodegradability data from the MITI-I test and expert knowledge for the most probable transformation pathways. A model was developed and integrated into an expert software system named CATABOL that is able to predict the probability of biodegradation of organic chemicals directly from their structure. CATABOL simulates the effects of microbial enzyme systems, generates the most plausible transformation pathways, and quantitatively predicts the persistence and toxicity of the biodegradation products. A subset of 300 organic chemicals were selected from Canada's Domestic Substances List and subjected to CATABOL to compare predicted properties of the parent chemicals with their respective first stable metabolite. The results show that most of the stable metabolites have a lower acute toxicity to fish and a lower bioaccumulation potential compared to the parent chemicals. In contrast, the metabolites appear to be generally more estrogenic than the parent chemicals.

Animals↗

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In silico modelling of hazard endpoints: current problems and perspectives.

Major scientific hurdles in the acceptance of quantitative structure-activity relationships (QSAR) for regulatory purposes have been identified. First, when quantifying important features of chemical structure complexities of molecular structure have often been ignored. More mechanistic modelling of chemical structure should proceed on two fronts: by developing a more in-depth understanding and representation of the multiple states possible for a single chemical by achieving greater rigor in understanding of conformational flexibility of chemicals; and, by considering families of activated metabolites that are derived in biological systems from an initial chemical substrate. Second, QSAR research is severely limited by the lack of systematic databases for important risk assessment endpoints, and despite many decades of research, the ability to cluster reactive chemicals by common toxicity pathways is in its infancy. Finally, computational tools are lacking for defining where a specific QSAR is applicable within the domain (universe) of chemical structures that are to be regulated. This paper describes some of the approaches being taken to address these needs. Applications of some of these new approaches are demonstrated for the prediction of chemical mutagenicity, where considerations of both molecular flexibility and metabolic activation improved the QSAR predictability and interpretations. Lastly, the applicability domain for a specific QSAR predicting estrogen receptor binding is presented in the context of a mechanistically-defined chemical structure space for large heterogeneous chemical datasets of regulatory concern. A strategic approach is discussed to selecting chemicals for model improvement and validation until regulatory acceptance criteria for risk assessment applications are met.

Endpoint Determination↗

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[Dyskeratosis of the oral mucosa among workers in an environment with occupational noxae].

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Bulgaria↗

PubMedDate not supplied

[Some problems in the treatment of abrasio dentis].

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Crowns↗

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[Lymphosarcoma--nodular form, localized in cervical region].

The authors describe three patients with lymphosarcoma--nodular form for a 13-year period, involving the cervical lymph nodes. The rarity of the disease is emphasized as well as the difficulties in the differential diagnosis with the chronic sialadenitis and lymphopathies. The clinical interpretation of the disease is difficult because of the lack of specificity in the clinical course and paraclinical studies. The accurate diagnosis is only possible by a pathohistological study. The authors underine that the nodular form of lymphosarcoma should be given consideration in the differential diagnosis of the diseases of lymph apparatus in cervical region.

Adolescent↗

PubMedDate not supplied

[Isolation of dental pulp from the deleterious effect of composition material by varnish films of dentin Adhesit and cyanacrylate B-100--experimental-morphological studies].

The protective properties of varnish films of dentin adhesit and cyanacrylate B-10 versus the toxic action of the compositional material have been studied in experiments on dogs. For that purpose, 45 cavities, class V with size 2:4; 1.5 mm were made. Dentin was isolated by a film from the experimental materials. The control group of teeth were made inlays from phosphate cement. The histopathological reaction of the dental pulp to the materials on trial was determined on day 3, and 1 and 3 months of the beginning of the experiment. No changes, characteristic for acute or chronic inflammatory reaction were established. The good, both immediate and late, results from the experiment are a good reason to admit that the adhesives obtained are suitable for varnish isolation of dental defects with superficial and moderate depth and could be applied with success in the clinical practice under the compositional material. They have no effect on the final aesthetic effect of the obturations.

Acrylic Resins↗