Toxicity of chemicals

Principles andMethods for Evaluating the Toxicity of Chemicals, Part 1, Environmental Health Criteria No. 6, World Health Organi2ation, Geneva,... 

Statement by the Committee of Toxicity of Chemicals in Food, Consumer Products and the... 

In a 1996 review, the Committee of Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) estimated the intake of isoflavones from soya-milk to be approximately 4 mg/kg/day over the first 4 months of life. This is greater than that associated with hormonal effects in premenopausal women, but the COT nonetheless supported the existing Department of Health s advice that... 

The LC50 is the lethal concentration of chemical (e.g. in air or water) that will cause the death of 50% of the sample population. This is most appropriate as an indicator of the acute toxicity of chemicals in air breathed (or in water, for aquatic organisms). Table 5.11 illustrates the use of LD50 values to rank the toxicity of substances. 

Objective Provide information on the identity, quantity, location, physical properties, and toxicity of chemicals at sites within the planning district. 

The toxicity of chemicals to living organisms is determined by the operation of both toxicokinetic and toxicodynamic processes (Chapter 2). The evolution of defense mechanisms depends upon changes in toxicokinetics or toxicodynamics or both, which will reduce toxicity. Thus, at the toxicokinetic level, increased storage or metabolic detoxication will lead to reduced toxicity at the toxicodynamic level, changes in the site of action that reduce affinity with a toxin will lead to reduced toxicity. 

Toxicity is the outcome of interaction between a chemical and a living organism. The toxicity of any chemical depends on its own properties and on the operation of certain physiological and biochemical processes within the animal or plant that is exposed to it. These processes are the subject of the present chapter. They can operate in different ways and at different rates in different species—the main reasons for the selective toxicity of chemicals between species. On the same grounds, chemicals show selective toxicity (henceforward simply selectivity ) between groups of organisms (e.g., animals versus plants and invertebrates versus vertebrates) and also between sexes, strains, and age groups of the same species. 

There do not appear to be any published studies to date of ANNs being used for the prediction of drug toxicity, although they have been used for the prediction of toxicity of chemicals such as pesticides [68, 69]. 

The need for rapidly accessible estimation of toxicity has led to the development of software and other algorithms that will generate estimations of toxicity, usually for organic compounds [79] such methodology is termed an expert system, which has been defined [34] as any formalised system, not necessarily computer-based, which enables a user to obtain rational predictions about the toxicity of chemicals. Essentially, expert systems fall into two classes— those relying on statistical approaches and those based on explicit rules derived from human knowledge. 

Usually aquatic toxicity of chemicals with general narcosis mechanism of action is described by the octanol/water partition coefficient [73]. However, log is a composite descriptor which has components of molecular volume and H-bond acceptor terms. Raevsky and Dearden [74] therefore used molecular polarizabihty (as a volume-related term) and the H-bond acceptor factor instead of log to model aquatic toxicity (log LC50) to the guppy for 90 chemicals with general narcosis mechanisms. This excellent correlation has statistical criteria better than that obtained for the same data using log Pofy, ... 

Adams WJ, Ziegenfuss PS, Renaudette WJ, et al. 1986. Comparison of laboratory and field methods for testing the toxicity of chemicals sorbed to sediments. In Poston TM, Purdy R, eds. Aquatic toxicology and environmental fate, Vol. 9. American Society for Testing and Materials Special Technical Publication 921,494-513. 

Frazier JM (1990) Multiple endpoint measurements to evaluate the intrinsic cellular toxicity of chemicals. J Mol Cell Toxicol 3 349-357... 

Encouraged by recent legislations all over the world aimed to protect human health and environment, alternative methods have proved their abilities to assess the toxicity of chemicals. Hence, a possible solution to the characterization of the toxicological and ecotoxicological risk of the chemicals could be represented by the application of in silico and in vitro techniques. 

Witzmann FA et al. Toxicity of chemical mixtures proteomic analysis of persisting liver and kidney protein alterations induced by repeated exposure of rats to... 

Quantitative Structure-Activity Relationship studies search for a relationship between the activity/toxicity of chemicals and the numerical representation of their structure and/or features. The overall task is not easy. For instance, several environmental properties are relatively easy to model, but some toxicity endpoints are quite difficult, because the toxicity is the result of many processes, involving different mechanisms. Toxicity data are also affected by experimental errors and their availability is limited because experiments are expensive. A 3D-QSAR model reflects the characteristics of... 

Munro, N.B., S.S. Talmage, G.D. Griffin, L.C. Waters, A.P. Watson, J.F. King, and V. Hauschild. The Sources, Fate and Toxicity of Chemical Warfare Agent Degradation Products." Environmental Health Perspectives 107 (1999) 933-974. 

Johnson, W.A. and M.T. Finley. 1980. Handbook of acute toxicity of chemicals to fish and aquatic invertebrates. U.S. Fish Wildl. Serv. Resour. Publ. 137. 98 pp. 

Norup, B. 1972. Toxicity of chemicals in paper factory effluents. Water Res. 6 1585-1588. 

Kenaga EE. 1983. Predictability of chronic toxicity from acute toxicity of chemicals in fish and aquatic invertebrates. Environ Toxicol Chem 1 347-358. 

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