Toxicology: Introduction, Principles, Tests, and Types
1. Introduction
Toxicology is defined as "the study of the adverse effects of chemical, physical or biological agents on living organisms and the ecosystem" and is based on the 16th century principle that any substance can be toxic if consumed in sufficient quantity.
In a general sense, the toxicity of a substance could be defined as the capacity to cause injury to a living organism. [1] A highly toxic substance will damage an organism if administered in very small amounts; a substance of low toxicity will not produce an effect unless the amount is very large. Thus, toxicity cannot be defined without reference to the quantity of a substance administered or absorbed, the way in which this quantity is administered (e.g. inhalation, ingestion, injection) and distributed in time (e.g. single dose, repeated doses), the type and severity of injury, and the time needed to produce that injury.
The vital factor that determines the amount of harm that a chemical compound produces is the quantity of the compound that comes in contact with a biologic system. This quantity of the compound is commonly called the "dose.". If a sufficient dose is taken into the body or comes in contact with a biologic mechanism, a harmful effect will be the consequence in the sense that the ability of that biologic mechanism to carry on a function is destroyed or seriously impaired. As the dose is increased from minimal to maximal levels, there is no sudden appearance of undesirable effects from any chemical agent. Rather, the response, whether it be beneficial or harmful, is a graded response and is related to progressive changes in dose. One of the most fundamental observations which may be made with respect to any biologic effect of a chemical agent is the relationship between the dose (or concentration) and the response that is obtained.
Thus, toxicology has developed into the study of the quantitative effects of chemicals on biologic tissue. Its focus is on the harmful actions of chemicals
Toxicology is defined as "the study of the adverse effects of chemical, physical or biological agents on living organisms and the ecosystem" and is based on the 16th century principle that any substance can be toxic if consumed in sufficient quantity.
In a general sense, the toxicity of a substance could be defined as the capacity to cause injury to a living organism. [1] A highly toxic substance will damage an organism if administered in very small amounts; a substance of low toxicity will not produce an effect unless the amount is very large. Thus, toxicity cannot be defined without reference to the quantity of a substance administered or absorbed, the way in which this quantity is administered (e.g. inhalation, ingestion, injection) and distributed in time (e.g. single dose, repeated doses), the type and severity of injury, and the time needed to produce that injury.
The vital factor that determines the amount of harm that a chemical compound produces is the quantity of the compound that comes in contact with a biologic system. This quantity of the compound is commonly called the "dose.". If a sufficient dose is taken into the body or comes in contact with a biologic mechanism, a harmful effect will be the consequence in the sense that the ability of that biologic mechanism to carry on a function is destroyed or seriously impaired. As the dose is increased from minimal to maximal levels, there is no sudden appearance of undesirable effects from any chemical agent. Rather, the response, whether it be beneficial or harmful, is a graded response and is related to progressive changes in dose. One of the most fundamental observations which may be made with respect to any biologic effect of a chemical agent is the relationship between the dose (or concentration) and the response that is obtained.
Thus, toxicology has developed into the study of the quantitative effects of chemicals on biologic tissue. Its focus is on the harmful actions of chemicals
References: 1. NAS/NRC, 1970; Sanockij, 1970 2 10. Zbinden, G. and Flury-Roversi, M. (1981). Significance of the LD50 test for toxicological evaluation of chemical substances. Archives of Toxicology 47, 77-99. 11. Balls, M. (1991). Why modification of the LD50 test will not be enough. Laboratory Animals 25, 198-206. 12. Balls, M. and Fentem, J.H. (1993). The on-going process to replace the LD50 test. Human Innovations and Alternatives 7, 544-547. 13. OECD (2001). Test Guideline 420. Acute Oral Toxicity – Fixed Dose Procedure 14 15. United Nations-Economic Commission for Europe (UN/ECE) (2003). Globally Harmonised System of Classification and Labelling of Chemicals (GHS). UN, New York and Geneva, 2003. 16. OECD (2001). Guidance Document on Acute Oral Toxicity Testing. Environmental Health and Safety Monograph Series on Testing and Assessment No. 24. 20. IPCS (1986). Principles and Methods for the Assessment of Neurotoxicity Associated with Exposure to Chemicals. Environmental Health Criteria Document No. 60. 23. OECD Monograph Series on Testing and Assessment No. 17, 1998 24