The nature and chemistry of toxicants

An environmental toxicant can be defined as a substance that, in a given concentration and chemical form, challenges the organisms of the ecosystem and causes adverse or toxic effects. 

With the evolution and development of mankind and modem society, different man-made substances (anthropogenics or xenobiotics) have been added to the toxic panorama. Furthermore, many substances or products (e.g. metals) have been collected and concentrated for medical or industrial purposes and then redistributed in a manner that, today, is causing toxic exposure and harm to the biosphere. These processes have been accelerating during the last three centuries and millions of tons of xenobiotics have been distributed in the environment. 

Awareness of the problems with xenobiotics started to emerge in the middle of the 20th century and there is still ongoing discussion today. Much research has been performed, much knowledge has accumulated, various actions have been taken and numerous substances and processes have been banned or restricted. In parallel, however, many new chemicals and products have been developed, in some cases to replace those substances that were phased out as environmental hazards and in other cases as components of new materials or applications. These new substances are continuously added to the environment, in many cases without thorough toxic evaluation or risk assessment, and they pose new risks to 

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Fires in laboratories can be incredibly dangerous. Besides the danger of receiving bums, burning chemicals can produce toxic fumes and the risk of explosions. Fortunately, in introductory lab courses the nature and amounts of flammable substances are quite limited so that worst case scenarios and explosions are not likely. This section discusses the most common situations that might occur in introductory laboratory courses and explains the necessary background information to help you understand the risks of fires in laboratories. Section 2.2.1 presents more about fires in advanced chemistry and research labs where the hazards are likely to be more significant. 

As noted in Section 2.1, the relationship between the chemical nature of substances and their toxic effects is addressed by the topic of toxicological chemistry (Figure 2.13). In addition to their chemical properties, toxicological chemistry addresses the sources and uses of toxic substances and the chemical aspects of their exposure, fate, and disposal. The theory of toxicological chemistry is treated by the science of quantitative structure-activity relationships (QSAR), which relates the chemical nature of substances to their reactions in biological systems. ... 

Toxicological chemistry is the seienee that deals with the chemical nature and reactions of toxic substances, including their origins, uses, and chemical aspects of exposure, fates, and disposal. Toxieologieal chemistry addresses the relationships between the ehemieal properties and moleeular structures of molecules and their toxicological effects. Figure 23.5 outlines the terms discussed above and the relationships among them. 

MEGREC constitutes a platform for the development of research and training in green chemistry in the countries of the Mediterranean basin, with focus on water management, the exploitation of local natural resources, the production and use of fertilizers, and monitoring and reducing the presence of toxic compounds in the food chain. With a clear focus on priorities for local areas, but with the extended know-how of all the partners. 

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