In the world as a whole there are three broad groups of diseases that account for a highly significant proportion of illness and death: communicable diseases; degenerative diseases; and neoplastic diseases (cancers). The relative frequency of each of these varies according to the socio-economic state of a country and the condition of its environment. Communicable diseases account for a large proportion of illness and death in developing countries, whereas infant mortality due to communicable diseases is extremely low in the developed world. On the other hand, degenerative diseases (such as those of the heart and circulatory system) and neoplastic diseases (cancer) account for a large proportion of illness and death in developed countries, where a significant proportion of the adult population becomes exposed to environmental factors that produce cancer and degenerative diseases. In the developing world, however, where infant mortality is relatively high, a much smaller proportion of people survive long enough to be exposed to agents capable of producing cancer and degenerative conditions. Even those who survive into adulthood may escape because the agents may not be present in the environment. It should be noted that these diseases are nevertheless widespread in the developing countries, but statistics on mortality and morbidity due to them are rarely available.

Human activities inevitably and increasingly introduce material and energy into the environment; when that material or energy endangers or is liable to endanger man's health, his well-being or his resources, indirectly or directly, it is called a pollutant. A substance may be considered a pollutant simply because it is in the wrong place, at the wrong time, and in the wrong quantity.

Pollutants can affect man with direct effects such as: acute effects from exposure to a toxic pollutant reaching man through air, water or food; long-term effects due to prolonged exposure to a pollutant at levels lower than those giving rise to overt toxic effects; synergistic interaction between pollutants or between a pollutant and malnutrition or disease; genetic effects that are manifested in future generations. Indirect effects on man may result from reduction of the food supply or deterioration of the environment. Such effects include: damage to plants and animals; disruption of ecological cycles such that a previously harmless species becomes a pest; damage to the human habitat (air pollutants that destroy forests and corrode buildings); water pollutants that destroy the recreational value of inland waters; alteration of the global climate (this is considered to be a future threat).

As modern dependence on chemicals for societal benefits has grown, the potential for widespread pollution or contamination has also increased. There are now some 70,000 chemicals on the commercial market, and many of these are currently used and released into the environment with little or no knowledge of their potential long-range effects. It is estimated that 1,000 new chemical enter the market each year. There are five potential sources of pollution from chemicals: (a) Chemical products themselves, such as CFCs, pesticides and nitrate fertilizers; (b) Hazardous waste and its treatment; (c) Chemical emissions, such as from factories, power plants and automobiles; (d) Accidents, such as the fire in 1986 that destroyed a chemical store in Switzerland belonging to Sandoz; and (e) Transport of chemicals.

Chemical agents of warfare include all gaseous, liquid or solid chemical substances which might be employed because of their direct toxic effects on man and animals. (This excludes substances whose effect is primarily physical, such as incendiary weapons, high explosives and smoke). Chemical weapons also include the chemical's precursors, the munitions and devices designed to deliver them, and any equipment specifically designed for their use in warfare.

Nerve agents (chemicals of the same family as organophosphorus insecticides) are the most lethal of the classical chemical warfare agents, killing by poisoning the nervous system and disrupting bodily functions. Blister agents (such as mustard gas) burn and blister the skin (causing more casualties than any other agent in the first world war). Vesicants are blistering and tissue-injuring agents which produce injuries similar to burns, although the mechanism behind the injury is different. Choking agents (such as phosgene) are highly volatile liquids. Toxins (such as mycotoxins and botulin toxin) are biological substances chemical substances produced biologically (although many of them have also been synthesized) which are very highly toxic. Tear gas and harassing agents are sensory irritants causing pain in the eyes, tear flow, and severe irritation of the upper respiratory tract (and have been widely used as riot control weapons); they can also cause skin irritation, nausea and vomiting. Psycho-chemicals are drug-like chemicals intended to cause temporary mental derangement, including psychosis. Cyanides (blood agents) cause headaches, weakness, disorientation and nausea in low doses; higher doses are acutely lethal causing circulatory effects, seizures and respiratory and cardiac failure. Incapacitating agents produce physiologic or mental effects, or both. They render individuals incapable of performing normal activities. DZ (3-quinuclidinyl benzilate) is the most commonly used. It is pharmacologically related to anticholinergic drugs and is present within some over-the-counter sleeping medications. Tear gases are used primarily for riot control and cause irritation to the eyes, respiratory tract, and skin. Herbicides may also be used to poison or defoliate plants.

The consumption of animal flesh (whether meat, fowl or fish) or the use of animal products (leather goods, products of bone-processing, eggs and cheese) is unethical, unaesthetic, uneconomic, and without nutritional justification. It may be considered unethical because human beings should not needlessly kill sentient animals. The consumption of animal flesh is not the most economic method of obtaining the highest yield of nutritional products from agricultural land. The economic and social costs of meat consumption include hugely inefficient use of freshwater and land, heavy pollution from livestock faeces, rising rates of heart disease and other degenerative illnesses and spreading destruction of forests.