Toxins are poisonous materials that interfere with vital metabolic processes to sicken or kill living organisms. Toxins can be either general poisons that kill many types of cells and organisms, or they can be extremely specific in their target and mode of action. Some are extremely reactive and can be lethal even in very dilute concentrations. Ricin , for instance, is a protein found in castor beans, and is one of the most toxic organic compounds known. Three hundred picograms (trillionths of a gram) injected intravenously is enough to kill an average mouse. That means that a few teaspoonsful of this substance, if divided and delivered in individual doses, could potentially kill all the mice in the world. Put another way, an amount of supertoxins that is invisible to the naked eye , if delivered in the right way, could be lethal.
An important principle of toxicology (the study of poisons) is that "the dose makes the poison." This dictum, first pronounced by the German physician Paracelcus in the sixteenth century, means that almost everything is dangerous at some level. Even compounds like table salt and water that are essential parts of our diet in reasonable amounts could make you very sick or even kill you if ingested in excess. Contrarily, even the most toxic compounds generally have a threshold level below which they are effectively harmless. Toxicity depends on the amount, time, mode of delivery of the toxin, as well as age and physiological state of the target organism . Among the most dangerous toxins are carcinogens (cause cancer ), mutagens (genetic damage), teratogens (birth defects ), and neurotoxins (nerve damage). Not all toxins are organic compounds. Many metals, such as lead , mercury, cadmium, and chromium, are highly poisonous as are elements such as arsenic and selenium, and minerals such as asbestos . Many people also assume that all human-made chemicals are poisonous, while all natural materials must be benign and wholesome. This is far from the truth. Many synthetic, industrial chemicals are relatively innocuous while perfectly natural materials, like some of those mentioned above, are extremely dangerous.
Toxic wastes, as their name implies, are unwanted materials known to be fatal to humans or laboratory animals at low doses or that are carcinogenic, mutagenic, teratogenic, or neurotoxic to humans or other life forms. Radioactive materials are considered especially dangerous, and their use and disposal is tightly regulated. Modern societies produce, use, and discard a vast array of toxic chemical substances. According to the Environmental Protection Agency (EPA), the United States generates about 265 million metric tons of officially classified hazardous and toxic wastes each year. This amounts to about one ton per year for every individual in the United States. Fortunately, most of this material is stored, recycled, converted to non-hazardous forms, or otherwise disposed of safely. Shockingly, however, at least 40 million metric tons (22 billion lb) of toxic and hazardous chemicals are released each year in the United States into the air, water, or land by unsound or illegal disposal methods. This represents an immediate health hazard to many people who live close to these disposal sites, and it may well represent a long-term health and ecological hazard to all of us. Scientists are discovering that persistent chemicals such as pesticides , dioxins, polychlorinated biphenyls (PCBs) , and mercury can be carried over long distances and accumulate to levels that appear to be causing worrisome health effects in wildlife and human populations thousands of miles and dozens of years from their original source.
The preferred hierarchy of waste management is to reduce, reuse, recycle, detoxify, and—only as a last resort—store safely. Reducing waste amounts means not making it in the first place. Often we can find alternative products or industrial processes that avoid creating a particular waste. Reuse means using a material for some other purpose or process. What is one person's unwanted waste can be a valuable resource for someone else. Recycling and detoxification involve chemical, biological, or physical treatments to change toxins into harmless forms that could be used in beneficial ways. Storage of toxic wastes requires specialized facilities in which materials are isolated from the environment by secure metal containers, impermeable plastic liners, compacted clay cushions, and other coverings that prevent materials from ever escaping. Permanent, secure waste disposal sites are both very expensive to construct as well as difficult to site and maintain.