What do we need to know about these threats to health, and even to life? We need to know how we may be exposed to it, how large or small a dose we are exposed to, whether the exposure is continuous or only occasional, how fast the toxic affects the body, and how fast it is naturally eliminated. The personality of each toxic may also be of interest.
Radioactive Strontium 90 acts chemically like Calcium, so that any ingested Sr90 tends to be incorporated in the bone, as is calcium, where the emitted radioactivity can destroy the hemoglobin-forming cells in the marrow of the bone. The only source of Sr90 was atmospheric testing of nuclear bombs, and since that has been stopped by international agreement, it is nothing to worry about. Radioactive Caesium 137 acts chemically like sodium and it enters the blood stream; fortunately it is rapidly removed in the urine. Cs137 is produced in nuclear power reactors and is like to pose a threat to people only when it accidentally leaks out into the atmosphere, as from the Fukushima Japanese nuclear reactor, and earlier Chernobyl Soviet nuclear reactor. Radioactive Iodine 131 also is expelled from nuclear reactor accidents. Its danger is to the thyroid gland, where it is absorbed and incorporated in a hormone, and induces cancers. Radon is a gas emanating from the radioactive decay of radium, uranium, and thorium in earth minerals. The main, and rather rare, exposure is from radon gas leaking into homes through the underlying ground. Due to the extremely small quantities that may be encountered, negative health effects occur only after decades of exposure. You can purchase a kit to test for radon in your home (do a Google search).
Everyone has heard of Carbon Monoxide because it is a favorite stuff for suicide. Merely run a car in a closed garage and the person will be asphyxiated by a build up of carbon monoxide. It acts by displacing oxygen from the red corpuscles of the blood, so that a person dies from lack of oxygen. Its effect is fast and, fortunately, reversible, so that it will be eliminated from the body after breathing good air for about five hours.
Arsenic is an interesting character with a long history as a poison. It has been used since ancient times by kings and politicians to kill an adversary. With a sufficiently large dose (about a gram, the size of a pea), death occurs quickly. In addition, extremely small doses ingested over a long time induce wide-spread cancers, as was documented in Bangladesh where people had been drinking well-water contaminated with arsenic from minerals in the water table.
The last class of toxic substances is POPs. These are typically chlorinated organic molecules, such as many pesticides and flame retardants, that not only persist a long time in the environment (thus contaminating the whole Earth), but persist a long time in the body. That is, they are eliminated only slowly from the body, and therefore, with frequent or continuous exposure, accumulate. They also accumulate and build up in the food chain, increasing in concentration from plankton to small oceanic crustaceans (e.g., krill) to anchovies and sardines to mackerel to salmon and tuna to dolphins, orcas, and whales. The bottom line for people is that continuous exposure to even very small quantities of POPs chemicals is a health hazard because they will accumulate in the body. They accumulate because they are only slowly eliminated from the body by the liver and kidneys. For example, infamous DDT is degraded by the liver to a related molecule, which persists for years before it is eliminated. POPs act only slowly on a person’s health, typically requiring decades before inducing a cancer or damaging the nervous system.
This is complex information and surely a person does not have to understand or remember it. The most important part is to know how to avoid exposure to different types of toxic substances. It may also be useful to know something of the factors that affect the degree of hazard, and the unique personalities of the various toxics.