Oceanography

There is a great variety of natural sources-minerals in rocks and soils, as well as artificial ones-pesticides, chemical manufacturing processes, burning of coal and oil, old thermometers, barometers, radio and television tubes, antifouling paint. Although the total tonnage of mercury exposed to air and water is small, compared to an element like iron, serious local difficulties can develop where disposal is in places where methyl mercury can be formed and work its way into the food chain.

The mercury poisoning that occurred at Minimata Bay in Japan is now a widely known incident. Inorganic mercury was dumped into the bay as waste from a large chemical plant. In 1953 a strange nerve disease appeared among residents of the area. It was traced to methyl mercury-bearing fish from the waters of the bay into which mercury wastes had been dumped. Even though the dumping practice has been stopped, the bottom muds still contain mercury, which can be converted to methyl mercury, released to the water, and so make its way from fish to man.

On the other hand, common salt, found in most waters, can be tolerated well beyond the tenth of one percent that limits the usual natural mixture of dissolved minerals. Even sea water, which contains 35,000 ppm dissolved salt, can be drunk slowly in small amounts, but the upper limit of salt content in water supplies for constant use is about 1,000 ppm, with 500 ppm being preferable. In arid countries much higher salt content is tolerated. In parts of North Africa drinking water with up to 3,000 ppm salts is used.

If a mineral is required for maintenance of an organism and is not provided in adequate amounts in foods, it must be artificially supplemented or be present in water. The classic example is that of iodine. Insufficient iodine causes an enlargement of the thyroid gland called goiter. In Midwestern United States the water supplies are low in iodine. Goiter was a widespread disease there until it became common practice to add iodine to table salt. In correcting iodine deficiency, it was simple to do it in a way that permitted each person or family to make a decision about supplementing iodine intake by using iodized salt. An alternative method would have been to increase the iodine in the public water supplies, in which case the consumers would have had no choice but to be medicated. We see in the iodine example the basis for one of the most controversial ethical questions of the day. Any treatment of water necessarily adds or removes something and so constitutes a mass medication in the broad sense. The kinds of water treatment that are generally acceptable involve addition or subtraction of substances that are absolutely necessary for general water use. The additions should be harmless, ideally without effect on color, taste, odor, or on any use to which the water is put. This ideal is not attainable, but basic water treatment-aeration, filtration, and chlorination -comes close to fulfilling these goals.

The great fluoride battle still rages; it has not been possible to solve it as easily as the iodine situation. The limits on the concentrations of fluoride that are so low that tooth decay is not inhibited and those that are so high that teeth are damaged are narrow; one half a part per million is too little and two parts per million are too much.

Even these narrow limits are not generally applicable; some people drink more water than others and thus get more fluoride. Especially in the case of children the amount of water drunk is generally directly correlated with the weather. One part per million fluorides may be too much for one person and two parts may be too little for another. To make the situation even worse, most of the direct benefits of fluoridation are restricted to the under fourteen age group. And finally, no entirely satisfactory optional substitute for water in controlling fluoride intake has been developed.

Silica, one of the most common constituents of ordinary rocks, is a major dissolved mineral in many waters, yet it seems to have no physiological effect at all; it can vary sixty fold from one water to the next without any apparent consequences beneficial or harmful. Beer, for example, contains four or five times as much silica as most drinking waters but it is obvious from the enormous quantities of beer consumed that silica has no bad effects.

Copper is an essential element for human metabolism. The normal diet may provide only a little more than is required so that an extra supplement in drinking water, although it may impart color, is beneficial. Copper is sometimes added to water to control growth of algae. Iron and manganese, in large quantities, may also cause objectionable color and taste, but they too are necessary for good health.

Cadmium and chromium are not essential elements and can even be highly toxic to the human body. Selenium, zinc, and nitrate also belong to this group. Nitrate is especially dangerous for infants who may drink it in water or milk.

There are many other substances in the water supplies that must be tested and controlled, but to speak of each one and its effects would require chapters if not books. One final consideration is the delivery of a safe water supply, which depends not only on the purity of the source, but on the quality of such equipment as water mains and storage tanks involved in the delivery to the consumer. Maintenance of equipment, which could corrode and release poisonous metals to the water, is vital. Lead pipes were once widely used in plumbing but they have been almost entirely eliminated except to carry corrosive waste waters.

Although it is true that most stream and lake waters in a virgin land could be drunk untreated, the establishment of a small settlement near the water source is sufficient to create local health problems and make water treatment necessary. Of the present 3.5 billion inhabitants of the earth, at least 1 billion regularly drink unsanitary water. Of these, 500 million are continually sick and 10 million die each year. They are the victims of bacteria and viruses and parasites that breed in the digestive tracts of humans and animals, and which, if they get into the water supply, cause diseases like typhoid, cholera, and dysentery. Some of the most important tests performed on drinking water supplies are for bacterial content. Only relatively recently have we learned to control water-borne bacteria and viruses. It was unsafe drinking water that caused massive cholera epidemics in London in the 1800s, yet it was not until the latter part of that century, under the influence of Pasteur’s theories, that the idea was abandoned that sickness was caused by impure “vapors” in the air and the necessity of disinfecting drinking water was understood.

Control of microorganisms is by filtration, aeration, and chlorination. Filtration through beds of sand and gravel removes suspended material and some bacteria and dissolved organic particles and clarifies the water; aeration destroys organics and kills many bacteria. If water is thoroughly mixed with air, oxygen “burns” the organic material and the bacteria have little left to live on. Streams with rapids are said to clean themselves in a short distance because of the excellent aeration. Sluggish rivers with much natural organic material or that have been polluted by organics, release foul-smelling gases as bacteria that live in the absence of oxygen break down the organic material. In water treatment plants the water is sprayed into the air to purify it and to improve its taste.

Chlorination is used around the world as the last crucial stage in removal of microorganisms. Most dangerous species yield to it easily but there are a few bacteria that are extremely resistant. They may ordinarily be absent from a water supply, but if they get in they may cause serious epidemics before they are discovered and the chlorine level and length of treatment are adjusted. It is not feasible to test routinely for all possible pathogenic organisms so the coliform bacillus is generally counted as an indicator of the presence of other bacteria. If coliforms are at a low level then most other harmful bacteria are also found in small numbers. Water containing more than about twenty-five coliforms a quart is unsafe.

Drinking water is also carefully and continuously tested to insure that other undesirable qualities such as taste, color, and odor are kept to a minimum. Iron is one of the worst offenders; it gives water a characteristic taste and can stain clothing at only two ppm. Many well waters with dissolved iron are clear when they come from the faucet but quickly precipitate a yellow iron oxide when mixed with air. The oxide is harmless if drunk but it stains glassware, sinks, cooking utensils and laundry. Waters with dissolved iron often carry a trace of hydrogen sulfide which, in concentrations far less than one ppm, gives a distinct rotten egg odor to the water. All kinds of new tastes and odors entering water supplies today are traceable to organic pollutants of a wide variety.