Nitrate and Phosphate - Page 2

In the 1970s, the Food and Drug Administration (FDA) responded to these concerns by dramatically cutting back on the quantity of nitrates and nitrites that could be added to foods. By 1981, however, a thorough study of the issue by the National Academy of Sciences showed that nitrates and nitrites are only a minor source of nitrosamine compared to smoking, drinking water, cosmetics, and industrial chemicals. Based on this study, the FDA finally decided in January 1983 that nitrates and nitrites are safe to use in foods. The addition of phosphates through the activities of humans can accelerate the eutrophication process of nutrient enrichment that results in accelerated ecological aging of lakes and streams. Phosphorus, especially in inland waters, is often the nutrient that limits growth of aquatic plants. Thus when it is added to a body of water, it may result in increased plant growth that gradually fills in the lake. Critical levels of phosphorus in water, above which eutrophication is likely to be triggered, are approximately 0.03 mg/l of dissolved phosphorus and 0.1 mg/l of total phosphorus. The discharge of raw or treated wastewater, agricultural drainage, or certain industrial wastes that contain phosphates to a surface water body may result in a highly eutrophic state, in which the growth of photosynthetic aquatic micro- and macro organisms are stimulated to nuisance levels.

Aquatic plants and mats of algal scum may cover the surface of the water. As these algal mats and aquatic plants die, they sink to the bottom, where their decomposition by microorganisms uses most of the oxygen dissolved in the water. The decrease in oxygen severely inhibits the growth of many aquatic organisms, especially more desirable fish (e.g., recreational catch fish such as trout) and in extreme cases may lead to massive fish kills. Excessive input of phosphorus can change clear, oxygen-rich, good-tasting water into cloudy, oxygen-poor, foul smelling, and possibly toxic water. Therefore, control of the amount of phosphates entering surface waters from domestic and industrial waste discharges, natural runoff, and erosion may be required to prevent eutrophication. Rocks may contain phosphates; those with calcium phosphate upon heat treatment with sulfuric acid serve as a source of fertilizers.

Phosphates, in addition to those found in fertilizers, are also present in such consumer products as detergent, baking powders, toothpastes, cured meats, evaporated milk, soft drinks, processed cheeses, pharmaceuticals, and water softeners. Phosphates are classified as orthophosphates (PO -3 4 , HPO -2, H 4 2PO4 , and H3PO4); condensed phosphates, or polyphosphates, which are molecules with two or more phosphorus atoms, oxygen atoms and in some cases, hydrogen atoms, combined in a complex molecule; and organically-bound phosphates. Orthophosphates in an aqueous solution can be used for biological metabolism without further breakdown. Orthophosphates applied to agricultural or residential cultivated land as fertilizers may be carried into surface waters with storm runoff and melting snow. Polyphosphates can be added to water when it is used for laundering or cleaning, for polyphosphates are present as builders of some commercial cleaning preparations for the public health sector. Massive algal blooms in lakes and floating foam on rivers aroused alarm in the United States in the 1970s.