The control of water and sodium balance is achieved through a complex interrelated system involving both nervous and hormonal systems. Uncontrollable losses can become important, however, in cases of gross deficiency of sodium intake. Normal loss of water and electrolytes in perspiration and expired air, about 900 mL, is considered to be unimportant in water and electrolyte homeostasis, because it is minor in comparison with renal and intestinal losses and functions. Normally 1.5 to 2 L of water and 2.3 g of sodium are lost each day in the urine about 100 mL of water and 350 mg of sodium are eliminated daily in the faeces. The standard 70-kg human adult contains approximately 69 g of metabolically active sodium and 45 L of water. Water and electrolyte balances are maintained by dietary intake in food and water and loss in urine, faeces, perspiration, expired air, active renal filtration, and ion absorption mechanisms. In domestic water softening using ion-exchange resins, for every 40 mg of calcium per litre exchanged the sodium concentration in the treated water will rise by 46 mg/L. Correction of pH with sodium hydroxide can cause a 12 mg/L increase in sodium depending on the buffering capacity of the water. Processes used to reduce lead and copper solvency in water supplies, involving partial desoftening of water, can increase sodium content by approximately 30 mg/L. Other sodium-containing chemicals are used in water processing: sodium fluoride (NaF) or sodium silico-fluoride (Na 2SiF 6) for fluoridation sodium hydroxide (NaOH), sodium carbonate (Na 2CO 3), and sodium bicarbonate (NaHCO 3) for corrosion control sodium hypochlorite (NaHClO 3) for disinfection and certain coagulants. The lime-soda ash purification process may contribute significant quantities of sodium if a large concentration of non-carbonate hardness must be removed. Large amounts of sodium-containing chemicals used in the treatment of public water supplies, as well as in domestic water-softening processes, can be important sources of sodium in drinking water. Footnote 15 In western Europe and North America, present sodium chloride consumption is estimated to be 5 to 20 g/day, with an average of approximately 10 g/day (which would supply 4 g of sodium per day). There are, as well, wide variations in sodium intake levels between individuals, and in the same individual from day to day. In Manitoba, where some supplies have 250 mg/L of sodium, Footnote 9 the contribution to total daily sodium could be about 400 mg or 15 percent. Some drinking water supplies have high sodium concentrations, influencing the impact of drinking water on total sodium intake. Footnote 9 Any estimate of total daily intake of sodium could be greatly altered by addition of salt to food during meal preparation or at the table. Footnote 12 Assuming a daily intake of 1.5 L of drinking water Footnote 14 at the national median sodium concentration of 5.6 mg/L, drinking water would contribute only 0.3 percent to the total sodium intake. Footnote 12 Thus, it is concluded that more than 80 percent of sodium in the Canadian diet is contributed by processing of foods by the food industry or in the home. Footnote 13 A 2500-kcal diet composed of unprocessed foods only contains 460 mg of sodium. Footnote 8 Levels, however, are still below the natural sodium concentrations found in many other surface water systems.Ī diet based on Canadian figures for food consumption contains 1.15 g of sodium per 1000 kcal per day, or 2.9 g of sodium per person per day (assuming a daily intake of 2500 kcal per person). Lawrence River system indicate that sodium levels for the system below Lake Huron have been steadily increasing as a result of anthropogenic activities. Footnote 8 The data accumulated over recent years for the Great Lakes -St. Footnote 4 For example, concentrations of 0.7 mg/L at the mouth of the Coppermine River, Northwest Territories, and 305 mg/L for the closed basin waters at Gravelbourg, Saskatchewan, have been reported. Sodium concentrations in Canadian surface waters range from less than 1 mg/L to more than 300 mg/L, depending upon the source of the sodium and the geography of the area. In ground waters, sodium concentrations normally range between 6 and 130 mg/L Footnote 7 much higher levels may be associated with saline salts as noted above. Sodium concentrations vary considerably depending on regional and local hydrological and geological conditions, the time of year, and salt utilization patterns. Because of the high solubility of sodium minerals, sodium is ubiquitous in the water environment.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |