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13. Inorganic Constituents and Physical Parameters

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13. Inorganic constituents and physical parameters 13.1 Aluminium 13.1.1 General description Identity Aluminium is a widespread and abundant element, accounting for some 8% of the earth's crust. It is found as a normal constituent of soils, plants, and animal tissues. Compound CAS no. Molecular formula Aluminium 7429-90-5 Al Aluminium oxide 1344-28-1 Al2O3 Aluminium chloride (hexahydrate) 7446-70-0 AlCl3.6H2O Aluminium sulfate 10043-01-3 Al2(SO4)3 Aluminium hydroxide 21645-51-2 Al(OH)3 Physicochemical properties (1) Property Al Al2O3 AlCl3.6H2OAl2(SO4)3 Al(OH)3 Melting point (°C) 660.37 2072 100 770 300 (decomposes) (decomposes) Boiling point (°C) 2467 2980 - - - Density at 20 °C (g/cm3) 2.702 3.965 2.398 2.71 2.42 Water solubility (g/litre) insoluble insoluble soluble 31.3 at 0 °C - Organoleptic properties In the presence of aluminium, levels of iron normally too low to cause problems may produce obvious discoloration of water. The incidence of discoloration in distribution system water, and therefore the frequency of consumer complaints, increases if the aluminium level exceeds about 0.1-0.2 mg/litre in the final water. Major uses Aluminium has many industrial and domestic applications. Its compounds are used as antacids, antiperspirants, food additives, and vaccine adjuvants. Aluminium salts are also widely used in water treatment as flocculants. Environmental fate Aluminium is usually present in treated drinking-water in the form of reactive species of low relative molecular mass; in natural waters, it is usually associated with particulate matter or organic complexes of high relative molecular mass (2). 13.1.2 Analytical methods Aluminium may be determined by colorimetry (lower detection limit 5 µg/litre) and by inductively coupled plasma emission spectrometry (lower detection limit 40 µg/litre). 13.1.3 Environmental levels and human exposure Air Aluminium is present in air at nanogram per cubic metre levels as a result of the weathering of aluminosilicate rocks and emissions from industrial sources, automobiles, and cigarette smoke (3). Water Aluminium may be present in natural waters as a consequence of leaching from soil and rock. In a survey of aluminium in raw waters in the USA, ranges of 14-290 µg/litre in groundwater and 16-1170 µg/litre in surface water were reported (4). In the United Kingdom, concentrations of 200-300 µg/litre were associated with low pH levels and 400 - 600 µg/litre with an afforested catchment (5). Aluminium salts are used as coagulants in water treatment. Residual aluminium concentrations in finished waters are a function of the aluminium levels in the source water, the amount of aluminium coagulant used, and the efficiency of filtration of the aluminium floe. Where residual concentrations are high, aluminium may be deposited in the distribution system, and a gradual reduction with increasing distance from the treatment plant may then be observed. Disturbance of the deposits by changes in flow rate may increase aluminium levels at the tap and render the water aesthetically unacceptable (6). Food The concentrations of aluminium in food vary widely depending on the nature of the foodstuffs. Studies suggest that aluminium leached from tea leaves can make a significant contribution to dietary intake (7). Use of food additives containing aluminium, such as preservatives, fillers, colouring agents, anticaking agents, emulsifiers, and baking powders, also increases dietary intake. In addition to its presence in food per se, aluminium leaching from cooking utensils may represent a potential source of dietary exposure (8, 9). Use of aluminium by the food industry in containers and packaging constitutes another dietary source (10). It should be noted that the ubiquitous nature of aluminium makes it difficult to ensure freedom from contamination throughout the various stages of analysis. The reported concentrations of aluminium in foodstuffs such as vegetables, which are readily contaminated with soil, appear to be decreasing as analytical techniques improve. Pharmaceuticals The use of antacids, analgesics, and other aluminium-containing medications is a significant source of exposure for some individuals (11, 12). Estimated total exposure and relative contribution of drinking-water A value of 20 mg/day has been suggested as a "typical" daily aluminium intake (13, 14). However, because of individual and geographical variations in eating and drinking habits, a range of 5-20 mg of aluminium per day is probably more realistic. Aluminium in drinking-water will usually contribute only a very small proportion of the total daily intake. If a contribution of 20 mg/day from food is assumed, an adult drinking 2 litres of water per day containing 200 µg of aluminium per litre would receive approximately 2% of his or her total intake from drinking-water. 13.1.4 Kinetics and metabolism in laboratory animals and humans Studies suggest that less than 1% of dietary inorganic aluminium is absorbed (15, 16). Factors affecting absorption may include vitamin D and fluoride (17) and the presence of complexing agents (18). Aluminium, once absorbed, appears to bind to serum proteins (19); it is eliminated from the body by the kidneys (17). Individuals with renal insufficiency tend to accumulate aluminium as a consequence of their inability to excrete it via the kidneys (20). 13.1.5 Effects on laboratory animals and in vitro test systems Short-term exposure Groups of 25 male Sprague-Dawley rats were fed diets containing basic sodium aluminium phosphates or aluminium hydroxide at mean aluminium doses ranging from 67 to 302 mg/kg of body weight per day for 28 days. No treatment-related effects on body weight, organ weights, haematology, and clinical chemistry were observed, and there was no evidence of increased aluminium concentrations in bone (21). In a study in which rats received drinking-water containing aluminium nitrate for 1 month, elevated aluminium levels were found in the heart and spleen, and histological changes were apparent in the liver and spleen at doses of 54 and 108 mg of aluminium per kg of body weight per day. No adverse effects were observed at a dose level of 27 mg of aluminium per kg of body weight per day (22). Rats fed diets containing aluminium hydroxide at 257 or 1075 mg of aluminium per kg of diet for 67 days, equivalent to 13 or 54 mg of aluminium per kg of body weight per day, exhibited elevated levels of aluminium in the tibia, liver, and kidneys. Reduced bone strengths were also noted at the highest dose level (23). Groups of 10 female Sprague-Dawley rats received aluminium nitrate in their drinking-water at doses of 0, 360, 720, or 3600 mg/kg of body weight for 100 days (equivalent to 0, 26, 52, or 260 mg of aluminium per kg of body weight per day). The only effect observed was depression of body weight gain associated with reduced water and feed intake at the highest dose level. Organ weight, histopathology of the brain, heart, lungs, kidneys, liver, and spleen, haematology, and some clinical chemistry indices were also examined (24). Rats given oral doses of 0.0025, 0.25, or 2.5 mg of aluminium per kg of body weight for 6 months exhibited some changes in behaviour and mild changes in the biochemistry of the testes at the highest dose level, but there were no significant effects at the lower doses (25). In a study in which dogs (4 per sex per dose) were fed diets containing basic sodium aluminium phosphate at 0, 3000, 10 000, or 30 000 mg/kg (mean daily aluminium doses of 4, 10, 27, or 75 mg/kg of body weight for males and 3, 10, 22, or 80 mg/kg of body weight for females) for 26 weeks, mild histopathological changes were observed in the liver, kidney, and testes of males in the highest-dose group, whereas brain aluminium concentrations were slightly elevated in females given the highest dose. No effects were noted at the lower dose levels (26). Long-term exposure Chronic oral intake of aluminium in the diet at doses of about 50 or 100 mg/kg of body weight per day decreased locomotor responses and slowed the acquisition of avoidance behaviour in rats (27). In other studies in rats, it was reported that aluminium produced osteomalacia (28) and microcytic anaemia (29), initiated impairment of kidney function (30), and caused damage to the lysosomes in the liver, spleen, and kidneys (31). Reproductive toxicity, embryotoxicity, and teratogenicity An increase in the aluminium content of the placenta and fetus was found when pregnant mice were given oral doses of aluminium chloride (equivalent to 0, 40, or 60 mg of aluminium per kg of body weight per day) on days 7-16 of gestation (32). No evidence of embryotoxicity or teratogenicity was found in a study of pregnant rats fed aluminium chloride in their diet on days 6-19 of gestation at doses of approximately 5 or 10 mg of aluminium per kg of body weight per day (33). A delay in weight gain and neuromotor development was reported in the offspring of rats given oral doses of aluminium chloride (equivalent to 155 or 192 mg of aluminium per kg of body weight per day) from day 8 of gestation to parturition (34). Mouse dams fed a diet containing 500 or 1000 mg of aluminium per kg (equivalent to 75 or 150 mg/kg of body weight per day) exhibited neurotoxicity, and their offspring showed neurological changes consistent with maternal toxicity and subsequent delayed development (35). In a study in which groups of 10 pregnant rats were given oral doses of aluminium nitrate of 0, 180, 360, or 720 mg/kg of body weight per day from day 14 of gestation to day 21 of lactation, offspring of dams receiving the highest dose exhibited depressed body weight gain (36).
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