Guidelines for drinking-water quality. Volume 1 - BVSDE

population, drinking-water is not a significant source of tin, and levels in drinking-water greater
than 1-2 µg/litre are exceptional. However, there is increasing use of tin in solder, which may be
used in domestic plumbing.
Tin and inorganic tin compounds are poorly absorbed from the gastrointestinal tract, do not
accumulate in tissues, and are rapidly excreted, primarily in the faeces.
No increased incidence of tumours was observed in long-term carcinogenicity studies conducted
in mice and rats fed stannous chloride. Tin has not been shown to be teratogenic or fetotoxic in
mice, rats, and hamsters. In rats, the NOAEL in a long-term feeding study was 20 mg/kg of body
weight per day.
The main adverse effect on humans of excessive levels of tin in foods (above 150 mg/kg), such
as canned fruit, has been acute gastric irritation. There is no evidence of adverse effects in
humans associated with chronic exposure to tin.
It was concluded that, because of the low toxicity of inorganic tin, a tentative guideline value could
be derived three orders of magnitude higher than the normal tin concentration in drinking-water.
Therefore, the presence of tin in drinking-water does not represent a hazard to human health. For
this reason, the establishment of a numerical guideline value for inorganic tin is not deemed
necessary.
Total dissolved solids
Total dissolved solids (TDS) comprise inorganic salts (principally calcium, magnesium,
potassium, sodium, bicarbonates, chlorides and sulfates) and small amounts of organic matter
that are dissolved in water. TDS in drinking-water originate from natural sources, sewage, urban
run-off, and industrial wastewater. Salts used for road de-icing in some countries may also
contribute to the TDS content of drinking-water. Concentrations of TDS in water vary considerably
in different geological regions owing to differences in the solubilities of minerals.
Reliable data on possible health effects associated with the ingestion of TDS in drinking-water are
not available, and no health-based guideline value is proposed. However, the presence of high
levels of TDS in drinking-water may be objectionable to consumers.
Uranium
Uranium is present in the earth's crust, principally in the hexavalent form. It is used primarily as a
fuel in nuclear energy plants and is introduced into water supplies as a result of leaching from
natural sources, from mill tailings, from emissions from the nuclear industry, from the combustion
of coal and other fuels, and from phosphate fertilizers. Although available information on
concentrations in food and drinking-water is limited, it is likely that food is the principal source of
intake of uranium in most areas.
Uranium accumulates in the kidney, and nephropathy is the primary induced effect in humans
and animals. In experimental animals, uranium most commonly causes damage to the proximal
convoluted tubules of the kidney, predominantly in the distal two-thirds. At doses that are not high
enough to destroy a critical mass of kidney cells, the effect is reversible, as some of the lost cells
are replaced.
Adequate short- and long-term studies on the chemical toxicity of uranium are not available, and
therefore a guideline value for uranium in drinking-water was not derived. Until such information
becomes available, it is recommended that the limits for radiological characteristics of uranium be
used (see Chapter 4). The equivalent for natural uranium, based on these limits, is approximately
140 µg/litre.