Unusual sources of aluminium and heavy metals in potable waters.

Aluminium in water supplies derives from natural sources and from the use of Al2(SO4)3 in water treatment. Heavy metals such as Pb, Cu, Zn and Cd can be added to water from pipework and solder. However, it is apparent that AI and other metals in potable waters can derive from deposits on pipe walls which can be subsequently mobilised when the supply and/or treatment process is changed. Concentrations of Al in domestic supply water of the Llanbrynmair area have been shown to increase from 1 µg to 50 µg L(-1) during its 18 km journey along the water main. Similarly, Pb concentrations in a public building in the Aberystwyth area are found to be extremely elevated due to the metal's mobilisation from encrustations occurring on the copper pipework.

The influence of acidic mine and spoil drainage on water quality in the mid-Wales area.

The many abandoned base metal mines of the mid-Wales ore field are sources of extensive pollution. Some of the mineralised veins contain large amounts of pyrite and marcasite and oxidative weathering of these produces sulphuric acid resulting in very acidic mine drainage waters. In addition, the spoil tips associated with these mines can contain abundant iron sulphides. Drainage waters from these sources have pH values as low as 2.6 and are heavily contaminated with metals such as Al, Zn, Cd and Ni.Two of the main rivers of the area, the Rheidol and Ystwyth, intercept heavily contaminated acidic drainage which has a marked effect on water quality. The Rheidol contains over 100 µg L(-1) Zn for 16 km downstream of the acid water influx. This level is over three times the recommended EEC limit for Zn in salmonoid waters of low hardness.

Some observations on heavy metal concentrations in soils of the Mendip region of north Somerset.

Topsoiis in the Mendip Hills of north Somerset are strongly enriched in Pb, Zn and Cd. While much of this enrichment is the result of pollution stemming from previous base metal mining, analyses of soil profile samples reveals that, in several cases, there is considerable enrichment of heavy metals with depth. This, together with relatively high levels of base metals in samples of the limestone and sandstone bedrocks, suggests that some of the enrichment in soil of heavy metals is due to natural processes.