Keywords: aggressiveness index, asbestos cement pipes, drinking water, water pipes, health effects, hydrodynamics, fibres, fibre release, public water supply, asbestos concentration, environmental pollution, water pollution
Water aggressiveness and hydrodynamic effects on the fibres release in asbestos-cement pipes for public water supply
SEM and TEM analyses of drinking water samples, collected during three years (1988, 1989 and 1990) from some Asbestos-Cement (A/C) distribution systems in Veneto Region (Italy), have shown that the release of fibres, with length greater than 10 μm, is, on average, quite low. Moreover, the asbestos concentration is not strictly dependent on Aggressiveness Index (A.I.) in the range 10.5-12.5. Possible reasons why asbestos release may not be directly correlated to A.I. have been discussed. All of the analysed pipes showed the inner surface covered by both inorganic (carbonates, sulphates, silicates, etc.) and biorganic (algae) slime. These deposits probably work as filtering membranes against the fibres' release. On the contrary, when the A/C pipes are not encrusted, their behaviour is noticeably different: upon contact with very aggressive waters the new A/C pipes release fibres in significant amounts. Also, the hydrodynamic shearing action, exerted by the water flow, can give rise to fibre release from new A/C pipes in the first working period. From the results obtained with a pilot plant, some useful suggestions on how to operate with newly installed A/C pipes can be drawn.