Silicon Crystals in Water of Autoclaved Glass Bottles

Crystals were detected in glass bottles containing autoclaved (standard cycle: 1218 C, 17 lb/in2, for 20 min) tap water. Bottles were fitted with a sipper tube and stopper. Crystals were observed twice at approximately a 6-month interval. Analysis of crystals and crystal-laden water by transmission electron microscopy and inductively coupled plasma and energy X-ray analysis revealed that the crystals were silicon. Subsequently, procedures and processes involved with preparation of water bottles were analyzed to determine the source or factors involved with silicon contamination. Analyses of silicon concentrations were performed on samples of tap water (0.88 to 1.20 ppm), tap water autoclaved in polycarbonate (0.89 to 1.20 ppm) and glass water bottles (0.84 to 11.0 ppm), glass and polycarbonate bottles after purposeful contamination of tap water with various amounts of alkaline detergent (1.10 to 1.70 ppm), and on steam condensate from the autoclave (0.23 and 0.47 ppm) to ascertain the source of silicon. Water from autoclaved glass bottles had greater concentrations of silicon, compared with unautoclaved tap water. Siliconized rubber stoppers and stainless-steel sipper tubes were excluded as sources of silicon contamination. Autoclaving glass bottles with stopper pieces did result in crystal formation, despite only modest increases in silicon concentration. Detergent contamination did not influence silicon concentrations. Analysis of the data indicated that autoclaving glass water bottles can lead to increases in silicon concentration and, under some circumstances, crystals may form.