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Environmental fate & pathways

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As inorganic substances and in view of their chemical structure, soluble silicates are not amenable to biodegradation.


In a simulation test following the OECD confirmatory test procedure, the elimination and influence of spray-dried sodium silicate (molar ratio 2.1) on the biological activity of a model sewage treatment plant was determined. Based on the same chemical properties of soluble silicates this study can be considered for potassium silicate as well. At doses of 25 mg/L, sodium silicate had no adverse effect on the biodegradation of easily degradable nutrients fed simultaneously: DOC (Dissolved Organic Carbon), pH and dry weight of activated sludge was comparable to the untreated control model plants. Visual inspection of colour and settling behaviour of activated sludge also did not reveal any differences between treated and untreated test runs. Elimination of sodium silicate in the model sewage treatment plant was only marginal: 90 - 100 % was detected in the effluent. The study was carried out in compliance with GLP and EU guidelines 82/242/EEC and 82/243/EEC (Richterich 1994 as cited in OECD SIDS 2004).

Furthermore, silica is continuously removed from water by biochemical processes: diatoms, radiolarians, silicoflagellates, and certain sponges serve as a sink for silicon by incorporating it into their shells and skeletons as amorphous biogenic silica, frequently referred to as opal (SiO2· nH2O). They can deplete dissolved silica in surface waters to less than 1 mg/L during blooms (Edwards 1973).