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Description of key information

Silicon is  known to be not bioconcentrated or bioaccumulated to soil dwelling organisms at harmfull levels. Certain animal species may take up silicon actively in high amounts.
Bioaccumulation from soil to terrestrial species could be expressed quantitatively by the biota-to-soil accumulation factor (BSAF). Alternatively, the concentration in the organism could be related to the concentration in soil pore water by calculating a BCF [L/kg]. For silica these factors do not give any useful or important information because silicon and silica is always present in the terrestrial environment and is not normally regarded as a hazardous or bioaccumulative contaminant.

Key value for chemical safety assessment

Additional information

Silicate is the major elemental species in soil and the backbone of soil and rock mineral structures. Available field monitoring information provides sufficient data on the bioaccumulation potential of silicon from soil to terrestrial species. Basic Kow-based estimation methods cannot and need not to be used to generate the terrestrial BCF information.

Silicon is taken up and essential element to some plant species. Although silicon is not known to be an essential mineral element for higher plants, it has many direct and indirect beneficial effects on their growth and development. Si is taken up as Si(OH)4by plants and transported and deposited mainly in the leafs, since Si transport and distribution follows that of water (Wiese et al. 2007).

Silicon is readily absorbed so that terrestrial plants contain it in appreciable concentrations, ranging from a fraction of 1% of the dry matter to several percent, and in some plants to 10% or even higher. In spite of this prominence of silicon as a mineral constituent of plants, it is not counted among the elements defined as "essential," or nutrients, for any terrestrial higher plants except members of theEquisitaceae (horsetails) (Epstein 1994).

The movement of silicon into plant species and the location of its deposition are extremely species-specific. The general intrinsic tendency of soluble silica to bioconcentrate in plants is low. Some plants growing at the same locality as others become heavily silicified (e.g. horsetails Casuarina sp.), while others do not. The amount of water passing through the plants is similar (Williams 1986). There seems to be species specific active control systems to regulate Si concentration within terrestrial plants, systems comparable to those known in the aquatic microalgae (diatoms).

Epstein, E. (1994) The anomaly of silicon in plant biology, Review, Proc. Natl. Acad. Sci. USA, Vol. 91, pp. 11-17, January 1994

Williams, R.J.P. (1986) Silicon Biochemistry, Ciba Foundation, Symposium 121, Wiley, ISBN 0-471-91025-2 

(Wiese et al. 2007).