Siloxanes - Consumption, Toxicity and Alternatives - Miljøstyrelsen

Summary and conclusions
Siloxanes are chemical compounds with a backbone of alternating silicium
(Si) and oxygen (O) atoms, each silicon atom bearing one or several organic
groups. Siloxanes are building blocks for silicone products or make part of
other products, such as cosmetics or paint. In colloquial language the term
silicones is often used synonymously with siloxanes.
The properties of the siloxanes and the silicone products depend on the length
of the Si-O backbone, the chemical groups attached to the backbone and the
presence of cross-links between the backbones. Silicone products are grouped
into silicone fluids, elastomers and resins. Silicone fluids are used for a wide
range of applications, silicone elastomers are mainly used for sealants and
rubbers, and resins are mainly used for paints. The most common siloxanes
are polydimethylsiloxane (PDMS) with different modifications.
Of particular interest to this study are the relatively small compounds: Siloxanes
with a cyclic structure and linear siloxanes with a small Si-O backbone
with a few Si-O moieties. The most common and the most investigated as to
toxicity are octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane
(D5). These compounds are widely used in cosmetic products and
maintenance products (e.g. wax) under the name cyclomethicone - among
other names. In the present report different names are used for the same
compounds depending on the names typically used in the different contexts.
Many of the compounds are volatile, and the users are directly exposed to the
compounds when using the products, and the compounds are to a high extent
released to the atmosphere or to wastewater.
Consumption of siloxanes in Denmark
The consumption of siloxanes by application area is shown in Table 1. The
estimates are to a large extent based on information on the use of siloxanes in
Western Europe under the assumption that the consumption pattern in Denmark
of most products will resemble the general consumption pattern in
Western Europe. Best estimates and an indication of the uncertainty of the
best estimate are given.
The total consumption is estimated at approx. 3,100 t/year. Considering the
uncertainty on applying the Western European consumption figures, the total
consumption in Denmark is estimated to be within the range of 2,400-3,800
t/year.
The type of the siloxanes used is indicated in Table 1. The type can roughly
indicate the potential for releases of the compounds to the atmosphere and
wastewater. Volatile fluids are released to the atmosphere, whereas other fluids
may end up in wastewater or released directly to surface water and soil. Elastomers
and resins will mainly end up in solid waste.
The main application area is silicone sealants for construction, which account
for about one third of the consumption. Besides, siloxanes are widespread,
used in a vide range of products: In cosmetics and toiletries, paints, cleaning
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