Tin dioxide

Endpoint summary

Additional information

According to WHO 2005: In the environment, tin compounds are generally only sparingly soluble in water and are likely to partition to soils and sediments. In water, inorganic tin may exist as either divalent (Sn2+) or tetravalent (Sn4+) cations under environmental conditions. Cations such as Sn2+ and Sn4+ will generally be adsorbed by soils to some extent, which reduces their mobility. Tin(II) dominates in reduced (oxygen-poor) water and will readily precipitate as tin(II) sulfide or as tin(II) hydroxide in alkaline water. Tin(IV) readily hydrolyses and can precipitate as tin(IV) hydroxide. The solubility product of tin(IV) hydroxide has been measured at approximately 10–56 g/litre at 25 °C. In general, tin(IV) would be expected to be the only stable ionic species in the weathering cycle (Wedepohl et al., 1978). Tin(II) can be hydrolysed into SnOH+, Sn(OH)20, and Sn(OH)3 − at low concentrations, whereas the Sn2(OH)2 2+ and Sn(OH)42+ polynuclear species predominate at higher concentrations (Seby et al., 2001). On release to estuaries, inorganic tin is principally converted to the insoluble hydroxide and is rapidly scavenged by particles, which are the largest sink.

 

Several data on tin accumulation in the environment and aquatic organisms are available. It has been noted that all the experiments and data related to tin accumulation and bioconcentration in plants and animals consider organic forms of tin, tin as metal and not with inorganic Sn-forms.

In the publication “Bioaccumulation of metals in juvenile rainbow trout (oncorhynchus mykiss) via dietary exposure to blue mussels”( Gillian McEneff, Brian Quinn, Chemosphere August 2017, the potential for metals to bioaccumulate in aquatic species, such as fish, via trophic level transfer was investigated. Metals, including Sn, were determined in the mussels and fish tissues (muscle and skin) collected at 0, 14 and 28 days, present in the Irish sea. Tin measurement was found to be lower than <0.1 μg g-1 dry, below specified MRL values (European Commission Regulation1881/2006) and deemed fit for human consumption.

 

The synoptic review “Tin hazards to fish, wildlife, and invertebrates, Ronald Eisler - U.S. Fish and Wildlife Service” has considered. Inorganic tin and its salts are not highly toxic due to their poor absorption, relative insolubility of their oxides, and rapid tissue turnover according to WHO 1980; Hassett et al. 1984.

The absorption can be just evaluated though the ingested inorganic tin, that is usually less than 5%, although up to 20% has been reported. Stannous compounds are more readily absorbed from the gastrointestinal tract than stannic compounds, but absorbed tin leaves the vascular system rapidly. Bone is the main site of tin deposition, followed by lung, liver, and kidney. Penetration of the blood-brain and placental barriers by inorganic tin seems to be very slight. Except for lung, inorganic tin does not accumulate in organs with increasing age. Absorbed inorganic tin is excreted mainly in the urine. Therefore even though there is evidence of slight penetration, Tin compounds are quickly eliminate.

 

 

According to WHO, 2005 it can be concluded that under environmental speciation conditions, inorganic tin compounds have low toxicity in both aquatic and terrestrial organisms, largely due to their low solubility, poor absorption, low accumulation in tissues, and rapid excretion.

 

Tin Dioxide has a very low solubility and in aqueous environment it is unlikely to be available for bioaccumulation.

 

NP Tin Oxide

Tin Dioxide NP has a very low solubility, like its non-nano form and in aqueous environment, the NP form is unlikely to be available for bioaccumulation.

The Study “Bioavailability of SnO2 nanoparticles evaluated by dietary uptake in the earthworm Eisenia fetida and sequential extraction of soil and feed,Serena Carbone, 2016” has been considered.

This study set out to investigate the exposure of soil biota to engineered nanoparticles (NPs) SnO2 and shows that SnO2 NPs does not bioaccumulated in earthworms and is rapidly excreted when worms were transferred to clean soil.Chemical extractions and measurements of uptake in earthworms showed that SnO2 NPs have a low bioavailability in soil and indicates that this nanomaterial should be of low concern in the context of environmental risk.

Tin Dioxide NP has a very low solubility and in aqueous environment it is unlikely to be available for bioaccumulation like the bulk form.