Tin in Biological Applications
Tin in Biological Applications
Although PVC stabilisation has long been the largest application sector for organotin compounds, the biological activity of certain organotins led to their extensive use as wood preservatives, agrochemicals, antifouling paints and disinfectants. At their peak in the mid-1980s, combined use of organotin biocides certainly accounted for annual tin consumption of several thousands of tonnes per annum.
However, many of these compounds, particularly tributyltin oxide (TBTO) and its derivatives, have been subject to intense pressure from environmental lobby groups for over 20 years and TBT is now more or less completely banned from use in marine anti-fouling paints. Although organotin biocides still find some use in crop protection (mainly tricyclohexyl and triphenyl compounds) and in antimicrobial / antifungal formulations (mainly TBT compounds), tonnages are much smaller these days and probably account for no more than a few hundreds of tonnes of tin per annum. There appears to be a general consensus within the industry that the use of triorganotin compounds will decline further in the years ahead.
One of the longest established pharmaceutical uses of tin compounds is that of tin(II) fluoride and, to a lesser extent, tin(II) pyrophosphate, in toothpastes, dentifrices, topical solutions and mouthwashes. The US Food & Drug Administration (FDA) has approved tin(II) compounds in toothpastes at levels up to 0.4%, and the American Dental Association has approved topical treatments containing up to 8% tin(II) fluoride.
The generic sector of oral healthcare has been highlighted as a likely growth area for tin chemicals in the medium term. It is clearly evident that patent activity by the major players in this market – Procter & Gamble ('Crest Pro-Health' and 'Oral-B Pro-Expert'), Unilever Colgate – Palmolive and Gaba International – all involving tin(II) salts in dental formulations, has been very intense over the past year or so. Indeed, the demand for tin(II) fluoride has raised questions about global production capacity, particularly because of increasing usage in toothpastes and, potentially, animal healthcare products (see below).
Tin(II) compounds have a long documented history of use in human and animal healthcare products, although actual tin consumption in this sector has been very limited, the main outlet being in the dental industry (see above). However, a recent development based on the synergistic antimicrobial activity of tin and zinc, has led to greatly increased market potential.
ITRI is working with a US-based company, Visions Marketing, to develop a range of animal healthcare formulations for preventing and treating skin diseases in bovine, equine, canine and other animal sectors. These formulations, comprising aqueous preparations of tin(II) fluoride and zinc sulphate, are patented and being marketed in the US under the 'Accelerator' trade name.
Potential tin tonnages are difficult to assess at this early stage, but figures in the range 500 – 1,000 tonnes per annum for the US alone are realistic. Future developments, including human healthcare products, are already under consideration and ITRI plans to follow this technology closely in the years ahead.