Nanotechnology researchers in the past few years have exploited the fact that the clay mineral halloysite with its hollow, tube-like structure, might be used to carry and slowly release such substance as agricultural pesticides, herbicides, and fungicides. Research continues in this field as well as in many other potential commercial uses involving halloysite’s unusual properties and nanotechnology (see US government licenses).
Because halloysite, a common weathering product of South China’s rocks, is able to entrap some of these agricultural chemicals and then release them slowly suggests that erosion of halloysite by wind and water from this region’s land currently may be facilitating the unwanted movement of agricultural chemicals to where they could be ingested or inhaled by humans. Water erosion may carry chemically-charged halloysite into surficial water supplies where the chemicals would be released slowly. Filtered water supplies used for human consumption in Hong Kong already are known to carry halloysite (Parham, 1978) but it is not known whether or not the halloysite is carrying agricultural chemicals.
TEM of halloysite from weathered syenite, Hong Kong, photo by W. Parham.
Large parts of South China long ago were deforested and still are subject to heavy erosion (Parham et al., 1993). In addition, large-scale earth movements associated with urbanization increases the likelihood that halloysite may be a significant air contaminant as well. Thus, if any chemically-charged halloysite is transported by wind erosion during the six month, monsoon dry-season it could be inhaled by humans with a subsequent internal chemical release. Halloysite is closely correlated with pesticide residues in the subsurface saprolite in Oahu, Hawaii, suggesting that the pesticide may be being held within halloysite tubes (Miller et al., 1988). Further, Lvov et al. (2008) postulate that biocides can be retained within halloysite tubes and released later.
A study to determine the presence or absence of tubular halloysite in South China’s air seems reasonable. Such a study might shed light as well on the fate of any agricultural chemical carried in the halloysite tubes as related to potential adverse effects on human health in South China.
Walter E. Parham, Ph.D., Sept. 21, 2010
References
US government licenses halloysite-related patents to applied materials, (accessed 1/6/11), http://www.patents.com/patentscommunity/blogs/KKyrylyuk/my-blog/225/us-government-licenses-halloysite-related-patents-to-applied-minerals
Lvov, Y. et al., 2008, Halloysite clay nanotubes for controlled release of protective agents, (accessed 1/6/11), http://www.ncbi.nlm.nih.gov/pubmed/19206476
Miller, M.E. et al., 1988, Hydrogeologic characteristics of subsoil and saprolite and their relation to contaminant transport central Oahu, Hawaii, Water Resources Res. Ctr. No. 178, 76 p.
Parham, W.E., 1978, (Abst.) Tubular halloysite in filtered water of Hong Kong, 15th Annual Mtg. Clay Minerals Society
Parham, W.E., Durana, P.J., and Hess, A.L. (eds.), Improving degraded lands: promising experiences from South China, Bishop Mus. Bull. in Botany 3, Bishop Museum Press, 1993, 241
Sept. 21, 2010, W. Parham
South China Degraded Land Issues 
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