THE MOVEMENT AND SURVIVAL OF NON-TUBERCULOUS MYCOBACTERIA IN HAWAI'I FROM RIPARIAN ZONES TO AQUIFERS TO HOMES

Nontuberculous mycobacterial (NTM) pulmonary infections in the Hawai’i are uncommon but have a relatively high incidence and mortality in immuno-compromised individuals compared to the mainland USA. We discuss the probable geochemical and hydrological mechanisms by which NTM thrives, including aquifer conditions favoring bacterial growth and transport.

Infection routes include inhalation of NTM in micro-droplets from home plumbing. On Oahu, infection rates are uneven across the Island. Higher adjusted disease rates are associated with elevated V concentrations in well waters. Elevated V concentrations promote bacterial growth in aquifers, within water distribution systems and in home plumbing via nitrogen (nitrate reductase) metabolic pathways. High V appears to be related to groundwater residence times, with elevated concentrations occurring in longer flow-path aquifers.

Vanadium is enriched in basalt and tends to follow Ti in the environment and as a result it is often immobile and concentrated in Hawaiian laterites. Recent analysis of ~4.5 Ma Hawaiian saprolites shows that weathering of basaltic protoliths produces fine-grained intergrowths of kaolinite and Fe-oxides, with a ~50% increase in fine-grained porosity. Magmatic Cr-spinel and ilmenite, however, are refractory, retaining primary igneous textures. Thus, although V is concentrated by leaching, it is retained in minerals that tend not to weather. Deeply-weathered laterites have released all of the V they are likely to do.

Beyond Cr-spinel and ilmenite, the main reservoir for Ti (~1 wt. % TiO₂) and V (~200 ppm) is clinopyroxene. This phase is usually consumed in the weathering zone but is present in the fresher aquifer basalts, and most dissolved V is derived from weathering of clinopyroxene in the aquifer. Concentrations are highest in systems with long water-rock contact times.

Recent work has also shown that NTM is common in Hawaiian streams and as a part of riparian biofilms. Surface and ground waters are intimately linked on short timescales owing to the high fracture permeability of basalt. Hawaiian aquifers are continually inoculated with NTM, which can then thrive in the presence of elevated V, especially where water-rock contact times are lengthy.