A transmission electron microscopy (TEM) study of silver nanoparticles associated with mine waste from New Caledonian nickel deposits: potential origins of silver toxicity in a World Heritage Site

The nature of silver nanoparticles associated with nickel-laterite ore deposits in New Caledonia (SW Pacific Ocean) is explored using transmission electron microscopy. The silver nanoparticles, dispersed in a matrix of amorphous silica, display complex textures such as linear aggregation and bimodal diameter distributions of 3–12 and 20–60 nm for one sample and 2–30 and 150–650 nm for the other, indicative of Ostwald ripening. These features as well as chemical heterogeneity (31–82% Ag—normalized X-ray energy dispersive spectrum), destructive assemblage interfaces, and amorphous and nanoparticle silica phases are consistent with those observed in epithermal gold deposits, potentially indicating a similar origin. Silver is highly toxic to a wide variety of organisms, and therefore, its significant presence in material directly related to mine runoff is a major threat to the New Caledonian environment, particularly the lagoons, which are listed as a World Heritage Site. Potential exists that the silver nanoparticles observed here provide the key to the origin of the toxic silver accumulation observed in New Caledonian reef organisms.