CRYSTALLINE SILICA EXPOSURE DURING COMMERCIAL SUGARCANE PRODUCTION

Respirable (<4 μm aerodynamic diameter) crystalline silica can cause the potentially fatal lung disease silicosis, and quartz and cristobalite have been classified as human carcinogens. Dusts containing quartz and (the high-temperature silica variety) cristobalite can be produced naturally, for example from volcanic eruptions, or from a variety of industrial processes such as rock quarrying and ceramic production.

The presence of respirable cristobalite in natural and industrial samples, and their association with respiratory disorders, has highlighted the importance in identifying other sources of respirable crystalline silica. Epidemiological studies have linked sugarcane burning with adverse respiratory health symptoms. Sugarcane (Saccharum officinarum) concentrates silica up to 7 wt. % and during harvesting, the sugarcane plants are burned to reduce the amount of material transported to the processing factory. Once the sugar has been extracted, the remaining residue (bagasse) is combusted to supply the electricity. It is suggested that the biogenic silica in the sugarcane could be altered by the combustion to form cristobalite, which could be contributory factor in the poor respiratory health of exposed populations.

Initial laboratory studies indicated that cristobalite could form in both the ash and emissions from burning sugarcane samples in a furnace. Samples of sugarcane leaf, particulate and ash from field burning and bagasse ash, were collected from sugarcane estates in South America. Cristobalite was found in the ash from the incinerated bagasse ash, but not in the airborne emissions from burning. The particulate concentrations, measured in the field and factory, exceeded many of the limits set as occupational guidelines.

The data on the chemical composition of the samples may help elucidate the mechanisms of toxicity and will contribute to our understanding of the impact from exposure to cristobalite-containing mixed dusts. Similar characterisation protocols can be applied to other biomass samples to deduce the possible risk of crystalline silica exposure and recommend preventative measures, particularly significant when considering the increase in renewable fuel use.