Open Cut » Environment
The inhalation of air containing elevated levels of crystalline silica is known to cause pneumoconiositic reactions (silicosis) in the lung and possibly cancers. The existence of silicosis has been known since ancient times in industrial occupations which resulted in the generation of excessive airborne silica. However, its prevalence has decreased dramatically in modern times as better regulation of industrial hygiene has been implemented. Silicosis is only infrequently found to have been caused by environmental rather than industrial exposure.
In 2005 California adopted a chronic Reference Exposure Level (REL) for respirable crystalline silica of 3µg/m³ as PM4. A chronic REL is defined as: "an airborne level of a chemical at or below which no adverse health effects are anticipated in individuals indefinitely exposed to that level". Silica concentrations in ambient air are not currently regulated in Australia by the Ambient Air NEPM. Victoria has developed assessment criteria based on the Californian regulations for respirable crystalline silica of 3 µg/m³ (PM2.5) for mining and extractive industries. There currently are no specific criteria for ambient air silica concentrations in NSW.
Intermittent ambient air sampling and continuous monitoring were carried out at two sites in the Hunter Valley during the period February to December 2010. The experimental program was specifically targeted to acquire data on silica (SiO2) concentrations in the Hunter Valley airshed. Particulate concentrations and meteorological data were continuously monitored using OSIRIS particle monitors. Intermittent sampling was undertaken with a MOUDI cascade impactor, which allowed collection of size-segregated particulate matter (PM) on a range of substrates which could subsequently be measured chemically, optically and gravimetrically.
A "worst case" analysis of silica and a-quartz concentrations estimated during the project gave a range of values of from 0.5 - 1.8 µg/m³ (PM4) and 0.2 - 1.4 µg/m³ (PM2.5). These values are significantly below the threshold value of 3 µg/m³ at or below which "no adverse effects are expected for indefinite exposure". Based on the Californian REL even sensitive individuals should not be at risk of contracting silicotic diseases were the values of silica and a-quartz concentration measured in the project to be found generally in the ambient air across the Hunter Valley.