Quartz exposure in agriculture: literature review and South African survey

To review the published literature on respirable quartz exposure and associated disease in agricultural related settings systematically and to describe personal respirable dust and quartz measurements collected on a sandy soil farm in the Free State province of South Africa.

The published studies on exposure to respirable silica and quartz in agriculture and related settings (to June 2009) were searched systematically through 'PubMed' and critiqued. A farm in the sandy soil region of the Free State province of South Africa producing typical crops for the region was identified and 138 respirable dust and respirable quartz measurements were collected from July 2006-August 2008 during major farming operations.

In total, 17 studies were identified: 11 investigated respirable quartz exposure on farms and 6 quartz-related diseases in agricultural settings. They provided convincing evidence of a respirable quartz risk on sandy soil farms but scant evidence of associated disease. Respirable quartz measurements from the South African farm ranged from not detectable to 626 microg m(-3) and confirmed the quartz risk as some concentrations exceeded generally accepted occupational exposure limits in all jobs evaluated, even though the majority of respirable dust concentrations were well below a commonly used occupational exposure limit of 2 mg m(-3). Twelve of 138 respirable dust measurements (9%) and 18 of 138 respirable quartz measurements (13%) exceeded commonly used occupational exposure limits of 2 mg m(-3) and 100 microg m(-3), respectively. The highest time weighted average respirable quartz concentration of 626 microg m(-3) was during wheat planting activities. Fifty-seven percent of the respirable quartz measurements exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) of 25 microg m(-3). Quartz percentages of the respirable dust ranged from 0.3 to 94.4% with an overall median of 13.4%.

Despite its ubiquity, little is known about quartz exposure in the agricultural industry; but this study demonstrates significant potential for overexposure in some settings. Further research is required to quantify quartz exposure and identify settings and tasks that place farmers and farmworkers at risk of quartz-associated diseases so that controls can be implemented.