Respirable quartz exposure on two medium-sized farms in southern Mozambique.

BACKGROUND: Little is known about the potential for overexposure to respirable quartz in farming, in most parts of the world. OBJECTIVES: To measure respirable dust and quartz exposure of tractor operators on two medium-sized dry climate farms. METHODS: This is a descriptive cross-sectional study of dust exposure of four tractor operators. Farms were selected by convenience sampling. The MDHS 14/3 and FTIR MDHS 101 HSE methods were used to measure dust and to analyze the mass of quartz in dust, respectively. RESULTS: Seventy respirable dust measurements were done. Respirable dust and quartz ranged from 0·01 to 2·88 and 0·001 to 0·30 mg/m(3), respectively. All operators had at least one respirable quartz exposure above 0·1 mg/m(3). Only 17% of respirable quartz concentrations were lower than the ACGIH TLV of 0·025 mg/m(3). CONCLUSION: The potential for overexposure to respirable quartz was demonstrated. There was a great deal of exposure variability on these farms which has implications for sampling strategies for dust in farming.

Respirable dust and quartz exposure from three South African farms with sandy, sandy loam, and clay soils.

OBJECTIVES: To quantify personal time-weighted average respirable dust and quartz exposure on a sandy, a sandy loam, and a clay soil farm in the Free State and North West provinces of South Africa and to ascertain whether soil type is a determinant of exposure to respirable quartz. METHODS: Three farms, located in the Free State and North West provinces of South Africa, had their soil type confirmed as sandy, sandy loam, and clay; and, from these, a total of 298 respirable dust and respirable quartz measurements were collected between July 2006-November 2009 during periods of major farming operations. Values below the limit of detection (LOD) (22 µg · m(-3)) were estimated using multiple 'imputation'. Non-parametric tests were used to compare quartz exposure from the three different soil types. RESULTS: Exposure to respirable quartz occurred on all three farms with the highest individual concentration measured on the sandy soil farm (626 µg · m(-3)). Fifty-seven, 59, and 81% of the measurements on the sandy soil, sandy loam soil, and clay soil farm, respectively, exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 25 µg · m(-3). Twelve and 13% of respirable quartz concentrations exceeded 100 µg · m(-3) on the sandy soil and sandy loam soil farms, respectively, but none exceeded this level on the clay soil farm. The proportions of measurements >100 µg · m(-3) were not significantly different between the sandy and sandy loam soil farms ('prop.test'; P = 0.65), but both were significantly larger than for the clay soil farm ('prop.test'; P = 0.0001). The percentage of quartz in respirable dust was determined for all three farms using measurements > the limit of detection. Percentages ranged from 0.5 to 94.4% with no significant difference in the median quartz percentages across the three farms (Kruskal-Wallis test; P = 0.91). CONCLUSION: This study demonstrates that there is significant potential for over-exposure to respirable quartz in farming and even clay soil farming may pose a risk. Soil type may determine whether exposure is >100 µg · m(3), but the job type and the manner in which the task is performed (e.g. mechanical or manual) may be important determinants of exposure. Identifying quartz exposure determinants (e.g. type of job) and modifiers will be of value to focus implementation of controls of particular importance in developing countries.

Quartz exposure in agriculture: literature review and South African survey.

OBJECTIVES: 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. METHODS: 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. RESULTS: 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%. CONCLUSION: 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.