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.

Are variance components of exposure heterogeneous between time periods and factories in the European carbon black industry?

Occupational exposure to chemical agents can vary enormously within- and between-workers, even when carrying out the same jobs. When repeated measurements are available, the variance components can be estimated using random- or mixed-effects models. Pooling the variance components across the fixed effects, in mixed-effects models, reduces the complexity of the models; especially, when there are a large number of fixed effects. The analyses presented in this paper tested the assumptions of homogeneity in the variance components between factories and surveys for inhalable dust exposure in the European carbon black manufacturing industry. In total, 5296 measurements from 1771 workers were available collected during two surveys carried out between 1991 and 1995. Workers were grouped into eight job categories, and for each of these separate mixed-effects models were developed, including factory, survey and in some cases the interaction term as the fixed effects. The likelihood ratio test was used to test the assumptions of homogeneity of the variance components. Statistically significant heterogeneity of the variance components was observed for two of the eight job categories, 'Fitter/Welder' and 'Warehouseman'. The heterogeneity was due mainly to differences in variance between the factories. When estimating the probability of overexposure for all the factories combined, there was little difference between the models with and without heterogeneous variance components for 'Fitters/Welders'. For the 'Warehousemen' the probability of overexposure in the last survey changed marginally from 4% in the pooled model to 6% in the heterogeneous model. Larger differences between the models were observed when estimating the probability of overexposure for individual factories, which was due to over- or under-estimation of the variance components in the pooled models. In conclusion, for most job categories pooling of the variance components appears to be justified in this database. In addition, no large differences were found when determining the industry-wide probability of 'overexposure' when comparing the pooled with the heterogeneous models. However, when evaluating the factory-specific probability of 'overexposure' or when using the models to provide exposure estimates for epidemiological studies heterogeneity in the variance components should be investigated.

A job-exposure matrix for potential endocrine-disrupting chemicals developed for a study into the association between maternal occupational exposure and hypospadias.

A study to assess the association between the prevalence of hypospadias and maternal occupational exposure to potential endocrine-disrupting chemicals was carried out using data from the congenital anomaly register of the Office for National Statistics. The occupation of the mother is recorded in this register and to facilitate the assessment of maternal occupational exposure, a specific job-exposure matrix for potential endocrine-disrupting chemicals was developed. Seven categories of contaminants were evaluated (pesticides, polychlorinated organic compounds, phthalates, alkylphenolic compounds, bi-phenolic compounds, heavy metals and other substances). Maternal occupations were all coded using the 1980 version of Categories of Occupations. Three occupational hygienists assessed the likelihood of exposure (unlikely, possible, probable) to these seven substance groups for all 348 possible job titles independently. Almost 30% of the job titles were classified as exposed to at least one substance category (possible or probable), with approximately 16% of the job titles being probably exposed to at least one substance category. Some examples of occupations with probable exposure to potential endocrine-disrupting chemicals include: farm workers, electricians, workers in the plastics industry, painters, printers, hairdressers, dental practitioners, laboratory workers, textile workers and cleaners. It is recognized that there are a lot of limitations to the use of job-exposure matrices in general and with the matrix presented in this paper in particular. However, the matrix forms the basis on which further developments on occupational exposure assessment of potential endocrine-disrupting chemicals could be founded. In addition, the job-exposure matrix has identified areas where more exposure information is required. For example, exposure to potential endocrine-disrupting chemicals can occur in occupations such as hairdressing and workers in beauty salons, where the working population is more likely to be female and for which little data exist on levels of exposure.