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.

Workplace determinants of endotoxin exposure in dental healthcare facilities in South Africa.

OBJECTIVES: Aerosols generated during dental procedures have been reported to contain endotoxin as a result of bacterial contamination of dental unit water lines. This study investigated the determinants of airborne endotoxin exposure in dental healthcare settings. METHODS: The study population included dental personnel (n = 454) from five academic dental institutions in South Africa. Personal air samples (n = 413) in various dental jobs and water samples (n = 403) from dental handpieces and basin taps were collected. The chromogenic-1000 limulus amebocyte lysate assay was used to determine endotoxin levels. Exposure metrics were developed on the basis of individually measured exposures and average levels within each job category. Analysis of variance and multivariate linear regression models were constructed to ascertain the determinants of exposure in the dental group. RESULTS: There was a 2-fold variation in personal airborne endotoxin from the least exposed (administration) to the most exposed (laboratory) jobs (geometric mean levels: 2.38 versus 5.63 EU m(-3)). Three percent of personal samples were above DECOS recommended exposure limit (50 EU m(-3)). In the univariate linear models, the age of the dental units explained the most variability observed in the personal air samples (R(2) = 0.20, P < 0.001), followed by the season of the year (R(2) = 0.11, P < 0.001). Other variables such as institution and total number of dental units per institution also explained a modest degree of variability. A multivariate model explaining the greatest variability (adjusted R(2) = 0.40, P < 0.001) included: the age of institution buildings, total number of dental units per institution, ambient temperature, ambient air velocity, endotoxin levels in water, job category (staff versus students), dental unit model type and age of dental unit. CONCLUSIONS: Apart from job type, dental unit characteristics are important predictors of airborne endotoxin levels in this setting.

The utility of biological monitoring for manganese in ferroalloy smelter workers in South Africa.

Five hundred and nine workers at a manganese (Mn) smelting works comprising eight production facilities and 67 external controls were studied cross-sectionally. Exposure measures from personal sampling included inhalable dust, cumulative exposure indices (CEI) and average intensity (INT = CEI/years exposed) calculated for the current job at the smelter and also across all jobs held by subjects. Biological exposure was measured by Mn in the blood (MnB) and urine (MnU) and biological effect was measured by serum prolactin. Average lifetime exposure intensity across all jobs ranged from near 0 (0.06 microg/m3) for unexposed external referents to 5 mg/m3. Atmospheric exposures and MnB and MnU distributions were consistent with published data for both unexposed and smelter workers. Associations between biological exposures and groups defined by atmospheric exposures in the current job were substantial for MnB, less so for MnU and absent for serum prolactin. Random sampling of MnB measurements representative of a group of workers with more than 1-2 years of service in the same job and notionally homogenous exposure conditions could serve as a cross-sectional predictor of atmospheric Mn exposure in the current job, as well as for surveillance of Mn exposure trends over time. Correlations at the individual level were only modest for MnB (33% of the variance in log atmospheric Mn intensity in the current job was explained by log MnB), much worse for MnU (only 7%). However, a receiver operating characteristic (ROC) analysis was performed which showed that it is possible to use a MnB cut-off of 10 microg/l (the 95th percentile in the unexposed) to good effect as a screening tool to discriminate between individual exposures exceeding and falling below a relatively strict atmospheric Mn exposure threshold at the ACGIH threshold limit value (TLV) of 0.2 mg/m3. MnU has no utility as a measure of biological exposure nor does serum prolactin as a measure of biological effect.

The nervous system effects of occupational exposure on workers in a South African manganese smelter.

Five hundred and nine production workers at a manganese (Mn) smelting works comprising eight production facilities and 67 external controls were studied cross-sectionally for Mn related neuroehavioural effects. Exposure measures from personal sampling included Mn in inhalable dust as cumulative exposure indices (CEI) and average intensity (INT). Biological exposure and biological effect measures included blood (MnB), urine (MnU) manganese and serum prolactin. Endpoints included items from the Swedish nervous system questionnaire (Q16), World Health Organisation neurobehavioural core test battery (WHO NCTB), Swedish performance evaluation system (SPES), Luria-Nebraska (LN), and Danish product development (DPD) test batteries, and a brief clinical examination. Potential confounders and effect modifiers included age, educational level, alcohol and tobacco consumption, neurotoxic exposures in previous work, past medical history, previous head injury and home language. Associations were evaluated by multiple linear and logistic regression modelling. Modelling assumptions were tested. Average exposure intensity across all jobs ranged from near 0 (0.06 microg/m3) for external controls to 5.08 mg/m3 for inhalable Mn, and was greater than the ACGIH TLV for 69% of subjects. Results from the large number of tests performed resolved into three groups. Group 1 shows differences between external unexposed referents and all the exposed and/or differences between internal low exposed referents and the rest of the exposed but no further exposure-response relationships. It includes the Santa Ana, Benton and digit-span tests from the WHO NCTB; the hand tapping and endurance tapping tests from the SPES; Luria-Nebraska item 2L; questionnaire items tired, depressed, irritated, having to take notes in order to remember things, and subjects' perception that they had sex less often than normal; a test of clinical abnormality; and increased sway under two conditions (eyes open without foot insulation, eyes open with foot insulation). Group 2 shows the presence of a more substantive exposure-response relationship. It consists of only two tests: and includes the WHO digit-symbol test (although the major impact is at low exposure and therefore counterintuitive, arguably placing this test in group 3) and the LN item 1R which has a step to a poorer score at high exposure. Group 3 contains the overwhelming majority of test results (almost all the questionnaire items, almost all the DPD tests including tremor, sway and diadochokinesia, and serum prolactin) which were either null or counterintuitive (did not make sense). The CEI was the strongest predictor of test abnormalities, except for the clinical test which was more strongly associated with blood manganese. Despite a comprehensive range of endpoints, and levels of exposure ranging from environmental to industrial, this large study of Mn workers found little convincing evidence for a continuum of effects, contributing further questions to current debates about the adequacy of the current ACGIH TLV.