Occupational exposure of workers to solar ultraviolet radiation at selected opencast mining operations in Namibia

Abstract

Introduction: Outdoor workers are exposed to higher solar ultraviolet radiation (UVR) than indoor workers. This puts them at risk of developing negative health effects on the skin and eyes depending on the periods of exposure and skin phototypes. Variations in job activities and associated postures determine the levels of solar UVR exposure in different body positions. Although evidence indicates that winter solar UVR exposure surpasses the International Commission on Non-Ionizing Radiation (ICNIRP) exposure guideline of 1.0 – 1.3 standard erythemal dose (SED) over an 8-hour period, many studies concentrate on solar UVR exposure during summer. The availability, and proper usage of photoprotective measures such as clothing, hats, sunglasses, and sunscreen reduce exposure to solar UVR. The personal exposure of outdoor workers at the selected opencast diamond mining operation in Namibia (22.9576°S, 18.4904°E) has not been quantified. Aim and objectives: The general aim of the thesis was to quantify the exposure of outdoor workers to personal solar UVR at two opencast diamond mining operations in Namibia. This aim was accomplished by determination of skin colour, the effectiveness of protective clothing, and evaluation of knowledge, attitudes and behaviour related to the risk of exposure to solar UVR of these workers. The aim was achieved through the following specific objectives, i) to quantify the personal exposure of Namibian outdoor opencast mineworkers to solar UVR at different body positions using electronic dosimeters and polysulphone badge dosimeters (PSF) during winter, ii) to establish the constitutive and facultative skin colour of Namibian outdoor opencast mineworkers using a colorimeter, iii) to evaluate the effectiveness of clothing as a protective measure against solar UVR exposure using polysulphone badge dosimeters during winter, and, iv) to evaluate the knowledge, attitudes and behaviour of Namibian outdoor opencast mineworkers related to the risk associated with chronic solar UVR exposure and photoprotection measures using a questionnaire. Methods: Measurements were conducted at two opencast diamond mining operations in Namibia over four days during winter (site A: 28 June to 4 July 2018, and site B: 6 to 11 July 2018). Outdoor job categories at these opencast mining operations were bedrock, engineering, metallurgy, and security. A total of 38 workers volunteered to participate in the study. The personal exposure of outdoor opencast mineworkers to solar UVR in Namibia was measured using electronic dosimeters based on Schottky Aluminium Gallium Nitride (AlGan) photodiode worn on the wrist, and PSF badges attached to the hard hat, nape, shoulder, and wrist. Skin colour was measured as individual typology angle (ITA) on the volar upper arm for constitutive skin colour (photoprotected) and dorsal forearm for facultative skin colour (photoexposed) using the Colorimeter CL 400 (Courage + Khazaka Electronics, GmbH, Germany). The PSF badges were placed above and under clothing on the shoulder to assess the effectiveness of clothing as a photoprotective measure. Knowledge, attitudes, and behaviours related to UVR exposure to the sun and the use of photoprotective measures were evaluated using a self-administered questionnaire. Ethical clearance was obtained from the North-West University Health Research Ethics Committee and the Namibia Ministry of Health and Social Services. All ethical requirements were observed through the different activities of this thesis. Findings and discussion: This thesis reports on findings of measurements from nine electronic dosimeters, 38 PSF badges and ITA, and 36 questionnaires. The mean daily solar UVR exposure measured on the wrist using electronic dosimeters and polysulphone dosimeters was not statistically different. The mean daily solar UVR exposure doses measured using the PSF badges at all body positions (2.07–3.69 SED) and job categories (2.00–3.11 SED), and a total of 89% of the doses measured with the electronic dosimeter (2.60 ± 1.92 SED) exceeded the exposure guideline range of the ICNIRP. The head of outdoor mineworkers in all categories of jobs received the highest levels of exposure. In general, the different body positions received high mean daily percentages of ambient solar UVR with the highest (214.70%) received on the heads of engineering workers. Most of the workers’ constitutive skin (photoprotected) was classified into phototypes III to VI (intermediate to black), while facultative (photoexposed) phototypes were classified into phototypes V (dark brown) and VI (black). This finding aligns with the demographics of Namibia, where 87.0% of the population consists of Black Africans. Significant differences were found in the ITA of phototypes V (dark brown), and VI (black), pointing to variations within the same phototypes. Also, constitutive (photoprotected) and facultative (photoexposed) phototypes differed significantly. This finding is in line with skin pigmentation that occurs because of adaptation to chronic exposure to solar UVR. Although darker skin phototypes are at a lower risk of skin cancer, they are still susceptible to other pigmentation disorders. Workplace-issued long-sleeved coveralls effectively blocked 97.3% of solar UVR on the shoulder. Higher levels of education were determined to be an indicator of knowledge of the risks of exposure to solar UVR and positive attitudes and behaviours regarding the use of photoprotective measures. A significant proportion of workers had educational levels spanning from no schooling (11%) to various stages of high school education (78%). This was associated with inadequate use of sunscreen (9%) and sunglasses (30%). Conclusions and recommendations: Outdoor workers at the two opencast diamond mining operations in Namibia are at risk of overexposure to solar UVR and the related negative health effects during winter regardless of skin colour and job category. Future solar UVR exposure studies should be conducted over longer periods to include larger sample sizes, different seasons, and other dosimeters to compensate for the failure of some electronic dosimeters experienced in this thesis. Photoprotection should be improved by supplementing the workplace-issued coveralls with photoprotective measures for the neck, eyes, and exposed skin. Poor use of sunscreen and sunglasses should be addressed through the implementation of training and education programmes, and follow-up assessments to determine the effectiveness of such programmes. Consideration should be given to different phototypes, workplace contexts, and education levels during the design and implementation of such intervention programmes. Limitations of this thesis are acknowledged.