Skin colour, photoprotective measures, and solar ultraviolet radiation exposure of workers on a macadamia nut and avocado farm

Abstract

Background: Outdoor agricultural workers such as farmers and farmworkers have been identified as an occupational group that is at high risk of exposure to solar ultraviolet radiation (UVR) during their work activities. Outdoor workers’ exposure to solar UVR need to be managed to prevent negative health effects such as skin cancer and ocular diseases. Skin colour and melanin content of skin provides a measure of genetic protection against exposure to high levels of solar UVR. Photoprotective measures such as wearing long sleeve clothing, broad-brimmed hats and sunglasses have been identified as measures that can reduce an individual’s exposure to solar UVR if used correctly. The solar UVR exposure of outdoor farmworkers has not previously been investigated in South Africa. Aims and objectives: The general aim of this thesis was to quantify the differences in skin colour and melanin content of facultative and constitutive skin of farmworkers on a macadamia nut and avocado farm in the Limpopo Province of South Africa, as well assessing the existing control measures and practices of those farmworkers together with their occupational exposure to solar UVR to determine if the exposure poses a risk to their health. The specific objectives were: (i) to determine the differences in skin colour (individual typology angle, ITA°) and melanin content (melanin index, MI) between the facultative and constitutive skin of farmworkers using skin bioengineering measurements, (ii) to assess the solar UVR practices, in particular the use of ocular protective measures, of the farmworkers on the farm using questionnaires, (iii) to determine the photoprotection provided by the clothing worn by farmworkers using polysulphone (PSF) badges on the shoulder both under and on top of the clothing and (iv) to assess the personal solar UVR exposure of outdoor farmworkers on the farm during autumn, spring and summer while carrying out their different work activities through polysulphone badges placed on their arms, top of the shoulder and top of any head covering worn. Methods: Outdoor and indoor farmworkers on the farm participated in this study. The skin colour and melanin content of the skin of farmworkers were classified using both a subjective method, namely questionnaires and objective methods namely measurement of ITA°) and MI. Outdoor farmworkers’ use of ocular photoprotective measures was determined with the use of a questionnaire. The photoprotection provided by the clothing worn by farmworkers was measured by placing a PSF badge on the shoulder beneath the clothing and on the outside

of clothing and classified according to the requirements of the AS/NZS 4399:2017 standard. The solar UVR exposure of outdoor and indoor farmworkers was measured by placing PSF badges on the shoulder, arm and top of the head during autumn, spring and summer during different work activities. Workers’ exposure was compared with the highest value of the International Commission of Illumination (CIE) occupational exposure limit, namely 1.3 SED (standard erythemal dose). Research ethics approval for this study was obtained from the North-West University Health Research Ethics Committee (NWU-00101-17-A1). Results: Significant differences were found between both the ITA° and MI measured on the constitutive (inner upper arm) skin and facultative (back of the hand) of farmworkers. The skin colour of the majority of farmworkers were objectively classified as falling in the Fitzpatrick Phototype V/Brown. A strong correlation was found between ITA° and MI which indicates that both objective methods are appropriate to determine the skin colour of darkly-pigmented skin. The majority of outdoor farmworkers (80%) never wore sunglasses while working outside. Although more than 70% of outdoor farmworkers wore a hat while working, they preferred to wear a cap rather than a broad-brimmed hat which provides better ocular photoprotection. Statistically significant differences were found between the solar UVR underneath and outside of clothing worn by farmworkers during autumn, spring and summer. Only 5% of clothing did not provide the minimum required photoprotection. More than 75% of farmworkers reported that they removed the long sleeve overall jacket they wear as part of their uniform at some point during the day which exposes their arms to solar UVR. Statistically significant differences were found between the solar UVR measured on the shoulder, arm and top of the head of outdoor farmworkers during spring and summer. The arm received the highest solar UVR exposure during autumn (7.8 SED) while the top of the head received the highest levels during spring (11.6 SED) and summer (13.9 SED). The solar UVR exposure of all body sites exceeded the daily CIE exposure limit for more than 80% of measurements during all three seasons. Conclusion: Skin colour and melanin content of farmworkers in this study was found to provide a high level of genetic photoprotection. It was also found that objective and subjective measurement of skin colour and can both be used to classify the skin colour of an occupational group in order to identify genetic photoprotection in workers. The use of ocular photoprotective measures by the outdoor farmworkers in this study was inadequate. The clothing worn by farmworkers in the study provided sufficient photoprotection, but removal of clothing during the day decreased its effectivity. The exposure of farmworkers to solar UVR exceeded the recommended CIE exposure limit during not only summer, but autumn and spring as well

which indicates that photoprotective measures should not only be in use during summer but also during the other two seasons. The solar UVR exposure of the outdoor farmworkers included in our study was generally higher than the exposure of farmers and farmworkers in other countries. Finally, ten recommendations are made to the macadamia nut and avocado farm to reduce farmworkers’ exposure to solar UVR. Limitations of this study were also