evolution of life on the Earth. In the last century, changes in lifestyle and .... resort guides and lifeguards (20). Several relevant papers were produced by ...
Peer-reviewed article
SUN CARE - OCCUPATIONAL EXPOSURE Giuseppe Casale
Occupational exposure to solar UV radiation
A short review of relevant papers on the quantification of exposure to solar ultraviolet (UV) radiation of outdoor workers GIUSEPPE R. CASALE1*, ANNA MARIA SIANI1, ALFREDO COLOSIMO2 *Corresponding author 1. Sapienza Università di Roma, Department of Physics, Rome, Italy 2. Sapienza Università di Roma, Department of Anatomical Sciences, Rome, Italy
KEYWORDS: Occupational exposure; solar ultraviolet (UV) radiation; threshold limit values (TLV). ABSTRACT: This paper intends to be a tentative summary of the state of knowledge on the quantification of occupational exposure to solar ultraviolet (UV) radiation by reviewing the relevant literature. The authors have already published some studies on this topic using polysulphone (PS) dosimetry, providing a significant contribution to the few studies on the quantification of UV exposure for professional outdoor workers in Italy. The paper also highlights the importance of such studies in the Mediterranean area and the Italian territory, with high potential to receive intense solar UV doses through most of the year.
INTRODUCTION Ambient ultraviolet radiation (280-400 nm) comprises about 5 percent of total solar radiation reaching the Earth’s surface. It is usually divided into UVA (320-400 nm) and UVB (280-320 nm), while UVC (100-280 nm) is completely absorbed in the upper atmosphere. Ambient UV is affected by a large number of factors: solar zenith angle (the angle between the vertical and the sun, which depends on local coordinates, time of day and time of year), altitude, state of the atmosphere (gases, mainly ozone, cloud cover and particulate) and ground reflectivity (1). Some of them can be sometimes difficult to measure and to quantify. In outdoor activities the human skin is exposed to solar ultraviolet radiation on a daily basis. Erythemal reaction is a well-known acute deterministic effect in human skin due to solar UV exposure, mainly in fair phototypes. Other effects on skin are chronic and include cutaneous malignant melanoma (CMM) and non melanoma (NMSC) skin cancers. Among NMSC, about 20 percent are squamous cell carcinomas (SCC) and 80 percent basal cell carcinomas (BCC), which are among the most frequent cancer types worldwide. CMM are very rare during childhood and youth, more frequent between 30 and 60 years. In 2006, WHO (2) estimated 56000 deaths per year worldwide attributed to solar UV exposure.
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A global estimate of new cases is around 100000 every year. An approximate estimate for Italy is 7000 new cases every year. On a five years basis, 4000 deaths among males (5 per 100000 inhabitants) and 3000 among females (6 per 100000 inhabitants) have been recorded, with peaks of 10 out of 100000 in Trieste, 6-7 in Genova, Veneto and Emilia Romagna (www.epicentro.iss.it). The incidence of CMM between 1980 and 2000 increased by 4-8 percent per year. SCC and BCC also increased during the last years. BCC are 50 times more frequent than CMM and affect young people between 25 and 30 years. Experimental and epidemiological evidences have showed that UV exposure is also a risk factor for some types of eye disorders (3, 4). In 2009, the International Agency for Research on Cancer (IARC) has reconfirmed solar radiation in Group 1, “carcinogenic to humans” (5). There are however beneficial health effects of UV radiation associated to vitamin D synthesis (6, 7). The UV band of the solar spectrum has deeply influenced the evolution of life on the Earth. In the last century, changes in lifestyle and behaviour of people and the increase of human migration out of homelands, have led to an increase or a decrease to UV exposure in comparison to past patterns. Moreover, some studies (8, 9) have suggested that higher temperatures due to global warming could compel people living at mid-latitudes to spend more time outdoors. Consequently, an ever growing number of papers on the quantification of solar UV exposure have been produced. This paper aims at summarizing the studies on the occupational exposures to solar ultraviolet radiation. Several works were conducted mainly in Australia, where the scientific community has been concerned for a while about deleterious UV induced diseases. Recently also in countries such as Italy the interest on this specific topic tends to increase.
MATERIALS AND METHODS Ambient and personal UV exposure Since not the whole UV band is equally effective in producing a biological effect, an action spectrum is used to take into account the effectiveness of UV radiation to produce a biological response. The action spectrum for erythema in
SUN CARE - OCCUPATIONAL EXPOSURE (hereafter called CIE TLV). A value of 10 SED is assumed as a CIE TLV for sun-adapted skin of Mediterranean subjects (18). An exposure greater than 10 SED can be associated to high risk. Web search Studies published in the literature were identified through a search performed using freely the web platforms available at the Physics Department of “Sapienza Università di Roma”: Scopus (http://www.scopus.com). The Web of Knowledge-ISI (Thomson Reuther, http:// www.isiwebofknowledge.com). Google Scholar (http://scholar.google.it). The terms “solar ultraviolet occupational exposure”, all contained “somewhere” in the text, were used as the key criterion of the search.
humans (10) has been widely employed in studies on human exposure. Ambient UV exposure (AE) is defined as the biologically effective radiant exposure incident on a horizontal surface, measured in J m-2. It can be provided by groundbased or satellite instruments. Anatomical sites are indeed differently exposed and receive levels of UV radiation which can be higher than those received from horizontal surfaces. Consequently AE can provide only an indication of individual UV exposure, for example through the solar UV index (11). This dimensionless parameter is determined as the biologically weighted irradiance, using the CIE (Commision Internationale de l’Eclairage) erythemal action spectrum (10), integrated up to 400 nm and divided by 25 mW m –2 (11). The UV Index values can range between 0 (during the night) and above 10 (in the tropics under clear skies and at high elevations). The personal exposure (PE) is usually related to the total amount of UV radiation, weighted by such action spectrum, reaching anatomical sites which are not horizontal. The proportion of ambient UV radiation received by an anatomical site is often provided through the exposure ratio (ER) which is a dimensionless parameter. It is defined as the ratio between PE on a selected anatomical site and the corresponding AE. Exposure ratio is slightly dependent on the environmental exposure conditions, but is strongly related to individual attitudes and posture during exposure (12). ER can be useful to compare different exposure conditions and periods. It was shown (2, 13, 14) that on average the body UV exposure varies between 5 to 15 percent of the corresponding AE, with the exception of outdoor workers whose exposures can reach 20-30 percent. Personal exposures can be determined using physical, chemical or biological dosimeters. The most commonly used UV dosimeters are polysulphone (PS) films which have a response to UV radiation similar to human skin (15, 16). Threshold Limit Values (TLV) The occupational threshold limit value (TLV) to UV radiation was set by the International Commission on Non Ionizing Radiation Protection (ICNIRP) and it is equal to 30 J m-2 per 8 h work for non protected skin using the American Conference of Governmental Industrial Hygienists (ACGIH) action spectrum (17). Such action spectrum considers both ocular and skin effects. The ACGIH TLV was originally used for exposure to artificial sources of UV radiation but in 2004 the ICNIRP recommended its application to outdoor UV exposures as well. The ACGIH TLV corresponds to about 1.0–1.3 SED (1 SED=100 J m-2) when the CIE erythemal effectiveness curve (10) is used
RESULTS Results from the web search: general considerations The web search using Google Scholar produced a total of about 6100 documents, since the early 1970’s. The documents were grouped by 10-years period (1972-1981, 1982-1991, 1992-2001 and 2002-2011). The number of documents to date (September 2011) were respectively 173, 439, 1220 and 3550. This result probably reflects the growing use of digital documents in the last decades without providing much information about the scientific interest on outdoor occupational exposure.
Figure 1. Number of papers dealing with “solar ultraviolet occupational exposure” as retrieved from Scopus and ISI research platforms
Afterward the search was limited only to peer reviewed papers using Scopus and ISI. The two platforms provided similar distributions of the papers (Figure 1) but different peak values. This can be explained by the modality of the web search: Scopus searches the string in the “article title, abstract and keywords”, while in ISI it is only possible to query by looking for the string in the “topic”. Two peaks in the number of peer reviewed papers were found (Figure 1): one at the end of the last century and one in recent years. In our opinion, this could be explained by the two majors issues concerning solar ultraviolet radiation effects that attracted the interest of scientists: at the end of the nineties, when the dangerous effects of solar UV were scrutinized and about ten years later when the beneficial effects of solar UV on vitamin D production were reconsidered, and are still under discussion. It should be noted that not all the papers collected through web search have the purpose of quantifying PE and provide Household and Personal Care TODAY - n 4/2011
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Tables SUN CARE - OCCUPATIONAL EXPOSURE Table 1. Summary of the key findings of the studies on the quantification of solar occupational exposure (for regions outside the Mediterranean). PS=polysulphone, BF=biospore film, EL=electronic devices
Table 2. Summary of the key findings of the studies on the quantification of solar occupational exposure in the Mediterranean region). PS=polysulphone, BF=biospore film, EL=electronic devices
Year Paper* Country
Occupation
Body site
ER
Method
Year Paper* Country
Occupation
Body site
ER
Method
1976
(27)
U.K.
Gardener
Chest
10%
PS
2008
(32)
Italy
Ski instructor
Face
60%-102%
PS
1983
(28)
Australia
Bricklayer
Vertex Shoulder Arm
78% 67% 66%
PS
2009
(34)
Spain
Lifeguard Gardener
Wrist Shoulder
27% 9%
BF
2011
(35)
Italy
(28)
Australia
Classroom teacher
Vertex Shoulder Arm
11% 11% 8%
PS
Vineyard growers
Back Arm
36%-87% 19%-60%
PS
1983
1983
(28)
Australia
Gardener
Vertex Shoulder Arm
69% 70% 59%
PS
1983
(28)
Australia
Physical educational teacher
Vertex Shoulder Arm
63% 53% 42%
PS
1983
(28)
Australia
Roof carpenter
Vertex Shoulder Arm
85% 67% 66%
PS
1994
(19)
Tasmania
Gardener
Chest Back
11% 24%
PS
1997
(21)
Australia
Farmer
Forehead Nose Cheek
21% 34% 25%
PS
2000
(28)
Germany
Lifeguard
Shoulder
55%
BF
2003
(24)
Australia
Building worker
Chest
26%
PS
2005
(29)
Ireland Denmark
Gardener
Wrist
4.5% 8.1%
EL
2007
(12)
Switzerland
Construction worker
Neck
35%
BF
2009
(31)
USA
Lifeguard
Wrist
20.5% PS
2009
(26)
Antarctica
Expeditioners
Chest
10%20%
PS
2010
(18)
Austria
Farmer
Face
12%
EL
* according to the reference number
* according to the reference number
Table 1. Summary of the key findings of the studies on the quantification of solar occupational exposure (for regions outside the Mediterranean). PS=polysulphone, BF=biospore film, EL=electronic devices. actual exposure data. Most of them, indeed, consider the measured exposures as a starting point for further implications on human health. However, our interest here is in summarising what is known about the assessment of the occupational exposure through measures of PE or ER. Occupational exposure: the state of knowledge With respect to the selected papers, our short review should be intended as an initial step for a further, more exhaustive search of published studies on the topic. The key findings of the studies conducted outside the Mediterranean on the quantification of solar occupational exposure are summarised in Table 1. Different methods were adopted to measure personal exposures: PS (polysulphone), BF (biospore film) and EL (electronic devices). More details on each technique can be found in the papers mentioned here. The percentage of the ambient UV radiation (ER) is also reported in the Table. Herlihy et al. (19) and Springbett et al. (6) showed that high rates of NMSC were found in outdoor workers subject to significant solar UV doses. In particular those at higher risk for developing SCC include fishermen, agricultural workers, ski resort guides and lifeguards (20). Several relevant papers were produced by Australian researchers (21-26, 28). Some other important works were conducted in Northern Europe (12, 18, 27, 29, 30) while very few information is available for workers in the USA (31). Studies for the Mediterranean region and Italy It is relevant to notice that no legislation or government programme aiming at protecting outdoor workers from UV exposure, is active at the present time in Italy. Following on the steps of Australian research, few studies were performed in the Mediterranean region (32-35) and very little quantitative information is available about occupational UV exposure (Table 2).
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Table 2. Summary of the key findings of the studies on the quantification of solar occupational exposure in the Mediterranean region). PS=polysulphone, BF=biospore film, EL=electronic devices.
DISCUSSION AND CONCLUSION Table 1 and Table 2 show a large variability in ER among the various working activities: from a minimum of 4.5 percent of the ambient exposure on the wrist of gardeners (29) to 102 percent on the face of ski instructors (32). This is due to the different postures assumed during the working activities, to the environmental conditions and to the orientation of the body site exposed to the sun. The tables also show the different protocols followed in these studies, to suit each particular case. Keeping in mind that a huge spread is unavoidable in this kind of research, and that the results obtained by the different methods (PS, BF and EL) could be difficult to compare, some conclusions should be taken into consideration. It is evident that quasi-horizontal body sites (head, shoulder) are characterised by higher ER values respect to quasivertical sites (chest, face, forehead, nose, cheek) which, however, not necessarily means that horizontal surfaces receive higher doses. Some anatomical sites are subject to more frequent posture changes during activity (i.e. wrist), for which typical ER values cannot be easily defined. The influence of the surrounding conditions is evident in the case of ski instructors (32), since they receive higher UV doses than AE due to snow reflection. Noticeable enough is that indoor activities, such as the classroom teacher (28), can show exposures comparable to those of outdoor workers (for example gardeners in 34). Some of the reviewed papers contain information not only on ER but also on the doses received by selected body areas. Such doses were compared against exposure limits
List of acronyms used in the text ACGIH: American Conference of Governmental Industrial Hygienists AE: Ambient Exposure BCC: Basal Cell Carcinoma CIE: Commission Internationale de l'Eclairage CMM: Cutaneous Malignant Melanoma ER: Exposure Ratio IARC: International Agency for Research on Cancer ICNIRP: International Commission on Non Ionizing Radiation Protection NMSC: Non Melanoma Skin Cancer PD: Personal Dose PE: Personal Exposure PS: Polysulphone SCC: Squamous Cell Carcinoma TLV: Threshold Limit Value UV: Ultraviolet UVA: Ultraviolet (320-400 nm) UVB: Ultraviolet (280-320 nm) UVC: Ultraviolet (100-280 nm) WHO: World Health Organization
SUN CARE - OCCUPATIONAL EXPOSURE (for example 18, 26, 35), showing that outdoor workers often receive UV exposures in excess of the TLV and of 10 SED (18, 35). These results were determined assuming that the dosimeters placed on specific anatomical sites could provide information on the dose received by the differently exposed body areas. It should also be mentioned that a single layer of ordinary clothing is not protective enough against UV radiation. As a matter of fact, a study conducted by Parisi and Wilson (36) showed that T-shirts, of different type and fabric, do not provide effective protection against solar UV radiation. This short review represents an effort to summarize the results derived from studies on the human UV exposures in targeted populations. Although our work needs to be extended, it was found that the quantification of occupational exposures requires further investigation mainly in the Mediterranean region. Moreover, the diversity of exposures related to the various working activities makes the comparison of the exposures a complex issue. Consequently, specific guidelines and a standard protocol should hence be adopted in dosimetric studies.
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