摘要：Occupational exposure to solar radiation may induce both acute and long-term effects on skin and eyes. Personal exposure is very difficult to assess accurately, as it depends on environmental, organisational and individual factors. The ongoing climate change interacting with stratospheric ozone dynamics may affect occupational exposure to solar radiation. In addition, tropospheric levels of environmental pollutants interacting with solar radiation may be altered by climate dynamics, so introducing another variable af- fecting the overall exposure to solar radiation. Given the uncertainties regarding the direction of changes in exposure to solar radiation due to climate change, compliance of outdoor workers with protective measures and a proper health surveillance are crucial. At the same time, education and training, along with the promotion of healthier lifestyles, are of paramount importance. var currentpos,timer; function initialize() { timer=setInterval("scrollwindow()",10);} function sc(){clearInterval(timer); }function scrollwindow() { currentpos=document.body.scrollTop; window.scroll(0,++currentpos); if (currentpos != document.body.scrollTop) sc();} document.onmousedown=scdocument.ondblclick=initialize Carlo Grandi, Massimo Borra, Andrea Militello and Alessandro Polichetti 344 regard, the Minimal Erythemal Dose (MED) is the ef- fective UVR dose able to induce a "just perceptible ery- thema" on a previously unexposed skin. As MED may be highly variable depending on phototype and other condi- tions, a Standard Erythemal Dose (SED) was introduced [5]; 1 SED is equal to 100 J/m 2 of UVR weighted on the standard action spectrum for erythema. UVR displays a high variability in terms of human exposure being strongly susceptible to the influence of both environmental and individual factors [3, 6, 7]. UVR at the ground depends on time of day (a signifi- cant UV exposure occurs between 9:00 a.m. and 3:00 p.m., sun time, with the maximum values between 11:00 a.m. and 1:00 p.m., being UVB much more af- fected than UVA), season, latitude (3-4% increase for each degree of latitude toward the equator) and alti- tude (an increase of 300 m in altitude determines a 4% increase of the UVR). Cloudiness is a key factor in de- termining the amount of UVR reaching the earth sur- face. For instance, a complete and thick cloud cover blocks almost all the UVB component (while a part of UVA still passes); on the opposite, an incomplete cloud cover or the presence of sparse cloudiness may even in- crease the UVR reaching ground, with respect to a clear sky, because of scattering and reflections. Moreover, human exposure at ground level is greatly affected by type, extension and spatial orientation of surrounding surfaces. Water surfaces (sea, lakes etc.) and the fresh snow, as well as surfaces of metallic structures, reflect a great proportion (up to 100%) of the incident UVR, determining high exposures. On the opposite, trees and vegetation in general may shield at various degree the UVR. Human exposure is mainly affected by the time spent outdoor and the type of activity. Single parts of the body are differentially exposed to solar UVR, de- pending on garments worn and on the position with respect to the sun or reflecting surfaces, which, in turn, depends on posture and movements. UV index is a tool to facilitate the communication of the intensity of solar UVR to the general public [8, 9]. The unit of the UV index is equal to 0.9 SED/h and the UV index value is generally included in the range between 1 (very low) and 10 (very high) sometimes reaching, at low latitudes and/or high altitudes, extreme 11+ values. In the last two decades, UV index has been generally provided daily (or even hourly) worldwide, with a good spatial reso- lution for an increasing number of locations. A radiative transfer model is applied for UV index calculation taking into account weather conditions; however, UV index is a measure of the direct UVR reaching the ground, not including all reflected or diffused components. The remaining part of the solar spectrum responds in a similar way to climate change. In particular, IRR, due to important absorption by water, is severely affected by the variability in cloud cover, contributing to the es- tablishment of thermal gradients and exacerbating the intensity of extreme weather events. HEALTH EFFECTS OF SOLAR RADIATION As optical radiation does not penetrate deeply biolog- ical tissues, skin and eyes are the main biological targets of SR, which however is also responsible of systemic ef- fects. Acute and long-term effects of SR, both deleteri- ous and beneficial, are summarized in Figure 1. Effects on wellbeing and circadian rhythms due to both natural and artificial light (see for instance [10]) continue to be poorly characterized. Consequently, their modula- tion by environmental factors is hard to study and any speculation is currently inappropriate. Health effects of SR are mostly attributed to UVR, with UVA and UVB differently propagating in and interacting with biological tissues as described herein- after. UVB may reach the basal layer of the epidermis while UVA, more penetrating, may reach the dermal tissue, which may absorb a significant fraction of the in- cident UVA [4]. At the eye level, UVR < 290 nm is com- pletely blocked by the corneal tissue while a significant proportion of UVA (60-80%) crosses the cornea and is absorbed by the lens; about 1% of the UVA incident to the eye surface may reach the retinal tissue [11,12]. UVR may be absorbed by macromolecules like DNA and proteins, altering their molecular structures. DNA is regarded as the main target of UVR and DNA lesions (mainly cyclobutane-pyrimidine dimers and 6-4-pho- toproducts) are produced by both UVB and UVA, although the former is much more efficient. DNA le- sions may trigger a lot of molecular events ultimately re- sponsible for both acute and chronic effects, but UVR, especially UVA, is also able to form Reactive Oxygen Species (ROS) in cells and to activate exogenous and endogenous photosensitizing molecules, leading to phototoxic and photoallergic reactions [13, 14]. Finally, UVR exposure may be associated to epigenetic altera- tions in skin cells [15]. UVR is responsible of both acute and chronic effects on skin and eye, depending on UV dose, dose rate and the susceptibility of the biological targets. At the skin level [2] the best-known acute effect is the erythema, whose severity may span from a just perceptible red- ding to oedema and blistering depending on the UVR dose. Erythema displays an induction threshold de- pending on phototype, part of the body and previous exposure, and an action spectrum showing an efficacy of UVB up to 2-3 orders of magnitude higher with re- spect to UVA. Melanogenesis (the process leading to tanning) is also an acute effect of UVR, displaying the same action spectrum of the erythema and essentially regarded as an adaptive reaction of the skin to the UVR insult. Melanin is a complex molecular structure able to absorb UVR (shielding effect) and to remove ROS: it is produced by melanocytes as granules, which may be transferred to keratinocytes. An immediate pigment darkening (essentially triggered by UVA and acting on the existing melanin) occurs within minutes during ex- posure, a persistent pigment darkening (triggered by UVA and UVB) takes place within few hours and a de- layed tanning (induced mostly by UVB and involving the synthesis of new melanin) arises after days since exposure and may last weeks or even months. Tanning depends critically on the phototype (Table 1). Albinism is a condition of congenital absence of melanin synthe- sis, with a consequent high photosensitivity. Thickening of the corneal layer (hyperkeratosis) is another adaptive reaction of the skin to UVR exposure.
关键词：climate change; solar radiation; ozone depletion; occupational exposure; outdoor workers
