Abstract
Near infrared or infrared A (IRA) accounts for over 40% of the solar spectrum (SS) and is able to reach subcutaneous tissue as well as the retina. Outdoor workers are occupationally exposed to solar radiation (SR), but the level of exposure may differ widely depending on the job performed, time spent outdoors, latitude, altitude, season, personal protection, etc. Until now, risk assessment and management for outdoor workers has focused on the prevention of both acute and long-term effects on the eye and the skin due to solar ultraviolet radiation (UVR) with little consideration of the other components of the SS (a possible exception is represented by visible radiation with reference to the eye). A growing body of evidence coming from in vitro studies indicates that IRA is involved in cellular reactive oxygen species (ROS) production and may interfere with the respiratory chain in the mitochondria. Moreover, it can modulate gene expression and some metabolic pathways. The biological action of IRA is only partly attributable to a thermal mechanism, should it be also involved in photochemical ones. The cellular and molecular pathways affected by IRA are partly similar and partly different with respect to those involved in the case of visible ultraviolet A (UVA) and ultraviolet B (UVB) radiation. Consequently, the net effect of the SS is very difficult to predict at different levels of the biological organization, making more difficult the final balance of health risk and benefits (for the skin, eye, immune system, blood pressure, etc.) in a given exposure situation. Moreover, few in vivo studies and no epidemiological data are presently available in this regard. Investigating this topic may contribute to better defining the individual exposome. More practically, it is expected to bring benefits to the risk assessment and management for outdoor workers exposed to SS, contributing to: (1) better definition of the individual profiles of susceptibility, (2) more focused preventive and protective measures, (3) better implementation of the health surveillance and (4) a more effective information and training.
Highlights
The spectral composition of solar radiation (SR) at the ground includes over 6% of ultraviolet radiation (UVR), 38–39% of visible radiation and about 55% of infrared (IR) radiation
It should be noted that, to what occurs in many other research fields, the introduction of
A more complete preventive and protective approach to outdoor workers exposed to SR requires to account for the whole solar spectrum (SS) as well as the complete set of potential health outcomes in outdoor scenarios characterized by different patterns of co-exposure to environmental and occupational physical, chemical and biological agents (Figure 4)
Summary
The spectral composition of SR at the ground includes over 6% of UVR, 38–39% of visible radiation and about 55% of infrared (IR) radiation. Visible radiation ranges from 380–400 to 700 nm, while IR, which constitutes about half of the whole SR, covers the spectral range from 700 nm to 1,000,000 nm and extends between far visible radiation (red) and the upper end of the radiofrequency spectrum It is subdivided into three bands: near IR (or IRA, 700–1400 nm), mid IR (infrared B or IRB, 1400–3000 nm) and far IR The possible interactions with other spectral bands of SR (especially UVB and UVA) and the role of IRA in determining the balance between adverse and beneficial effects of exposure to SR in outdoor workers are discussed, with a sub-focus on the immune system. Before discussing concerns regarding solar IRA, it is useful to summarize biological and health effects due to SR, largely attributed to UVR
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