Human exposure to Al can be roughly divided into two different main types. These include exposure through normal daily consumer products and occupational exposure due to the handling of Al materials. Because Al is abundant in the soil and has many beneficial properties, it is found naturally in many fruits, vegetables, and grain products, as well as in many consumer products. Among other objects, several cosmetics, toothpastes, sunscreens and antiperspirants contain Al. In addition, Al packaging and Al containers dissolve at least some Al in the preservative contents. Such exposure through consumer products is daily and is not related to the occupational exposure identified in this study. In laser welding, the Al fume released into the air is part of the occupational exposure to which those involved and present in the welding process are exposed in addition to the normal exposure of Al through consumer products. The occupational exposure to Al is exposed to all workers who work in processes that fabricate or process Al. These include the Al powder industry, the Al metal
processing industry and Al foundries. In such production facilities, most of the Al that ends up in the human body ends up in the air through respiration, either by being absorbed into the lungs or airways. The amount of Al absorbed through the skin and ingested orally can considered to be almost negligible compared to the amount of Al absorbed through inhalation. First objects exposed to Al in the air in the body through inhalation can be seen in Figure 17. (Tietz et al. 2019, pp. 3503-3504; Buchta et al. 2003, pp. 539-540.)
Figure 17. Inhalation of Al welding gases, fumes and dust (Mod. Spiegel-Ciobanu, Costa &
Zschiesche 2020, p. 2).
The composition of the gas mixture released into the air during the welding process is studied by several different methods, as it is essential what particles the welding fume contains. This information is essential because different kinds and sized particles affect the human body in different ways. Welding fume is studied, for example, using photometer and powder and dispersion analyser, and these can be used to determine the size of the particles at unit density. In addition, secondary neutral mass spectrometer can be used to determine the compositions of successive layers of weld particles. Equipment used for laser welding all belongs to class 4 lasers and must be provided with a separate enclosure. Within this enclosure, the fumes of laser welding can be examined with reasonable accuracy. It has been found that in laser welding, in general, the fume particles are largely spherical, about micrometre in size and contain a composition exactly equivalent to that of laser cutting fumes. Laser welding processes are practically typically fully automated, that their processes
can be adjusted to the optimum and the amount of flue gases can be kept as low as possible.
It has been found that the fumes released into the air by laser welding without filler material are of the same level as metal active gas welding. When the filler material is used, the number of particles released into the air increases as there is more meltable material. Emissions are lower the better the welding parameters are adjusted. The optimally adjusted laser beam only melts the material in barely the right amount, that the amount of welding fumes released into the air is as low as possible. Similarly, the energy source of laser welding is important. When using traditional CO2 laser welding, the emissions are higher than when using modern solid-state lasers. (Palmer & Eaton 1995, pp. 18-19; Warming et al. 2018, pp. 30-31.)
Al is generally considered to be a non-toxic and safe material in most everyday applications.
However, fine Al that accumulates in the body has been found to be toxic in numerous animal experiments and is confirmed to cause dialysis encephalopathy, for example. The safe reputation of Al contributes to the fact that no separate legislation has been defined to limit the exposure to it. There are also no specific exposure limits in the legislation for the exposure through digestion, skin or inhalation. In normal daily life, Al accumulates in the body through digestion, among other objects, originating from wide variety of foods consumed. In case of laser welding, exposure does not happen through digestion, it accumulates in the body almost completely through inhalation.
Al can be absorbed into human body in four different ways - Through skin
- Through respiratory tract - Through lungs
- Through digestive tract
In laser welding, most of Al is absorbed through respiratory tract and lungs. Particulate Al that ends up in the airways initially ends up, at least in part, in the olfactory epithelium and further in nerve cells in the nasal cavity. Al particles can end up through the mucous membranes in the gut or along nerve connections even to the brain. The particulate Al that ends up in the lungs initially ends up in the lung epithelium and lung tissue. Of these, Al particles propagate mainly into the bloodstream and through it throughout the body. The health effects of Al released into the human body are manifold and difficult to elucidate. The
effects of high Al levels have been studied in various animal experiments, and have been found to contribute to growth retardation, delayed development, impaired reproductive performance, and shorter life expectancy (Page et al. 2012, pp. 516-521). Some of these adverse effects have also been found to be inherited by the offspring. (Exley 2013, pp. 1807-1812; Page et al. 2012, pp. 519-521.)