State Institution “Institute of Occupational Health named after Yu. I. Kundiiev of the National Academy of Medical Sciences of Ukraine”, Kyiv
ABSTRACT. The article presents the peculiarities of changes of concentrations of nanoparticles in the working air during welding operations over time, which are characterized in most cases by a sharp increase in their emission during the first minutes after welding and reducing with ambiguous fluctuations within 30 minutes and over. Also, data on the formation of nanoparticles in various production processes associated with the production of nanoproducts, which concentrations may exceed the exposure levels recommended in the EU countries, which requires both the improvement of technological processes and the development of safety measures when working with nanoscale objects, have been summarized.
Keywords: nanoparticles, welding aerosols, air of working zone.
The widespread development and introduction of nanotechnologies makes it possible to successfully solve many problems of improving the standard of living, energy supply, ecology and contributes to progress in industry, science, technology, medicine, environmental protection, agriculture, and other sectors of the national economy. According to existing predictions, production of nanomaterials, and, therefore, their number and diversity will rapidly increase in the near future [1].
This will inevitably lead to the entry of significant quantities of nanomaterials into the environment, their accumulation in the biota components and abiotic environment, with the subsequent possible transfer to humans and the manifestation of the harmful effects of nanoparticles on living organisms. And due to the low level of knowledge with nano-objects, which properties differ significantly from those in a macro-state, manifestations of behavioural features in real conditions are possible, which may entail new dangers. [2‒7].
The peculiarities of the toxic action of nanoparticles, in contrast to the macro forms of substances, depend on many factors: their physical nature, surface properties, structure of nanoclusters and nanoparticles, the diversity of sizes, shapes, methods of production and dispersion, concentration, composition, impurities, as well as the effects of biomodification and biotransformation of the same material, biological model on which tests are conducted [8].
The main sources of nano-sized particles both in the environment and in the working air are industrial production (chemical synthesis, mechanosynthesis, electron beam synthesis in vacuum, etc.), laboratory synthesis of nanomaterials (oxides of silicon, titanium, zinc, iron, cerium, aluminium, metallic nanoparticles of iron, copper, cobalt, nickel, aluminium, silver, gold, carbon nanotubes, fullerenes, nanoparticles of biopolymers and recombinant viruses, carbon nanotubes), as well as by-products of human activities (welding, foundry, work products of gasoline and diesel engines), accompanied by the release of NPs [9, 10].
When examining workplaces associated with nanotechnology, a significant excess of nanoparticle content was found from 5 to 68 times in the working air directly during the production process compared to the control (background) parameters [2].
According to a large number of research studies, nanoparticles are more toxic than ordinary microparticles, able to penetrate through cellular barriers, as well blood-brain barrier into the central nervous system in unchanged form, circulate and accumulate in organs and tissues, cause pathomorphological changes in internal organs, and also are extremely difficult excreted from the body [11, 12,13].
By the level of impact on human health, suspended particles, especially small ones, are classified by the World Health Organization as priority pollutants. Therefore, one of the new current trends in modern hygienic studies is the assessment of the hazard of nano-sized particles, the aerodynamic diameter of which is less than 0.1 µm.
It should be noted that among the complex of harmful industrial factors accompanied by the formation of nano-sized particles, welding aerosols (WAs) have the most negative impact on the human body. The biological activity of metal compounds that are part of WAs depends on their ability to bind to blood and tissue proteins, increase permeability of cell membranes, block intracellular and extracellular enzymatic systems, which ultimately leads to the development of abnormal changes in the body. According to the results of the analysis of the working conditions of workers engaged in various welding methods, it has been established that the performance of such work is accompanied by the formation of harmful chemical factors consisting of WA toxic components, as well as flux dust. These factors depend on the welding method, qualitative composition of the metal, etc. Studies of the presence of harmful substances in the working air and breathing zone of workers engaged in various types and methods of welding have revealed that the chemical factor is the most unfavourable one. The concentration of the solid component and other harmful substances in the WAs in the breathing zone of welders increases in proportion to the rate of their formation in the arc zone [14, 15].
Therefore, assessment of changes of concentrations of nano-sized particles in the working air under production conditions over time can be the basis for developing measures to reduce their danger.
Materials and methods. The counting concentration of nanoparticles in the working air was measured using a DAS-2702 diffusion aerosol spectrometer (Russia) with an air flow rate of 0.5 L/min. The concentration of ultradispersed particles was registered every minute after the end of welding.
A diffusion aerosol spectrometer combines diffusion batteries and a condensation particle counter. The capabilities of the device include determination of the total counting concentration of particles in the range from 3 to 200 nm, the distribution width, and distribution spectrum by sizes in the range from 3 to 200 nm. The distribution spectrum according to the method of calculation [16] is unimodal and allows to determine the following parameters: counting concentration of particles in the range of maximum concentration (particles in cm3); particle size range, which accounts for the maximum concentration (nm). Measuring the time of one set of values was 0.8–1.2 minutes.
The following electrodes were used in the study: 14-25, 14-26, 14-27, 14-30, 14-32, АNО-36, АNО-12, Cristal. Studies were conducted in the welding test complex of Institute of Occupational Health named after Yu. I. Kundiiev of the National Academy of Medical Sciences of Ukraine.
WA samples were taken in accordance with the standard DSTU ISO 15011-1:2008 [17] by the method of complete capture of aerosol, which is formed during welding using a special stand with an FPP filter installed on the path of movement of WA from the cover of the welding zone.
Results and discussion. As a result of conducted studies it was found that the largest emission of nano-sized particles into the air immediately after welding (1st to 2nd minute) was for electrodes Crystal, 14-32, ANO-12, 14-30 and 14-27 (Table 1) At the same time, the primary emission of nanoparticles for the electrodes 14-26, ANO-36 and 14-25 was significantly lower compared to the first group of electrodes (5 to 15 times).
Table 1
Changes of the concentrations of nanoparticles in the working air during welding with the studied electrodes over time (particles/cm3)
Further, from the 5th to 30th minute, a gradual decrease in counting concentrations of nano-sized particles was observed for virtually all electrodes (excluding ANO-36 and 14-25). Moreover, immediately after welding (first minute), the counting concentrations of nanoparticles with ANO-12 and ANO-36 electrodes were different, and later (from the 5th to 30th minute), their dynamics virtually did not differ. For example, ANO-12 was characterized not only by a high emission of nanoparticles in the first minute after welding (261,705 particles/cm3), but also showed a slight decrease over time — even 20 minutes after welding, it remained quite high (147,595 particles/cm3). And after 30 minutes, values comparable with those of the other studied electrodes — 14-25, 14-26, 14-27, 14-30 were recorded. The exception was for ANO-36 electrode, after using of which for welding, despite the initial insignificant concentrations of nanoparticles, further showed a tendency to increase of the total concentration.
The highest increase in particle emission from 1 to 100 nm immediately after welding was observed when using a Crystal electrode — 264,854 particles/cm3 (Fig. 1.), and the smallest — when using electrode 14-25 and amounted to 16,994 particles/cm3 (Table 2) Subsequently, from the 5th to 30th minute, the actual increase in the concentrations of NPs in the working air decreased in 6 out of 8 studied electrodes (except for 14-25 and ANO-36), which may be due to the agglomerations of NPs due to the lack of their stabilization.
Fig. 1. Changes of the concentrations of particles 1–100 nm in size in the working air when using the Сrystal electrode over time
Table 2
Increment of the concentrations of nanoparticles in the working air during welding with the studied electrodes over time (particles/cm3)
Changes in the increment of nanoparticle concentrations in the welder’s working air over time (similarly to the Сrystal electrode) in the first 1–2 minutes of the study was also maximal when using other electrodes: 14-30, 14-27, 14-32, and ANO-12 (7.34 to 9.98 times, respectively) compared to the corresponding background values. The increment in the concentrations of nanoparticles for electrodes 14-25, ANO-36 and 14-26 was significantly lower than that of other electrodes in this experiment 1–2 minutes immediately after the welding procedure (1.73 and 2.95 times, respectively) and relatively higher in the next 5 to 20–30 minutes than in the first term of the study.
Previously, when studying other electrodes (MP-3, TsNIIN-4, NZh-13), it was also established that during welding, ultradispersed particles with a diameter from 1 to 100 nm are formed and enter the working air, and their concentrations depended on the composition and diameter of the welding electrode, as well as the distance from the place of burning of the electrode, welding method, qualitative composition of the metal, and they increased in proportion to the speed of their formation in the arc zone [18].
Welding led to a sharp increase in the concentration of ultradispersed particles 1–2 minutes after electrode burning. The closer the distance from the burning arc zone, the higher the NP concentration was — at a distance of 1 m from the arc zone, the total concentration of ultradispersed particles using the MP-3 electrodes was 140,426 particles /cm3, which was almost three times higher than at 2 m from the arc zone (48,284 particles/cm3). In the next 2 minutes, the concentration of ultradispersed particles sharply decreased and amounted to 10,564–12,315 particles/cm3, while no particles up to 50 nm in size inclusively were registered. At the same time, a significant number of particles with sizes ranging from 100 to 200 nm was registered, which can be explained by the agglomeration of NPs.
In general, changes in the concentration of ultradispersed particles over time during welding in real time was characterized as follows: during the first 1–2 minutes after welding, in most cases, there is a sharp increase in the concentration of ultradispersed particles, as well as its fall, followed by ambiguous fluctuations in the concentrations of nanoparticles for 30 minutes or more and some restoration of the background levels after welding, depending on the type of electrode and its diameter, as well as the distance from the welding zone. With increasing distance from the place of welding, the concentration of particles decreases.
Features of changes in the concentrations of nano-sized particles over time were also observed in other technological processes associated with the production of nanoproducts. For example, during the operation of the electron-beam apparatus UE-202 for the production of nanomaterials and powders with a nanostructure for aviation, engines, gas pumping turbines, the maximum concentration of particles ranging in size from 1 to 100 nm in the working air was 135,618 particles/cm3 (Table 3), which is much higher than the exposure levels recommended in EU countries (20,000–40,000 particles/cm3). The minimum particle concentration from 1 to 100 nm was 14,666 particles/cm3, that is, it corresponded to the acceptable level [19].
When studying the total concentration of particles from 0 to 100 nm in the working air of a planetary mill for the mechanical activation and mechanosynthesis of nano-sized metal powders [20,21], it was found that it is very low — at the level of a common laboratory room. With the drums closed, the concentration stably varied between 8,738–11,225 particles/cm3.
At the same time, when opening the drums in the first minute, the concentration increased to 13,530 particles/cm3, (the first peak from 11 to 12 minutes), however, already in the next minute it decreased to 10,446 particles/cm3 and remained stable until the exhaust hood was activated.
When carrying out the physicochemical synthesis of cadmium sulphide (CdS) nanoparticles under various conditions: the synthesis of CdS nanoparticles stabilized with thioglycolate acid in an alkaline medium (NaOH) and the synthesis of CdS nanoparticles stabilized with gelatin without heating (at a temperature of about 20 °C), as well as the synthesis of CdS nanoparticles with gelatin heated to 45–50 °C, it has been established that particle concentration of 1 to 100 nm in the working air of a researcher engaged in the physicochemical synthesis of nano-sized cadmium sulphide predominantly fluctuated between 21,000 and 42,000 particles/cm3 [22], which almost did not exceed the exposure levels recommended in EU countries (20,000–40,000 particles/cm3).
For example, during the synthesis of CdS nanoparticles stabilized with thioglycolate acid in an alkaline medium without heating (46 minutes after the start of measurements), the concentrations of nanoparticles in the air were registered at the level of 23,000–26,000 particles/cm3. Concentrations of nanoparticles ranging in size from 1 to 100 nm in the air 3 minutes after synthesis with heated gelatin (26 minutes after the start of measurements) increased from 28,000 to 42,000 particles/cm3. At the same time, the synthesis of CdS nanoparticles with gelatin without heating (37 minutes after the start of measurements) did not affect the total concentration of particles of 1–100 nm in the air, which fluctuated both before and after the synthesis within 21,000–29,000 particles/cm3.
In other production processes (smelting of secondary lead, processing of plant materials, dosing of chrysotile asbestos) [22, 23], the concentration of NPs in the working air was between 5,000 and 50,000 (Table 3).
Table 3
The levels of emission of nanoparticles in various production processes [22, 23]
Therefore, it was concluded that such a nanotechnological process as electron-beam synthesis in a vacuum, as well as production processes, the purpose of which is not to obtain nanomaterials (electric welding, smelting of secondary lead), have the greatest potential danger.
According to the literature, during the study of ultradispersed aerosols [24, 25, 26], fundamentally different characteristics of suspended particles were obtained by counting concentration of nanoparticles in the working air for various types of production processes at the mining, industrial-rubber and chemical industries. For comparison, studies of values similar by the algorithm in the working areas of administrative employees or engineering staff (IS) who are not involved in production processes were used. For example, in the working air of a mining enterprise in the underground working conditions there is a relatively large number and weight concentration of ore particles with sizes ranging from 0.5 to 3 μm, the counting concentration of nanoparticles does not differ from the control; above the ground: in the process of flotation — a high counting concentration of nanoparticles and a low weight concentration of suspended substances; in the process of granulation — the maximum counting concentration of nanoparticles is higher than the control one by 19–26 times; in the process of product overload — the maximum counting concentration is 6 times higher than the control one. In the working air of the workshops of the industrial-rubber enterprise (as compared to the control workplace), the significant excess of the counting concentration of particles at workplaces was from 4 to 11.2 times. Chemical production was characterized by a higher level of the counting concentration of particles in the maximum distribution in the workplace — 10,683 particles per cm3. At the same time, in three out of seven workplaces in production, lower counting concentrations were obtained, which was consistent with high humidity at workplaces of operators of absorption, precipitation, preparation of raw materials and supply of semi-finished products and products. The increased counting concentration of nanoparticles compared to the control values was obtained at the workplace of the operators of oxidation — 32,844 particles per cm3 (3 times), condensation — 48,544 particles per cm3 (4.5 times), production of chemical reagents — 53,583 particles per cm3, (5 times).
The formation of a stable aerosol is also possible at different stages of the synthesis/processing of oxide and metal nanopowders in a research laboratory. The concentrations of aerosol particles in the working air (the number of particles/cm3) were determined in the range from 14 to 723 nm [27]. The laboratory included 6 sectors of nanomaterial synthesis/processing. During measurement, each sector was put into operation when the other sectors were turned off. The average daily concentration of the working laboratory was determined 3times a day (at 10:00 am, 01:00 pm and 06:00 pm) for 6 months with constant production of nanostructured materials, and ranged from 31,200 to 6,081,000 particles/m3. Moreover, their last maximum amounts were registered at the stages of disaggregation of dried nanopowders in a high-speed mill. When restoring hydroxide and oxide nanopowders, the total number of NPs was 2,562,000. At other stages of the processes, the concentrations of NPs was from 30,400 to 55,800, and the average daily concentration in the laboratory was 35,300.
The highest prevalence of nano-aerosols in workplaces is associated with the formation of particles during high-temperature processes (such as refining and processing, thermal spraying, welding, cutting and grinding metals). Burning processes are also accompanied by the formation of nanoparticles. Particle size depends on the conditions for obtaining them, although the primary particles will mainly have a diameter from 10 to 50 nm. If the content of the initially formed particles is high, then they quickly coagulate with each other to form agglomerates, which may be larger than those established for the nanoparticles. It is believed that these open (fractal type) agglomerates of primary particles after sedimentation in the respiratory tract will reveal significant similarity in behaviour with nanoparticles. Simple estimates show that a 50 % reduction in particle content is expected in 20 hours due to coagulation upon counting concentration of particles of 10-3 m-3, and with a counting concentration of particles of 1014 m-3, the same reduction will occur in 55 hours [26, 28].
Nanotechnology, like any new technology, has not only undoubted advantages but also the potential danger of harmful effects on human health and natural ecosystems. According to the analysis of a large number of research studies, nanoparticles are more toxic than ordinary microparticles, able to penetrate through cellular barriers, as well as blood-brain barrier into the central nervous system in unchanged form, circulate and accumulate in organs and tissues, resulting in more pronounced pathomorphological changes in internal organs (e. g. formation of granulomas in lungs, liver cirrhosis, glomerulonephrosis), and also are extremely difficult excreted from the body due to their stability [7].
Among the production processes with the highest risk of harmful effects of nano-sized aerosols, electric arc welding and cutting of metals, pyrometallurgical processes of metal refining, the gas-aerosol exhaust of diesel engines, production and use of paint and varnish nanomaterials, application of protective nanocoatings are distinguished [29].
Concentrations of nano-sized particles in different production processes may exceed the exposure levels recommended in the EU countries, which requires both the improvement of technological processes and the development of safety measures when working with nano-size objects.
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Надійшла до редакції 15.02.2019 р.