Welding dust contains dangerous
Chromium exists in several different chemical forms, one is toxic and carcinogenic, while another is required for good health. This makes the measurement of the toxic form more complicated because it is not sufficient simply to measure the overall chromium level. Twenty European laboratories worked together on studies to improve the accuracy of the determination of chromium species in environmental monitoring. They also developed two reference materials to help laboratories to check the reliability of the measurements.
Chromium, whose chemical symbol is Cr, is a trace element that exists in a number of forms, all with very different properties. As elemental metal, it is stable and non-toxic and in the trivalent form, Cr (III), it is essential to human life as it plays a vital role in releasing energy from fats and sugars.
However, hexavalent chromium, Cr (VI), is the most toxic member of the chromium family; there is much evidence to suggest it is capable of causing nose, eye and throat irritations in cases of limited exposure and liver or kidney damage and cancer of the respiratory tract in more extreme cases.
Cr (VI) is present in dust that stainless steel welders are exposed to and it exists in water soluble compounds such as chromates. Consequently, it must be monitored closely to ensure that we are protected from its harmful effects. Legislation, including two EC Directives, state the maximum allowed concentration for chromium in drinking water and that continuous monitoring is necessary.
Monitoring air quality in places where welders work and in drinking and waste water is complicated by the fact that testing laboratories must not simply measure the total concentration of chromium; Cr (III) and Cr (VI) must be considered separately as only one of these species is harmful. Prior to the work done in this project, there were many discrepancies between laboratories in the results of measurements for the different chromium species. This made it difficult to obtain the meaningful results required to protect European people from the health risk.
The welders wear filter monitors to evaluate the levels of Cr (VI)-containing dust in the air. This way, the contamination risks related to the dust entering their lungs are better assessed. To test the levels of Cr and Cr (VI) in the workplace air, the filters are washed with water and then the total amount of both Cr (VI) and Cr soluble in water is measured. Drinking water must also be monitored closely to ensure that the level of Cr (VI) is safe.
In order to improve the reliability of the measurements made in water and air analysis laboratories, two certified reference materials (CRMs) were prepared. One was developed to help measure levels of Cr (III), Cr (VI) and total Cr content of drinking water. The other aids measurements of Cr (VI) and Cr on welding dust filters.
Overcoming difficulties to prepare two reference materials
Making the water CRM was particularly challenging as the preparation of any CRM requires a large number of samples to be prepared and each of these has to contain exactly the same known amount of each
Cr species. It is indeed difficult to achieve this as well as the long term stability that is required; the CRMs must be valid for several years. The project participants did many studies together to share expertise and resolve any difficult issues. Problems arose because Cr (VI) may be converted to Cr (III). Once the project team worked out which conditions (pH, temperature, type of container, etc.) stabilised the chromium levels, the one thousand water samples had to be freeze-dried to guarantee an unlimited shelf life.
The second challenge was to produce at least a thousand samples of filter monitors with similar levels of Cr (VI) to what would be found on filters contaminated in the workplace. Each of the many filters in the batch had to have precisely the same levels of Cr (VI) dust and like the water CRMs, they had to retain the same composition over the several years that they would be available. The task was to contaminate many samples in the same way, with dust that is the same particle size as the dust welders inhale. This was done with a specially designed air sampler.
In preparing these tools to help testing laboratories, the work was done in special clean rooms and the scientists had to wear special clothing to prevent the materials from being contaminated by other dust, which would distort the levels of Cr (VI) and Cr measured.
Wide European involvement
Method comparison and performance studies were completed. The 20 laboratories working on the project went through a detailed study to improve the complicated measurement methods used to measure the different chromium species in water and air filters. Each brought different experience in the field of chromium measurements. Some are specialists in water analyses, while others focus on the analysis of air dust.
The group held a number of detailed technical meetings in Brussels as part of the interlaboratory studies. During these sessions, all results were scrutinised scientifically. Only with close collaboration could the participants detect possible sources of error and identify pitfalls in the different techniques. Each laboratory was able to exchange knowledge and experience and thus improve their skills. It was only by working together that these experts were able to provide reference materials that are guaranteed to have a specific Cr level.
A useful tool
The CRMs are used by many national and international institutions worldwide to
monitor the quality of drinking water, natural or surface water. Accurate monitoring is also necessary to protect workers from high exposures to dangerous chromium compounds. Industries and private laboratories find the CRMs useful to improve their skills in chromium analysis. If this monitoring is effective, the risks are better assessed. If the risks are then reduced as a result, there can be a decrease in the number of days workers have to take off due to illness. Consequently, there may be a positive effect on industries as productivity and competitiveness would increase.
For reference, the two CRMs described are CRM 544 (freeze-dried water) and CRM 545 (welding dust on filter).