Painted toys need careful handling.
A standard supporting the European Toy Safety Directive requires
reproducible testing methods to be used to measure levels of toxic
elements found in paint used on children's toys. To improve the
quality of paint coating analysis, this project produced three Certified
Reference Materials for seven toxic elements. These materials will
benefit the toy testing laboratories and national bodies responsible
for their accreditation. Indirectly they will improve the safety
of children in Europe.
The Toy Safety Directive lays out essential safety limits that must be met before toys may be sold in the European Union. It states maximum levels for the "migration of toxic elements from toy materials", including paint. Measuring the amount of soluble trace metals in paint is not as easy as you might think.
For the results to be meaningful, it is important to measure not the total amount of the substance, but instead, the amount that will be transferred from the toy to the child's body. Many of the toxic elements, namely antimony, arsenic, barium, cadmium, chromium, lead, mercury and selenium, have found their way into paint pigments over the years. As a result, laboratories need to use precisely defined extraction processes to get the right amount of the metal to migrate from the sample, ready to be measured.
When laboratories took part in a survey to compare their test results using the European standard, the variation was enormous, even between experienced expert laboratories using their best techniques and equipment. With less experienced laboratories, there may be even greater variations.
The way forward
The project partners thought a series of Certified Reference Materials would really help to improve laboratory performance. This is because the CRMs gives testing laboratories a reliable tool to check that their procedures are valid and are producing accurate results that can be easily compared to any other laboratory also using the CRM. Using CRMs is a key aspect of gaining laboratory accreditation. They are also valuable for training staff to use the analytical method correctly.
The CRMs produced in this work represent several years of work, involving ten laboratories from six European countries. These laboratories are all either nationally approved for toy testing or experts in reference material certification studies. Long before reference materials preparation, the project team performed an extensive interlaboratory comparison to assess and improve the cutting-edge measurement techniques available at that time. In this study, each participant received a set of two paint samples, one on aluminium and the other flaked, and a solution containing known amounts of each metal. The latter was for calibration purposes.
Each laboratory measured the toxic metal contents of the three materials, using a range of analytical spectroscopic techniques. They then compared results, which varied least for the calibration solutions and most for the painted panel. The measurement data were more similar for some metals than others and mercury results varied the most. It was clear to these laboratories that they, and other laboratories, could improve the quality of their measurements with CRMs.
On discussing the reasons behind the variation, the partners decided that the standard did not describe the procedure to extract the metals from the paint in enough detail. So, before they started preparing the CRMs, they added some supplementary notes to the standard. These notes describe the way to scrape the paint off the panel, sample size, temperature and filtration methods that would be used in the certification
The project coordinator's (Laboratory of the Government Chemist, or LGC, in the UK) next step was to prepare the reference materials. They chose paints and materials to paint that reflect common toy manufacturing practice. These were mild steel coated with alkyd resin paint, plastic coated with acrylic paint, alkyd resin paint flakes and aluminium and beech wood each coated with nitrocellulose paint.
Preparing the paint
Paint came from a specialist paint manufacturer, Trimite Ltd, in the UK. Between 80 and 35 litres of each type of paint were used. The next challenge involved contaminating the paints so that they contained close to maximum levels of the toxic element. By adding base paint and tinters or pigments, LGC achieved a "realistic" contaminated paint. However, because the amount of metal added is not proportional to the amount that can migrate, this had to be done on a trial and error basis.
An experienced paint spraying company, Auto Imagination Ltd sprayed the large batches of paint on to the 2,500 panels, each measuring 15 cm X 10 cm, for each reference material. Over five kilograms of dried paint flakes were also prepared.
Once the panels had been prepared, the LGC tested them to make sure that the materials would be stable over different temperatures and time and that toxic metal content was the same between sample panels in each batch. When it was clear that the panels' homogeneity and stability would not cause any problems, the certification began.
Success at last
The same ten laboratories that had taken part in the preliminary study measured each of the five different paint samples for the eight toxic elements, using the amended procedures that they had developed previously. After considerable discussion and statistical analysis of the results, the laboratories found the variation in their results had generally improved. The laboratories' data for the painted steel and plastic and the paint flakes were in close enough agreement to certify the concentration of each metal, except mercury. A broader spread of results for the painted wood prevented these reference materials from being certified. As reference materials, however, they can still be used to help laboratories in their daily quality control.
Through this study, each participant could measure up their test results against other European organisations and find new ways to improve. Through the three CRMs and the two reference materials, all toy testing laboratories across Europe and further afield have access to tools to help ensure the quality and comparability of their toxic element measurements. With more reliable test results, toy and paint manufacturers and parents can be better assured that toys are safe.