Analysis of Toy Cars for Heavy Metal Content
Two different digestion methods were followed, and both confirmed the presence of Ba and Fe, although the concentrations obtained by each method differed: higher values m/m% was obtained for all samples digested by HCl than for samples digested by acetic acid. Trace amounts of many natural occurring chemical elements such as sodium, magnesium and iron are needed for the proper functioning of the human body1. However, there are also elements which are toxic to the human body such as mercury, lead, thallium, arsenic, cadmium, nickel, selenium and barium. These metals are part of a loosely defined group known as “heavy metals”.
The toxicity of most heavy metals are caused by the fact that they accumulate in the body over time, and interfere with biological activities, for example mercury, which irreversibly inhibits enzyme activity, and lead, which also inhibits enzyme activity and interferes with neurotransmitters, causing a wide range of side effects, some of which are life threatening2. These heavy metals are used in many industrial manufacturing applications which include the manufacturing of pesticides, batteries, alloys, electroplated metal parts, textile dyes, and of particular importance for this study, paints3.
According to studies in the USA, it appears that paints are the leading cause of lead poisoning amongst children, and in particular, the paint found on toys4. In an attempt to ensure the safety of toys, certain international regulations have been formulated. ASTM F-963 is a set of regulations that cover many different safety aspects related to toys, including their heavy metal content. ASTM F-963 prescribes different digestion methods for different toys, all of them aimed at imitating the human digestive system, to determine how much of a certain element will be leached out of a sample and be available for absorption during a given time.
For paints the ASTM F-963 does not recommend total digestions of the toy, but rather scraping off the paint, as the surface of a toy is the part most likely to be digested by the human stomach. 5 Various techniques and instruments can be used to analyse the digested and prepared samples, the different choices mostly dependent on the concentration range, and the elements being tested for. For this study the analysis method of choice was ICP-OES, inductively coupled plasma optical emission spectroscopy6.
This type of spectroscopy uses an inductively coupled plasma to excite atoms and ions to emit electromagnetic radiation at wavelengths unique to particular elements. The intensity of the emission can be correlated to the concentration of the specific element within a sample. One of the advantages of ICP-OES is that it is not only able to detect specific elements quantitatively, but it is also capable of performing multi-elemental qualitative scans. This is extremely convenient when determining in advance whether it will be worthwhile to analyse quantitatively for a specific element.
ICP-OES can also detect more than 70 elements, making it very versatile. 7 However, it does have a few disadvantages. It doesn’t have very low detection limits, with its dynamic range being a high ppm range. This instrument is also very expensive, and the argon used for the plasma, is also a rather expensive inert gas. Furthermore this instrument does not allow the detection of isotopes, but fortunately this is of very little importance for this specific study7. Preparation of standards Standards were prepared for calibration curves for detection of Ba and Fe.
Ba(NO3)2 was used to prepare a 5 ppm Ba stock solution, from which 2 ppm, 1 ppm, 0. 5 ppm,0. 25ppm, 0. 1 ppm and 0. 005 ppm solutions were made up by dilution. FeSO4. 7H2O was used to prepare a 5 ppm Fe stock solution, from which 2 ppm, 1ppm, 0. 5 ppm, 0. 1 ppm, 0. 05 ppm and 0. 02 ppm solutions were made up by dilution. The solutions were measured by ICP-OES. 2. Sample preparation Paint was scraped down from yellow and from black toy cars. The yellow batch was mixed to homogenise it, as was the black batch. 3. Sample digestion according to method 1 5 paint sample of yellow paint (? 100 mg) and 5 samples of black paint (? 00 mg) were weighed out. To each sample was added acetic acid (10 mL, 4%).
The samples were left to stand for 24 hours in darkness. The samples were then filtered, and the extractions diluted to 50 mL. All the samples were measured by ICP-OES. 4. Sample digestion according to method 2 5 paint sample of yellow paint (? 100 mg) and 5 samples of black paint (? 100 mg) were weighed out. To each sample was added HCl (5 mL, 0. 1 M). The HCl containing samples were heated in a water bath at 37 °C in darkness for 1 hour, with agitation. This was followed by 1 hour in the water bath in darkness without agitation.
The samples were the filtered and the extractions diluted to 50 mL. All the samples were measured by ICP-OES. All analysis was done on a ICPS-7510 Shimadzu instrument. RESULTS 1. Qualitative broad scan Before starting quantitative analysis, a qualitative elemental broad scan was performed to see what metals were present in sufficient quantities to merit analysis. Ba was the only discovered heavy metal, along with Fe and Ca. The decision was made not to analyse for Ca, as it is present in all water sources, and the ICP-OES almost always gives false concentration values for Ca.
It was then decided to analyse only for Ba and Fe. . Barium A calibration curve was drawn from the intensities measured for the series of prepared standard solutions, giving a linear trend line y = 8. 7928x – 0. 4183, R? = 0. 9995, where y = intensity, and x = concentration. After measuring the standards, all the prepared samples were measured and from the calibration curve the concentration of Ba in both the yellow and black paint, prepared by different digestion methods, could be determined. Table 1 gives the summarized data obtained from the measurements. Table 1. Summarized data for Ba concentrations for different paint colours and digestion methods.