You can learn alot about the safety of your materials by checking out the labelling on the package. If none is provided then you can check the manufacturing company on-line and request an MSDS sheet (Material Safety Data Sheet) that will cover detailed safety information about the product. This is your responsibility and the only trustworthy source for this type of information. Trust me when I say that the average person working at an art supply store doesn't know the details about each products safety. You have to take responsibilty for this yourself.
Here are a couple of different labels I have found on art supplies in North America. The "AP" label and the "CL" label. These "seals" are US but can be found on products throughout North America as well. There may be different labelling in different countries and different organizations that test art materials for toxicity all over the world. In the US the organizations are called the ASTM and the ACMI. Just to explain the label a bit more the ACMI stands for The Art & Creative Materials Institute. At the bottom of the label you will see the reference to the ASTM which is The American Society for Testing and Materials. I just want to show you these two labels so that you may be familiar with them next time you notice them on the art materials that you are purchasing.
"AP" - is a rating found on a product that is considered to be non-toxic by the ACMI in accordance with the ASTM. You will find this label on many children's art supplies. If you don't see this on your art supplies you can always contact the shop where you purchased the item and/or the manufacturer and request the MSDS sheets for the item so that you can see for yourself if the item is safe. For example the information in this article was supplied by the art manufacturer Winsor & Newton on their website here: http://www.winsornewton.com/resource-centre/health-safety-data-information/ where you can find MSDS sheets for their products available for checking out online.
"CL" - this rating indicates potential risk and is rated so by the ACMI in accordance with the ASTM.
"The "CL" seal (replaced the "HL" seal in 2000) is used for products which are potentially hazardous, with appropriate phrases. For example, some cobalt colours may be labelled with this warning:
"Warning: May produce allergic reaction by skin contact. Contains cobalt. Avoid skin contact. Wash hands after use. Keep out of reach of children." " - winsornewton.com