How safe are the art materials you use every day?
The three pictures below, for example, is one MSDS for a tube of Winsor & Newton's Cadmium Orange oil paint:
These MSDS (Material Safety Data Sheets) are easily available online. Each tube of paint & each art material of any type or brand has its own MSDS.
Personally, I refuse to use all paints that contain lead and the MSDS tells me this.
A good place to get instant (free) access to information would be a big online art supplier like Dick Blick. Also, any manufacturer will supply these data sheets on request.
Paint thinners can be reused. But when the solvent will no longer clear upon standing, it is exhausted and you will need to dispose of it.
Used thinners are a toxic waste.
Call your local recycling center for disposal instructions. I keep my spent thinners in a storage can and take it to the dump once a year on "Toxic Waste Day." Because it is a bio-hazard, I do NOT dump it into the soil.
To protect our precious water supply, no artist's materials, including acrylics, oil/water media and watercolors, should be washed down the drain - ever.