The name WD-40 stands for “water displacement, formulation successful in 40th attempt.” Convair, a unit of General Dynamics, first used WD-40 to protect the outer skin of the Atlas missile from rust and corrosion.
Polycarbonate is a transparent plastic that is commonly used in greenhouses, and polystyrene is typically used for styrofoam and soft drink lids among other items.
Generally it is safe as long as you don’t ingest it, or breathe in the fumes for a prolonged period of time. Try to avoid contact with your skin and don’t leave it around children unattended.
WD-40 can irritate skin so it is not recommended to use it on your joints or for arthritis pain relief despite old wives tales touting it as a cure for arthritis and other ailments.
Fill a 5 gallon bucket with water and pour the entire thing into the toilet to to force it to flush. Spray the WD-40 directly onto the hard water stains and all over the inside of the bowl.
Let it sit for 5-10 minutes. Clean another part of the bathroom and the outside of the toilet while you wait. Use a toilet brush to scrub away the stains. Flush the toilet and repeat the steps if necessary.