Am i drinking toxins from the plastic of bottled water sitting in my car all day in the sun ?

Perhaps: The question of whether dehp used in the production of many plastic containers has toxicity for humans after chronic exposure remains unanswered. Some reports say definitely not; others say perhaps. There is evidence of chronic toxicity in laboratory animals. Use your prudence & your good judgment. There are alternatives to plastic water bottles. I use an aluminum bottle.

Likely: It has been shown that sunlight increases the leaching of plastic in bottled water. We don't fully know the consequences of this, but it certainly doesn't seem safe to me. I would suggest a stainless steel or glass water bottle. Glass is the safest, but also fragile. Stainless steel may still have some chemical issues. Hard to say. But it is probably safer than plastic.