Lead in vacuum seal bottles is avoidable, if it’s something you’re worried about it’s not hard to get lead free. I also highly doubt anything plastic is better for the environment in the long term, given that no plastic is going to last without degradation for that many years compared to something made of metal. And once that plastic does degrade it’s going straight into a landfill or the environment with all the other microplastics. Maybe optimistically it could be recycled once or twice, but beyond that you get diminishing returns and it’s trash again.

They might technically edge out metal production on one or two measurements, like power used (since you don’t have to smelt plastic), but as a society we have to stop pretending the plastic we use isn’t going to degrade. Plastic is temporary, then it turns into brittle, environmentally poisoning trash. There’s not a good reason to use it for something that can be easily replaced by metal.