1. Toxins over large timescales.(also I’m assuming they aren’t the only thing in the landfill) Most modern plastics won’t leech toxins onto your food in the short time it takes from field to fridge. However microplastics are a concern and they do end up on fruit and vegetables that are in plastic packaging. The amount of course varies.(factors such as type of plastic, temperature, friction, shipping method all impact this) The study of microplastics on human health is quite young but initial results don’t paint a pretty picture.

2. Good point! Errors in foundations or any permeable gaps can still cause leachate to escape. There is also the concern of gases escaping during the lifetime of landfills as well.

You also have an issue of land usage. We have a limited amount of land and that amount is expected to decrease as sea levels rise. I think landfills don’t provide much bang for buck in terms of land value as opposed farms, parks, (I’ve heard of landfills being turned into parks but we still have the concerns of low to moderate containments in the surrounding soil) nuclear/solar/wind farms (although luckily you can still use landfills for these since contact with the public would be minimal), and wildlife habitats. Any ban on plastics, even if it reduces the waste going to landfills by a tiny or fractional amount. Sounds like a win to me