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You can try solarizing, but that will take awhile.

Boiling water kills, too.

This article will offer more suggestions:

https://www.gardeningknowhow.com/special/organic/weed-it-and-reap-how-to-make-your-garden-more-appealing-without-chemicals.htm

This article tells how you can mix your own soil for raised beds. For a lighter layer in the bottom, you could use shredded bark or wood chips.

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/best-soil-raised-garden-beds.htm

Pressure treatments are always a type of copper based material. Copper in such forms is highly toxic to soil life and plants, and leaches from the wood very easily. Plants will take this up in the roots, and either suffer from them, or pass the copper agents into their fruits and other plant parts. If you intend to consume the plants, then you will be consuming the copper preservatives, since they cannot be broken down by the plants.

Usually, pressure treated wood does not decay, and will have some sort of greenish or blue hue from the oxidizing copper. Sometimes, they have a label.

Lining will not stop the chemicals from leeching into the ground around your yard, and since you will not want the roots to remain wet and soggy the lining will need to be perforated. This means that the roots will still have access to the treated wood and the copper based sealants used. These sealants leech from wood very quickly, and with ease, so I do not recommend using them at all, even with lining.

https://www.gardeningknowhow.com/edible/vegetables/vgen/raised-vegetable-gardens.htm

There is quite a bit of information to cover, here. These articles will help you to iron out those details:

https://www.gardeningknowhow.com/garden-how-to/info/are-railroad-ties-safe.htm

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/best-soil-raised-garden-beds.htm

https://www.gardeningknowhow.com/edible/vegetables/vgen/raised-vegetable-gardens.htm

https://www.gardeningknowhow.com/edible/vegetables/vgen/raised-bed-soil-depth.htm

Unfortunately, it has already been leaching out into the area since they were installed. They should not be used, at all, for gardening. The splintering has not made it any more dangerous than it has been, other than the chance of getting one of those in your foot.

Vacuuming the pieces will not put you in any more danger than using it as a garden border will. It will all carry, about, the same risk over time.

Personally, I would have them removed and replaced with anything else to stop the chemical leaching that is occurring over time, but using a shop vac for the pieces can be OK for now.