pressure treated wood alternatives?

[momofmine]

Hi folks,
We live in a 100-year old house with a hand-dug, dirt basement. It is very damp and musty, despite having a dehumidifier that runs constantly, and the smell often comes up into one room in particluar. I feel like this is very bad for our health, and it is also just not good for the house. The walls down there are starting to crumble a bit too (they are just dirt and stone). I had someone come and look at what to do (putting a sump pump in, laying down gravel and black plastic for a vapor barrier), and he recommended putting up a little retaining wall of sorts, to hold back the dirt and to make a shelf where I could store some things. He wants to use pressure-treated 2x6's, and when I asked him if there were any alternatives, he couldn't think of any. Finally he said maybe I could use landscaping bricks, but that would be really expensive and take up a lot of space.

I am concerned about using the pressure-treated wood, and am looking for an alternative. Does anyone have any ideas, or know of a resource I could ask?
Many thanks!!

[ChocolateNummies]

How do you feel about composite wood products? Building supply stores carry dimensional 'lumber' made of recycled wood and plastic. I don't what kind of plastic or what other ingredients may be incorporated nor have I compared cost but the end product is resistent to moisture, bugs, etc.

Other options would be rot-resistent woods like cedar but those can get pricey depending on your needs.

Can you pour a concrete wall? Just thinking out loud.

[momofmine]

Thanks for your ideas. Yes, I am thinking of just asking them to go with concrete, and to just stay away from any kind of wood product down there. I mean, even if it lasts 20 years, that is short in the long run.
Thanks!