Brick is clay. Not sure why it would be unsafe. And barb is correct that much PVC breaks down in UV light, some faster than others.

Dan

You can paint PVC with a heavy duty outdoor latex paint to protect it. But mostly PVC only turns yellow and gets a bit brittle. It won't just fall apart or decompose... but don't hit it with the lawnmower after it's been in the sun for a couple of years.

It shouldn't leach anything into the soil, although protective paint probably will. PVC is approved for water for human consumption. And I've used it for water used with some very sensitive marine organisms with no ill effects.

Honestly... I vote for concrete block or brick. I can't imagine they'd be unsafe unless you purchased something that was chemically treated or colored somehow.

The only thing I can find refering to brick as a hazard in the garden is as a tripping hazard. Since brick is fired clay I'd think, given all the uses proposed for brick in the garden, it is pretty inert and would not tend to contribute a bit of calcium like concrete can.

PVC rated for exterior UV exposure is sold under the name Carlon, grey in colour.
Regular PVC/CPVC water pipe won't stand up to the task.

As to whether plastics of any formulation leach into soil is as controversial as the use of peat moss, or bread in compost.

From an aesthetic point of view imho pvc would be ugly. If you want something durable and looks nice I would go with stripstone or cobble rock. Stripstone is definitely not cheap though.

From UF :
Soils formed from high Ca materials, such as limestone, marl, or sea shells, tend to be alkaline. This condition is common to coastal soils and the soils of south Florida. It is also common to encounter alkaline soils in the home landscape as a result of calcium-rich building materials (i.e., concrete, stucco, etc) that may be left in the soil following construction.
In Florida , cement blocks and clay leach alkaline into the soil .
Since the OP is in SW FL , cement blocks or brick may not be the best choice .

Anything made of cement, which is lime, can as it fails leach lime into the soil no matter where you garden. Bricks, made of clay a relatively inert substance, has no lime to leach although unless fired for outdoor use bricks do tend to fall apart from the moisture and revert back to the inert clay they were made of.

Typical old-fashioned bricks are made of clay and shale, but there is such a thing as calcium silicate brick. It isn't very common in the US, but I recall seeing some in Florida, which has more lime and sand than clay and shale.

Anything made of cement, which is lime, can as it fails leach lime into the soil no matter where you garden.

Regular, common, pedestrian brick, cinder block, stacked used concrete is not going to leach anywhere close to any amount of lime that will in any way change the pH of your soil anywhere near more than anything like an inch or two away from the brick in any time frame that is meaningful to human enterprise.

Dan

My first choice would be dry-laid rocks. But not a look everyone likes and it is a problem where there is soil heaving.

The concern about cement blocks leaching into the soil may be aleviated with this product below. I've not used it, but looks possible.

...SNIP....The sealer is not chemically aggressive - it is comparable to a mild soap solution. You can walk in it during application, but it is slippery. You can seal one half of the basement first and finish the other half later.
....SNIP....Waterproofing new concrete
As concrete cures, it inevitably develops capillaries. Allow the concrete to cure for at least 28 days and then, deep-seal the poured walls and slab with RadonSeal Standard in 2 applications. This seals the concrete against water, vapor, and gasses, as well as bonds and strengthens the concrete. In case of concrete block walls, let the mortar cure for at least 14 days before applying RadonSeal Plus.

Here is a link that might be useful: Radon seal

There are issues with PVC. I'm not sure about leaching from the rigid outdoors grade UV stabilised stuff, it might be alright. I just personally reached the point where I'd heard about it so much that I would avoid it where possible. Sorry I can't help with your specific question but if you google you can find out all sorts of things. I don't know quite where the line is between the scaremongering and the legitimate concern, but I can't imagine PVC being safer than bricks. As for bamboo, wouldn't that be treated with some sort of preservative, or can you source untreated landscaping bamboo in the US?

PVC = Polyvinyl chloride

http://toxtown.nlm.nih.gov/text_version/chemicals.php?id=84

Watch the movie, "Blue Vinyl" - funny and informative. http://www.imdb.com/title/tt0303307/ "The hazards of bio-accumulation, pollution, and the makeup of what we commonly hope are benign plastics are tackled in this documentary."