Composting plants grown in potentially contaminated soil

I'm a home gardener living in an urban area. From what I can tell, because our garage is an old barn, the property used to be some kind of farm many, many years ago until urban sprawl surrounded it. It looks like the previous owners did some bad landscaping or construction. They covered the earth with awful fill dirt that has plastic, junk, rusty metal, and who knows what else strewn throughout the soil. I haven't ordered a soil test. I don't want to invest time, money, and labor into a soil analysis because I will be moving into a new place later this year.

In the meantime, I'm intensively gardening raised beds and composting in the backyard. Other than grass clippings, crop residues from the garden, and other urban sources of composting materials (e.g., leaves and coffee grounds), I have lots of weeds that I allow to grow and a big lilac shrub. If we assume the soil is contaminated, perhaps with lead for example, would it be unsafe to compost plants grown directly in the soil, such as weeds and the lilac shrub? Do weeds and shrubs accumulate contaminants as much as, say, the Brassica family? I've heard that plants like weeds accumulate minerals and nutrients from very deep within the soil and so their contaminant accumulation would be minimal to nonexistent. I'm unsure if that's true or not. Would composting "eliminate" (for lack of a better word) the contaminants and produce a safe compost? There seems to be a lot of information on eating plants in contaminated soil, but I can't find any information about composting contaminated plants.

Hi Jack,
Welcome to Permies.  Whether or not weeds accumulate nasties depends on the root structure.  Deep rooted plants are likely to accumulate what ever the roots are sitting in.  Shallow rooted weeds should not have the same issue.
The answer about composting depends on what and whether contaminants are present.  To play perfectly safe,  use organic potting mix until you move.
Best wishes.

I want to start with I don't know. But I know a little slice of the pie you're looking at. When we bought our current place, the home's water was supplied from a sandpoint well in the basement and the water was full of lead. Like 500x the EPA recommendation! It turns out that it used to be common to unclog dry sandpoints by firing shot down the well...crazy by our standards today, for sure! We ended up connecting to a modern, drilled well 100' feet off and now our water is fine. But along the way, we did a fair amount of research on filtering the lead and what it would look like if we irrigated with our leady water. My recollection was that the government said it's safe to use for soil irrigation. (We didn't really buy that and just capped the well, but it probably does mean there's some level of safety -- that veggies mostly don't pick up lead from soil.)

From what I have read here on the forum if the compost pile gets hot folks will not need to worry about nasties.

Here is a thread that does some discussion on that:

https://permies.com/t/224248/composting/Hot-Compost

While what Anne said is true for biological contamination (E. coli or worms for example), heavy metals are not degraded by hot composting. Hot composting kills the dangerous bacteria, but 60°C does not even melt lead, to take an example of a heavy metal.

Bioaccumulation of the heavy metals and other chemical contaminants depends on the plant species, the soil pH, and on the available nutrients. For example, cadmium uptake by plants can be reduced by using biochar as a soil amendment.

There are plants that can be planted to help with metal contamination.

Bracken fern is one.

Also planting mushrooms is also another way to remediate the soil:

https://permies.com/t/216479/Heavy-Metals-Soil

https://permies.com/t/29229/heavy-metal-contamination-urban-fill

Whatever is in your soil will be in your ground water. Whatever is in the soil will be taken up by any plants. Whatever is in any plants you eat from contaminated soil, will end up in you. What is in the plants will be returned to the soil when the plants are composted. There are ways to remove the poisons from the soil, but that means removal. It doesn't mean leaving them in a closed loop.