Heavy Metals in Soil

Recently, through a soil test, I learned that our soil has higher than normal amounts of arsenic in it.
I tested the soil for lead and arsenic because I learned that our property used to be a fruit tree orchard, and that in the past it was common practice to use a lead-arsenic type of pesticide on fruit trees.  The lead levels were within normal background levels for our area.  But the arsenic was high.
I asked our Penn State Agricultural Extension Agency and Pennsylvania Master Gardeners about what this means for the us growing our food in the soils.
No one seemed to have a definitive answer.  
The Environmental Protection Agency has 'safe' limits for arsenic in water, but no guidelines for arsenic in soils.

I would be grateful to know how to remediate our soils, and how to be sure that the food we grow is healthy.
I also wonder if the higher than normal arsenic levels is an indicator that we could have any other heavy metals in our soils?

The Test Results:                         17.00 mg/kg,  
Normal Soil Concentrations:      6 to 10 mg/kg -1      (I don't know what -1, superscript, means?)

Thanks Community!  It's wonderful to have a community to share my challenge with!

Adrienne,

I'm afraid I don't have any specific answers for you as I've got no experience with arsenic-contaminated soils.

I have worked on a project that had lead-contaminated soils due to its location: it was near a busy road dumping the lead, from leaded petrol/gasoline, nearby. The advice was not to eat too many brassica species grown on the site as, apparently, brassicas will readily bio-accumulate lead (especially in its organic form, as it was in leaded fuel).

This knowledge led me to think about decontaminating a lead-polluted site by growing large numbers of brassicas for several seasons and removing the plant material. I'm not sure how much of the lead, as a proportion, it would remove from the soil but I'm certain it would have an effect. The obvious downside would be a loss of fertility and the question of where to move the contaminated plant material.

I had a quick search to see if I could identify any species/genera that would effectively bio-accumulate arsenic and I couldn't find any obvious answers. There might be similar metals that such species are known for. You could also consider mycelial remediation as certain fungal species, oyster mushrooms being a good one, are known to accumulate metals.

There are 2 basic answers.  1 is to find chemicals that bind arsenic.  2 is remove it.   For that suggest putting this in your google search and reading. "plants that collect arsenic from soil"  
Might be slow but would let you gather it.  Would have to bring in other nutrients to replace what is lost along with the plant removal.  Alternately saw a couple of articles on mushrooms absorbing large amounts.  Could you then grow mushrooms on the plant biomatter and just dispose of the mushrooms?

Something to consider is that soil levels can vary widely in all components, including metals. If you have the ability/money, maybe consider testing in a few more places/depths to get a feel for the arsenic level variation, especially where you want to grow crops. It's conceivable that you find higher levels only in the upper few inches, which would suggest removing that layer. Of course this may not be the case, so getting a better soil profile could be useful.

The NIH did a study on heavy metals in San Diego since there is an increase in urban gardening and some of the soil has a history of industrial use. They stated "The general background levels of arsenic contamination in Southern California, without anthropogenic input, are between 0.6 and 11 mg/kg, and the safety limit for school sites in Southern California is 12 mg/kg (Bradford et al., 1996)." Their solution to reduce any risk was to build raised beds with clean soil.

Note: mg/kg is the same as mg kg-1. Just a notation variation.

"Due to limitation of available resources, no boundary layer was placed between the raised bed soil and existing site, reinforcing the need for continued monitoring (see Discussion). All seasonal fruits and vegetables are now grown in these raised beds. Heavy metal and arsenic measurement of vegetables grown in the raised beds, including leafy green vegetables such as lettuce, kale, and Swiss chard, showed no detectable levels of heavy metals or arsenic. In contrast, nutrient metals were detected in these leafy green vegetables, including zinc (Zn), copper (Cu), and manganese (Mn)."

So it sounds like raised beds may be a good approach.

Just off the top of my head, if I had a well or pond, I would have the water tested.  I would have the fruit from the trees tested.   I agree with a previous post that suggested raided beds.   And I would have a sample of those vegetables tested.  

I would like to recommend learning about growing mushrooms.

Also, there are plants that can help remediate soil.  Bracken Fern is one.

https://academicjournals.org/journal/AJEST/article-full-text-pdf/7CE1F3765071

I hope you or others will find this helpful about why I suggested mushrooms:

https://usfblogs.usfca.edu/sustainability/2022/02/03/mycoremediation-how-fungi-can-repair-our-land/

Wow, this is all very helpful.  

While I have tested different areas of the yard, I have not tested various depths, this I might do in a really small area where I could remove some soil, if a test shows deeper levels to have lower levels of arsenic.  

The fungus / mushroom ideas sound like the most feasible possibility for the rest of the yard.  I see mushrooms pop up every year.
While we have a sunny, medium to dry area, (not wet) where I want to grow food, there are a lot of twigs and tree limbs and rotten wood laying around.
I believe Dr. Elaine Ingham, says decaying wood produce a fungal dominated soil, while grasses / greens produce more bacterial dominated soils.  So if fungus can help, we got the stuff for Huegel culture.  

It's important to me to try to do this with what we have.  I really don't have much money or equipment.  It's me and my shovel.

We do not have any ponds on our site, but until I found out we had higher than normal arsenic levels, I had thought about creating at least some small pools.
but I do wonder about our well water.  It's not hooked up as yet, but when I tested that water for Iron it came back very high.  If understand correctly, acidic water leaches metals from rocks.  As we live in an area where coal mining was and is still being done.  I would not be surprised if the aquafer that feeds our well is effected by the mining.  

Thanks for all the info.

Arienne said, "I believe Dr. Elaine Ingham, says decaying wood produce a fungal dominated soil, while grasses / greens produce more bacterial dominated soils.  So if fungus can help, we got the stuff for Huegel culture.

If you have wood chips available Adding them will be very beneficial:

https://permies.com/t/208993/permaculture/Wood-Chip-Win

https://permies.com/t/22404/Wood-Chip-Gardening

I remember Novella Carpenter (of Farm City) writing about this issue but couldn't find it in my copy of that particular book when I looked this evening. It may be in a more recent book.

She and a partner farmer got access to some land there in Oakland but there was heavy metal contamination. As I recall, they used the leaves of the plants there to remediate, removing every scrap of the leaves off of the property until it tested at acceptable levels. I think they did raised beds with a barrier in the meantime.

I will try to dig up the reference but if anyone else knows about this approach or knows where she wrote about this, maybe they can chime in with more details.

Datura is a weedy flower that is good at removing other heavy metals. Perhaps you could use it like a cover crop, dispose of the biomass, then retest next year.
https://www.ijsr.net/archive/v4i5/SUB154732.pdf

Before considering Datura, I feel a lot of research would be very helpful.

Since this plant is highly poisonous.

Most folks have heard of this plant as Jemsonweed which is usually responsible for animal deaths.

All species of Datura are extremely poisonous and potentially psychoactive, especially their seeds and flowers, which can cause respiratory depression, arrhythmias, fever, delirium, hallucinations, anticholinergic syndrome, psychosis, and even death if taken internally.

https://en.wikipedia.org/wiki/Datura

Here are some plants, from the ones from the link below:

Water hyacinth, due to its various capabilities, such as its fast growth, high pollution tolerance, and high absorption capacity, is frequently employed in contaminant remediation. ...

It has been stated that Azolla has a great capability to amass noxious elements (mercury, cadmium, chromium, copper, nickel, and zinc) due to its strong competence to absorb toxic heavy metals. ...

Water lettuce has been verified as an effective plant for metal decontamination, metal depollution, and urban sewage treatment ...

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9104525/

Since you mentioned the EPA, I might add to this since you respect them enough to mention them.  I lived in Western Montana for years.  The homes were cheap in Anaconda and there's a reason why.  There was a massive amount of contamination in the area and they were recovering a massive area with an extremely expensive and decades long clean up.  I would watch enormous pieces of heavy equipment day after day and year after hear hauling the topsoil away to be replaced.  I've included a link to the EPA's own website dedicated to the cleanup project.  Arsenic was one of the materials being remediated in the massive clean up effort.  I can tell you from observation that the cleanup was valley wide, not just limited to a town.  To give the readers of this post an idea of scale, it was a 300 square mile clean up site.  I can tell you as a former resident of the general area (I avoided the clean up areas for my residence) it was amazing to see.  Here is the link:

https://www.epa.gov/newsreleases/anaconda-montana-now-thriving-after-more-three-decades-clean-efforts-epa-state

Many people that I personally knew at the time that lived within the boundaries of the site and that were affected told me that they had their soil replaced.  I know it sounds like a big project but when you really look at the actual process it's not really that difficult with the use of some equipment.  You can make your own decisions.  I'm just giving you a hand with some pertinent information.  

Best of luck

'... since you respect them (the EPA) enough to mention them..'...

- Well, 'respect' might be very optimistic term for how I feel.   It's more that I have no idea at all what soil test numbers actually mean to the healthiness of the plants we eat. So I was just hoping to at least get a clue from the EPA or Agricultural extension agency.  Seem the National Institute of Health might have more info than anyone.  But since, I am thinking, there are all kinds of 'Special Interests" in all of these organizations, I try to look at what they say critically.  Probably, lots of well-meaning people, many educated (but perhaps mainly in conventional systems).  

The lack of information about heavy metals in backyard gardens... is case in point.

I imagine, the thinking goes something like this  (Hoping & Wishing to be wrong):  
If safe limits were found for a greater range or soil contaminants they would become 'enforceable' and big ag would have a fit.
It would be expensive in time, money, and enforcement to check all places where our food was grown for all potential heavy metals.

Lead has the lead... this one does get a lot of attention.  Do farmers who sell on the open market have to pass a soil lead level test?  

Couple of comments:
- the type of soil you have will play a big role in how to remediate. Clay holds on to nutrients, minerals and also lead and arsenic, I assume. But if you have sand, you may be in luck and the lead/arsenic may leach away to lower layers.
- whatever remediation you do, I would start small and take before and after samples, samples from different depths. Do the same with a plot you don't do anything with. This will tell you: a) how the remediation improves the soil each year (so you can calculate how many years it will take) but also b) how the soil improves if you don't do anything, if any at all.

As somebody with land next to a cemetery, I understand your plight, luckily we are somewhat uphill from the cemetery so no arsenic leaching that we are aware of. Good luck in your efforts

M