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Heavy Metals In Soil And Amendments

Discussion in 'Organic Soil' started by Homesteader, Mar 13, 2018.

  1. I have been doing some digging through and figured I would share it. It seems to me as a cannabis smoker cadmium is our most concern as a heavy metal due to its uptake from plants being much greater than lead and arsenic etc. but as a soil maker lead is a great concern as well when mixing and handling dirt and amendments. Amendments of most concern would be rock phos and super phos but also crustaceans or oyster shell due to their ability to immobilize heavy metals.

    "Cadmium availability is influenced by several soil properties. Plants uptake cadmium through their roots, but uptake is lowest when soil pH is higher (6.2); organic carbon (organic matter) levels are higher and levels of soil calcium (Ca), iron (Fe) and zinc (Zn) are adequate"

    "Cadmium is concentrated in particular parts of plants. As a general rule, leaves contain the most Cd, followed by storage roots and tubers, and then seeds or grain and fleshy fruits. Fleshy leaf crops (lettuce, spinach) tend to have higher levels than pumpkin, cucumber etc. Storage root crops (garlic, parsnip, carrot, beetroot, onion, potato) can also all contain significant levels of cadmium, depending on levels present in the soil."

    "Superphosphate (super) is manufactured by attacking a rock phosphate rock source material with sulphuric acid."

    "Earlier superphosphate was made from rock phosphate from Nauru which had high levels of C0d0 contamination i.e. 600mgCd/kg P in the superphosphate."

    Guanos are generally low in cadmium but all manures contain at least trace amounts in varying quantities.

    " It appears that cadmium is the heavy metal of greatest concern in fertilizer. In a Washington State Department of Agriculture study that considered the plant uptake of arsenic, lead, and cadmium (coincidently, the only three metals that California regulates), cadmium was found to be of the greatest concern because cadmium builds up in the soil and plants can take it up. Some plants, such as lettuce, were found to contain more cadmium in the plant when more was available in the soil. In one study area, there was a clear linear relationship between cadmium in soil and cadmium in plants. Arsenic and lead were not taken up by plants in the same way as cadmium. "


    Cadmium accumulation in crops
    Last edited: Mar 13, 2018
  2. A really interesting presentation from Dr Andrew Margenot mostly concerning Pb as it is of much concern due to leaded gasoline which has dusted more urban areas and caused higher amounts of lead levels in soil nationwide.

    Interestingly plant uptake is not as dangerous as direct exposure (83% of exposure is from small grain dust and only 3% from indirect exposure). Wear a mask when mixing amendments and soil. Root crops and low to the ground greens have more heavy metals than fruits due to their contact with soil. High levels of lead in water didn't seem to effect levels in the crops.

    Compost can help decrease availability and stop plants from taking up as much lead ( 40 min mark.)

    Lead poisoning and health

    Lead (Pb) Toxicity: What Are the Physiologic Effects of Lead Exposure? | ATSDR - Environmental Medicine & Environmental Health Education - CSEM
    Last edited: Mar 13, 2018
    GT21, Perception and oldskol4evr like this.
  3. got to agree with the rock dust,i noticed myself last time i used the stuff was hard for me to breath that night,been using azomite every sense,truth be told ,we cant control any of this cause it was sure enough here and will be as long as we live,always make great sense to wear protection at any level while mixing everything,even dust from your compost pile will mess with the lungs
    GT21, kansabis and Homesteader like this.
  4. Analysis of azomite shows trace amounts of cadmium but in the amounts people use, I question how realistic those numbers would be when people are using cups of the stuff in a single grow bag.

    Cadmium in super rock phos would depend on the source. Some areas in Northern Africa are incredibly high but to know where your rock comes from seems like a difficult task.
    GT21 and oldskol4evr like this.
  5. Hempry


    My Soil Prof. always said as soon as your pH drops to the 5s metals will start coming loose in your soil and lead to toxicity. This makes me wonder about peat based potting mixes that are only kept in the acceptable pH range by lime buffering it up out of the 5s. Almost every "what's this deficiency" post lately where promix or similar peat based potting mix is used looks like metal tox to me. I have bad luck with the stuff unless I mix it 50/50 with perlite; but, if water is stagnant in the least, leaves burn just like a pH drop metal tox. I'm guessing if it burned the leaves it's still in '
  6. oh hell no,i use 2lbs in a raised bed 2ft by 12 ft,rock dust is way over rated and price is up there with the hipe,i amend with meals and throw a little azomite in every winter and im done,let that soil work with compost to feed me,lmao
    GT21 likes this.
  7. i use 1;1;1 method,1 5 gal bucket peat,1 compost,1 bucket half and half perlite and vermiculite,add half cup blood,1/2 bone meal,1/2 cup azomite,works real good ,still fluffy but not if you dig,then i top dress ewc,barly malt and steel oats in once a month with my magic plants in tent,i feed extreme blend with a 1/8 tsp of fulvic acid and that the whole grow,also forgot 1 tsp of humic acid with the once a month feed,thats it,compost is were it at for plants i believe
    GT21 likes this.
  8. Check out tennessee brown rp!

  9. I think the Tennessee brown is soft rock unless I am mistaken, which is the leftovers after leaching from mining high grade ore used for super rock phos. It is my understanding that this would be the lowest levels of heavy metals of all rock phos but I wasn't able to find any analysis online.
    Friendlyguy likes this.

    You can checkout these guys..they might test it
    Homesteader likes this.
  11. Last edited: May 18, 2018
    Friendlyguy likes this.
  12. tweedy


    Glad I am not one of the only ones to be concerned with heavy metals in amendments. I always look up anything I plan on putting in the soil on Oregon Department of Ag. They have a very strict program and seem to test regularly/put things on stop sale that are misadvertised or dangerous.

    On a side note, time for a theory:

    Cadmium stress/toxicity induces thiol production in plants (the skunk/rotten egg/garlic/whatever smell, etc). While no one has ever tested for thiol production in cannabis I propose that the reason we smell skunk is a response to cadmium levels in the soil.

    On that note, I don't think "roadkill skunk" is really a thing, I think there were just certain plants that had a strong propensity to produce thiols in response to cadmium rich diets. If you were growing with shitty fertilizers or on land with high cadmium levels you would certainly see a difference in the flower.

  13. Thought sulfur does that? I think coot was saying that in an interview, someone posted it on here...
    tweedy likes this.
  14. tweedy


    Certainly plays a role in a lot of a plant's functions. Thiols are an organosulfate. A sulfur containing compound that make certain smells.
  15. Im sure when people say they have an N def, i suspect it could be heavy metal tox. It blocks the S N tansduction pathways. It explains in detail in the link i posted..its taking it up like its sulfur maybe too...humans absorb lead and store it in the body like calcium...calcium/lead absorbtion in us in a way is similar to S/cd absorbtion in
  16. Friendlyguy likes this.