An Elm Dirt company·Kansas City, MissouriCDFA Certified Organic
Elm Dirt, Together We GrowRemediation

Contaminant group

Heavy Metals

Lead, arsenic, chromium and cadmium are elements, so nothing destroys them. Biology changes where they sit and what form they take, and organisms in our products have published research on both.

What biology does
Binds
Microbes in our products
P. putida, P. stutzeri, C. testosteroni and 8 more
Shows up at
Wildfire Burn Scars, Brownfields, Abandoned Mine Lands
Diagram: Heavy Metals, microbial action, outcomeMetal ions in soil water and on soil particles. Microbes reduce, oxidize, precipitate or bind metal ions at their cell surfaces. Breakdown: changes form. Metals are elements, so biology can change their form and mobility and cannot destroy them. Binding: in the research. Microbes and compost bind and precipitate metals, lowering how much moves or reaches plants, and monitoring confirms that it holds.01 CONTAMINANT02 MICROBIAL ACTION03 OUTCOMEPbAsCdCr Heavy MetalsMetal ions in soil water and onsoil particles.Microbial actionMicrobes reduce, oxidize,precipitate or bind metal ions attheir cell surfaces.CO2H2OCHANGES FORMBreakdownMetals are elements, sobiology can change theirform and mobility andcannot destroy them.IN THE RESEARCHBindingMicrobes and compost bindand precipitate metals,lowering how much movesor reaches plants, andmonitoring confirms thatit holds.Diagram: Heavy Metals, microbial action, outcomeMetal ions in soil water and on soil particles. Microbes reduce, oxidize, precipitate or bind metal ions at their cell surfaces. Breakdown: changes form. Metals are elements, so biology can change their form and mobility and cannot destroy them. Binding: in the research. Microbes and compost bind and precipitate metals, lowering how much moves or reaches plants, and monitoring confirms that it holds.01 CONTAMINANTPbAsCdCrHeavy MetalsMetal ions in soil water and on soilparticles.02 MICROBIAL ACTION Microbial actionMicrobes reduce, oxidize, precipitateor bind metal ions at their cellsurfaces.03 OUTCOMECO2H2OCHANGES FORMBreakdownMetals are elements, sobiology can change their formand mobility and cannotdestroy them.IN THE RESEARCHBindingMicrobes and compost bind andprecipitate metals, loweringhow much moves or reachesplants, and monitoringconfirms that it holds.
Fig. 1How biology acts on heavy metals, as described in the peer-reviewed literature. Rates depend on soil, moisture, oxygen and temperature, and are confirmed by lab testing over months.
On this page (8 sections)
  1. What Elm Dirt does about metals in soil
  2. What it is
  3. Where it comes from
  4. Why it matters
  5. Three mechanisms
  6. What the research shows about microbes in our products
  7. What to expect
  8. Studies

Because metals are elements, no organism can destroy them. Biology moves them, binds them or changes their chemical form, and any of those changes can reverse if soil conditions shift.

What Elm Dirt does about metals in soil

Since nothing destroys a metal, the first decision is direction: hold it in place or take it out. Those two goals pull against each other, because immobilization locks metals down while phytoextraction deliberately makes them more available so plants can absorb them and be harvested. Fungal bioleaching mobilizes them further, which helps on excavated soil and is risky over shallow groundwater. Depth to water, planned land use, and whether anyone will harvest and handle contaminated plants all decide it, and the decision comes before anything goes in the ground.

Our products carry metal-binding and redox-transforming organisms for holding and root-zone organisms that support plant-assisted removal, so the biology we apply follows from that choice.

Either way we build soil structure and organic matter, because cover, structure and dust control do most of the work of keeping lead out of a child’s hands or a tomato. A bound metal is still a metal, so any immobilization program needs long-term monitoring by an independent lab built in from the start.

What it is

Lead, arsenic, chromium, cadmium, mercury, copper and zinc drive most site decisions. Arsenic is technically a metalloid and is handled like the rest in a risk assessment.

Chemical form counts as much as amount, since chromium(VI) is mobile and highly toxic while chromium(III) is much less of both. Arsenite is more mobile and more toxic than arsenate. One element can be a serious hazard or a mostly inert mineral, depending on its oxidation state and what it is bound to.

Where it comes from

  • Lead comes from old paint around older buildings, historic leaded gasoline along roads, shooting ranges and industrial sites, and EPA names deteriorating lead-based paint and contaminated soil and dust as primary exposure sources [1].
  • Arsenic comes from historic orchard pesticides, wood preservatives, mining, natural geology
  • Chromium comes from plating, tanning, pigment and alloy production
  • Cadmium comes from batteries, plating, phosphate fertilizer, smelter fallout
  • Mixed metals turn up in mine tailings, smelter zones, brownfields, ash from fires and incineration

Metals don’t break down or evaporate, so they stay in the soil until someone removes them or something changes how easily they move.

Why it matters

Lead and arsenic usually drive decisions on homes and farms because the exposure routes are direct: kids playing in soil, dust tracked indoors, uptake into garden produce. On farmland, cadmium matters because some crops take it up readily.

Regulators rarely ask whether the metal is gone. They ask whether it can reach a person, a plant or groundwater.

Three mechanisms

In immobilization, bacteria push metal ions to their cell surfaces, where polysaccharides act as nucleation sites and the metals crystallize, mostly as carbonates [2]. Reduction does similar work, turning chromium(VI) into chromium(III) and uranium(VI) into uranium(IV) [3][4].

Biosorption relies on fungal and yeast cell walls, which carry charged groups that bind metal ions directly. Dead biomass works too, since no metabolism is needed [5][6].

Phytoextraction takes metals out of the soil in plant tissue, and microbes speed that up by conditioning the root zone and easing plant stress [7][8].

What the research shows about microbes in our products

Independent lab analysis (Biome Makers) identified these organisms in Elm Dirt products, and peer-reviewed research shows each can act on the metals listed.

Organism Metals What the research documents
Cupriavidus metallidurans Cd, Zn, Cu, Pb, Hg, Ni, Cr Dedicated efflux systems plus carbonate nucleation on the cell surface [2]
Trichoderma harzianum Cd, As Field result: with biochar on contaminated soil, plant metal uptake rose several-fold and total soil cadmium fell 19.0 to 49.6 percent, arsenic 38.8 to 53.8 percent [7]
Penicillium simplicissimum Cr, Pb, Cu, Cd, Zn, U Biosorption and bioaccumulation, with the mechanism imaged by electron microscopy and spectroscopy [5]
Mucor circinelloides Pb, Cd, As Biosorption plus enhanced phytoextraction; the combination beat either the fungus or the plant alone in soil [9]
Desulfovibrio vulgaris Cr, U Anaerobic reduction and bioprecipitation [3][4]
Ensifer adhaerens As, Cr Arsenite oxidation and chromium reduction in the same organism [10]
Saccharomyces cerevisiae Pb, Zn, Cd Cell-wall biosorption [6]
Variovorax paradoxus Cd ACC deaminase buffers plant stress so plants build the biomass that phytoextraction depends on [8]

What to expect

A metal that has been bound can come loose again, since a pH change, draining or flooding, or decay of the organic matter holding it can return it to a mobile form.

Each zone of a site gets one route, because holding and removing work against each other.

When metals leave in plant tissue, the plants become a waste stream that has to be harvested and managed, or the metal goes back into the soil.

Immobilization can show change within a season. Phytoextraction is measured in growing seasons and often runs for years, with an independent lab tracking it throughout.

Studies

  1. US Environmental Protection Agency. Protect Your Family from Sources of Lead. epa.gov/lead
  2. Diels L, Van Roy S, Taghavi S, Van Houdt R (2009). From industrial sites to environmental applications with Cupriavidus metallidurans. Antonie van Leeuwenhoek 96(2):247–258. doi:10.1007/s10482-009-9361-4
  3. Lovley DR, Phillips EJ (1994). Reduction of chromate by Desulfovibrio vulgaris and its c₃ cytochrome. Applied and Environmental Microbiology 60(2):726–728. doi:10.1128/aem.60.2.726-728.1994
  4. Lovley DR, et al. (1993). Reduction of uranium by cytochrome c₃ of Desulfovibrio vulgaris. Applied and Environmental Microbiology 59(11):3572–3576. doi:10.1128/aem.59.11.3572-3576.1993
  5. Chen SH, Cheow YL, Ng SL, Ting ASY (2019). Mechanisms for metal removal established via electron microscopy and spectroscopy: a case study on metal tolerant fungi Penicillium simplicissimum. Journal of Hazardous Materials 362:394–402. doi:10.1016/j.jhazmat.2018.08.077
  6. Kotrba P, Ruml T (2010). Surface display of metal fixation motifs of bacterial P1-type ATPases specifically promotes biosorption of Pb²⁺ by Saccharomyces cerevisiae. Applied and Environmental Microbiology 76(8):2615–2622. doi:10.1128/AEM.01463-09
  7. Yao S, et al. (2023). Combination of biochar and Trichoderma harzianum can improve the phytoremediation efficiency of Brassica juncea and the rhizosphere micro-ecology in cadmium and arsenic contaminated soil. Plants 12(16):2939. doi:10.3390/plants12162939
  8. Belimov AA, et al. (2020). Microbial consortium of PGPR, rhizobia and arbuscular mycorrhizal fungus makes pea mutant SGECd(t) comparable with Indian mustard in cadmium tolerance and accumulation. Plants 9(8):975. doi:10.3390/plants9080975
  9. Sun L, et al. (2017). Enhanced bioremediation of lead-contaminated soil by Solanum nigrum L. with Mucor circinelloides. Environmental Science and Pollution Research 24(10):9681–9689. doi:10.1007/s11356-017-8637-x
  10. Li X, et al. (2023). Physiological, biochemical, and genomic elucidation of the Ensifer adhaerens M8 strain with simultaneous arsenic oxidation and chromium reduction. Journal of Hazardous Materials 441:129862. doi:10.1016/j.jhazmat.2022.129862

Working on a site with heavy metals?

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