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

Contaminant group

PAHs & Semivolatile Organics

Soot and tar compounds left behind by fire, fuel and industry. Soil biology has one of its longest research records on this class, and six organisms in our products have published PAH or phthalate work.

What biology does
Breaks down
Microbes in our products
P. putida, P. stutzeri, C. testosteroni and 4 more
Shows up at
East Palestine, Ohio, Train Derailments, Wildfire Burn Scars
Diagram: PAHs & Semivolatile Organics, microbial action, outcomeFused aromatic rings, from two-ring naphthalene to five-ring benzo[a]pyrene. Bacteria and fungi oxidize the rings, and heavier PAHs often need the two working together. Breakdown: in the research. Rings are cleaved into smaller organic acids, then carbon dioxide, water and new biomass. Binding: in the research. Biochar and compost hold the heaviest PAHs in place, limiting how far they move while biology works on them.01 CONTAMINANT02 MICROBIAL ACTION03 OUTCOME PAHs & Semivolatile OrganicsFused aromatic rings, fromtwo-ring naphthalene to five-ringbenzo[a]pyrene.Microbial actionBacteria and fungi oxidize therings, and heavier PAHs oftenneed the two working together.CO2H2OIN THE RESEARCHBreakdownRings are cleaved intosmaller organic acids,then carbon dioxide,water and new biomass.IN THE RESEARCHBindingBiochar and compost holdthe heaviest PAHs inplace, limiting how farthey move while biologyworks on them.Diagram: PAHs & Semivolatile Organics, microbial action, outcomeFused aromatic rings, from two-ring naphthalene to five-ring benzo[a]pyrene. Bacteria and fungi oxidize the rings, and heavier PAHs often need the two working together. Breakdown: in the research. Rings are cleaved into smaller organic acids, then carbon dioxide, water and new biomass. Binding: in the research. Biochar and compost hold the heaviest PAHs in place, limiting how far they move while biology works on them.01 CONTAMINANTPAHs & Semivolatile OrganicsFused aromatic rings, from two-ringnaphthalene to five-ringbenzo[a]pyrene.02 MICROBIAL ACTION Microbial actionBacteria and fungi oxidize the rings,and heavier PAHs often need the twoworking together.03 OUTCOMECO2H2OIN THE RESEARCHBreakdownRings are cleaved intosmaller organic acids, thencarbon dioxide, water and newbiomass.IN THE RESEARCHBindingBiochar and compost hold theheaviest PAHs in place,limiting how far they movewhile biology works on them.
Fig. 1How biology acts on PAHs & semivolatile organics, 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 (7 sections)
  1. What Elm Dirt does about PAHs and SVOCs
  2. What it is
  3. Where it comes from
  4. Why it matters
  5. What the research shows about microbes in our products
  6. What to expect
  7. Studies

What Elm Dirt does about PAHs and SVOCs

Biology has a good record on this class, so the plan is simple. We apply living biologicals and Class A compost carrying bacteria and fungi together, since the heaviest PAHs respond to the pairing better than to either group alone. Then we get air and roots into the ground. Most PAH degraders need oxygen, and PAHs break down faster in planted soil than in bare soil because roots feed a larger degrading population [1].

Where the heavy fraction sits tight, biochar holds what biology can’t reach quickly, so the site doesn’t wash its problem downstream while the lighter fraction comes down. We work with local applicators, take a baseline, treat, and resample on a schedule through an independent lab using standard EPA methods.

What it is

Polycyclic aromatic hydrocarbons are a group of more than 100 chemicals formed when coal, oil, gas, garbage or other organic material burns incompletely [2]. Each is built from fused carbon rings, two at the small end and six or more at the large end.

A PAH’s behavior depends largely on how many rings it has: two- and three-ring PAHs such as naphthalene and phenanthrene are lighter, more soluble and degrade fairly fast. Five- and six-ring PAHs such as benzo[a]pyrene are heavy and nearly insoluble, bind hard to soil, and include the compounds of most concern for cancer.

On a lab report, PAHs fall under SVOCs (semivolatile organic compounds), usually run by EPA Method 8270. Phthalates come out of the same analysis, so they are covered here too.

Where it comes from

Anywhere carbon burns incompletely, or tar and heavy oil get handled:

  • derailments and chemical fires, where open burning of fuel and cargo coats the surrounding soil
  • wildfire, which leaves PAHs in burn scars along with ash and a water-repellent surface layer
  • vehicle exhaust along roads and rail corridors
  • coal tar, creosote-treated wood and asphalt sealcoat
  • former manufactured-gas plants, coking works and refineries, some of the most PAH-contaminated ground in the country
  • volcanoes and forest fires [2]

PAHs cling to soil particles, though some move down into groundwater, and microorganisms break them down over weeks to months [2].

Why it matters

The U.S. Department of Health and Human Services has determined that some PAHs may reasonably be expected to be carcinogens, and several have caused lung, stomach and skin cancer in laboratory animals [2]. Animal studies also show reproductive effects and harm to development from exposure before birth.

People meet site PAHs through direct contact with soil and dust, and through soil that erodes off site.

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 PAHs or related semivolatile compounds.

Organism What the research documents
Comamonas testosteroni In PAH-contaminated soil, 81 percent of the phenanthrene, 63 percent of the naphthalene and 38 percent of the benzo[a]pyrene removed by day 25, while the soil’s own degrading population grew more active [3]
Pseudomonas putida Mineralization of PAHs and dioxin-like heterocycles, genome-mapped; part of the consortium in a 365-day diesel field study [4][5]
Pseudomonas fluorescens Naphthalene pathway, tracked through a two-year contained field release; activity rises in the root zone [6][1]
Acinetobacter calcoaceticus A biosurfactant from this species raised phenanthrene desorption and degradation in bioslurry, which is the bioavailability problem on aged sites [7]
Trichoderma harzianum Oxidative enzyme activity on PAHs; degradation of dibutyl phthalate [8][9]
Mucor circinelloides Crude-oil bioremediation by an isolated strain [10]
Terrabacter sp. A dioxygenase from this group converts phenanthrene, fluorene, pyrene and fluoranthene, the heavier rings [11]

The best published benzo[a]pyrene result came from a defined bacterial-fungal coculture, which mineralized 53 percent of added radiolabelled benzo[a]pyrene in contaminated soil over 100 days [12]. The researchers tracked the labelled carbon all the way out as carbon dioxide, and the soil extract was measurably less mutagenic afterward. Few studies show toxicity dropping as well as concentration. Our products carry both groups of organisms.

Phthalates, from the same lab report, are a clean fit. Comamonas testosteroni carries phthalate dioxygenase, one of the best-characterized enzymes of its class [13], and strains of the species completely cleared 100 mg/L of phthalic and terephthalic acid [14]. Pseudomonas putida grows on diethyl phthalate and phthalic acid [15].

What to expect

Lighter and heavier PAHs come down at very different rates, with the two- and three-ring fraction breaking down in weeks to months and the five- and six-ring fraction taking many months to more than a year. The 25-day soil study above shows the gap in a single dataset, where 81 percent of the phenanthrene was removed against 38 percent of the benzo[a]pyrene [3].

On aged sites the bottleneck is usually bioavailability, because PAHs work their way into soil organic matter where enzymes can’t easily reach them. The organisms on old industrial ground are capable and the problem is contact, which is why biosurfactant producers and soil structure get attention.

A PAH treatment runs from months to a year or more, and an independent lab confirms the result.

Our soil-restoration pilot in East Palestine, Ohio treats PAHs and SVOCs on this plan.

Studies

  1. Kamath R, Schnoor JL, Alvarez PJ (2004). Effect of root-derived substrates on the expression of nah-lux genes in Pseudomonas fluorescens HK44: implications for PAH biodegradation in the rhizosphere. Environmental Science & Technology 38(6):1740–1745. doi:10.1021/es0306258
  2. Agency for Toxic Substances and Disease Registry. ToxFAQs: Polycyclic Aromatic Hydrocarbons (PAHs). CDC ToxFAQs
  3. Lu Q, et al. (2022). Effects of Comamonas testosteroni on dissipation of polycyclic aromatic hydrocarbons and the response of endogenous bacteria for soil bioremediation. Environmental Science and Pollution Research 29(54):82351–82364. doi:10.1007/s11356-022-21497-z
  4. Wang W, et al. (2021). Genetic mapping of highly versatile and solvent-tolerant Pseudomonas putida B6-2 (ATCC BAA-2545) for mineralization of PAHs and dioxin-like compounds. Environmental Microbiology 23(8):4309–4325. doi:10.1111/1462-2920.15613
  5. Szulc A, et al. (2014). The influence of bioaugmentation and biosurfactant addition on bioremediation efficiency of diesel-oil contaminated soil: feasibility during field studies. Journal of Environmental Management 132:121–128. doi:10.1016/j.jenvman.2013.11.006
  6. Ripp S, et al. (2000). Bioluminescent most-probable-number monitoring of a genetically engineered bacterium during a long-term contained field release. Applied Microbiology and Biotechnology 53(6):736–741. doi:10.1007/s002530000343
  7. Zhao Z, Selvam A, Wong JW (2011). Synergistic effect of thermophilic temperature and biosurfactant produced by Acinetobacter calcoaceticus BU03 on the biodegradation of phenanthrene in bioslurry system. Journal of Hazardous Materials 190(1-3):345–350. doi:10.1016/j.jhazmat.2011.03.042
  8. Zafra G, Cortés-Espinosa DV (2015). Biodegradation of polycyclic aromatic hydrocarbons by Trichoderma species: a mini review. Environmental Science and Pollution Research 22(24):19426–19433. doi:10.1007/s11356-015-5602-4
  9. Ahuactzin-Pérez M, et al. (2014). Fungal biodegradation of dibutyl phthalate and toxicity of its breakdown products on the basis of fungal and bacterial growth. World Journal of Microbiology and Biotechnology 30(11):2811–2819. doi:10.1007/s11274-014-1705-1
  10. Yehia RS (2023). Highlighting the potential for crude oil bioremediation of locally isolated Cunninghamella echinulata and Mucor circinelloides. Brazilian Journal of Microbiology 54(3):1969–1981. doi:10.1007/s42770-023-01008-z
  11. Zhou HW, Zhou MJ (2007). Cloning and functional study of a novel aromatic-ring-hydroxylating dioxygenase gene. Nan Fang Yi Ke Da Xue Xue Bao 27(5):717–719. PMID 17644853.
  12. Boonchan S, Britz ML, Stanley GA (2000). Degradation and mineralization of high-molecular-weight polycyclic aromatic hydrocarbons by defined fungal-bacterial cocultures. Applied and Environmental Microbiology 66(3):1007–1019. doi:10.1128/AEM.66.3.1007-1019.2000
  13. Mahto JK, et al. (2021). Molecular insights into substrate recognition and catalysis by phthalate dioxygenase from Comamonas testosteroni. Journal of Biological Chemistry 297(6):101416. doi:10.1016/j.jbc.2021.101416
  14. Vural C, Ettadili H (2024). Biodegradation of phthalic acid and terephthalic acid by Comamonas testosteroni strains. Folia Microbiologica 69(6):1343–1353. doi:10.1007/s12223-024-01176-x
  15. Shariati S, Pourbabaee AA, Alikhani HA (2023). Biodegradation of diethyl phthalate and phthalic acid by a new indigenous Pseudomonas putida. Folia Microbiologica 68(3):477–488. doi:10.1007/s12223-022-01022-y

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