Bio/Phytoremediation

Bioremediation & Phytoremediation...

How Nature Helps Clean Soil

Bioremediation is the use of living microorganisms like bacteria, protozoa, nematodes, and fungi… also known as the soil food web….to break down, transform, or stabilize pollutants in soil and water. These organisms either consume contaminants, lock them in place, or convert them into less harmful forms. Plants too have a role to play in bioremediation because they are also living organisms that live above ground, including the grass and lawns we walk and play on, the ornamentals we plant around our home and the shade trees that line our city streets. Many are known for accumulating pollutants in their roots, branches and leaves and this process is known as phytoremediation. Using strictly fungi is known as mycoremediation.

In California, bioremediation is regulated under the California Code of Regulations (CCR) Title 22, overseen by the Department of Toxic Substances Control (DTSC). These rules ensure cleanup methods protect human health and the environment.

How Bioremediation Works

Microorganisms naturally present in soil can break down pollutants like petroleum, solvents, and pesticides. Sometimes they need a boost of oxygen, water and food in the form of carbohydrates, both simple and complex to activate them. Just like people need proper hydration, diet, sun and housing, microorganisms flourish and populate when they are nurtured under the right conditions. This “in situ” (in‑place) method is often faster and cheaper than excavating and removal of the topsoil. Additionally, it avoids the unintended consequences of off-site emissions from hauling and the compounding of pollutants in a single site like a landfill.

Phytoremediation: Using Plants to Clean Soil

Some plants can absorb heavy metals such as lead, cadmium, zinc, copper, nickel, and arsenic through their roots. Others are tolerant of metals that allow them to grow and stabilize contaminated soils, preventing erosion and keeping pollutants from spreading.

After these plants grow and accumulate metals, they can be harvested and composted on‑site, then tested to evaluate whether the finished compost can be used or taken off-site for appropriate redistribution elsewhere. In some cases, the plants that do establish themselves after a fire can be incorporated into the existing landscape provided they remain as ornamentals and not part of your edible garden.

Composted plant material will still contain the metals those plants absorbed, but testing often show the concentrations remain below health‑based screening thresholds, allowing the finished compost to be used safely off site and in low public exposure areas. Compost functions as a warehouse for microbial life, and it also holds abundant living and non‑living carbon, resources far too valuable to discard in a landfill or be burned causing other unintended consequences.

Plants That Help Clean Contaminated Soil

(California natives + common urban ornamentals + naturalized species)

Below are a list of plants that are known to accumulate, tolerate, or stabilize heavy metals and are useful in post‑fire landscapes, urban gardens, and disturbed soils.

California Native Species

• California Poppy (Eschscholzia californica) – tolerant of serpentine soils high in nickel and chromium.

• Wright’s Cudweed (Pseudognaphalium canescens) – thrives in stressed, post‑fire soils; useful for stabilization.

• California Buckwheat (Eriogonum fasciculatum) – uptakes lead and zinc; supports pollinators.

• Telegraph Weed (Heterotheca grandiflora) – accumulates lead; common in disturbed soils.

• Willows (Salix spp.) – absorb cadmium, nickel, and zinc.

• Poplars (Populus spp.) – deep roots extract metals and solvents.

• Cattails (Typha spp.) – filter metals in wetland soils.

• California Black Walnut (Juglans californica) – stabilizes metals in riparian soils.

Urban Ornamentals & Drought‑Tolerant Landscape Plants

• Bougainvillea (Bougainvillea spp.) – accumulates cadmium, copper, zinc, and lead. Removal of lead and cadmium from wastewater sludge using bougainvillea sp. through phytoremediation technique / Ahmad Na’im Abdul Rahman, Nurul Nadiah Mohd Firdaus Hum and Zitty Sarah Ismail - UiTM Institutional Repository

• Lavender (Lavandula spp.) – accumulates lead, cadmium, and zinc. Assessment of heavy metal uptake in lavender (Lavandula angustifolia Mill.) from contaminated urban sediment | Discover Plants | Springer Nature Link

• Rosemary (Salvia rosmarinus) – uptakes lead, cadmium, and zinc. Investigating the pollution of irrigated plants (Rosmarinus officinalis) with polluted water in different growth stages using spectrometer and K-means method | Environmental Science and Pollution Research | Springer Nature Link

• Lantana (Lantana camara) – accumulates cadmium, lead, and zinc.

• Oleander (Nerium oleander) – accumulates manganese, lead, copper, cadmium, and iron.

• Cape Leadwort / Plumbago (Plumbago auriculata) – tolerates and accumulates lead and zinc.

• Sweet Alyssum (Lobularia maritima) – stabilizes disturbed soils; related species are nickel accumulators. Phytoextraction of cobalt (Co)-contaminated soils by sweet alyssum (Lobularia maritima (L.) Desv.) is enhanced by biodegradable chelating agents | Journal of Soils and Sediments | Springer Nature Link

• Evening Primrose (Oenothera spp.) – known to accumulate cadmium and zinc. Phytoextraction of cobalt (Co)-contaminated soils by sweet alyssum (Lobularia maritima (L.) Desv.) is enhanced by biodegradable chelating agents | Journal of Soils and Sediments | Springer Nature Link

• Black Nightshade (Solanum nigrum) – accumulates lead, cadmium, and arsenic. Zinc Enhances Cadmium Accumulation in Shoots of Hyperaccumulator Solanum nigrum by Improving ATP-Dependent Transport and Alleviating Toxicity

• Ladies’ Tobacco (Nicotiana glauca) – accumulates lead and cadmium; thrives in disturbed soils. Zinc Enhances Cadmium Accumulation in Shoots of Hyperaccumulator Solanum nigrum by Improving ATP-Dependent Transport and Alleviating Toxicity

How Soil Food Web Microbes and Fungi Help

Microbes use enzymes to break down organic pollutants like petroleum, pesticides, and solvents. While heavy metals cannot be broken down, microbes and fungi can:

• Bind metals so they don’t move

• Transform metals into less bioavailable forms

• Store metals inside their cells

• Support plant uptake through root‑zone interactions

This partnership between the soil food web, plants and fungi is the foundation of ecological soil recovery and the biological systems approach 301 Organics approaches each of its projects with.

SOURCES:

https://dtsc.ca.gov/proven-technologies-remedies-documents/?form=MG0AV3

https://dtsc.ca.gov/dtsc-website-archive/results-promising-for-in-situ-bioremediation/

https://phys.org/news/2023-05-fungi-california-pollution.html?form=MG0AV3&form=MG0AV3#google_vignette

https://link.springer.com/article/10.1007/s00449-024-02978-6?form=MG0AV3 The function of microbial enzymes in breaking down soil contaminated with pesticides: a review

https://link.springer.com/article/10.1007/s12033-019-00187-1?form=MG0AV3 Biochemical Characteristics of Microbial

https://www.nrcs.usda.gov/plantmaterials/capmcrb11380.pdf

https://livetoplant.com/california-native-plants-natural-solutions-for-soil-erosion/

https://calscape.org/Eriogonum-fasciculatum-%28California-Buckwheat%29

https://krishi.icar.gov.in/jspui/bitstream/123456789/51977/1/Comparative%20Evaluation%20of%20Phytoremediation%20Potential%20of%20Indian%20Mustard.pdf

https://link.springer.com/chapter/10.1007/978-981-99-0397-9_14

https://link.springer.com/chapter/10.1007/978-3-030-89984-4_12