The term “biopesticides” refers to biological agents that include the use of botanicals, pathogenic microbial species like fungi, bacteria, and viruses, as well as the natural competitors of pests, including parasitoids and predators, nematodes and semiochemicals, to control the pest level. 

Since nicotine was employed to regulate plum beetles from the 17th century, plant extracts were likely the first agricultural biocontrols. Agostino Bassi first showed that the white-muscadine fungus (Beauveria bassiana) could be used to create an infectious sickness in silkworms in 1835, which led to the beginning of research incorporating biological agents for insect pests in agriculture. In the 19th century, experiments using petroleum-based oils as plant protectants had been documented. 

An increasing number of studies and biocontrol suggestions were created during the early 20th century, causing institutional growth in research on agriculture. Biopesticides significantly influence the sustainability of the agricultural economy. 

Biological resources that are crucial to agriculture should be considered ecosystem-beneficial, which justifies the use of biopesticides in integrated pest management programs. They are organic molecules derived from living things (biological enemies) or their byproducts (semi-chemicals, phytochemicals, or microbial products) capable of controlling pests through non-toxic processes. They are regarded as low-risk, secure items for both people and their surroundings.  

Classification of Biopesticides

The Environmental Protection Agency has divided biopesticides into three main categories in accordance with the type of component they use, i.e., Microbial, Biochemical, and Plant-Incorporated Protectants. 

Microbial biopesticides

• The majority of broad-spectrum, pest-specific biopesticides fall into the microbial category. Microbial pesticides use microorganisms such as bacteria, viruses, fungi, and protozoans as biological components. 
• These types of species are precisely delivered to the target species. 
• Microbial biopesticides are environment-friendly, host-specific, and self-replicating. Bt (B. thuringiensis) is one of the most commonly employed bacteria to combat insect pests to control insect pests. 
• Lepidopterans, coleopterans, and dipterans are just a few of the many problems that it is used to fight off. 
• The most prevalent commercially available bacterial species as bio-pesticides are Bacillus popilliae, B. thuringiensis, Clostridium bifermentans, Pseudomonas alcaligenes, Pseudomonas aureofaciens, Saccharopolyspora spinosa, Serratiaentomophila, and Streptomyces avermitilis; as for fungi-based pesticides, Beauveria bassiana, Metarhizium anisopliae, Nomuraea rileyi, Trichoderma viride, Paecilomyces farinosus, and Verticillium lecanii. The use of baculoviruses (BV) as viral biopesticides is every day. 

Mode of action of B thuringiensis

B.thuringiensis can be used as a source of poisonous genes that, when expressed in plants, provide toxic particles harmful to several insect pests. 

The steps involved are:

1. Insects ingest endotoxin produced by bacteria during spore formation in leaves (B. thuringiensis)
2. The alkaline (pH 9–12) midgut environment in insects such as Lepidopterans causes the crystals to dissolve.
3. The solubilization of protein crystals releases and activates proteins such as cry protein in the insect’s gut.
4. The activated protein binds to the specific receptor present in the gut wall of insects, causing pore formation.
5. The pore formation leads to an osmotic imbalance between intracellular and extracellular environments, and cell lysis occurs.
6. As a result, the microvilli are destroyed, the insect ceases feeding, and it eventually dies.

Biochemical Pesticides

• Biochemical pesticides are plant-derived compounds that use non-toxic ways to control pests. 
• On the contrary, traditional insecticides often consist of synthetic substances that directly kill or inactivate the bug.
• For instance, this pesticide comprises insect sex pheromones, which prevent mating, and various other scented plant extracts, such as phytochemicals that attract insect pests and function as toxicants, insect growth regulators, repellents, and antifeedants.
• These pesticides affect an insect’s physiology, metabolic pathway, or neurological system through ingestion, inhalation, or absorption by the insect’s cuticle. Restricting spiracles inhibits insect breathing, which causes asphyxia.
• It will disrupt the insect membrane’s ion channel and ion pump, disrupting signal transduction at the cellular level.
• Monoterpenes is an essential oil that works as a neurotoxin by interfering with the acetylcholinesterase enzyme, vital in transmitting nerve impulses in insects, resulting in their paralysis and eventual demise. 
• Additionally, it prevents the synthesis of DNA, RNA, and proteins.

Plant-Incorporated Protectants

• Plant-incorporated protectants, genetically modified plants, or manipulated plants have the toxin-producing genes to combat the pest. For instance, the Bt gene is transferred in the cotton plant.
• The target gene is transferred into transgenic plants using Agrobacterium-mediated transfer, gene guns, or ballistic techniques. The above methods were applied to rice, corn, wheat, and maize. 
• Additionally, the plant-incorporated protections may pose some hazards, including those to non-target pests, human health, the environment, the spread of the PIP gene to other plants, and the appearance of herbicide- or insect-resistant organisms.

Biopesticide Formulation

• Biopesticide formulations are similar to those of synthetic pesticides. Active ingredients and inert or inactive substances are combined in biopesticide formulations.
• The formulation intended to manage the target pest contains one or more active ingredients (such as ethylene or B.thuringiensis), as well as inert additives (such as kerosene, beeswax, and propane) serve to improve the application and efficacy of the active ingredients.
• Based on their formulations, biopesticides are divided into dry and liquid.
• Dry materials include dust powders, granules, seed dressings, wettable powders, and wettable-dispersible powders, whereas emulsions, suspensions, emulsifiable concentrates, and ultra-low volume liquids are all examples of liquids.

Adavanatges of Biopesticides

Biopesticide holds some pros over synthetic pesticides:

• Biopesticides are less harmful than synthetic pesticides since they are made from natural components, thereby being gentler for the environment.
• Compared to synthetic pesticides, biopesticides are frequently more targeted in their effects and are more unlikely to harm non-target species.
• Biopesticides can aid in reducing the emergence of resistance to pesticides in pests, increasing the durability of pest control measures.
• In contrast to synthetic pesticides, biopesticides frequently leave less residue, lowering the risk of food and water pollution.
• Biopesticides are compatible with organic farming and can protect crops without jeopardizing the organic certification.

Disadvantages of Biopesticides

Biopesticide has a few cons, which are as follows:

• Biopesticides are photodecomposed by ultraviolet light, radiation, and heat and must be used only in the morning.
• Only a specific species or group of insects are poisoned by microbial insecticides; the others may still exist and inflict damage.
• Some of the fungal pesticides are expensive.
• Possibly having a shorter life span than synthetic pesticides, biopesticides are less practical to store and utilize.
• Biopesticides may need specialized tools or application methods, making them more challenging to apply.

References

1. Bharti, V., & Ibrahim, S. (2020). Biopesticides: Production, Formulation and Application Systems. International Journal of Current Microbiology and Applied Sciences, 9(10), 3931–3946. https://doi.org/10.20546/ijcmas.2020.910.453
2. Rajamani, M., & Negi, A. (2021). Biopesticides for Pest Management. In V. Venkatramanan, S. Shah, & R. Prasad (Eds.), Sustainable Bioeconomy (pp. 239–266). Springer Singapore. https://doi.org/10.1007/978-981-15-7321-7_11
3. Schünemann, R., Knaak, N., & Fiuza, L. M. (2014). Mode of Action and Specificity of Bacillus thuringiensis Toxins in the Control of Caterpillars and Stink Bugs in Soybean Culture. ISRN Microbiology, 2014, 1–12. https://doi.org/10.1155/2014/135675

The global population is continually increasing, and there is a growing demand for protein-rich food. However, traditional livestock farming cannot fulfill the current population’s required quantity of protein-rich food. Therefore, to meet the need of the current population, an alternative protein source known as single-cell protein (SCP) was developed in the mid-20th century.

Previously, the single-cell protein was termed as ‘microbial protein.’ Later a new term ‘single cell protein’ replaced the term’ microbial protein. Further, it is called “single-cell” protein because these microorganisms are typically grown and harvested as individual cells rather than as part of a larger organism.

Sources of Single Cell Protein (SCP) Production

Microorganisms are the only source of single-cell protein. Microorganisms that have the following characteristics are selected for the production of single-cell proteins;

1. The microorganisms should be able to accumulate a substantial protein content within their cellular structures.
2. Microorganisms with a fast growth rate are preferable as they allow for more efficient and scalable production processes.
3. The selected microorganisms should be non-toxic and safe for human consumption or animal feed.
4. Select of microorganisms that is able to survive under various environmental conditions, such as temperature, pH, and salinity.
5. The microorganisms should be capable of utilizing a wide range of substrates or feedstock for growth and protein production.
6. The microorganisms should possess genetic manipulation capabilities depending on the desired protein or compound to be produced.
7. Microorganisms selected for SCP production should be flexible to large-scale cultivation and downstream processing.

Some of the examples of microorganisms used in the production of single-cell protein are as follows;

1. Algae: Chlorella pyrenoidosa, Scenedesmus actus, Spirulina maxima
2. Bacteria: Achromobacter delvacvate, Bacillus megaterium, Cellumonas spp, Methylomonas clara, Pseudomonas spp.
3. Actinomycetes: Nocardia spp, Thermomonospora fusca,
4. Fungi:

• Yeast- Candida lipolytica, C.utilis, B.utilis, Saccharomyces cerevisiae, S.fragilis, Rhodotorula glutinis, Torulopsis spp.
• Molds– Aspergillus niger, Trichoderma viride, Paecilomyces varioti.
• Mushrooms– Agaricus campestris, Morchella crassipes

Nutritional value of Single Cell Protein

Microorganisms not only contain large quantities of protein, but they also contain carbohydrates, fats, vitamins, mineral salts, as well as non-protein nitrogenous substances (NPN) such as amino acids. Therefore, the average composition of single-cell protein, according to Al-Mudhafr et al. (2019), is given in the table below;

Production of Single Cell Protein

Production of single-cell protein completes within various steps that are as follows;

Step 1: Selection of strains:

It is a crucial step as the quality of protein depends on the type of microbe used for production. Only the microbes that have a fast growth rate and do not harm the consumers by producing toxic effects are preferable. Further, a suitable substrate required for the growth of the selected microbe should also be chosen.

Step 2: Fermentation: 

The selected microbes are then placed in a fermenter that is equipped with an aerator, thermostat, pH meter, etc, or in the trenches or ponds. Microbes are grown in fed-batch culture.

Step 3: Harvesting: 

When the colonies of microbes are fully developed, they are then harvested. The bulk of cells are separated from fermenters by decantation.

Step 4: Post-harvest treatment: 

After harvesting, cells are subjected to post-harvest treatment that includes; separation by centrifugation, washing, drying, etc.

Step 5: Single cell protein (SCP) processing for food: 

The dried cells are further processed to remove impurities, enhance nutritional content, and enhance texture and flavor.

Applications of Single-Cell Protein

Single-cell protein has a wide range of applications in various sectors. These are as follows;

1. Protein supplement: SCP can be useful as a supplement or substitute for traditional protein-rich ingredients like meat, soy, and fish meal. SCP offers a sustainable solution to address the increasing global demand for protein, particularly in regions with scarce protein sources.
2. Health food: Single-cell protein (SCP) can be utilized in producing healthy foods due to its high nutritional value and functional properties. It can be incorporated into weight management foods like meal replacement shakes or low-calorie snacks. Similarly, it can also be used to control obesity, instant energy source, etc.
3. In therapeutics and natural medicines: Single-cell protein (SCP) has potential applications in therapeutics and natural cures, including the production of therapeutic proteins, drug delivery systems, natural medicine production, probiotics, nutraceuticals, and antimicrobial agents.
4. In cosmetics: Single cell protein (SCP) can also be utilized as an ingredient to produce cosmetic products.
5. Poultry and cattle feed: Single-cell protein (SCP) can be a valuable ingredient in poultry and cattle feed. It serves as a sustainable alternative to traditional protein sources like soybean meal or fish meal.

Advantages of Single Cell Protein (SCP)

Single-cell protein has several benefits that are as follows;

1. Single-cell proteins can be produced in a short duration due to the rapid succession generation of microorganisms.
2. The genetic content of microorganisms can be easily adaptable. As a result, diverse amino acid compositions can be produced.
3. The single-cell proteins are highly rich in protein content.
4. It requires the cheapest raw material as a substrate for the growth of microorganisms.
5. It can be produced at any season in a controlled environment.
6. Its production does not require a large land area and is ecologically beneficial.

Disadvantages of Single Cell Protein (SCP)

Despite having many benefits, single-cell proteins also have some disadvantages, such as;

1. In some cases, toxic secondary metabolites in single-cell proteins may be present.
2. Single-cell protein (SCP) from certain microorganisms may lack essential nutrients, such as certain amino acids or vitamins. Therefore, ensuring a well-balanced nutritional profile in single-cell protein (SCP) can be challenging.
3. Some single-cell proteins (SCP) derived from some microorganisms might have allergic effects in susceptible individuals. Therefore, it is important to thoroughly evaluate the allergenicity of single-cell proteins and consider potential risks for consumers.
4. Kidney stones or gout might develop if consumed in higher amounts.
5. It can also cause the stimulation of gastrointestinal reactions due to poor digestibility.

References

1. R.C. Dubey and S. Chand. A Text Book of Biotechnology. S.Chand & Company Pvt. Ltd. 5th edition 2014.
2. Adnan W. H. Al-Mudhafr and Abeer M. A. Al-Garawy. Microbiological Sources and Nutritional Value of Single Cell Protein (SCP). J. Nutrition and Food Processing, 2019. 2(2);Doi:10.31579/2637-8914/013.  

Pollution all around the world has increased exponentially due various human activities. Recently, New Delhi was claimed to be one of the highly polluted city in the world. So, the leading countries of the World now, is focusing on controlling the pollution in an environmentally friendly and most cost-effective approach. 

. Not only controlling the pollutants, bioremediation, helps in restoring the areas  impacted by different pollution.  

The term bioremediators or biodegraders are used for denoting organisms used in bioremediation. These organisms have the ability to transform harmful substances into less toxic forms through their metabolic processes.  

The bioremediators can either degrade the pollutants directly or by producing enzymes and other biochemical agents which aid in degrading the contaminants. There are different factors that determine the effectiveness of the bioremediation methods like environmental circumstances and biodegraders used. Based on the factors, bioremediation method are divided in various types. 

Types of Bioremediation

Bioremediaton has been able to remedify wide range of pollutants like petroleum hydrocarbons, pesticides, solvents, heavy metals, and many organic compounds. It is sustainable alternative to traditional remediation method like excavation and chemical treatment. It is also applicable in areas where available methods can be expensive and impractical. 

The effectiveness and efficacy of biormediation depends on many other factors like concentration and type of concentrations, availability of biodegraders, and different environmental conditions. So, based on these factors there are seven different types of bioremediation; in situ bioremediation, phytoremediation, mycoremediation, ex situ bioremediation, biosimulation, and bioaugumentation.   

In situ bioremediation

The biological treatment of contaminants in the contaminated area or surface without removing any polluted material is called in situ bioremediation (ISB). It typically occurs in the cleaning of groundwater. ISB applies the concept of microbiology, chemistry, hydrogeology, and engineering for planned and controlled microbial degradation of specific classes of organic matter. ISB manipulates the degree of oxidation or reduction, which helps degrade the chemicals with microbial-catalyzed biochemical reactions. Types of microorganisms, geological conditions, and contaminant types should be considered for accomplishing the degradation.  

For example, chlorinated solvents in groundwater plumes require adding an organic carbon source, electron acceptor, nutrients, and microbial cultures to stimulate the degradation. Anaerobic reductive dechlorination, oxidation, reductive dechlorination, and aerobic co-metabolism are the primary biological processes degrading the chlorinated solvent compounds.  

The delivery method of the various amendments to the target area is crucial when forming the ISB systems. The delivery mechanisms commonly used are:

• Good vertical recirculation.
• Horizontal good recirculation.
• Direct liquid amendment injection.
• Gas amendment injection.
• Filtration trench recirculation.
• Pass-through (reactive cell) designs. 

Ex situ bioremediation

Ex-situ bioremediation treats soil and water by exacting in a controlled environment outside the original location. Petroleum hydrocarbon mixtures, phenols, cresols, some pesticides, and polycyclic aromatic compounds are the source of carbon and energy for microorganisms. 

Microbes degrade the carbon source into carbon dioxide and water. Different types of ex-situ bioremediation commonly available are; biopiles, composting, land farming, and bioreactors. 

1. Composting is the simple and most common technique of ex-situ bioremediation technique. It is usually applicable in treating agricultural, municipal solid wastes, and sewage sludge. These organic wastes converts into valuable components like hummus. It is also applicable in the treatment of contaminated soil. Mesophilic and thermophilic bacteria degrade, transform, or stabilizes the organic waste compounds. 
2. Biopiles are also called bio-cells, bio-heaps, bio-mounds, and compost cells. It is heavily applicable for remediating different petrochemical contaminants in soils and sediments. This technique combines landfarming and composting, providing a favorable environment for indigenous aerobic and anaerobic microbes. It also controls the physical losses of the contaminants by leaching and volatilization. The piling technique consists of a treatment bed, an aeration system, an irrigation and nutrient system, and a leachate collection system. 
3. Landfarming, also called land treatment or application, is simple ex-situ bioremediation. Here the materials are excavated and deposited in a large flat impermeable surface for increasing interaction between polluted soil and the atmosphere. This interaction helps in improving the aerobic microbial activity in the ground. 
4. The bioreactor is a biochemical processing system helpful in removing pollutants from wastewater or pumped groundwater using microbes and treatment of polluted soils in liquid or solid slurry. The mixing of contaminated soil with water and other additives occurs inside the bioreactor system to maintain contact between microbes and pollutants in optimum environmental conditions for degradation. 

Bioaugmentation

Adding selected strains/mixed cultures of organisms to the contaminated areas increases the ability of a pre-existing microbial community to degrade the pollutants. The two main strategies applied in bioaugmentation are augmentation by enrichment indigenous microbes and augmentation by enrichment of non-indigenous microbes.  

The most common method of applying bioaugmentation is the addition of microorganisms directly to the affected site so that these can transform harmful compounds into less dangerous material. The addition may attach to the carrier to form biofilm or exist alone and use contaminants as the primary carbon and energy sources. Compared to pure bacterial culture, mixed flora is preferrable for bio enhancement and bioaugmentation due to its higher ability to degrade and adapt according to the situation. 

Biosimulation

Factors like nutrients, temperature, pH, oxygen, moisture, soil properties, oxygen, and contaminants can limit hydrocarbon bioremediation. Biostimulation consists of modifying the environment to stimulate existing bacteria with bioremediation ability. The stimulation occurs by addition of various limiting nutrients and electron acceptors like phosphorus, oxygen, carbon, or nitrogen. These nutrients may be low, which constrains microbial activity. 

The addition of compounds in the treatment areas can improve pollutant degradation by optimizing the conditions like pH, temperature control, aeration, and the addition of nutrients. This technique is appropriate for the removal of petroleum pollutants from the soil. The advantage of this technique is the use of already present native microorganisms, which are already acclamatized to the subsurface environment and are distributed spatially within the subsurface. 

Mycoremediation

Using fungi or their derivatives to remediate environmental pollutants is called mycoremediation. It is a comparatively eco-friendly and cost-effective method. 

Fungi are an ideal choice because their growth is robust, they have vast hyphal networks, they can produce versatile extracellular ligninolytic enzymes, and they resist heavy metals. Additionally, the fungus has a high surface area to volume ratio and adaptability to fluctuation pH, temperature, and metal-binding proteins. 

This technique applies in the in-situ bioremediation of pollutants like dyes, pharmaceutical drugs, and herbicides. It can also occur in bioreactors with controlled physiochemical conditions to promote microbial growth. 

Phytoremediation

Using plants and associated soil microbes to reduce the concentrations and toxic effects of contaminants from the environment is called phytoremediation. It is a cost-effective environmental restoration technology. 

The method is an alternative to engineering procedures that are usually more destructive. The plants uptake pollutants through their roots and either store them in their tissues or break them down by natural metabolic processes. Phytoextraction, photodegradation, phytostabilization, and hemofiltration are some of the methods used for phytoremediation. 

However, this technique is limited to the root zone of plants and with limited application where the concentrations of contaminants are toxic to plants. 

Factors Affecting Efficacy and Effectiveness 

Some factors influence the efficacy and effectiveness of the methods used for bioremediation, which are as follows: 

1. Environmental conditions: Environmental conditions play a significant role in the growth of microbes and the proper degradation of contaminants. The environmental conditions include oxygen concentration, pH, temperature, moisture content, and nutrient level. Considering these environmental factors are necessary for implementing the correct method of bioremediation. 
2. Contaminant concentration and type: The higher the contaminant concentration, the more difficult to remediate the pollutants because the elevated concentration limits microbial activity. Additional steps may be required to enhance the activity in increased concentrations. Likewise, the type of contaminant also influences the selection of suitable bioremediation methods. Contaminants are either easily degradable or recalcitrant or hard to degrade. Microbes and plants can quickly degrade simple pollutants. The recalcitrant pollutants require specific enzymes or metabolic pathways for degradation. 
3. Bioavailability of contaminants: If the pollutants are easily accessible and susceptible to degradation, i.e., more bioavailable, it is easier to interact with bio remediate. But if the contaminants are tightly bound, i.e., less bioavailable, the accessibility of mediators may decrease. So, further treatments like adding surfactants or chelating agents must be done to increase the bioavailability of the pollutants. 
4. Diversity and population of microbes: Types and the number of microbes present in the contaminated areas also play essential roles when selecting bioremediation techniques. The indigenous people of microbes can have the ability to degrade the contaminants, but sometimes there might be need for addition of diverse strains.
5. Toxicity and inhibitory substances: Some contaminants, after degradation, can produce or are themselves toxic or inhibit microbes’ growth. The limitation of microbes’ growth reduces the effectiveness of bioremediation. A thorough study of the type of contaminant and their toxicity is critical in developing strategies to detoxify these compounds for successful bioremediation.   
6. Timeframe: Some bioremediation techniques require more time to complete remediation, like biosimulation techniques. In contrast, some methods require less time for completion but involve logistic challenges like landfarming bioremediation. So, the timeframe is essential for increasing effectiveness and efficacy. 
7. Site characteristics: The geographical features, hydrogeological conditions, soil type, and other aspects of the site for bioremediation is other factors that play a crucial role in the efficacy and effectiveness of bioremediation. Studying the site characteristics beforehand will aid in selecting the correct technique for bioremediation.  

Advantages of Bioremediation

The advantages of bioremediation for addressing environmental contaminations are as follows:

1. Cost-effective: There are other methods of remediating pollutants of environment except bioremediation like excavation and incineration which are expensive. Bioremediation is the most cost-effective option available for controlling and removing pollution from the environment. The equipment required, energy, and labor requirements is less expensive especially in the cases the site is inaccessible and extensive.  
2. Environmental sustainability: Bioremediation is an environmentally friendly technique because it relies on natural processes and organisms to degrade or transform pollutants. It protects from harsh chemicals and damaging excavation methods. These properties minimize further harm to the environment and ecosystems.  
3. Restoration of affected area: The degradation by another method besides bioremediation may cause disruption and damage to the affected area. Bioremediation believes in the degradation of pollutants in natural processes, which restores soil fertility, water quality, and overall ecosystem health. This method not only helps in the restoration of the affected area but also the growth of the area.
4. Long-term and versatile effectiveness: Bioremediation applies to contaminants like petroleum hydrocarbons, pesticides, heavy metals, solvents, and organic compounds. Different organisms and techniques are applicable for specific pollutants, which allows versatility in degrading different types of contamination. Likewise, this method targets the source of contamination, which promotes the degradation of persistent pollutants. This method can also adapt and respond to changing conditions, assisting in ongoing or complex contamination scenarios.    

Risks of Bioremediation

Although bioremediation is highly beneficial and widely used for environmental cleaning, it has some risks, which are as follows:

1. Bioremediation may lead to the production of more toxic compounds than already existing components. These toxic compounds can also be motile and transfer from a contaminated area to another unaffected area. For example, trichloroethane (TCA) degradation produces vinyl chloride, which is more toxic and carcinogenic than TCA.
2. Polycyclic aromatic compounds and some chlorinated compounds are not easily degradable by microbes. 

So, there is requirement of proper research in bioremediation selection to remove environmental pollutants successfully.

References and further reading

• Cristorean, Carmen & Micle, Valer & Sur, Ioana. (2016). A critical analysis of ex-situ bioremediation technologies of hydrocarbon polluted soils. ECOTERRA – Journal of Environmental Research and Protection. 
• Godleads Omokhagbor Adams, Prekeyi Tawari Fufeyin, Samson Eruke Okoro, and Igelenyah Ehinomen, “Bioremediation, Biostimulation and Bioaugmention: A Review.” International Journal of Environmental Bioremediation & Biodegradation, vol. 3, no. 1 (2015): 28-39. doi: 10.12691/ijebb-3-1-5.
• Wexler, P. (2014) ‘Bioremediation’, in Encyclopedia of toxicology. third. Amsterdam: Academic Press, pp. 435–489. 
• Ren, H., & Zhang, X. (2020). Biological technologies for cHRPs and risk control. In High-risk pollutants in wastewater (pp. 209–236). Amsterdam, Netherlands: Elsevier.
• Akhtar, N., & Mannan, M. A. (2020). Mycoremediation: Expunging environmental pollutants. Biotechnology Reports, 26. doi:10.1016/j.btre.2020.e00452  
• Greipsson, S. (2011) Phytoremediation. Nature Education Knowledge 3(10):7 
• Kapahi, M., & Sachdeva, S. (2019). Bioremediation Options for Heavy Metal Pollution. Journal of health & pollution, 9(24), 191203. https://doi.org/10.5696/2156-9614-9.24.191203