Lead (Pb)

  • Atmospheric Emissions: Industrial processes, particularly those involving lead smelting, mining, and combustion of fossil fuels, release lead particles and gases into the air.

  • Vehicle Emissions: The burning of leaded gasoline in vehicles was a significant source of lead emissions in the past, though it has been largely phased out in many countries.

  • Industrial Waste Discharge: Improper disposal of industrial waste, including wastewater and solid waste containing lead, can contaminate soil and water bodies.

  • Mining and Ore Processing: Mining activities, especially in lead ore-rich areas, can release lead into the environment through the extraction and processing of ores.

  • Smelting Operations: Lead smelting operations involve heating lead-containing materials to extract the metal, resulting in the release of lead particulates and fumes.

  • Incineration: Burning of waste, including items containing lead, in incinerators can release lead particles and emissions into the air.

  • Contaminated Soils: Lead-contaminated soil from industrial sites, mining areas, or improper waste disposal can be transported through wind erosion or water runoff.

  • Construction and Demolition: Construction and demolition activities, particularly in older structures, can release lead dust and debris into the air and soil.

How Does Lead Enter The Environment?

  • Paints and Coatings: Deteriorating lead-based paints and coatings, commonly used in older buildings, can release lead dust into the environment.

  • Plumbing Systems: Lead pipes, plumbing fixtures, and solder in older homes and buildings can leach lead into drinking water, particularly when water is corrosive.

  • Industrial Discharges: Industrial facilities, such as metal manufacturing, battery manufacturing, and electronic waste recycling plants, may discharge lead-containing effluents into nearby water bodies.

  • Landfills: Improper disposal of lead-containing products and waste in landfills can result in leaching of lead into surrounding soil and groundwater.

  • Agricultural Practices: The use of lead-containing pesticides and fertilizers in agricultural activities can contribute to lead contamination in soil and water.

  • Lead-acid Batteries: Improper disposal or recycling of lead-acid batteries, commonly used in vehicles and various industries, can lead to the release of lead into the environment.

Glutathione

How Does Lead Affect The Environment?

  1. Soil Contamination: Lead can accumulate in the soil through various sources such as lead-based paint, mining activities, industrial emissions, and the use of lead-containing pesticides and fertilisers. In the early twentieth century, the ophthalmologist John Lockhart Gibson (1860-1944) traced the growing cases of ‘ocular motility impairments’ and ‘visual disturbances’ in children to lead paint exposure. Discoveries such as those made by Gibson fuelled a campaign of research and inquiry, followed by public health warnings that eventually lead industries to phase out the use of lead and eventually for government to ban its use in a number of products and processes. Lead-based paint has been banned in the UK since 1992 and in the US since 1978. Despite regulatory improvements limiting the amount of lead-containing products available, lead is still used in a number of domestic and industrial products, assuring its continued circulation. Once in the soil, lead persists for long periods due to its low mobility and binding affinity to soil particles.

  2. Soil Degradation: Lead contamination can degrade soil quality and fertility, leading to reduced agricultural productivity. It inhibits the growth and development of plants by disrupting nutrient uptake, enzyme activities, and metabolic processes.

  3. Crop Contamination: Lead in soil can be taken up by plants, leading to crop contamination. It primarily accumulates in the roots, but significant amounts can also transfer to the above-ground parts, including edible portions such as fruits and vegetables. Consumption of lead-contaminated crops can pose health risks to humans, especially if they are not properly washed or cooked.

  4. Phytotoxicity: Lead is highly toxic to plants, even at relatively low concentrations. It interferes with various physiological processes, such as photosynthesis, respiration, and enzyme activities, leading to stunted growth, chlorosis (yellowing of leaves), and reduced yield.

  5. Soil Microbial Activity: Lead pollution can adversely affect soil microbial communities and their functions. Soil microorganisms play crucial roles in nutrient cycling, organic matter decomposition, and maintaining soil health. Lead inhibits microbial growth and activity, disrupting these essential processes and impairing soil fertility.

  6. Leaching and Groundwater Contamination: Depending on soil properties and conditions, lead can slowly leach from contaminated soil and contaminate groundwater. This can pose a significant threat to drinking water supplies, as groundwater serves as a primary source for many communities.

  7. Ecological Effects: Lead contamination in soil can disrupt the soil food web and impact soil-dwelling organisms such as earthworms, beneficial insects, and soil microorganisms. These organisms play vital roles in soil structure formation, nutrient cycling, and overall ecosystem health.

Health Consequences:

a. Neurotoxicity: Lead primarily affects the central nervous system, especially in children. It can impair neurodevelopment, leading to decreased IQ, cognitive deficits, learning disabilities, and behavioural problems.

b. Haematological Effects: Lead exposure can disrupt the synthesis of haemoglobin, resulting in anaemia.

c. Cardiovascular Effects: Lead has been associated with increased blood pressure, hypertension, and cardiovascular diseases.

d. Renal Effects: Prolonged lead exposure can lead to kidney damage, impaired renal function, and increased risk of chronic kidney disease.

e. Reproductive and Developmental Effects: Lead exposure can adversely affect fertility and featal development, and cause adverse pregnancy outcomes such as premature birth and low birth weight.

f. Carcinogenicity: Lead has been classified as a probable human carcinogen (Group 2A) by the International Agency for Research on Cancer (IARC). It has been linked to an increased risk of kidney and lung cancers.

  • Fusarium graminearum

    Kingdom: Fungi

    Division: Ascomycota

    Class: Sordariomycetes

    Order: Hypocreales

    Family: Nectriaceae

    Genus: Gibberella

    Species: G. zeae / F. graminearum

    Fusarium graminearum taxonomy

  • Aspergillus versicolor

    Class: Eurotiomycetes

    Genus: Aspergillus

    Division: Ascomycota

    Species: A. versicolor

    Aspergillus versicolor

  • Auricularia polytricha

    Kingdom: Fungi

    Phylum: Basidiomycota

    Class: Basidiomycetes

    Order: Auriculariales

    Family: Auriculariaceae

    Genus: Auricularia

    Species: polytricha

    Auricularia polytricha

  • Metarhizium anisopilae

    Kingdom: Fungi

    Division: Ascomycota

    Class: Sordariomycetes

    Order: Hypocreales

    Family: Clavicipitaceae

    Genus: Metarhizium

    Species: M. robertsii / M. anisopilae

    Metarhizium anisopilae

  • Penicillium chrysogenum

    Kingdom: Fungi

    Division: Ascomycota

    Class: Eurotiomycetes

    Order: Eurotiales

    Family: Trichocomaceae

    Genus: Penicillium

    Species: P. chrysogenum

    Penicillium chrysogenum

  • Penicillium janthinellum

    Kingdom: Fungi

    Division: Ascomycota

    Class: Eurotiomycetes

    Order: Eurotiales

    Family: Trichocomaceae

    Genus: Penicillium

    Species: P. janthinellum

    Penicillium janthinellum

  • Phanerochaete chrysosporium

    Kingdom: Fungi

    Division: Basidiomycota

    Class: Agaricomycetes

    Order: Polyporales

    Family: Phanerochaetaceae

    Genus: Phanerochaete

    Phanerochaete chrysosporium

Mycoremediation processes for lead (Pb):

  • Bioaccumulation

  • Absorption

  • Adsorption

  • Intracellular accumulation

  • Complexation

  • Biotransformation (oxido-reduction)

  • Volatilisation

  • Ion-exchange

  • Precipitation

  • bioleaching

Intracellular enzymatic processes:

  • Cytochrome P450

  • monooxygenases 

Cell-bound enzymes:

  • phenol monooxygenases 

  • quinone reductase 

  • dehalogenases 

  • transferases 

  • cytoplasmic protein

  • Metal-binding protein

Extracellular enzymes:

  • oxidoreductases 

  • lignin peroxidases 

  • laccases

  • manganese peroxidases 

Cell wall components:

  • Cell wall phospholipids

  • Fungal melanin

  • N- acetylglucosamine

  • Chitin

Functional groups:

  • Methyl & Methylene

  • isocyanate functional group

  • amine

  • alkane

  • carbonyls

  • carboxyl

  • hydroxyl

  • imidazole

  • phosphonate

  • phosphodiester groups

Forms of application:

  • Dried fungal biomass (living)

  • Fungal pellet

  • Dried fungal biomass (immobilised)

  • Aqueous solution immobilised fungal biomass (Ca-alginate)

  • Immobilized cells in a sol–gel matrix

  • Immobilized fungi on Luffa cylindrica

General trend: Effects of pH on metal ion uptake capacity by immobilised biomass
Fungal Species Removal % pH Time Biomass Type References
Aspergillus flavus 83.63% 5.0 120min Immobilised T. Akar & S. Tunali
Aspergillus niger
98% 		6.0 240min Immobilised A. Nuban & A. Safitri 2021

Aspergillus tubingensis F12
90.8% 		5.0 5ml/min EPS Tang et. al 2021

Aspergillus versicolor 		30%

5.5 180min Immobilised Cabuk et. al 2004

Auricularia polytricha
99.22		 6.0 30min Immobilised Zhang et. al 2011

Candida utilis
83%		 6.0 9ml/min Immobilised S. Ali 2013

fusarium graminearum
90%		 5.0 120min immobilised Anaemene, I. A 2012
Lepiota hystrix 99% 6.0 30min Immobilised Kariuki et. al 2017

Metarhizium anisopilae 		20%

 5.5 180min Immobilised Cabuk et. al 2004

Mucor hiemalis, EH8, EH11		 93%, 97%

 5.7, 5.7 48hr Living biomass Hoque & Fritscher 2019

Mucour rouxii
99%		 6.0 5hr live biomass yan & Viraraghavan 2003

Penicillium canescens
94.4%		 5.0 4hr live biomass Say et. al 2003

Penicillium chrysogenum
99.9%		 6.5 120min Immobilised Bayrak et. al 2023

Penicillium lanosumcoeruleum
27%		 5.5 180min Live biomass Ilhan et. al 2004

Penicillium purpurogenum
91.5%		 5.0 4hr Live biomass Say et. al 2007

Phanerochaete chrysosporium
86.48%
99.72%		 5.0
6.0		 72Hr
7days 		Live biomass
Dried biomass		 He et. al 2022
Sharma, K.R., Giri, R. & Sharma, R.K 2023

Phlebia brevispora
97.5%
99.76%		 6.0 7 days Dried biomass Sharma, K.R., Giri, R. & Sharma, R.K 2023

Phlebia floridensis
99.77 %		 6.0 7 days Dried biomass Sharma, K.R., Giri, R. & Sharma, R.K 2023

Pleurotus ostreatus
93% 		5.0 30mins Immobilised Eliescu et. al 2019

Rhizopus nigricans 		43%

 4.0 20mins Immobilised Zhang et. al 1998

Saccharomyces cerevisiae
70%		 5.0 4 days Live biomass Massoud et. al 2019

General Trend: Effect of temperature °C on metal ion uptake by immobilised biomass

Please note: These graphs are not showing specific data sets, they simply show general trends on the effect of selected variables across relevant literature. There are species which defy these common trends, showing high strong removal capacities under extreme conditions (pH, Temperature).

The Effects of Lead Pollution Continued…

Lead pollution in soil can significantly impact microbial communities in several ways:

  1. Reduced Microbial Biomass: Lead exposure can lead to a decrease in microbial biomass in soil. Microbes may experience inhibited growth and reproduction due to the toxic effects of lead, resulting in a decline in overall microbial populations.

  2. Altered Microbial Composition: Lead pollution can alter the composition and diversity of soil microbial communities. Certain groups of microorganisms may be more sensitive to lead than others, leading to shifts in community structure. This can disrupt the balance of beneficial microorganisms and potentially favor the proliferation of more resistant or opportunistic species.

  3. Impaired Enzyme Activities: Microbes produce various enzymes that play a crucial role in nutrient cycling, nitrogen-fixing, organic matter decomposition, and other essential soil processes. Lead can inhibit enzyme activities, particularly those involved in the metabolism of carbon, nitrogen, and phosphorus. This disruption can impair nutrient availability and cycling in soil ecosystems.

  4. Disrupted Symbiotic Relationships: Many microorganisms in soil form symbiotic associations with plants, such as mycorrhizal fungi that assist in nutrient uptake. Lead pollution can interfere with these symbiotic relationships, leading to reduced plant-microbe interactions and compromised plant health.

  5. Genetic and Functional Changes: Lead exposure can induce genetic changes in microbial populations, including alterations in gene expression and DNA damage. These genetic changes can impact the functional potential of microbial communities, affecting their ability to carry out essential ecosystem processes.

Examples of species known to have been affected by lead poisoning

Fungal Species:

  1. Aspergillus niger

  2. Penicillium chrysogenum

  3. Trichoderma sp.

  4. Fusarium sp.

  5. Rhizopus sp.

  6. Aspergillus fumigatus

  7. Candida albicans

  8. Saccharomyces cerevisiae

  9. Phanerochaete chrysosporium

  10. Pleurotus ostreatus

Bacterial Species:

  1. Bacillus subtilis

  2. Pseudomonas aeruginosa

  3. Escherichia coli

  4. Staphylococcus aureus

  5. Streptomyces sp.

  6. Rhodococcus sp.

  7. Arthrobacter sp.

  8. Azotobacter sp.

  9. Bacillus cereus

  10. Burkholderia cepacia

Fish Species:

  1. Common Carp (Cyprinus carpio)

  2. Brown Trout (Salmo trutta)

  3. Rainbow Trout (Oncorhynchus mykiss)

  4. Atlantic Salmon (Salmo salar)

  5. Northern Pike (Esox lucius)

  6. Walleye (Sander vitreus)

  7. Perch (Perca spp.)

  8. Catfish (e.g., Channel catfish - Ictalurus punctatus)

Bird Species:

  1. Bald Eagle (Haliaeetus leucocephalus)

  2. California Condor (Gymnogyps californianus)

  3. Common Loon (Gavia immer)

  4. Mallard (Anas platyrhynchos)

  5. Canada Goose (Branta canadensis)

  6. American Kestrel (Falco sparverius)

  7. Peregrine Falcon (Falco peregrinus)

  8. Red-winged Blackbird (Agelaius phoeniceus)

Several microorganisms in soil have been found to be affected by lead pollution. Some examples include:

  1. Arbuscular Mycorrhizal Fungi (AMF): These beneficial fungi form symbiotic associations with plant roots, aiding in nutrient uptake. Lead exposure can reduce the abundance and diversity of AMF in soil, impacting their ability to support plant growth.

  2. Nitrogen-Fixing Bacteria: Certain nitrogen-fixing bacteria, such as those belonging to the genus Rhizobium, are essential for nitrogen fixation in legume plants. Lead pollution has been shown to inhibit the activity of these bacteria, leading to reduced nitrogen availability for plants.

  3. Soil Bacterial Communities: Various bacterial groups in soil, such as Actinobacteria, Firmicutes, and Proteobacteria, can be influenced by lead pollution. Studies have demonstrated shifts in the relative abundance and diversity of these bacterial taxa in response to lead contamination.

  4. Soil Fungal Communities: Lead pollution can also affect fungal communities in soil. For example, studies have shown altered abundance and composition of fungal groups like Ascomycota and Basidiomycota in lead-contaminated soils.

Insect Species:

  1. Honeybees (Apis mellifera)

  2. Butterflies (e.g., Monarch butterfly - Danaus plexippus)

  3. Dragonflies (e.g., Common whitetail - Plathemis lydia)

  4. Beetles (e.g., Ground beetles - Carabidae family)

  5. Ants (e.g., Carpenter ants - Camponotus spp.)

  6. Grasshoppers (e.g., Melanoplus spp.)

  7. Moths (e.g., Indian mealmoth - Plodia interpunctella)

  8. Bees (e.g., Bumblebees - Bombus spp.)

Amphibian Species:

  1. Northern Leopard Frog (Lithobates pipiens)

  2. American Bullfrog (Lithobates catesbeianus)

  3. Wood Frog (Lithobates sylvaticus)

  4. Green Frog (Lithobates clamitans)

  5. American Toad (Anaxyrus americanus)

  6. Fowler's Toad (Anaxyrus fowleri)

  7. Red-backed Salamander (Plethodon cinereus)

DNA Damage

Lead exposure can induce changes in the DNA of microbial populations. The toxic effects of lead can lead to alterations in gene expression and DNA damage. These genetic changes can have consequences for the functional potential of microbial communities and their ability to carry out essential ecosystem processes.

For example, lead exposure can result in altered gene expression related to important processes such as nitrogen cycling, carbon metabolism, and heavy metal resistance. This can disrupt nutrient cycling, soil respiration rates, and the ability of microorganisms to tolerate and detoxify heavy metals. Additionally, lead-induced genetic changes may impact the abundance and diversity of antibiotic-resistance genes, potentially contributing to the spread of antibiotic resistance in microbial communities.

While the specific mechanisms and DNA changes induced by lead exposure can vary across studies, it is evident that lead pollution can have significant effects on microbial genetic composition and functionality

Enzyme disruptions

In soil, enzymes facilitate the breakdown and transformation of organic matter, including plant residues, animal waste, and microbial biomass. They are involved in processes such as cellulose and hemicellulose degradation, lignin modification, protein hydrolysis, lipid metabolism, and polysaccharide breakdown. This enzymatic decomposition of complex organic compounds into simpler forms releases nutrients, such as carbon, nitrogen, phosphorus, and sulfur, making them available for uptake by plants and other organisms.

Microbial enzymes also participate in the cycling of elements, including carbon, nitrogen, and phosphorus. For example, carbon-degrading enzymes like cellulases and ligninases break down plant-derived carbon compounds, facilitating carbon mineralization and release as carbon dioxide. Nitrogenase enzymes are responsible for nitrogen fixation, converting atmospheric nitrogen into ammonium, which can be utilized by plants. Enzymes involved in nitrification and denitrification are pivotal in nitrogen cycling, converting ammonium to nitrate and nitrate to nitrogen gas, respectively. Phosphatases hydrolyze organic phosphorus compounds, releasing inorganic phosphate that is vital for plant growth.

These microbial enzymes exhibit specificity towards particular substrates, and their activities are influenced by factors such as pH, temperature, moisture, nutrient availability, and the composition of organic matter in the soil. Enzyme activity can be regulated by the presence of inhibitors, co-factors, and specific environmental conditions.

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