Bioremediation of Environmental Contaminants – Lecture Review

These flashcards cover key definitions, laws, strategies, advantages, disadvantages, microbial examples, and Antarctic case studies discussed in the lecture on bioremediation of xenobiotic contamination.

What are xenobiotics?

Man-made (or unnaturally high-level) compounds that are non-biodegradable and accumulate in the environment.

Give three industrial examples of xenobiotic pollutants.

Pesticides (e.g., DDT), PCBs/dioxins, and chlorinated solvents/dyes.

Which book sparked public awareness of synthetic pesticide dangers in the 1960s?

Rachel Carson’s “Silent Spring.”

What U.S. law (1980s) made waste generators responsible for hazardous waste ‘from cradle to grave’?

The Resource Conservation and Recovery Act (RCRA).

List two physical or chemical remediation ‘quick fixes’ contrasted with biological options.

Incineration, landfilling, soil washing, solvent extraction, or sparging.

Define bioremediation.

Use of living organisms (directly or via their products) to degrade hazardous pollutants into less-toxic compounds.

Name the three major bioremediation strategies.

Natural attenuation, biostimulation, and bioaugmentation.

Natural attenuation relies on microbes.

Indigenous (native).

Key requirement before choosing natural attenuation.

Bio-assessment to confirm degraders are naturally present.

Main advantage and disadvantage of natural attenuation.

Advantage: very cost-effective; Disadvantage: slow and site management/monitoring needed.

What is biostimulation?

Addition of nutrients/electron acceptors to the site to enhance the activity of native degraders.

Two challenges associated with biostimulation.

Lag time for microbes to respond and possible competition by non-target microbes.

Define bioaugmentation.

Introduction of specialized exogenous microbial populations capable of degrading the contaminant.

Why is field performance of bioaugmentation often lower than lab results?

Environmental conditions differ and introduced microbes may not compete/survive well in situ (‘microbes are like teenagers – hard to control’).

Why are microbial consortia preferred over single strains in petroleum degradation?

They offer richer metabolic networks and more complete breakdown of complex hydrocarbon mixtures.

Give five bacterial genera known to degrade petroleum.

Pseudomonas, Acinetobacter, Flavobacterium, Rhodococcus, Mycobacterium.

What Australian company provides site-specific bioremediation consulting?

Microbial Insights Australia (MicroNOVO).

Why is oil a difficult pollutant?

It is a complex mixture of alkanes, aromatics, cycloalkanes requiring multiple metabolic pathways for degradation.

Four common approaches to oil spill bioremediation.

Dispersants, nutrient addition (biostimulation), bioaugmentation with known degraders, and combination in-situ strategies.

Name a widely used but toxic dispersant banned in the UK.

Corexit 9500.

Cost comparison: bioremediation vs incineration per cubic yard (approx.).

Bioremediation ~$75; incineration or secure landfill $200–$800.

List two key disadvantages of bioremediation.

Scale-up unpredictability and site-specific performance variability; regulatory hesitance; possible switch of microbes to alternate energy sources.

Largest offshore oil spill in U.S. history that used biostimulation & bioaugmentation.

Deepwater Horizon (Gulf of Mexico, 2010).

Native microbe that helped consume Deepwater Horizon oil.

Colwellia spp.

Bioaugmented bacterium used at Deepwater Horizon.

Alcanivorax borkumensis.

Why is Antarctic soil contamination a concern despite vast ice coverage?

Only <0.4 % is ice-free; wildlife, stations and contamination concentrate in these rare soils, which have unique, fragile microbial ecosystems.

International agreement requiring remediation of Antarctic contamination.

1991 Protocol on Environmental Protection to the Antarctic Treaty.

Main petroleum remediation method used on Macquarie Island (Sub-Antarctic).

In-situ biostimulation via aeration and nutrient (air-sparging + fertilizer) addition.

Typical ‘plateau’ concentration reached after Macquarie Island and Casey Station clean-ups.

~1,000 mg total petroleum hydrocarbons (TPH) per kg soil.

Macquarie Island study: how did microbial diversity change as hydrocarbons declined?

Proteobacteria dominance decreased and overall community diversity increased (more ‘natural’ taxa reappeared).

Spiking experiment finding: which genus increased with higher diesel levels?

Pseudomonas (and Parvibaculum).

What unexpected problem arose in Casey Station biopiles after urea fertilization?

Nitrite accumulation due to disrupted nitrogen cycle, creating toxicity.

Engineering features of Casey Station biopiles.

Composite barrier containment, annual mixing, and one-time mineral fertilizer addition.

Why are logistics a major constraint for Antarctic remediation?

All materials must be shipped, then transferred by helicopter, inflatable boat, or amphibious LARC; weather is extreme.

Give two alternative technologies considered when 1,000 mg kg⁻¹ plateau is insufficient.

Biopiles/composting or soil washing with different fertilizers.

Explain ‘how clean is clean enough’ challenge.

Need site- and region-specific regulatory limits (e.g., Antarctic guidelines) to define acceptable residual contaminant levels and ecosystem recovery.

Two broad advantages of in-situ bioremediation in remote areas.

Minimal site disturbance and reduced need to transport contaminated soil (‘dig and haul’ impractical).

What is the primary goal of bioremediation?

Detoxify or mineralize contaminants, thereby removing environmental liability and enabling ecosystem restoration.