5 Environmental Fate, Persistence, and Biodegradation_f9597db08f06df10b01ef90cdbd36d4d

Environmental Fate, Persistence, and Biodegradation

Lecture Overview

• Lecture 5 coverage:

  • Environmental fate of chemicals

  • Persistence of chemicals and examples (PBTS, POPs, PFCs, PCBs, plastics)

  • Types of degradation

  • Focus on biodegradation, including examples such as the Deepwater Horizon Oil Spill

  • The relationship between molecular structure and biodegradation

  • Positive and negative contributions to biodegradation

  • Successful substitutions for biodegradable products (surfactants, chelants, antifoulants)

  • Estimation of biodegradation using group contribution theory

Learning Objectives/Outcomes

• List classes of molecules that persist in the environment.

• Understand different types of degradation and their roles in the environment and society through examples and case studies.

• Recognize parameters affecting biodegradation rates.

• Apply predictive rules for biodegradation potential based on molecular structure.

• Acknowledge successful molecular substitutions leading to biodegradable products.

Environmental Fate of Chemicals

• Inquiry into the fate of synthetic chemicals and products in the environment.

• Discuss whether they degrade or persist indefinitely.

• Engage in class discussions to enhance understanding.

Chemical Persistence

Definition

• Persistence: Ability of a chemical to remain unchanged in the environment for extended periods.

  • ICCA (2001): Persistent substances resist degradation under aerobic and anaerobic conditions.

Characteristics

• Persistent chemicals: Examples include PBTS, POPs, PFCs, PCBs.

  • Measure persistence by their physicochemical properties and bioaccumulation tendency.

Examples of Persistent Chemicals

• Polychlorinated Biphenyls (PCBs):

  • Introduced in the 1940s for applications in plastics, adhesives, and lubricants.

  • Characteristics: thermally stable, bioaccumulate, mostly banned but persistent.

• Polyfluorinated Compounds (PFCs):

  • Introduced in the 1950s, used in coatings to repel water and oil.

  • Extremely persistent due to strong C-F bonds.

• Polybrominated Compounds (PBCs):

  • Introduced in the 1970s as flame retardants.

  • Persist in the environment and bioaccumulate.

Types of Degradation

• Photolysis: Decomposition under sunlight.

• Thermolysis: Decomposition through heat.

• Hydrolysis: Breakdown in water.

• Biodegradation: Breakdown by microbial action.

Biodegradation

Definitions

• Biodegradation: Transforming chemicals by microbial organisms via metabolic or enzymatic action.

• Criteria for biodegradability:

  • "Ready" biodegradability: 70% removal of organic carbon in a 28-day test.

  • "Ultimate" biodegradability: 60-70% conversion to CO₂ in 28 days.

Factors Affecting Biodegradation Rates

• Environmental conditions such as pH, temperature, and availability of microorganisms.

• Physical and chemical properties of chemicals (complexity, water solubility).

• Molecular structure: types and numbers of chemical bonds.

Successful Substitution for Biodegradable Products

Surfactants

• Definition: Compounds that reduce surface tension, used for cleaning and emulsifying.

• Example: Replacement of non-biodegradable TPS with biodegradable LAS.

• Importance of surfactants in reducing environmental impact.

Chelants

• Chelants prevent adverse effects from metal ions in cleaning products.

• Common non-biodegradable chelants (e.g., EDTA) lead to environmental concerns.

• Alternatives like EDDS are biodegradable and non-hazardous.

Antifoulants

• Antifoulants like tributyltin oxide (TBTO) are persistent and toxic; banned globally.

• Sea-Nine 211 is a biodegradable replacement for marine applications.

Biodegradation Estimation Using Group Contribution Theory

Introduction

• Group contribution theory estimates biodegradation potential based on molecular structure.

• Predictions range from 0 (no degradation) to 1 (certain degradation).

Calculation Process

• Formula for estimating biodegradation rates by evaluating structural contributions:

  • [ I = 3.199 + a_1f_1 + a_2f_2 + ... - 0.00221 \times MW ]

Case Studies and Examples

• Practical examples illustrate how to estimate the biodegradation potential of chemicals like isopropanol and diphenyl ether by applying the group contribution theory and understanding their molecular structure.

Conclusion

• Understanding the environmental fate, persistence, and biodegradation of chemicals is crucial for effective environmental management and the development of sustainable products.

Environmental Fate, Persistence, and Biodegradation

Lecture Overview

Lecture 5 Coverage:

• Environmental Fate of Chemicals: Examination of how synthetic chemicals are distributed in the environment, their behaviors, and interactions with ecological systems.

• Persistence of Chemicals: Investigation into classes of chemicals, including Persistent Bioaccumulative Toxics (PBTs), Persistent Organic Pollutants (POPs), Per- and Polyfluoroalkyl Substances (PFAS), Polychlorinated Biphenyls (PCBs), and plastics, which persist in the environment.

• Types of Degradation: Overview of various degradation processes affecting chemicals in the environment.

• Focus on Biodegradation: Detailed analysis of biodegradation processes with case studies, specifically referencing the Deepwater Horizon Oil Spill, to illustrate practical applications and challenges.

• Molecular Structure Relationship: Exploration of how molecular structure influences biodegradation potential, highlighting key functional groups that affect microbial breakdown.

• Contributions to Biodegradation: Identification of positive and negative ramifications of substances and practices that impact biodegradation rates.

• Successful Substitutions: Overview of successful substitutions for biodegradable products, including surfactants, chelants, and antifoulants that mitigate environmental impacts.

• Estimation of Biodegradation: Methodologies for estimating biodegradation potential using group contribution theory, which allows for predictive assessments.

Learning Objectives/Outcomes

• Classes of Molecules: Accurately list and categorize various groups of molecules that exhibit persistence in the environment and understand their ecological implications.

• Degradation Roles: Evaluate and compare the different types of degradation and their significance in environmental contexts through multiple case studies and real-world examples.

• Biodegradation Rates: Recognize and describe key parameters that affect biodegradation rates, including environmental, chemical, and biological factors.

• Predictive Rules Application: Apply principles of predictive biodegradation potential based on specific molecular structures, facilitating a deeper comprehension of synthetic chemical interactions in ecosystems.

• Molecular Substitution Awareness: Acknowledge and promote the importance of developing and adopting successful molecular substitutions that lead to environmentally friendly, biodegradable products.

Environmental Fate of Chemicals

• Inquiry Focus: Investigate the fate and transport of synthetic chemicals within various environmental compartments (air, water, soil) and assess their degradation pathways or potential for long-term persistence.

• Class Discussions: Encourage interactive discussions to enhance understanding and foster critical thinking regarding chemical pollutants and biosafety.

Chemical Persistence

Definition:

• Persistence: Defined as the ability of a chemical to remain chemically unchanged within the environment for extended periods.

ICCA (2001) Definition:

• Persistent substances typically resist transformation or degradation under both aerobic (oxygen-rich) and anaerobic (oxygen-poor) conditions.

Characteristics:

• Persistence is evaluated based on their physico-chemical properties (e.g., solubility, vapor pressure) and their tendency to bioaccumulate in biological systems.

Examples of Persistent Chemicals:

• Polychlorinated Biphenyls (PCBs):

  • Introduced in the 1940s, PCBs were widely used in industrial applications such as plastics, adhesives, and lubricants due to their excellent insulating properties.

  • Characteristics: Highly thermally stable, bioaccumulate significantly in the food chain, and have been mostly banned globally, though they continue to be detected in the environment due to their persistency.

• Polyfluorinated Compounds (PFCs):

  • Introduced in the 1950s, they are used in various applications including protective coatings that repel water and oil.

  • Extremely persistent due to the strong C-F bonds that inhibit degradation, these compounds have raised concerns regarding their long-term ecological impacts.

• Polybrominated Compounds (PBCs):

  • Used as flame retardants since the 1970s, these compounds are persistent environmental contaminants and can bioaccumulate, presenting potential risks to human health and wildlife.

Types of Degradation

• Photolysis: Decomposition of substances through the action of sunlight, breaking down chemical bonds.

• Thermolysis: Breakdown of substances due to exposure to elevated temperatures, which can lead to the release of various harmful byproducts.

• Hydrolysis: Chemical process of water breaking down compounds; can lead to the formation of potentially harmful degradation byproducts.

• Biodegradation: The process by which microbial organisms metabolize chemicals and convert them into simpler, non-toxic compounds.

Biodegradation

Definitions:

• Biodegradation: The process of transforming chemicals by microbial organisms through metabolic or enzymatic actions that lead to their breakdown into simpler substances.

Criteria for Biodegradability:

• “Ready” Biodegradability: Defined as achieving at least 70% removal of organic carbon in a standardized 28-day test.

• “Ultimate” Biodegradability: Indicates a conversion of 60-70% of a substance into CO₂ within the same time frame, reflecting a complete breakdown of the material.

Factors Affecting Biodegradation Rates:

• Various factors such as environmental conditions (pH, temperature), the physical and chemical properties of the substances involved (e.g., polarity, molecular weight), along with biological aspects, significantly influence the rates of biodegradation.

Successful Substitution for Biodegradable Products

• Surfactants:

  • Definition: Compounds designed to reduce surface tension in liquids, enhancing cleaning and emulsifying processes.

  • Examples: The replacement of conventional non-biodegradable surfactants (such as linear alkylbenzene sulfonates) with biodegradable alternatives like linear alkyl sulfonates (LAS) to reduce environmental burdens.

• Chelants:

  • Importance: Chelants are used to bind metal ions in products to prevent ecological toxicity.

  • Examples: The common non-biodegradable chelant EDTA has environmental persistence issues, while alternatives such as EDDS (Ethylene Diamine-N,N'-Disuccinic Acid) are biodegradable and pose minimal ecological risks.

• Antifoulants:

  • Definition: Biocides used to prevent the accumulation of organisms on submerged surfaces in marine environments.

  • Examples: The use of tributyltin oxide (TBTO) has been globally banned due to its high toxicity and persistence, while Sea-Nine 211 serves as a biodegradable alternative that minimizes ecological impact.

Biodegradation Estimation Using Group Contribution Theory

Introduction:

• Group contribution theory serves as a predictive framework for estimating biodegradation potential based on molecular structure attributes.

Predictions:

• Predictions are quantified on a scale from 0 (indicating no expected degradation) to 1 (indicating certain degradation).

Calculation Process:

• The formula for estimating biodegradation rates evaluates the structural contributions, incorporating molecular weighting factors:[ I = 3.199 + a_1f_1 + a_2f_2 + ... - 0.00221 \times MW ]

Case Studies and Examples:

• Application of the group contribution theory to practical examples, such as isopropanol and diphenyl ether, highlights the methodological processes used to derive biodegradation potentials based on their respective molecular structures, emphasizing the importance of understanding chemical backbone modifications for improved environmental outcomes.

Conclusion

Understanding the environmental fate, persistence, and biodegradation of chemicals is crucial for the development and implementation of effective environmental management strategies. This knowledge not only assists in the design of sustainable products but also informs policy decisions aimed at regulating harmful substances in order to mitigate their impacts on ecosystems and human health.