2.2 Environmental partitioning and distribution of pollutants
3 min read•august 7, 2024
Environmental pollutants move and accumulate in complex ways. This section explores how chemicals distribute between air, water, and soil, and how they build up in living things. Understanding these processes is key to predicting a pollutant's impact.
We'll look at sorption, partition coefficients, and Henry's law to see how pollutants spread in the environment. Then we'll dive into and to grasp how chemicals concentrate in food chains, affecting ecosystems and human health.
Partitioning Processes
Sorption Mechanisms
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- Sorption describes the process by which a chemical substance becomes attached to a solid surface
- Adsorption occurs when a chemical adheres to the surface of a solid material (soil particles, sediments)
- Involves interactions between the chemical and the surface, such as van der Waals forces, hydrogen bonding, or electrostatic interactions
- Adsorption can be reversible or irreversible depending on the strength of the interactions
- Absorption involves the penetration of a chemical into the interior of a solid material (uptake by plants, diffusion into microplastics)
- Absorbed chemicals are incorporated into the internal structure of the solid
- Absorption is often a slower process compared to adsorption
Partition Coefficients
- () describes the distribution of a chemical between soil and water phases at equilibrium
- Represents the ratio of the concentration of a chemical in soil to its concentration in water
- Higher values indicate a greater affinity of the chemical for soil, leading to reduced mobility and bioavailability
- Depends on soil properties (organic matter content, clay content) and chemical properties (hydrophobicity, polarity)
- () describes the distribution of a chemical between air and water phases at equilibrium
- Represents the ratio of the concentration of a chemical in air to its concentration in water
- Higher values indicate a greater tendency for the chemical to partition into the air phase
- Influenced by the chemical's vapor pressure and water solubility
Environmental Distribution
Henry's Law Constant
- () describes the partitioning of a chemical between air and water at equilibrium
- Represents the ratio of a chemical's partial pressure in air to its concentration in water
- Higher values indicate a greater tendency for the chemical to volatilize from water to air
- Temperature-dependent, with higher temperatures favoring volatilization
- Important for predicting the fate and transport of chemicals in the environment (pesticides, industrial solvents)
Fugacity
- is a measure of a chemical's escaping tendency from a particular phase or compartment
- Expressed in units of pressure (pascals) and represents the partial pressure of a chemical in a mixture
- Chemicals move from high fugacity to low fugacity compartments to achieve equilibrium
- Fugacity models are used to predict the distribution of chemicals in the environment (air, water, soil, )
- Considers the chemical's properties, environmental conditions, and transfer processes between compartments
Biological Accumulation
Bioaccumulation
- Bioaccumulation refers to the uptake and accumulation of a chemical in an organism's tissues over time
- Occurs when the rate of uptake exceeds the rate of elimination or metabolism
- Can occur through various routes (ingestion, inhalation, dermal absorption)
- Bioaccumulation factor (BAF) quantifies the extent of accumulation relative to the chemical's concentration in the environment
- Lipophilic and persistent chemicals (PCBs, DDT) are more likely to bioaccumulate in organisms
Biomagnification
- Biomagnification describes the increasing concentration of a chemical in organisms at successively higher trophic levels in a food chain
- Occurs when a chemical is transferred from prey to predator, resulting in higher concentrations at each trophic level
- Biomagnification potential depends on the chemical's persistence, bioaccumulation potential, and trophic transfer efficiency
- Can lead to high concentrations of chemicals in top predators (mercury in fish, PCBs in marine mammals)
- Has implications for ecosystem health and human exposure through consumption of contaminated organisms
Key Terms to Review (12)
Air-water partition coefficient: The air-water partition coefficient is a ratio that quantifies the distribution of a chemical compound between air and water phases, indicating how readily it evaporates from water into the atmosphere. This coefficient is crucial for understanding the environmental behavior of pollutants, helping to predict their movement and concentration in different environmental compartments.
Bioaccumulation: Bioaccumulation is the process by which organisms accumulate contaminants in their bodies over time, often from their environment or food sources. This phenomenon can lead to higher concentrations of harmful substances in the tissues of an organism compared to the surrounding environment, significantly impacting health and ecological dynamics.
Biomagnification: Biomagnification is the process by which the concentration of toxic substances increases as they move up the food chain, affecting organisms at higher trophic levels more severely. This phenomenon connects various aspects of ecological interactions and highlights the importance of understanding how pollutants behave in ecosystems and impact wildlife health.
Distribution Model: A distribution model is a mathematical framework used to predict the spread and concentration of pollutants within various environmental compartments such as air, water, and soil. It helps in understanding how these substances partition between different phases, influencing their bioavailability and potential ecological impacts. By simulating various environmental conditions, these models can aid in risk assessment and management of pollution.
Fugacity: Fugacity is a concept used to describe the tendency of a chemical species to escape from one phase and enter another, essentially quantifying its 'escaping power' in environmental systems. It is particularly important for understanding how pollutants partition and distribute themselves among different environmental compartments such as air, water, and soil. By relating fugacity to concentration, it helps predict where a pollutant is likely to accumulate and how it might impact various ecosystems.
Heavy metals: Heavy metals are a group of metallic elements that have a high density and are toxic at low concentrations, including elements like lead, mercury, cadmium, and arsenic. Their persistence in the environment and potential to accumulate in living organisms makes them a significant concern in ecotoxicology, influencing various ecological and health-related outcomes.
Henry's Law Constant: Henry's Law Constant is a value that quantifies the solubility of a gas in a liquid under equilibrium conditions, defining the relationship between the concentration of the gas in the liquid and the partial pressure of that gas above the liquid. This constant is crucial for understanding how pollutants partition between air and water, influencing their distribution and behavior in various environmental media.
Log Kow: Log Kow, or the logarithm of the octanol-water partition coefficient, is a measure that indicates how a chemical compound partitions between an organic solvent (octanol) and water. This ratio helps to understand a pollutant's hydrophobicity and bioavailability, which are crucial for predicting its environmental behavior and potential effects on aquatic organisms. A higher log Kow value generally suggests that the substance is more likely to accumulate in organisms and sediments rather than remain dissolved in water, influencing its transport and fate in the environment.
Microbial degradation: Microbial degradation is the process by which microorganisms, such as bacteria and fungi, break down complex organic substances into simpler compounds. This natural phenomenon plays a critical role in the biogeochemical cycling of nutrients and the detoxification of pollutants in various environments, impacting the environmental partitioning and distribution of harmful substances.
Partition Coefficient: The partition coefficient is a ratio that describes how a chemical substance distributes itself between two immiscible phases, typically an organic solvent and water. It indicates the preference of a compound for one phase over the other, which is crucial for understanding its behavior in the environment. This property is essential in assessing the environmental fate of pollutants, as it influences their bioavailability, toxicity, and movement through different media such as soil, water, and living organisms.
Sediment: Sediment refers to particles of organic or inorganic material that accumulate at the bottom of a body of water, often as a result of erosion and weathering. It plays a crucial role in environmental processes, affecting pollutant distribution and partitioning, as well as serving as a habitat for various organisms. Understanding sediment dynamics is essential for assessing how pollutants interact with the aquatic environment and how they may be transported or transformed over time.
Soil-water partition coefficient: The soil-water partition coefficient (K\_d) is a numerical value that quantifies the distribution of a chemical between soil and water, providing insight into how pollutants are absorbed by soil particles versus remaining in soil water. This coefficient plays a critical role in determining the fate and transport of contaminants in the environment, influencing both their bioavailability and potential for leaching into groundwater. A higher K\_d value indicates greater adsorption to soil, while a lower value suggests more pollutants remain dissolved in water.