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
(Kd) 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 Kd 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)
(KAW) 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 KAW 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
(H) 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 H 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