3.3 Factors influencing bioavailability and accumulation
4 min read•august 7, 2024
Toxicants don't just float around harmlessly. Their impact depends on how easily organisms can absorb them. Environmental factors like pH, temperature, and salinity play a big role in this process.
Chemical properties of toxicants matter too. How they change form in the environment and inside organisms affects their ability to accumulate. Biological factors like an organism's fat content and ability to get rid of toxins also influence accumulation.
Environmental Factors
pH Impacts on Toxicant Bioavailability
Top images from around the web for pH Impacts on Toxicant Bioavailability
Frontiers | Species Sensitivity to Toxic Substances: Evolution, Ecology and Applications View original
Is this image relevant?
1 of 3
pH level influences the solubility and speciation of toxicants in the environment
Acidic conditions (low pH) can increase the solubility of metal toxicants, making them more bioavailable
Alkaline conditions (high pH) can decrease the solubility of metal toxicants, reducing their bioavailability
Changes in pH can affect the ionization state of organic toxicants, altering their bioavailability
Acidic conditions can increase the bioavailability of weakly acidic organic toxicants (phenols)
Alkaline conditions can increase the bioavailability of weakly basic organic toxicants (amines)
Temperature and Salinity Effects on Toxicant Uptake
Temperature influences the metabolic rate and physiological processes of organisms, affecting toxicant uptake and accumulation
Higher temperatures generally increase the uptake and accumulation of toxicants due to increased metabolic activity
Lower temperatures can slow down the uptake and accumulation of toxicants
Salinity affects the osmotic balance and ion exchange processes in aquatic organisms, impacting toxicant uptake
Changes in salinity can alter the bioavailability of toxicants by affecting their solubility and speciation
Estuarine and marine organisms may be more susceptible to toxicant uptake due to the presence of dissolved ions that compete with toxicants for binding sites
Organic matter content in sediments and soils can bind and immobilize toxicants, reducing their bioavailability
Toxicants can adsorb to organic matter, making them less available for uptake by organisms
Higher organic matter content generally decreases the bioavailability of hydrophobic organic toxicants (PCBs, PAHs)
Particle size of sediments and soils affects the surface area available for toxicant adsorption and desorption
Smaller particle sizes (clay, silt) have a higher surface area-to-volume ratio, providing more binding sites for toxicants
Larger particle sizes (sand, gravel) have a lower surface area-to-volume ratio, resulting in reduced toxicant adsorption
Chemical Properties
Speciation and Its Impact on Toxicant Bioavailability
Speciation refers to the different chemical forms in which a toxicant can exist in the environment
Metal toxicants can exist as free ions, complexes with organic or inorganic ligands, or in different oxidation states
Organic toxicants can exist in different ionization states or as complexes with dissolved organic matter
The bioavailability of a toxicant depends on its speciation in the environment
Free metal ions are generally more bioavailable than complexed or precipitated forms
Neutral organic toxicants are often more bioavailable than ionized forms due to their lipophilicity
Biotransformation and Its Role in Toxicant Bioaccumulation
Biotransformation is the process by which organisms modify toxicants through enzymatic reactions
Phase I reactions (oxidation, reduction, hydrolysis) introduce or expose functional groups on toxicants
Phase II reactions (conjugation) attach polar molecules to toxicants, increasing their water solubility and facilitating excretion
Biotransformation can affect the potential of toxicants
Some biotransformation reactions can detoxify toxicants, reducing their bioaccumulation potential
Other biotransformation reactions can activate toxicants, creating more toxic metabolites that can accumulate in organisms (PAHs, PCBs)
Biological Factors
Lipid Content and Its Influence on Toxicant Accumulation
Lipid content of an organism plays a crucial role in the accumulation of lipophilic toxicants
Organisms with higher lipid content (fatty fish) tend to accumulate more lipophilic toxicants compared to lean organisms
Lipophilic toxicants partition into lipid-rich tissues, leading to higher bioaccumulation
The distribution of lipids within an organism can affect the accumulation of toxicants in specific organs or tissues
Toxicants may preferentially accumulate in lipid-rich organs such as the liver, brain, and adipose tissue
Reproductive organs and eggs may also have higher toxicant levels due to their lipid content
Excretion Rate and Its Impact on Toxicant Bioaccumulation
Excretion rate determines the ability of an organism to eliminate toxicants from its body
Organisms with efficient excretory mechanisms (fish with well-developed gills and kidneys) can eliminate toxicants more rapidly, reducing their bioaccumulation
Organisms with slower excretion rates (mollusks, crustaceans) may accumulate toxicants to a greater extent
The balance between uptake and excretion rates influences the overall bioaccumulation of toxicants in an organism
If the uptake rate exceeds the excretion rate, toxicants will accumulate over time
If the excretion rate matches or exceeds the uptake rate, the organism can maintain a steady-state level of toxicants or even reduce their body burden
Key Terms to Review (1)
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.