Bioconcentration

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In aquatic toxicology, bioconcentration is the accumulation of a water-borne chemical substance in an organism exposed to the water. [1] [2]

Contents

There are several ways in which to measure and assess bioaccumulation and bioconcentration. These include: octanol-water partition coefficients (KOW), bioconcentration factors (BCF), bioaccumulation factors (BAF) and biota-sediment accumulation factor (BSAF). Each of these can be calculated using either empirical data or measurements, as well as from mathematical models. [3] One of these mathematical models is a fugacity-based BCF model developed by Don Mackay. [4]

Bioconcentration factor can also be expressed as the ratio of the concentration of a chemical in an organism to the concentration of the chemical in the surrounding environment. The BCF is a measure of the extent of chemical sharing between an organism and the surrounding environment. [5]

In surface water, the BCF is the ratio of a chemical's concentration in an organism to the chemical's aqueous concentration. BCF is often expressed in units of liter per kilogram (ratio of mg of chemical per kg of organism to mg of chemical per liter of water). [6] BCF can simply be an observed ratio, or it can be the prediction of a partitioning model. [6] A partitioning model is based on assumptions that chemicals partition between water and aquatic organisms as well as the idea that chemical equilibrium exists between the organisms and the aquatic environment in which it is found [6]

Calculation

Bioconcentration can be described by a bioconcentration factor (BCF), which is the ratio of the chemical concentration in an organism or biota to the concentration in water: [2]

[2]

Bioconcentration factors can also be related to the octanol-water partition coefficient, Kow. The octanol-water partition coefficient (Kow) is correlated with the potential for a chemical to bioaccumulate in organisms; the BCF can be predicted from log Kow, via computer programs based on structure activity relationship (SAR) [7] or through the linear equation:

[8]

Where:

at equilibrium

Fugacity capacity

Fugacity and BCF relate to each other in the following equation:

[6]

where ZFish is equal to the Fugacity capacity of a chemical in the fish, PFish is equal to the density of the fish (mass/length3), BCF is the partition coefficient between the fish and the water (length3/mass) and H is equal to the Henry's law constant (Length2/Time2) [6]

Regression equations for estimations in fish

EquationChemicals Used to obtain equationSpecies Used
84 Fathead Minnow, Bluegill Sunfish, Rainbow Trout, Mosquitofish
[4] 44Various
36 Brook trout, Rainbow trout, Bluegill Sunfish, Fathead minnow, Carp
[9] 7Various
13Various

Uses

Regulatory uses

Through the use of the PBT Profiler and using criteria set forth by the United States Environmental Protection Agency under the Toxic Substances Control Act (TSCA), a substance is considered to be not bioaccumulative if it has a BCF less than 1000, bioaccumulative if it has a BCF from 1000 to 5000 [10] and very bioaccumulative if it has a BCF greater than 5,000. [10]

The thresholds under REACH are a BCF of > 2000 L/kg bzw. for the B and 5000 L/kg for vB criteria. [11]

Applications

A bioconcentration factor greater than 1 is indicative of a hydrophobic or lipophilic chemical. It is an indicator of how probable a chemical is to bioaccumulate. [1] These chemicals have high lipid affinities and will concentrate in tissues with high lipid content instead of in an aqueous environment like the cytosol. Models are used to predict chemical partitioning in the environment which in turn allows the prediction of the biological fate of lipophilic chemicals. [1]

Equilibrium partitioning models

Based on an assumed steady state scenario, the fate of a chemical in a system is modeled giving predicted endpoint phases and concentrations. [12]

It needs to be considered that reaching steady state may need a substantial amount of time as estimated using the following equation (in hours). [13] [14]

For a substance with a log(KOW) of 4, it thus takes approximately five days to reach effective steady state. For a log(KOW) of 6, the equilibrium time increases to nine months.

Fugacity models

Fugacity is another predictive criterion for equilibrium among phases that has units of pressure. It is equivalent to partial pressure for most environmental purposes. It is the absconding propensity of a material. [1] BCF can be determined from output parameters of a fugacity model and thus used to predict the fraction of chemical immediately interacting with and possibly having an effect on an organism.[ citation needed ]

Food web models

If organism-specific fugacity values are available, it is possible to create a food web model which takes trophic webs into consideration. [1] This is especially pertinent for conservative chemicals that are not easily metabolized into degradation products. Biomagnification of conservative chemicals such as toxic metals can be harmful to apex predators like orca whales, osprey, and bald eagles.[ citation needed ]

Applications to toxicology

Predictions

Bioconcentration factors facilitate predicting contamination levels in an organism based on chemical concentration in surrounding water. [12] BCF in this setting only applies to aquatic organisms. Air breathing organisms do not take up chemicals in the same manner as other aquatic organisms. Fish, for example uptake chemicals via ingestion and osmotic gradients in gill lamellae. [6]

When working with benthic macroinvertebrates, both water and benthic sediments may contain chemical that affects the organism. Biota-sediment accumulation factor (BSAF) and biomagnification factor (BMF) also influence toxicity in aquatic environments.[ citation needed ]

BCF does not explicitly take metabolism into consideration so it needs to be added to models at other points through uptake, elimination or degradation equations for a selected organism.

Body burden

Chemicals with high BCF values are more lipophilic, and at equilibrium organisms will have greater concentrations of chemical than other phases in the system. Body burden is the total amount of chemical in the body of an organism, [12] and body burdens will be greater when dealing with a lipophilic chemical.

Biological factors

In determining the degree at which bioconcentration occurs biological factors have to be kept in mind. The rate at which an organism is exposed through respiratory surfaces and contact with dermal surfaces of the organism, competes against the rate of excretion from an organism. The rate of excretion is a loss of chemical from the respiratory surface, growth dilution, fecal excretion, and metabolic biotransformation. [15] Growth dilution is not an actual process of excretion but due to the mass of the organism increasing while the contaminant concentration remains constant dilution occurs.

The interaction between inputs and outputs is shown here:
[15]
The variables are defined as:
CBis the concentration in the organism (g*kg−1). [15] t represents a unit of time (d−1). [15] k1 is the rate constant for chemical uptake from water at the respiratory surface (L*kg−1*d−1). [15] CWD is the chemical concentration dissolved in water (g*L−1). [15] k2,kE,kG,kB are rate constants that represent excretion from the organism from the respiratory surface, fecal excretion, metabolic transformation, and growth dilution (d−1). [15]

Static variables influence BCF as well. Because organisms are modeled as bags of fat, lipid to water ratio is a factor that needs to be considered. [6] Size also plays a role as the surface to volume ratio influence the rate of uptake from the surrounding water. [15] The species of concern is a primary factor in influencing BCF values due to it determining all of the biological factors that alter a BCF. [6]

Environmental parameters

Temperature

Temperature may affect metabolic transformation, and bioenergetics. An example of this is the movement of the organism may change as well as rates of excretion. [15] If a contaminant is ionic, the change in pH that is influenced by a change in temperature may also influence the bioavailability [1]

Water quality

The natural particle content as well as organic carbon content in water can affect the bioavailability. The contaminant can bind to the particles in the water, making uptake more difficult, as well as become ingested by the organism. This ingestion could consist of contaminated particles which would cause the source of contamination to be from more than just water. [15]

Related Research Articles

Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance faster than it can be lost or eliminated by catabolism and excretion. Thus, the longer the biological half-life of a toxic substance, the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high. Bioaccumulation, for example in fish, can be predicted by models. Hypothesis for molecular size cutoff criteria for use as bioaccumulation potential indicators are not supported by data. Biotransformation can strongly modify bioaccumulation of chemicals in an organism.

In the physical sciences, a partition coefficient (P) or distribution coefficient (D) is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium. This ratio is therefore a comparison of the solubilities of the solute in these two liquids. The partition coefficient generally refers to the concentration ratio of un-ionized species of compound, whereas the distribution coefficient refers to the concentration ratio of all species of the compound.

<span class="mw-page-title-main">Aquatic toxicology</span> Study of manufactured products on aquatic organisms

Aquatic toxicology is the study of the effects of manufactured chemicals and other anthropogenic and natural materials and activities on aquatic organisms at various levels of organization, from subcellular through individual organisms to communities and ecosystems. Aquatic toxicology is a multidisciplinary field which integrates toxicology, aquatic ecology and aquatic chemistry.

<span class="mw-page-title-main">Biomagnification</span> Process of progressive accumulation in food chain

Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance, e.g a pesticide, in the tissues of organisms at successively higher levels in a food chain. This increase can occur as a result of:

<span class="mw-page-title-main">Ecotoxicology</span>

Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels. Ecotoxicology is a multidisciplinary field, which integrates toxicology and ecology.

The fugacity capacity constant (Z) is used to help describe the concentration of a chemical in a system. Hemond and Hechner-Levy (2000) describe how to utilize the fugacity capacity to calculate the concentration of a chemical in a system. Depending on the chemical, fugacity capacity varies. The concentration in media 'm' equals the fugacity capacity in media 'm' multiplied by the fugacity of the chemical. For a chemical system at equilibrium, the fugacity of the chemical will be the same in each media/phase/compartment. Therefore equilibrium is sometimes called "equifugacity" in the context of these calculations.

<span class="mw-page-title-main">Galaxolide</span> Chemical compound

Galaxolide is a synthetic musk with a clean sweet musky floral woody odor used in fragrances. It is one of the musk components that perfume and cologne manufacturers use to add a musk odor to their products. Galaxolide was first synthesized in 1956, and used in the late 1960s in some fabric softeners and detergents. High concentrations were also incorporated in fine fragrances.

The Biotic Ligand Model (BLM) is a tool used in aquatic toxicology that examines the bioavailability of metals in the aquatic environment and the affinity of these metals to accumulate on gill surfaces of organisms. BLM depends on the site-specific water quality including such parameters as pH, hardness, and dissolved organic carbon. In this model, lethal accumulation values are used to be predictive of lethal concentration values that are more universal for aquatic toxicology and the development of standards. Collection of water chemistry parameters for a given site, incorporation of the data into the BLM computer model and analysis of the output data is used to accomplish BLM analysis. Comparison of these values derived from the model, have repeatedly been found to be comparable to the results of lethal tissue concentrations from acute toxicity tests. The BLM was developed from the gill surface interaction model (GSIM) and the free ion activity model (FIAM). Both of these models also address how metals interact with organisms and aquatic environments. Currently, the United States Environmental Protection Agency (EPA) uses the BLM as a tool to outline Ambient Water Quality Criteria (AWQC) for surface water. Because BLM is so useful for investigation of metals in surface water, there are developmental plans to expand BLM for use in marine and estuarine environments.

Persistent, bioaccumulative and toxic substances (PBTs) are a class of compounds that have high resistance to degradation from abiotic and biotic factors, high mobility in the environment and high toxicity. Because of these factors PBTs have been observed to have a high order of bioaccumulation and biomagnification, very long retention times in various media, and widespread distribution across the globe. Most PBTs in the environment are either created through industry or are unintentional byproducts.

<span class="mw-page-title-main">1-Octanol</span> Chemical compound

1-Octanol, also known as octan-1-ol, is the organic compound with the molecular formula CH3(CH2)7OH. It is a fatty alcohol. Many other isomers are also known generically as octanols. 1-Octanol is manufactured for the synthesis of esters for use in perfumes and flavorings. It has a pungent odor. Esters of octanol, such as octyl acetate, occur as components of essential oils. It is used to evaluate the lipophilicity of pharmaceutical products.

A mode of toxic action is a common set of physiological and behavioral signs that characterize a type of adverse biological response. A mode of action should not be confused with mechanism of action, which refer to the biochemical processes underlying a given mode of action. Modes of toxic action are important, widely used tools in ecotoxicology and aquatic toxicology because they classify toxicants or pollutants according to their type of toxic action. There are two major types of modes of toxic action: non-specific acting toxicants and specific acting toxicants. Non-specific acting toxicants are those that produce narcosis, while specific acting toxicants are those that are non-narcotic and that produce a specific action at a specific target site.

Tissue residue is the concentration of a chemical or compound in an organism's tissue or in a portion of an organism's tissue. Tissue residue is used in aquatic toxicology to help determine the fate of chemicals in aquatic systems, bioaccumulation of a substance, or bioavailability of a substance, account for multiple routes of exposure, and address an organism's exposure to chemical mixtures. A tissue residue approach to toxicity testing is considered a more direct and less variable measure of chemical exposure and is less dependent on external environmental factors than measuring the concentration of a chemical in the exposure media.

A polar organic chemical integrative sampler (POCIS) is a passive sampling device which allows for the in situ collection of a time-integrated average of hydrophilic organic contaminants developed by researchers with the United States Geological Survey in Columbia, Missouri. POCIS provides a means for estimating the toxicological significance of waterborne contaminants. The POCIS sampler mimics the respiratory exposure of organisms living in the aquatic environment and can provide an understanding of bioavailable contaminants present in the system. POCIS can be deployed in a wide range of aquatic environments and is commonly used to assist in environmental monitoring studies.

<span class="mw-page-title-main">Cashmeran</span> Chemical compound

Cashmeran is a chemical compound used in fragrances.

Equilibrium partitioning Sediment Benchmarks (ESBs) are a type of Sediment Quality Guideline (SQG) derived by the US Environmental Protection Agency (EPA) for the protection of benthic organisms. ESBs are based on the bioavailable concentration of contaminants in sediments rather than the dry-weight concentration. It has been demonstrated that sediment concentrations on a dry-weight basis often do not predict biological effects. Interstitial water concentrations, however, predict biological effects much better. This is true because the chemical present in the interstitial water (or pore water) is the uncomplexed/free phase of the chemical that is bioavailable and toxic to benthic organisms. Other phases of the chemical are bound to sediment particles like organic carbon (OC) or acid volatile sulfides (AVS) and are not bioavailable. Thus the interstitial water concentration is important to consider for effects to benthic organisms.

Bioavailability, in environmental and soil sciences, represents the amount of an element or compound that is accessible to an organism for uptake or adsorption across its cellular membrane. In environmental and agricultural applications, bioavailability most often refers to availability of contaminants, such as organic pollutants or heavy metals, in soil systems and is also used frequently in determining potential risk of land application of sewage sludge or other inorganic/organic waste materials.

<span class="mw-page-title-main">Passive sampling</span>

Passive sampling is an environmental monitoring technique involving the use of a collecting medium, such as a man-made device or biological organism, to accumulate chemical pollutants in the environment over time. This is in contrast to grab sampling, which involves taking a sample directly from the media of interest at one point in time. In passive sampling, average chemical concentrations are calculated over a device's deployment time, which avoids the need to visit a sampling site multiple times to collect multiple representative samples. Currently, passive samplers have been developed and deployed to detect toxic metals, pesticides, pharmaceuticals, radionuclides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other organic compounds in water, while some passive samplers can detect hazardous substances in the air.

<span class="mw-page-title-main">UV-328</span> Chemical compound

UV-328 is a chemical compound that belongs to the phenolic benzotriazoles. It is a UV filter that is used as an antioxidant for plastics.

The n-octanol-water partition coefficient,Kow is a partition coefficient for the two-phase system consisting of n-octanol and water. Kow is also frequently referred to by the symbol P, especially in the English literature. It is also called n-octanol-water partition ratio.

<span class="mw-page-title-main">Groundwater contamination by pharmaceuticals</span> Aquifer contamination by medical drugs

Groundwater contamination by pharmaceuticals, which belong to the category of contaminants of emerging concern (CEC) or emerging organic pollutants (EOP), has been receiving increasing attention in the fields of environmental engineering, hydrology and hydrogeochemistry since the last decades of the twentieth century.

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