Definitions and Terminology Related to Biomagnification

The term biomagnification has classically been defined as the condition where the contaminant concentration in an organism exceeds the contaminant concentration in its diet when the major chemical exposure route to the organism is from food. By extension the term food web biomagnification has been defined as the increase in contaminant concentration with increasing trophic status of organisms sampled from the same food web.

Biomagnification and food web biomagnification were originally coined from observations of chlorinated pesticide bioaccumulation in aquatic food webs. However, the term biomagnification (see Persistent Organic Pollutants) has been applied to other contaminants including mercury, heavy metals, and certain compounds of biogenic origin. The first demonstration of biomagnification was described for dichlorodiphenyldichloroethane (DDD), closely related to the pesticide dichlorodiphenyltrichlor-oethane (DDT), in Clear Lake California. Rachel Carson subsequently used the term 'biological magnifiers' in her book, Silent Spring, to describe how earthworms concentrate DDT residues from soil in their bodies and transfer these residues to robins who consume them which in turn achieve even greater concentrations of the pesticides than worms. The term 'biological magnification' was later used by Woodwell to describe the 'systematic increase in DDT residues with trophic level' in his description of DDT trophodynamics in a salt marsh near Long Island, New York. Biological magnification subsequently became truncated to the commonly used term 'biomagnification' in later years.

The mechanism of biomagnification as applied to organic chemicals, particularly compounds demonstrating physical properties of low water solubility and high hydrophobicity, was intensely studied and vigorously debated in the 1980s and 1990s. During this period, biomagnification was conceptually distinguished from the process of bioconcentration which refers to chemical bioaccumulation (see Bioaccumulation) due to exposure of contaminant across respiratory exchange surfaces (i.e., gills and lungs). Research conducted in the 1960s and 1970s demonstrated how physical-chemical properties controlled environmental partitioning and diffusive flux of hydrophobic substances. Hydrophobic organic contaminants tend to distribute preferentially to organic phases which includes organic carbon of soils and sediments and lipid phases of organisms. Equilibrium partitioning theory (see Food-Web Bioaccumulation Models) was subsequently used to equate bioconcentration in animals to the equilibrium lipid/water distribution coefficient. Although equilibrium partitioning theory described laboratory bioconcentration data well and predicted laboratory bioconcentration factors (BCFs; defined as the lipid-normalized chemical concentration in the animal divided by the chemical concentration in water), it failed to fully account for elevated contaminant concentrations accumulated by upper-trophic-level animals in the field.

The failure to validate equilibrium partitioning as a theory explaining biomagnification prompted redefinition of the term, as applied to hydrophobic organic susbstances, to describe the thermodynamic context of biomagnification. Under this new definition, biomag-nification refers to the condition where the chemical potential achieved in an animal's tissues exceeds the chemical potential in its food and its surrounding environment. Similarly, food web biomagnification was redefined as the increase in chemical potential of organisms with increasing organism trophic status. In practice, chemical potentials are not directly measured, but rather are compared relatively across different samples by normalizing the chemical concentration in a sample by the sample partitioning capacity for the chemical/sample matrix of interest. Since hydrophobic organic contaminants distribute primarily to neutral lipids within organisms, expression of lipid-normalized chemical concentrations have been used as surrogate measures of chemical potentials when comparing biomagnification between biological samples. Alternatively, chemical fuga-city (see Food-Web Bioaccumulation Models) is used as a proxy for chemical potentials when comparing equilibration of contaminants between interacting abiotic and biotic samples. These data analysis methods apply to hydrophobic organic chemicals but do not necessarily apply to mercury or other contaminant classes which undergo biomagnification by the classic definition, but do not exhibit preferential internal distribution to lipids within animals.

The biomagnification factor (BMF) for organic contaminants is defined as the ratio of the lipid-normalized chemical concentration in the animal to the lipid-normal-ized chemical concentration in its diet. A BMF value greater than 1 indicates that the animal has achieved a greater chemical potential than its diet. Since organisms may include multiple food items in their diet, the BMF can also be expressed according to the weighted average lipid-normalized chemical concentrations in its various food items. Similarly, when the BCF value is shown to exceed the n-octanol/water partition coefficient (Kow; a standard laboratory-measured partition coefficient used as a surrogate measure of the equilibrium lipid/water partition coefficient) this indicates that the chemical potential achieved in the animal exceeds that of water. Similar expressions can be derived for air-breathing animals by comparing the lipid-normalized concentration in

Phvtnnlanktnn

Phvtnnlanktnn

Normalized Concentration

Figure 1 Food web biomagnification of polychlorinated biphenyls (PCBs) in Lake Ontario. Data for aquatic organisms collected in Lake Ontario during 1984 from Oliver BG and Niimi AJ (1988) Trophodynamic analysis of polychlorinated biphenyl congeners and other chlorinated hydrocarbons in the Lake Ontario ecosystem. Environmental Science and Technology 22: 388-397. Data on Herring gulls collected in Lake Ontario during 1985 from Braune BM and Norstrom RJ (1989) Dynamics of organochlorine compounds in herring gulls: III. Tissue distribution and bioaccumulation in Lake Ontario Gulls. Environmental Toxicology and Chemistry 8: 957-968.

Figure 1 Food web biomagnification of polychlorinated biphenyls (PCBs) in Lake Ontario. Data for aquatic organisms collected in Lake Ontario during 1984 from Oliver BG and Niimi AJ (1988) Trophodynamic analysis of polychlorinated biphenyl congeners and other chlorinated hydrocarbons in the Lake Ontario ecosystem. Environmental Science and Technology 22: 388-397. Data on Herring gulls collected in Lake Ontario during 1985 from Braune BM and Norstrom RJ (1989) Dynamics of organochlorine compounds in herring gulls: III. Tissue distribution and bioaccumulation in Lake Ontario Gulls. Environmental Toxicology and Chemistry 8: 957-968.

the animal/air concentration ratio with the octanol/air partition coefficient.

Determination of food web biomagnification requires establishment of the trophic level (see Trophic Index and Efficiency) of different organisms included in the sampling program. Traditionally this has been carried out using diet analysis and establishing discrete trophic steps (see Figure 1). More recently, emphasis has been placed on use of stable isotopes of carbon and nitrogen to define continuous trophic positions (see Trophic Index and Efficiency) for different organisms in a sampled food web. The food web magnification factor (FWMF) has been defined as the slope generated from a regression of the logarithm of lipid-normalized chemical concentrations in biota expressed against trophic level on the independent axis.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Responses

  • olga
    Why ddt in biota of salt marsh increased?
    6 years ago
  • Fulgenzia
    Who coined the term biological magnification?
    6 years ago
  • karolin
    Which is primarily related to biomagnifications?
    3 years ago
  • JANINA
    Who coined the term biomagnification?
    3 years ago
  • tammy
    Which is primarily related to biomagnification?
    3 years ago
  • Salvia Oldbuck
    Which is primilarly related to biomagnification?
    2 years ago
  • thomas
    Which os primarly realeated to biomagnification?
    2 years ago

Post a comment