Biodilution
Encyclopedia
Biodilution is the decrease in concentration of an element
or pollutant
with an increase in trophic level
. This effect is primarily caused by the observed trend that an increase in algal biomass will reduce the overall concentration of a pollutant per cell, which ultimately contributes to a lower dietary input to grazers (and higher-level aquatic organisms).
The primary elements and pollutants of concern are heavy metals such as mercury
, cadmium
, and lead
. These toxins have been shown to bioaccumulate up a food web. In some cases, metals, such as mercury, can biomagnify. This is a major concern since methylmercury
, the most toxic mercury species, can be found in high concentrations in human-consumed fish and other aquatic organisms. Persistent organic pollutants, such as carcinogenic polycyclic aromatic hydrocarbons and alkylphenols, have also shown to biodilute in the marine environment.
Numerous studies have linked lower mercury concentrations in zooplankton found in eutrophic(nutrient-rich and highly productive) as compared to oligotrophic (low nutrient) aquatic environments. Nutrient enrichment (mainly phosphorus and nitrogen) reduce the input of mercury, and other heavy metals, into aquatic food webs through this biodilution effect. Primary producers, such as phytoplankton, uptake these heavy metals and accumulate them into their cells. The higher the population of phytoplankton, the less concentrated these pollutants will be in their cells. Once consumed by primaryn, these phytoplankton-bound pollutants are incorporated into the consumer’s cells. Higher phytoplankton biomass means a lower concentration of pollutants accumulated by the zooplankton, and so on up the food web. This effect causes an overall dilution of the original concentration up the food web. That is, the concentration of a pollutant will be lower in the zooplankton than the phytoplankton in a high bloom condition.
Although most biodilution studies have been on freshwater environments, biodilution has been shown to occur in the marine environment as well. The Northwater Polynya, located in Baffin Bay, was found to have a negative correlation of cadmium, lead, and nickel with an increase in trophic level Cadmium and lead are both non-essential metals that will compete for calcium within an organism, which is detrimental for organism growth.
Most studies measure bioaccumulation and biodilution using the δ15N isotope of nitrogen. The δ15N isotopic signature is enriched up the food web. A predator will have a higher δ15N as compared to its prey. This trend allows the tropic position of an organism to be derived. Coupled to the concentration of a specific pollutant, such as mercury, the concentration verses trophic position can be accessed.
While most heavy metals bioaccumulate, under certain conditions, heavy metals and organic pollutants have the potential to biodilute, making a higher organism less exposed to the toxin.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
or pollutant
Pollutant
A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...
with an increase in trophic level
Trophic level
The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
. This effect is primarily caused by the observed trend that an increase in algal biomass will reduce the overall concentration of a pollutant per cell, which ultimately contributes to a lower dietary input to grazers (and higher-level aquatic organisms).
The primary elements and pollutants of concern are heavy metals such as mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
, cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
, and lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
. These toxins have been shown to bioaccumulate up a food web. In some cases, metals, such as mercury, can biomagnify. This is a major concern since methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
, the most toxic mercury species, can be found in high concentrations in human-consumed fish and other aquatic organisms. Persistent organic pollutants, such as carcinogenic polycyclic aromatic hydrocarbons and alkylphenols, have also shown to biodilute in the marine environment.
Numerous studies have linked lower mercury concentrations in zooplankton found in eutrophic(nutrient-rich and highly productive) as compared to oligotrophic (low nutrient) aquatic environments. Nutrient enrichment (mainly phosphorus and nitrogen) reduce the input of mercury, and other heavy metals, into aquatic food webs through this biodilution effect. Primary producers, such as phytoplankton, uptake these heavy metals and accumulate them into their cells. The higher the population of phytoplankton, the less concentrated these pollutants will be in their cells. Once consumed by primaryn, these phytoplankton-bound pollutants are incorporated into the consumer’s cells. Higher phytoplankton biomass means a lower concentration of pollutants accumulated by the zooplankton, and so on up the food web. This effect causes an overall dilution of the original concentration up the food web. That is, the concentration of a pollutant will be lower in the zooplankton than the phytoplankton in a high bloom condition.
Although most biodilution studies have been on freshwater environments, biodilution has been shown to occur in the marine environment as well. The Northwater Polynya, located in Baffin Bay, was found to have a negative correlation of cadmium, lead, and nickel with an increase in trophic level Cadmium and lead are both non-essential metals that will compete for calcium within an organism, which is detrimental for organism growth.
Most studies measure bioaccumulation and biodilution using the δ15N isotope of nitrogen. The δ15N isotopic signature is enriched up the food web. A predator will have a higher δ15N as compared to its prey. This trend allows the tropic position of an organism to be derived. Coupled to the concentration of a specific pollutant, such as mercury, the concentration verses trophic position can be accessed.
While most heavy metals bioaccumulate, under certain conditions, heavy metals and organic pollutants have the potential to biodilute, making a higher organism less exposed to the toxin.