In a trophic transfer experiment, for biomagnification/ minification (BMF) calculation, does one have to consider toxicant concentration in a single prey or in multiple prey? e.g. one protozoa may feed onto several bacteria.
It depends.
If you have an experimental setup in laboratory the concentration in a single prey is sufficient. For calculation see OECD 305 (Fish bioaccumulation).
http://www.oecd-ilibrary.org/test-no-305-bioaccumulation-in-fish-aqueous-and-dietary-exposure_5k91hsp7szf8.pdf;jsessionid=2r4hbeql2wtnb.x-oecd-live-01?contentType=/ns/Book&itemId=/content/book/9789264185296-en&containerItemId=/content/serial/2074577x&accessItemIds=/content/serial/2074577x&mimeType=application/pdf
If you monitoring data it is more complicated, you should than take into account toxicant in all prey. Maybe you can even weight the concentrations based on the food selection?
if I interpreted your question correctly, I believe you have to consider the total toxicant concentration in the prey. i.e, if you know how much is the concentration in all the bacteria that protozoa will fed on, and make sure that everything was eaten, then that should be considered the toxicant concentration in food, for the BMF calculation.
I hope that helps.
I would draw a distribution function of several biomagnification factors and choose the 95. percentile from that, unless I wanted to protect a specific species only.
The following is an example showing how bio-magnification takes place in nature: An anchovy eats zoo-plankton that have tiny amounts of mercury that the zoo-plankton has picked up from the water throughout the anchovies lifespan. A tuna eats many of these anchovies over its life, accumulating the mercury in each of those anchovies into its body. If the mercury stunts the growth of the anchovies, that tuna is required to eat more little fish to stay alive. Because there are more little fish being eaten, the mercury content is magnified.
Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.
The following is an example showing how bio-magnification takes place in nature: An anchovy eats zoo-plankton that have tiny amounts of mercury that the zoo-plankton has picked up from the water throughout the anchovies lifespan. A tuna eats many of these anchovies over its life, accumulating the mercury in each of those anchovies into its body. If the mercury stunts the growth of the anchovies, that tuna is required to eat more little fish to stay alive. Because there are more little fish being eaten, the mercury content is magnified.
Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.
The following is an example showing how bio-magnification takes place in nature: An anchovy eats zoo-plankton that have tiny amounts of mercury that the zoo-plankton has picked up from the water throughout the anchovies lifespan. A tuna eats many of these anchovies over its life, accumulating the mercury in each of those anchovies into its body. If the mercury stunts the growth of the anchovies, that tuna is required to eat more little fish to stay alive. Because there are more little fish being eaten, the mercury content is magnified.
Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.
Biomagnification is about increase of a chemical'c CONCENTRATION up the trophic levels. Of course it depends on prey-predator relationship (in particular, on the predator's edacity you mention) but it also depends on the predator's toxicokinetics (do not forget that chemicals are not only eaten but also metabolised and excreted) - but all these variables do not enter into calculation of the BMF which is merely the ratio of the equilibrium tissue concentrations predator to prey, is not it? You certainly determine mean concentrations in many aninal units and you should assess their variability, then you may get different BMFs for different subpopulations and so on - but all these important aspects of biomagnification are outside the formula for BMF calculation. Any objections?
I believe that Dr. Koelmans agrees with what I tried to say far less succinctly. As he is a specialist while I am not, this agreement is very satisfactory for me. So, having no way (nor right) to upvote my own answer I've gladly voted his up.
Amount of toxicant in relation to biomass - detoxification /time based degradation will be the factor of consideration about BIOMAGNIFICATION
Be aware that biomagnification, as a measure of trophic transfer of pollutants, can be problematic for a number of reasons.
The tissue concentration of pollutants that can be metabolized (or whose uptake or loss depends on metabolic rate) can vary with body size, simply because of the relationship between body size and metabolism in multicellular organisms. So, a predator may have a larger concentration of pesticide in its tissues because it is larger that its prey.
Moriarty and Walker (1987) noted the consequences of a small body size for prey species – their higher metabolic rate means they are likely to consume more food (and possibly more pollutant) per unit body weight, but will metabolize the contaminant more rapidly. A larger predator, with its slower metabolic rate, will tend to lose or degrade the contaminant more slowly, and, for this reason alone, may achieve a higher concentration (rather than as a result of its trophic position). I think Sara Griesbach et al (1982) were the first to demonstrate this with a very clever mathematical model for DDT and showed that body-size alone could account for its ‘biomagnification’ up a food chain. You can read a full account of the issue in Frank Moriarty’s textbook (1988).
Boris is thus right to emphasize the significance of metabolism, and the toxicokinetics of different species - especially for organic pollutants that may be degraded by the tissues. The assimilation and excretion of toxic metals may also be linked to metabolism and so concentrations may again reflect body-size.
This is one of the fundamental problems in interpreting these ratios, but there are others. Because of these metabolic processes, biomagnification can only be meaningful when both predator and prey have come to equilibrium with their pollutant source, when their uptake is balanced by loss. In the real world the ratio will thus be changing all the time (and will also typically vary with age, sex and season) and hence Karl’s valuable suggestion to measure the variation within the 95% percentiles.
Griesbach S, Peters R H, Yuoakim S (1982) An allometric model for pesticide bioaccumulation. Can. J. Fish Aquatic Sci. 39, 727-735.
Moriarty F, Walker C H (1987). Bioaccumulation in food chains – a rational approach. Ecotoxicol. Environ. Safety. 13, 208-215
Moriarty, F. Ecotoxicology (2nd edn.) Academic Press, London.
Thank you all for the wonderful discussion. Thanks Albert Koelmans for your reply. I found it most logical in my experimental scenario. Can you please help me with few references in this regard?
Dear Alan: yours is an excellent essay contemplating the biomagnification as a complex process understanding of cannot be reduced to one simple index (such as BMF). Therefore I've just upvoted it gladly although it is not, strictly speaking, an answer to the original question. I think such deviations from original (not always really interesting) questions can be just what makes the ResGate discussions exiting and informative, even if they are sometimes but confusing the issue. Yours is an example of the first. Thank you!
This is can be resolved in multiple ways:
1) you can model the values as per the USEPA models for pesticide residue in food chain.
2) I would prefer you take multiple values, and consider 95 or 99 percentile of the distribution.
3) presently we are working on transport models for certain agrochemical resides (NPK, heavy metals and pesticides) in wetland and agricultural ecosystems.
The extent of biomagnification of a chemical (Hg) is usually expressed in terms of biomagnification factor (BMF). It is the ratio of that chemical's concentration in the organism (predator) of a particular trophic level and the concentration in the organisms's food ( i.e. concentration in the prey of the lower trophic level of that organism):
BMF =Cb/Cd
Cb= the concentration of the chemical (Hg) in an organism of a particular trophic level
Cd= the concentration of the chemical (Hg) in the food of that organism i.e. the prey of its immediate lower trophic level
You may consult the following ref.
Moriarty F, Walker C H (1987). Bioaccumulation in food chains – a rational approach. Ecotoxicol. Environ. Safety. 13, 208-215
In a trophic transfer experiment when calculating biomagnification or minification factors (BMF), it is important to consider the cumulative toxicant concentration that a predator accumulates from all available prey items, rather than just from a single prey.
For example, if a protozoan feeds on multiple bacteria, the total toxicant concentration in the protozoan should reflect the combined concentrations from each bacterium it has consumed. This approach gives a more accurate representation of the bioaccumulation process, as predators often consume multiple prey over time, leading to a more complex interaction with toxicants within their food web.
Thus, when calculating BMF, you should account for the overall exposure from all prey items to capture the dynamics of biomagnification effectively.
Hey guys!
Can you please elaborate the technique or method for determining extact trophic position or probable one, without employing stable isotope analysis as this facility is rarely available.