A REPORT ON

BIOMAGNIFICATION

SUBMITTED BY:

HARSH RAWAT

ROLL NO: 10100EN022

COMPUTER SCIENCE AND ENGINEERING

DATE:

20/04/2011

BIOMAGNIFICATION

Biomagnification, also known as bioamplification or biological

magnification , is the increase in concentration of a substance, such as

the pesticide DDT, that occurs in a food chain as a consequence of:

Persistence (can't be broken down by environmental processes)

Food chain  energetics

Low (or nonexistent) rate of internal degradation/excretion of the

substance (often due to water-insolubility)

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.

Although sometimes used interchangeably with 'bioaccumulation,' an

important distinction is drawn between the two, and with

bioconcentration, it is also important to distinct between sustainable

development and overexploitation in biomagnification.

Bioaccumulation occurs within a trophic level, and is the increase in

concentration of a substance in certain tissues of organisms' bodies

due to absorption from food and the environment.

Bioconcentration  is defined as occurring when uptake from the water

is greater than excretion (Landrum and Fisher, 1999)

Thus bioconcentration and bioaccumulation occur within an organism, and

biomagnification occurs across trophic (food chain) levels.

There are two basic terms we are discussing here.  Bioaccumulation refers

to how pollutants enter a food chain; biomagnification refers to the

tendency of pollutants to concentrate as they move from one trophic level

to the next.  Here are some definitions of these terms:

Bioaccumulation:

increase in concentration of a pollutant from the environment to the first organism in a food chain

Biomagnification:

increase in concentration of a pollutant from one link in a food chain to another

We are concerned about these phenomena because together they mean that even small concentrations of chemicals in the environment can find their way into organisms in high enough dosages to cause problems.  In order for biomagnification to occur, the pollutant must be:

1. long-lived2. mobile3. soluble in fats4. biologically active

Biodilution is also a process that occurs to all trophic levels in an aquatic

environment; it is the opposite of biomagnification, thus a pollutant gets

smaller in concentration as it progresses up a food web.

Lipid, (lipophilic) or fat soluble substances cannot be diluted, broken

down, or excreted in urine, a water-based medium, and so accumulate

in fatty tissues of an organism if the organism lacksenzymes to degrade

them. When eaten by another organism, fats are absorbed in the gut,

carrying the substance, which then accumulates in the fats of the

predator. Since at each level of the food chain there is a lot of energy loss,

a predator must consume many prey, including all of their lipophilic

substances.

For example, though mercury is only present in small amounts

in seawater, it is absorbed by algae (generally as methylmercury). It is

efficiently absorbed, but only very slowly excreted by organisms (Croteau

et al., 2005). Bioaccumulation and bioconcentration result in buildup in

the adipose tissue of successive trophic levels: zooplankton, small nekton,

larger fish etc. Anything which eats these fish also consumes the higher

level of mercury the fish have accumulated. This process explains why

predatory fish such as swordfish and sharks or birds

like osprey and eagles have higher concentrations of mercury in their

tissue than could be accounted for by direct exposure alone. For example,

herring contains mercury at approximately 0.01 ppm and shark contains

mercury at greater than 1 ppm (EPA 1997).

If a pollutant is short-lived, it will be broken down before it can become dangerous.  If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms.  If the pollutant is soluble in water it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for a long time.  It is traditional to measure the amount of pollutants in fatty tissues of organisms such as  fish.   In mammals, we often test the milkproduced by females, since the milk has a lot of fat in it and because the very young are often more susceptible to damage from toxins (poisons).  If a pollutant is not active biologically, it may biomagnify, but we really don't worry about it much, since it probably won't cause any problems.

Current status

In a review of a large number of studies, Suedel et al. (1994) concluded

that although biomagnification is probably more limited in occurrence

than previously thought, there is good evidence

that DDT,DDE, PCBs, toxaphene, and the organic forms

of mercury and arsenic do biomagnify in nature. For other contaminants,

bioconcentration and bioaccumulation account for their high

concentrations in organism tissues. More recently, Gray (2002) reached a

similar substances remaining in the organisms and not being diluted to

non-threatening concentrations. The success of top predatory-bird

recovery (bald eagles, peregrine falcons) in North America following the

ban on DDT use in agriculture is testament to the importance of

biomagnification.

Substances that biomagnify

There are two main groups of substances that biomagnify. Both are

lipophilic and not easily degraded. Novel organic substances are not easily

degraded because organisms lack previous exposure and have thus

not evolved specific detoxification and excretion mechanisms, as there

has been no selection pressure from them. These substances are

consequently known as 'persistent organic pollutants' or POPs.

Metals are not degradable because they are elements. Organisms,

particularly those subject to naturally high levels of exposure to metals,

have mechanisms to sequester and excrete metals. Problems arise when

organisms are exposed to higher concentrations than usual, which they

cannot excrete rapidly enough to prevent damage. These metals are

transferred in an organic form.

Novel organic substances

DDT

HCB

PCBs

Toxaphene Monomethylmercury

Inorganic substances

Arsenic

Cadmium

Mercury

Mercury in fish

Fish and shellfish concentrate mercury in their bodies, often in the form

of methylmercury, a highly toxic organic compound of mercury.[citation

needed] Fish products have been shown to contain varying amounts of heavy

metals, particularly mercury and fat-soluble pollutants from water

pollution. Species of fish that are long-lived and high on the food chain,

such as marlin, tuna, shark, swordfish, king mackerel, tilefish, northern

pike, and lake trout contain higher concentrations of mercury than others.

The presence of mercury in fish can be a health issue, particularly for

women who are or may become pregnant, nursing mothers, and young

children.

Classic example: DDT

DDT stands for d ichloro,   d iphenyl   t richloroethane .  It is a chlorinated hydrocarbon, a class of chemicals which often fit the characteristics necessary for biomagnification.  DDT has a half-life of 15 years, which means if you use 100 kg of DDT, it will break down as follows:

Year Amount Remaining

0 100 kg

15 50 kg

30 25 kg

45 12.5 kg

60 6.25 kg

75 3.13 kg

90 1.56 kg

105 0.78 kg

120 0.39 kg

This means that after 100 years, there will still be over a pound of DDT in the environment.  If it does bioaccumulate and biomagnify, much of the DDT will be in the bodies of organisms.  DDT actually has rather low toxicity to humans (but high toxicity to insects, hence its use as an insecticide).  Because it could be safely handled by humans, it was extensively used shortly after its discovery just before WW II.  During the war, it was used to reduce mosquito populations and thus control malaria in areas where US troops were fighting (particularly in the tropics).  It was also used on civilian populations in Europe, to prevent the spread of lice and the diseases they carried.  Refugee populations and those living in destroyed cities would have otherwise faced epidemics of louse-born diseases.  After the war, DDT became popular not only to protect humans from insect-borne diseases, but to protect crops as well.  As the

first of the modern pesticides, it was overused, and soon led to the discovery of the phenomena of insect resistance to pesticides, bioaccumulation, and biomagnification.

By the 1960's, global problems with DDT and other pesticides were becoming so pervasive that they began to attract much attention.  Credit for sounding the warning about DDT and biomagnification usually goes to the scientist Rachel Carson, who wrote the influential book Silent Spring (1962).  The silent spring alluded to in the title describes a world in which all the songbirds have been poisoned.  Her book of course was attacked by many with vested interests.  

I recently came across an essay from Jonathan Tolman at the Competitive Enterprises Institute which completely misses the main point we get from Silent Spring.  I guess the fact that people are still scared of the book 35 years later says something about its message.  Sure, scientific discoveries have shown weaknesses in some of Carson's positions, but the basic message that indiscriminate use of pesticides will have lasting and detrimental effects remains strong.  The author's point in the CEI essay seems to be that if nature makes dangerous chemicals, why should we be concerned when humans make more dangerous chemicals and in huge quantities, then spread them around out of airplanes so everyone gets a dose?  It's amazing what people will say to make a buck.  I note that his on-line resume lists a bachelor's degree in Political Science, presumably that degree qualified him for work as an environmental and chemical analyst.

Biomagnification: how DDT becomes concentrated as it passes through a food chain

The figure shows how DDT becomes concentrated in the tissues of organisms representing four successive trophic levels in a food chain.

The concentration effect occurs because DDT is metabolized and excreted much more slowly than the nutrients that are passed from one trophic level to the next. So DDT accumulates in the bodies (especially in fat). Thus most of the DDT ingested as part of gross production is still present in the net production that remains at that trophic level.

This is why the hazard of DDT to nontarget animals is particularly acute for those species living at the top of food chains.

For example,

spraying a marsh to control mosquitoes will cause trace amounts of DDT to accumulate in the cells of microscopic aquatic organisms, the plankton, in the marsh.

In feeding on the plankton, filter-feeders, like clams and some fish, harvest DDT as well as food. (Concentrations of DDT 10 times greater than those in the plankton have been measured in clams.)

The process of concentration goes right on up the food chain from one trophic level to the next. Gulls, which feed on clams, may accumulate DDT to 40 or more times the concentration in their prey. This represents a 400-fold increase in concentration along the length of this short food chain.

There is abundant evidence that some carnivores at the ends of longer food chains (e.g. ospreys, pelicans, falcons, and eagles) suffered serious declines in fecundity and hence in population size because of this phenomenon in the years before use of DDT was banned (1972) in the United States.

Case study: Long Island Estuary (Figure 22.1 in Cox)

Cox reports on a study done in 1967 on Long Island Sound.  The levels of DDT in tissues of various animals in the sound showed bioaccumulation factors of 800x, and  biomagnification factors up to 31 times.  When we look at the whole food chain, the overall magnification is over 200,000x!

water to zooplankton: 800x

zooplankton  to fish #1:

31x

fish #1  to fish #2: 1.7x

fish #2 to  gull: 4.8x

overall:  202,368x

While DDT isn't particularly lethal (except to insects, and we need many of them around), it has a number of sub-lethal effects.  Most prominent is the phenomenon of shell-thinning in birds, particularly carnivorous birds (raptors) - birds that eat other birds, birds that eat carrion (dead animals), and birds that eat fish. Ospreys are one of the raptors that have been adversely affected, as have bald eagles. Other fish-eating water birds have been affected as well.  Because of the DDT, the shells are too thin to brood.   Many populations have recovered following the banning of DDT in the US, but migratory birds may be exposed to pesticides in other countries.  Recently, some studies have shown effects on sex ratios in some species of birds, with the males becoming "feminized", presumably the result of compounds in the environment mimicing the female hormone estrogen.

Heavy metals and other substances

DDT is not the only toxin to biomagnify.  All of the following have the potential to biomagnify:

Substance Use & Problems Links

PCB's

polychlorinated biphenyls

insulators in transformers

plasticizer fire retardant

biomagnifies impairs reproduction widespread in aquatic

systems

as airborne contaminants in sediments in the Mississippi River

PAH's

polynuclear aromatic hydrocarbons

component of petroleum products

carcinogenic

Heavy metals:

mercury copper cadmium chromium

mercury from gold mining

many from metal processing

may affect nervous

from an interesting student project

heavy metals in the Mississippi River - great source!

lead nickel zinc tin (TBT or tributyltin)

system may affect reproduction

Cyanide

used in leaching gold used in fishing

toxic

effects on coral reefs health information proposed gold mine and its

effects report of a spill of cyanide

Selenium

concentrated by farming desert soils

reproductive failures toxic

selenium at a wildlife refuge in Wyoming

Modern pesticides, such as carbamates and organophosphates, are "safer" in that they are not persistent, one of the requirements for biomagnification.  They are, however, more toxic, and insects are developing resistance to them.  It must be remembered that we use pesticides for more that making pretty produce.  Pesticides are sometimes necessary to protect a basic food supply and to protect human health. The concept of integrated pest management, or IPM, has been developed to improve control of pests while decreasing the need for pesticides.  IPM uses a variety of methods to control pests.  These include biological controls, and cultural practices such as timing planting and harvest to avoid periods of peak activity by pest species, and scouting to determine how big a problem the pests are actually causing (rather than just spraying to prevent a problem that may never arise).  Economics are watched closely; pesticides are never used if the cost of the pesticide would exceed the cost of the crops being saved (you'd be amazed at how often people have spent more on pesticides than the crop was worth). IPM relies heavily on information, and the internet is being used extensively.

Other pollutants:

Other pollutants of importance are plastics, radioisotopes (which may be both toxic and radioactive!) and oil.  Plastics are eaten by many organisms and can cause mechanical injury, strangulation, or starvation. Radioisotopes can damage biological molecules, particularly DNA, leading to cancer, other illnesses, or death.  Oil smothers aquatic organisms, cutting them off from oxygen.  It can also infiltrate the insulating feathers of seabirds (or fur of sea-going mammals) and cause them to die from hypothermia (or cause them to sink). Oil spills are a serious problem in marine environments.

Regulations:

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)

1972 requires registration of pesticides for specific uses

London Dumping Convention

1972 ratified by 64 countries bans deliberate discharge of various toxic or other wastes

International Convention for the Prevention of Pollution from Ships (MARPOL)

1988 prohibits dumping of plastics at sea ratified by 40 countries