Biomagnification

 Biomagnification is the process by which a compound (such as a pollutant or pesticide) increases its concentration in the tissues of organisms as it travels up the food chain. It is also known as bioamplification or biological magnification. The contaminants might be heavy metals such as mercury, arsenic, and pesticides such as polychlorinated biphenyls and DDT.

These substances are taken up by the organisms through the food they consume. When the organisms in the higher food chain feed on the organisms in the lower food chain containing these toxins, these toxins get accumulated in the higher organisms.

Thus, Biomagnification occurs when substances such as pesticides or heavy metals move up the food chain by working their way into the environment. Biomagnification can occur in almost all types of ecosystems. e. g terrestrial, aquatic.

 Pollutants in rivers or lakes are taken up by microorganisms like plankton and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals and humans. The substances become concentrated in tissues or internal organs as they move up the chain. As a result, organisms at the top of the food chain generally suffer greater harm from a persistent toxin or pollutant than those at lower levels.

 

The increase in concentration of a pollutant occurs in a food chain as a result of: 

1. Persistence (not broken down by environmental processes)

2. Bioenergetics in the food chain (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 and fats which carries the pollutant, which then accumulates in the fats of the predator)

3. Low rate of internal degradation/excretion of the substance often due to water-insolubility 

In order for biomagnification to occur, the pollutant must be persistent:

1.long-lived

2.mobile

3.soluble in fats

4.biologically active

 Persistent pollutants 

• 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 (Persistent pollutants) are retained for a long time- Lipid or fat soluble substances cannot be diluted, broken down, or excreted in urine.

• They accumulate in fatty tissues of an organism if the organism lacks enzymes to degrade them.

 Eg., DDT :dichloro diphenyl trichloroethane.- chlorinated hydrocarbon, used as pesticide

•DDT has a half-life: 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	0.39g

 

 

Causes of Biomagnification

The major causes of biomagnification:

1.     Agriculture

The agricultural pesticides, insecticides, fertilizers and fungicides are very toxic and are released into the soil, rivers, lakes, and seas. These substances contain small amounts of heavy metals such as mercury, arsenic, copper, lead and cadmium. These cause health issues in aquatic organisms and humans.

2.     Organic Contaminants

Manures and industrial products like  pharmaceuticals and personal care products contain contaminants. These substances have an adverse impact on the health of humans, animals, and wildlife.

3.     Industrial Activities

The industries and factories release toxic substances that are released into the soil, lakes, oceans, and rivers. The gaseous emissions pollute the environment which enters into the food chain leading to biomagnification.

4.     Mining Activities in the Ocean

Mining activities are carried out in the deep sea to extract metal like zinc, aluminium, cobalt, silver and gold. The mining process generates a large amount of selenium and sulphide, which deposits in water and destroys the oceans and coastal regions. These toxic substances are absorbed by the aquatic organisms and they move higher in the food chain to other organisms.

Effects of Biomagnification

Ø  Impact on Human Health- Biomagnification makes humans more prone to cancer, kidney problems, liver failure, birth defects, respiratory disorders, and heart diseases.

Ø  Effects on Reproduction and Development of Marine Creatures- The toxic chemicals accumulate in the important organs of aquatic organisms that affect their reproduction and development processes.

Ø  For eg., the shells of the eggs of the sea-birds are very thin that might get crushed by the birds themselves during incubation. The toxic chemicals, mercury and selenium destroy the reproductive organs of aquatic creatures.

Ø  Destruction of Coral Reefs- Cyanide that is used in leaching gold and fishing is the main cause of the destruction of coral reefs. Coral reefs are the dwelling and feeding grounds for many sea creatures. Their destruction affects the lives of many aquatic animals.

Ø  Disruption of Food Chain- The chemicals and toxins which are released into the water bodies disrupt the food chain. The small organisms absorb the toxins which are eaten up by larger animals. These toxins, thus, get accumulated in the higher level of organisms.

Effect of pH on microbial growth and distribution

pH is a measure of the hydrogen ion activity of a solution. pH is defined as the negative logarithm of the hydrogen ion concentration (expressed in terms of molarity).

pH = ^-log [H⁺] = log(1/[H⁺])

The pH scale extends from pH 0.0 to pH 14.0.

The habitats in which microorganisms grow vary widely-from pH 0 to 2 at the acidic end to alkaline lakes and soil that may have pH values between 9 and 10.

pH strongly affects microbial growth. Each species has a definite pH growth range and pH growth optimum.

• Acidophiles have their growth optimum between pH 0 and 5.5; 
• Neutrophiles, between pH 5.5 and 8.0; 
• Alkalophiles prefer the pH range of 8.0 to 11.5. 
• Extreme alkalophiles have growth optima at pH 10 or higher.

In general, different microbial groups have characteristic pH preferences. Most bacteria and protists (protozoa and algae) are neutrophiles. Most fungi prefer more acidic surroundings, about pH 4 to 6; photosynthetic protists also seem to favour slight acidity.

Many archaea are acidophiles. For example, the archaeon Sulfolobus acidocaldarius is a common inhabitant of acidic hot springs; it grows well around pH 1 to 3 and at high temperatures. The archaea Ferroplasma acidarmanus and Picrophilus oshimae can grow at pH 0, or very close to it.

Although microorganisms will often grow over wide ranges of pH and far from their optima, there are limits to their tolerance

Maintenance of pH

Drastic variations in cytoplasmic pH can harm microorganisms by disrupting the plasma membrane or inhibiting the activity of enzymes and membrane transport proteins. Most procaryotes die if the internal pH drops much below 5.0 to 5.5. Changes in the external pH also might alter the ionization of nutrient molecules and thus reduce their availability to the organism.

Microorganisms respond to external pH changes using mechanisms that maintain a neutral cytoplasmic pH. Several mechanisms for adjusting to small changes in external pH have been proposed.

Ø  The plasma membrane is impermeable to protons.

Ø  Neutrophiles have an antiport transport system to exchange potassium for protons.

Ø  Extreme alkalophiles like Bacillus alcalophilus maintain their internal pH closer to neutrality by exchanging internal sodium ions for external protons.

Ø  Internal buffering also may contribute to pH homeostasis.

•      If the external pH becomes too acidic, other mechanisms come into play.

ü  When the pH drops below about 5.5 to 6.0, Salmonella enterica serovar Typhimurium and E. coli synthesize an array of new proteins as part of their acidic tolerance response (ATR).

ü  A proton-translocating ATPase is activated and makes more ATP or  pump protons out of the cell and thus contributes to this protective response, 

ü  If the external pH decreases to 4.5 or lower, chaperone proteins such as acid shock proteins and heat shock proteins are synthesized. These prevent the acid denaturation of proteins and aid in the refolding of denatured proteins.

Microorganisms frequently change the pH of their own habitat by producing acidic or basic metabolic waste products. Fermentative microorganisms form organic acids from carbohydrates, whereas chemolithotrophs like Thiobacillus oxidize reduced sulfur components to sulfuric acid. Other microorganisms make their environment more alkaline by generating ammonia through amino acid degradation. Because microorganisms change the pH of their surroundings, buffers often are included in media to prevent growth inhibition by large pH changes.

Phosphate is a commonly used buffer and is a good example of buffering by a weak acid (dihydrogen phosphate, H₂PO₄^-) and its conjugate base (monohydrogen phosphate, HPO₄ ^2-).

H⁺ + HPO4 ^2-⎯⎯→ H₂PO₄^- 

OH^- + H₂PO₄^-   ⎯⎯→ HPO₄ ^2- + HOH

If protons are added to the mixture, they combine with the salt form to yield a weak acid. An increase in alkalinity is resisted because the weak acid will neutralize hydroxyl ions through proton donation to give water.

Peptides and amino acids in complex media also have a strong buffering effect.

 

pH	[H+] Molarity		Environmental examples	Microbial examples
0	10–0	Increasing acidity	Concentrated nitric acid	Ferroplasma, Picrophilus oshimae
1	10–1		Gastric contents, acid thermal springs	Dunaliella acidophila
2	10–2		Lemon juice Acid mine drainage	Cyanidium caldarium, Thiobacillus thiooxidans, Sulfolobus acidocaldarius
3	10–3		Vinegar, ginger ale Pineapple
4	10–4		Tomatoes, orange juice Very acid soil
5	10–5		Cheese, cabbage Bread	Physarum polycephalum, Acanthamoeba castellanii
6	10–6		Beef, chicken Rain water Milk, Saliva	Lactobacillus acidophilus,        E.coli, Pseudomonas aeruginosa, Euglena gracilis, Paramecium bursaria
7	10–7	Neutrality	Pure water, Blood	Staphyloccus aureus
8	10–8	Increasing alkalinity	Seawater	Nitrosomonas spp.
9	10–9		Strongly alkaline soil,  Alkaline lakes
10	10–10		Soap	Microcystis aeruginosa, Bacillus alcalophilus
11	10–11		Household ammonia
12	10–12		Saturated calcium hydroxide solution
13	10–13		Bleach, Drain opener
14	10–14

                         The pH scale and microorganisms with their growth optima.