Bioaccumulation• The accumulation of a substance likepesticides (DDT), methylmercury or otherorganic chemicals in an organism or partof an organism(tissue) is calledbioaccumulation.● Bioaccumulation refers to the gradualbuild-up of pollutants in living organisms.
Explanation● It is increase in concentration of a pollutantfrom the environment to the first organism ina food chain.● Organisms at any trophic level may becapable of bioaccumulation.● The affected organism has a higherconcentration of the substance than theconcentration in the organism surroundingenvironment.
● Bioaccumulation is the net result ofthe interaction of uptake,storage andelimination of a chemical.● The substances enter the organismthrough respiration, food intake,epidermal contact with substances andother means.
Kinds of bioaccumulation● Organismal bioaccumulation● Trophic transfer● Soil bioaccumulation
Organismal accumulation● Compounds present in anorganisms environment mayconcentrate in the body over time.● For example, fish that swimfrequently in contaminated watermay build up pollutants in theirfatty tissues.
Trophic transfer● The accumulated substance transfer fromone trophic level to other● Higher the the trophic level, highr theconcentration of pollutant● For example: Organisms at the top of thefood chain as humans or polar bears, canreceive the highest concentrations.
Soil accumulation● Accumulants, toxic substances etcthat are dumped into surroundingfrom specific waste site, bind tosoil particles and persist until theyare removed through erosion,uptake by plants ormicroorganism.
Factors on which bioaccumulationdepends● Uptake of substance● Storage of substance, storage capacity● Elimination of substance● Hydrophobicity● Concentration of pollutant in water● Age, sex and type of organism
Rate of accumulation● Accumulation is measured in parts permillion (ppm).● This refers to one particle of a givensubstance mixed with 999 999 otherparticles.● eg oysters can concentrate DDT from0.001 ppm in sea-water to 700ppm intheir bodies.
Biomagnification● The tendency of pollutants to concentrate asthey move from one organism to the next iscalled biomagnification.● It is the increase in concentration of apollutant from one link in a food chain toanother.● It is the process in which pollutants not onlyaccumulate, but also become moreconcentrated at each trophic level.
Expalanation● Characters of pollutants:long lives, biologicaly active,mobile, solublein fats● Biomagnification is simply increase in concentration ofsubstance in a food chain, not in organism.● Conservative pollutants are not metabolized and thereforwhen an organism containing a pollutant is eaten, they aresimply passed on to predator and accumulate in its tissue.
pathway for biomagnification● Pollutants enter organisms viadifferent routes eg. though the mouthand digestive tract or across gillsurfaces.● Small aquatic organisms absorb mosttoxins directly from the water
Leaves eaten bycaterpillarCaterpillar eaten byFrogFrog eatenby HawkSeeds sprayed toprotect them frominvertebratesSeeds eatenby finch Finch eaten byHawkPesticide soaksinto the soilPesticide absorbedby earthwormEarthworm eatenby BlackbirdBlackbird eatenby HawkSpray lands on treeleaves
The Effect of the Pollutant● Human activity creates many harmfulpollutants.● Pollutants are taken up by plants.● The pollutants are then transferredalong the food chain until they reachthe highest trophic level.
Synergism● Organisms may ingest or absorb more than one pollutant at a time. Twopollutants may interact to produce a toxic effect which is greater than thecombined effect of the two pollutants simply added together i.e. one of thepollutants may increase the mortality caused by the other. This is calledsynergism.● e.g High concentrations of lead, zinc and mercury are each capable ofslightly reducing the growth rate of aquatic protozoa, but when actingtogether the overall effect is much higher.
Important pollutants● POP● PCB● Heavy metals● POP(persistent organic pollutants)POPs are harmful, carbon-containing compounds thatremain in water and soil for many years. E.g. DDT
DDT● DDT(dichloro diphenyl trichloroethane)● a toxic POP that was used as a pesticide to control disease carryingmosquitoes.● Effects:low toxicity to humans but high toxicity to insects.It does bioaccumulate and biomagnifiesdamage the organisms health and decline in wildlife population.potentially carcinogeniccause type2 diabetespencreatic cancer
PCBs (polychlorinated biphenyls)● PCBs were once widely used in industrial products but are now banned inNorth America. PCBs were used in the manufacture of paint, plastics andadhesives.● PCBs are chemically stable, hydrophobic and lipid soluble, hence they canrapidly bioaccumulate.● Effects :Aquatic ecosystems are most sensitive to PCBs. Organisms at hightrophic levels, like the orca, retain high levels of the pollutant.Caused the decline of European Otter and population of Seal.interfere with the hormonal control of oestrus and ovulation, seriouslyreducing reproductive ability and weaken the immune system of marinemammals.In humans, PCBs may increase the risk of anaemia andsusceptibility to infectious diseases.
Heavy metals● Heavy metals enter the biosphere, they do notdegrade, and they can not be destroyed.● Mercury, cadmium, lead and tin are the heavymetals most frequently endangering humanhealth.● All enter the food chain through industrialwaste and bioaccumulate in aquatic andmarine environments.
Mercury● Almost all mercury compounds are toxic and can bedangerous at very low levels in both aquatic andterrestrial ecosystems.● The most important pathway for mercurybioaccumulation is through the food chain.● In the water, plants and small organisms like planktontake up mercury through passive surface absorption orthrough food intake.
Methylmurcury● In the environment, particularly lakes, waterways and wetlands,mercury can be converted to a highly toxic, organic compoundcalled methylmercury through biogeochemical interactions.● Methylmercury biomagnifies through the food chain aspredators eat other organisms and absorb the contaminants thattheir food sources contained.● EffectsIt can cross the blood-brain and placental barriers,allowing it to react directly with brain and fetal cells.Methymurcury concentration in fish may also be affectedto humans.