Bioamplification and Bioaccumulation Study Guide

Overview of Bioamplification and Bioaccumulation

  • Bioamplification and Bioaccumulation are key ecological concepts within the SNC1W curriculum, focusing on how toxins enter, persist, and intensify within biological systems.

Bioamplification (Biomagnification)

  • Definition: Bioamplification, which is also commonly known as Biomagnification, refers specifically to the increase in the concentration levels of toxins as one moves up the hierarchical levels of a food chain.
  • Chemical Solubility Requirements:   - For bioamplification to occur, the chemical toxin must be HIGHLY fat-soluble.   - This solubility is a critical factor because if a chemical were not fat-soluble, the organism's body would typically process and release the toxin through urine.   - Because the toxins dissolve in fat, they are stored in the fatty tissues of organisms rather than being excreted.
  • Accumulation Mechanism in Predators:   - When a carnivore consumes an animal, it does not just eat the animal; it accumulates and absorbs all of the chemicals stored in that animal’s fat.   - The predator retains these chemicals for its entire natural life.   - Consequently, animals positioned high on the food chain (apex predators) accumulate massive, disproportionate amounts of chemicals compared to those at lower trophic levels.

Case Study: DDT (Dichlorodiphenyltrichloroethane)

  • Usage History: DDT was a chemical pesticide widely sprayed to combat mosquito populations.
  • Entry into the Food Chain:   - Upon being sprayed, DDT residue would settle on surfaces such as leaves and grass.   - This residue serves as the entry point for the toxin into the ecosystem's food web.
  • Example Food Chain Pathway:   - Grass $\rightarrow$ Cricket $\rightarrow$ Frog $\rightarrow$ Snake $\rightarrow$ Hawk.
  • The Mathematical Progression of DDT Concentration:   - Grass: A single blade of grass may receive 11 unit of DDT when an area is sprayed.   - Cricket: A single cricket eats 100100 blades of grass. At 11 unit per blade, the cricket accumulates 100 units100\text{ units} of DDT. (Biological status: No harm).   - Frog: A single frog consumes 2525 crickets. At 100 units100\text{ units} per cricket, the frog accumulates 2,500 units2,500\text{ units} of DDT. (Biological status: No harm).   - Snake: A single snake consumes 2020 frogs. At 2,500 units2,500\text{ units} per frog, the snake accumulates 50,000 units50,000\text{ units} of DDT. (Biological status: No harm).   - Hawk: A single hawk consumes 1010 snakes. At 50,000 units50,000\text{ units} per snake, the hawk accumulates a total of 500,000 units500,000\text{ units} of DDT.
  • Biological Impacts on Large Birds:   - While lower-level organisms show no immediate harm, the extreme concentration in hawks has devastating physiological consequences.   - Any DDT concentration above 100,000 units100,000\text{ units} causes the shells of eggs to become thinner.   - Consequently, when adult birds sit on their eggs to incubate them, the shells lack the structural integrity to support the weight and break.   - This led to significant population drops for large carnivorous birds during the 1950s, 1960s, and 1970s.
  • Secondary Ecological Effects of DDT:   - Wasps and Caterpillars: DDT spraying eliminated a specific wasp species that naturally preyed on caterpillars. Without their natural predator, caterpillar populations exploded, leading to the physical destruction of the thatched roofs of local villagers.   - Geckos and Cats: DDT accumulated in geckos. These geckos were then eaten by cats.   - Rat Plague: As cats died from toxic accumulation (or related failures), rat populations flourished due to the lack of feline predators. This eventually led to outbreaks of the plague.
  • Global and Current Status of DDT:   - DDT is currently banned in Canada, which has allowed bird populations to recover.   - Current pesticides are generally designed not to be fat-soluble, reducing the risk of bioamplification.   - DDT is still utilized in parts of South America and Africa because it is inexpensive and effective at killing mosquitoes, which carry diseases responsible for millions of deaths annually.
  • Other Toxic Effects: Some chemicals have been linked to sperm health issues in mammals and instances where baby whales refuse their mother's milk.

Case Study: India’s Vulture Population Crisis

  • The Situation: Between the years 2002 and 2006, approximately 97%97\% of India's vulture population died off. Vultures play a critical role in the environment by consuming the carcasses of dead cows.
  • Scientific Investigation:   - Initial observations showed that vultures were only symptomatic for a very short period before death.   - Autopsies revealed the cause of death was acute kidney failure.   - Scientists initially suspected a virus, but experiments showed that healthy birds did not contract any illness when housed with sick birds.
  • The Conclusion: The source was traced back to the vultures' diet. The toxin was identified as Diclofenac, an anti-inflammatory drug administered to cattle. When vultures fed on the carcasses of cattle treated with this drug, the Diclofenac caused their kidneys to shut down.
  • Policy Change: Due to these findings, Diclofenac was banned in late 2006.

Bioaccumulation Overview

  • Definition: Bioaccumulation refers to the specific amount of a toxin that builds up within a single organism over the course of its lifetime.
  • Generational Buildup: When a species reproduces, the toxins remaining in the tissue are passed on. A species will start its life with a baseline level of the toxin inherited from the parent, leading to progressively higher concentrations in future generations naturally over time.
  • Mercury in Fish: A primary example of bioaccumulation is found in fish populations. Fish consume mercury through their diet, leading to a buildup of methylmercury over their lifespan. This presents a danger both to the fish and the humans who consume them.

Mercury Concentration in Seafood (Consumption Guidelines)

Highest Mercury (Avoid Eating)
  • King Mackerel
  • Shark (Note: Fish in trouble/low numbers or destructive catch methods)
  • Swordfish (Note: Fish in trouble)
  • Marlin (Note: Fish in trouble)
  • Bigeye or Ahi Tuna (Note: Fish in trouble)
  • Orange Roughy (Note: Fish in trouble)
  • Tilefish (Note: Fish in trouble)
High Mercury (Limit to 3 servings or less per month)
  • Bluefish
  • Grouper (Note: Fish in trouble)
  • Spanish or Gulf Mackerel
  • Canned Albacore Tuna
  • Chilean Sea Bass (Note: Fish in trouble)
  • Yellowfin Tuna (Note: Fish in trouble)
Least Mercury (Safer Choices)
  • Anchovies, Butterfish, Catfish, Clam, Mullet, Crab (Domestic), Oyster, Herring, North Atlantic/Chub Mackerel, Sardine, Scallop (Note: Fish in trouble), American Shad, Shrimp (Note: Fish in trouble), Pacific Sole, Crawfish/Crayfish, Ocean Perch, Atlantic Croaker, Plaice, Squid (Calamari), Tilapia, Flounder (Note: Fish in trouble), Pollock, Freshwater Trout, Atlantic Haddock (Note: Fish in trouble), Hake, Canned/Fresh Salmon (Note: Farmed salmon may contain PCBs/chemicals), Whitefish, Whiting.

Distinction Summary

  • Bioaccumulation: Refers to the increase in concentration of a pollutant specifically within a single organism.
  • Biomagnification / Bioamplification: Refers to the increase in concentration of a pollutant throughout a food chain as it passes from prey to predator.