Biomagnification sim
Push a sprayer's pump handle to spray a persistent insecticide, and watch its concentration climb eight times at each step of a farm or estuary food chain until the top carnivores pass the harm level; switch on plastics to see why plastic pieces do not build up the same way.
Ecosystems: biomagnification of a persistent insecticide along food chains, why top carnivores are hit hardest, and plastic pieces in a marine chain · covers the O-Level, IGCSE topic
What the sim shows
Biomagnification. Push the pump sprayer's handle all the way down to spray a persistent insecticide (a DDT-like one, which is not broken down and dissolves in fat) once (or, on the handle, Arrow Down sprays, Arrow Up takes a spray back, Home starts again with none and End sets 10). A board behind the bench shows the insecticide's concentration in each level of the food chain, in ppm (mg of insecticide per kg of body mass), with the top carnivores at the top. In the farm field the crop plants are sprayed directly; in the estuary, where the river from the farm meets the sea, rain washes the insecticide off the farm and down the river into the water and the plankton take it in. Each animal eats many organisms from the level below and stores the insecticide in its fat instead of excreting it, so the same insecticide is packed into less body mass at each step: the concentration climbs at every level and the top carnivores, the sparrowhawks or the ospreys, are hit hardest. Above about 5 ppm their eggshells are thin and break. The estuary's plastics option shows plastic pieces eaten in the same chain: most pass out in the faeces, so they do not build up the same way, but large items tangle animals or block their gut, and plastic pieces can carry other persistent chemicals stuck to them, which can then build up. Many countries banned DDT for farm use from the 1970s, and birds of prey recovered. Simplified on purpose: all the numbers are illustrative (≈), chosen to show the pattern; real values differ from place to place; each chain is treated on its own, with one kind of organism at each level; real food webs have many; at every feeding step 10% of the food's mass becomes the feeder's body mass and 80% of the insecticide in the food is kept, so the concentration is 8 times higher at each step; real steps differ; the plankton hold 800 times the concentration of the water they live in (illustrative); every spray adds the same amount, nothing is broken down, and each level is shown once the insecticide has passed up the chain (in real life this takes months to years); one harm level, about 5 ppm, is used for both birds of prey; real effects such as thin eggshells start over a range; plastic pieces: 8% of the pieces eaten stay in the body and the rest pass out in the faeces (illustrative); in real seas the evidence that plastic pieces build up the chain is weak; the board's bars are on a log scale (each step on the scale is ten times the one before); the cards, pictures and sprayer are not to scale; the model sprayer holds water.
- Pump handle: push it all the way down to spray once
- Bar length: the insecticide's concentration, on a log scale (each step ×10)
- Red dashed line: the harm level for the birds of prey (≈ 5 ppm)
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
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