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Water Pollution and Bioindicators
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Which one of the following is not a bioindicator of water pollution?Bioindicators of water pollution are organisms whose presence shows that the water is polluted with organic matter and is poor in dissolved oxygen.
Blood-worms (larvae of Chironomus) contain haemoglobin and can live in water with very little oxygen, so they indicate pollution.
Sludge-worms (Tubifex) live in the organic sludge at the bottom of heavily polluted water.
Sewage fungus (a slimy growth of bacteria such as Sphaerotilus and associated organisms) grows in water receiving sewage.
Stone flies (Plecoptera), on the other hand, have nymphs that need clean water rich in dissolved oxygen; they disappear when the water becomes polluted.
Their presence therefore indicates clean, unpolluted water, so they are not indicators of water pollution.
So the answer is stone flies.