Pollution — Practice · Grade 12 Science

Chapter: Pollution, Carbon & Climate Evidence

What this practice covers

By the end of Pollution you should be able to:

9 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: pollutant, point-source pollution, nonpoint-source pollution, eutrophication, biomagnification.

Problem 1

Which of the following is an example of nonpoint-source pollution?
  1. A pipe discharging waste from a single factory into a river
  2. Smoke pouring from one power plant's smokestack
  3. Fertilizer and motor oil washing off lawns and roads across a whole watershed
  4. Untreated sewage released from one broken outfall pipe
Answer and explanation

Fertilizer and motor oil washing off lawns and roads across a whole watershed

Nonpoint-source pollution comes from many scattered, hard-to-identify sources at once, like runoff spread across an entire watershed, rather than from a single identifiable outlet.

Problem 2

Biomagnification refers to the way that
  1. decomposers break pollutants down into harmless molecules
  2. a pollutant spreads evenly through the air until it is harmless
  3. a factory's scrubber removes pollutants before they leave the smokestack
  4. a persistent pollutant becomes more concentrated in organisms at each higher step of a food chain
Answer and explanation

a persistent pollutant becomes more concentrated in organisms at each higher step of a food chain

Because predators eat many contaminated prey and store rather than excrete the toxin, persistent pollutants grow more concentrated at each higher trophic level.

Problem 3

Algae tissue contains 0.02 ppm of a persistent pesticide, which biomagnifies about 10 times at each step of the food chain algae → insects → small fish → heron. About what is the concentration, in ppm, in the heron?
Answer and explanation

20 ppm

Three steps of tenfold magnification: 0.02 × 10 × 10 × 10 = 0.02 × 1,000 = 20 ppm. This supplied teaching factor applies between feeding levels; water-to-organism uptake is bioconcentration.

Problem 4

Explain how fertilizer running off farm fields can create an oxygen-starved 'dead zone' in a bay.
Answer and explanation

The fertilizer adds extra nutrients to the water (eutrophication), which fuels a huge algal bloom. When the algae die, decomposers break them down and use up the water's dissolved oxygen. With the oxygen gone, fish and other organisms suffocate, leaving a lifeless 'dead zone.'

Problem 5

Why is nonpoint-source pollution generally harder to control than point-source pollution?
  1. It comes from many scattered, diffuse sources spread across the landscape, so there is no single pipe or stack to regulate
  2. It only occurs indoors, where it cannot be measured
  3. It is always invisible, while point-source pollution can always be seen
  4. Nonpoint pollution is always chemically more toxic than point-source pollution
Answer and explanation

It comes from many scattered, diffuse sources spread across the landscape, so there is no single pipe or stack to regulate

Point sources can be sampled and regulated at one outlet, but nonpoint pollution seeps in from countless diffuse locations at once, making it far harder to pinpoint and fix.

Problem 6

A stream carries 2 mg/L at 100 L/s. Find mass load. Show the reasoning, not just the conclusion.
Hints

Keep concentration and mass per time distinct.

Answer and explanation

200 mg/s.

Problem 7

Why distinguish hazard from exposure when assessing pollutant effects?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

A substance's harmful potential does not alone determine dose or risk; route, amount and duration matter.

Problem 8

Within-organism accumulation differs from food-web magnificationWithin-organism accumulation differs from food-web magnificationWater / uptakeExposureOrganism storageBioaccumulationPredator dietPossiblebiomagnificationPersistent, bioavailable compounds can behave differently.Not every pollutant accumulates or magnifies through a food web.
Original process distinction; no specific chemical concentration or universal factor is asserted.
Interpret the supplied visual. Does a high concentration in one fish alone prove biomagnification?
Answer and explanation

No. It can show exposure/accumulation but a trophic comparison with compatible concentrations is needed for magnification.

Bioaccumulation is buildup within an organism when uptake exceeds elimination over time. Biomagnification is increasing concentration across trophic positions through dietary transfer under appropriate persistence, uptake and elimination conditions. The concepts are related but not identical. Some compounds do neither, and comparing different tissues or wet/dry mass bases can mislead. Specify the chemical, tissue, concentration basis and food-web evidence before asserting a universal higher-predator pattern.

No. It can show exposure/accumulation but a trophic comparison with compatible concentrations is needed for magnification.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 9

An outlet flows 200 L/min at 3 mg/L. Find pollutant mass emitted in 1 h. Treatment captures 80% into sludge with no chemical destruction; find waterborne and captured mass.
Answer and explanation

Initial mass=200×60×3=36000 mg=36 g. Waterborne residual=7.2 g; captured mass=28.8 g. The captured material remains in the full system account.

Initial mass=200×60×3=36000 mg=36 g.

Waterborne residual=7.2 g; captured mass=28.8 g.

The captured material remains in the full system account.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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