Particles of plastic smaller than which size are classified as microplastics?
- A.5 millimetres
- B.5 centimetres
- C.5 micrometres
- D.5 nanometres
Correct answer
Explanation
The correct answer is A, 5 millimetres. Microplastics are conventionally defined as plastic particles less than five millimetres across. They are of two kinds: primary microplastics, manufactured small, such as the microbeads once used in face washes and the pellets used as industrial feedstock; and secondary microplastics, formed when sunlight, waves and abrasion break down bottles, bags and fishing gear, and when synthetic fibres shed in laundry water. Option B is wrong because five centimetres would cover bottle caps and fragments counted as macroplastic litter. Option C is wrong because particles below five micrometres fall within the still smaller class discussed as nanoplastics and fine fractions, not the standard definition. Option D is wrong for the same reason, at a scale smaller still. The five-millimetre figure is the one to write in an exam.
Read the full article: Marine Pollution, Oil Spills and Ocean Acidification
Practice Questions
View allOcean acidification is caused mainly by the absorption of which gas by seawater?
- A.Nitrogen
- B.Carbon dioxide
- C.Methane
- D.Sulphur dioxide
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Carbon dioxide dissolves in seawater and reacts with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions; the extra hydrogen ions lower the pH, and they also combine with carbonate ions, leaving less carbonate for shells and coral skeletons.
Read the full explanation →Minamata disease, first recognised in Japan, is caused by poisoning from which element?
- A.Cadmium
- B.Arsenic
- C.Mercury
- D.Lead
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Methylmercury discharged with factory effluent into Minamata Bay entered fish and shellfish, biomagnified up the food chain and poisoned the people who ate them, producing the nervous disorder named after the bay and recognised in 1956.
Read the full explanation →Eutrophication of coastal waters leads most directly to which condition?
- A.A rise in dissolved oxygen that helps fish
- B.Depletion of dissolved oxygen and the formation of dead zones
- C.A fall in water temperature
- D.An increase in water salinity
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Eutrophication begins with nitrogen and phosphorus from fertiliser, detergent and sewage. The nutrients feed an algal bloom; the bloom is short-lived, and when it dies the bacteria that decompose the mass consume large amounts of dissolved oxygen.
Read the full explanation →The Exxon Valdez oil spill of 1989 took place in which waters?
- A.Gulf of Mexico
- B.Prince William Sound, Alaska
- C.Persian Gulf
- D.Bay of Bengal
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The tanker Exxon Valdez struck a reef in Prince William Sound in 1989, releasing crude oil that coated a long stretch of a cold, sheltered coastline where oil breaks down slowly, and killing large numbers of seabirds, sea otters and salmon.
Read the full explanation →MARPOL, the convention of 1973 with its Protocol of 1978, deals with which subject?
- A.Prevention of pollution from ships
- B.Trade in endangered species
- C.Protection of wetlands of international importance
- D.Transboundary movement of hazardous waste
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MARPOL is the International Convention for the Prevention of Pollution from Ships, adopted in 1973 and modified by the Protocol of 1978, and it is the main pollution instrument of the International Maritime Organization.
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