RAS question
Microplastics are defined as plastic particles smaller than:
Correct answer: (D) 5 mm.
Microplastics are plastic particles smaller than 5 mm in size.
Explanation
Microplastics are not just any small plastic litter; the commonly used upper size limit is 5 mm. The OECD report notes that microplastics are generally treated as plastic particles smaller than 5 mm, while also recognising that definitions vary by particle type. The OECD classifies microplastics as fragments, fibres, pellets or beads, and categorises them as primary particles made at micro scale or secondary particles produced when larger plastics fragment. Breakdown of larger plastics, synthetic clothing fibres and cosmetic microbeads fit that framework. Since 10 mm and 25 mm exceed the usual upper limit, and 1 mm is narrower than it, 5 mm is the exam-relevant definition.
Why the other options are wrong
- (A) 10 mm is above the commonly employed 5 mm upper size limit for microplastics, so it is too large for this definition.
- (B) 1 mm is too narrow because particles between 1 mm and 5 mm still fall within the usual microplastic range.
- (C) 25 mm is far beyond the 5 mm cut-off and does not fit the usual size threshold for microplastics.
Concept
Environment & Ecology classifies pollution partly by particle-size threshold. The chosen cut-off affects how plastic particles are identified, grouped by source, and framed for mitigation.