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Recycling plants face a persistent challenge known as contamination, in which non-recyclable materials or improperly sorted items reduce the value and usability of otherwise recyclable waste. A single greasy pizza box mixed into a batch of paper, for instance, can render an entire load unsuitable for standard paper recycling, since the oil weakens the fibres during reprocessing. To combat this, many facilities have installed optical sorting systems that use infrared light to distinguish plastic types automatically, reducing reliance on manual sorting. Even with this technology, however, plants report that public confusion over which items belong in recycling bins remains the largest single cause of contamination, exceeding equipment errors by a wide margin.