Earlier in the 20th century, industry relied mainly on relatively clean industrial waste, but the quantities of materials separated from municipal solid waste have increased again since the 1980s.48 The economics of recycling is changing over time. For example, the cost of recycling electronic equipment in the US is approaching the point of producing a profit without individuals or businesses having to pay a fee to recycle their equipment. Figure 5.1 shows that secondary resource prices closely follow fluctuations in their corresponding virgin material.