Cathode Ray Tubes

Since the 1950s, CRTs have been used in television and computer screens. Historically, their production has grown in step with computer demand (Williams, 2003). In 2001, the global CRT monitor industry was valued at US $19.5 billion, producing 108 million units. This figure is expected to fall due to the increasing popularity of LCD monitors (Williams, 2003).

The CRT of a typical monitor accounts for approximately 50% of the monitor’s weight, and contains a veritable cocktail of elements (Table 1) of which lead is considered the most important due to its high content (up to 20%) in the funnel glass component of a CRT (Lee et al., 2004).

Table 1: Components of crt panel and funnel glass (reconstructed from Lee et al., 2004)

Type of Glass	Major Elements (>5% wt)	Minor Elements (<5% wt)
Panel	Silicon, oxygen, potassium, barium, and aluminium	Titanium, sodium, cesium, lead, zinc, yttrium, and sulphur
Funnel	Silicon, oxygen, iron, and lead	Potassium, sodium, barium, caesium, and carbon

In most basic terms, a CRT creates the visual image displayed by the monitor, by employing the interaction between an electron tube and a phosphor coated screen (Anonymous, 2003). In order to avoid radiation exposure to the viewer, the funnel glass of the CRT contains high concentrations of lead-oxide (Lee et al., 2004). According to the US Environmental Protection Agency’s (EPA) toxicity characteristic leaching procedure (TCLP), the lead found in funnel glass is considered a hazardous waste because it far exceeds the TCLP threshold of 5 mg/L leached, with values ranging from 10-20 mg/L leached per monitor (Lee et al., 2004). Williams (2003) also found that CRT monitors exceeded TCLP limits for zinc leachate, thus classifying it as a hazardous waste. The hazard truly occurs when monitors are permitted to weather in landfills, releasing these toxic chemicals into soil, and subsequent water systems.

Lead is especially an issue in waste disposal because it becomes bioavailable in soils with increasing pH, and becomes available to animals and humans through the food chain and soil dust inhalation (Martinez-Villegas et al., 2004). Once in the body, it can attack proteins and DNA (Bechara, 2004) as well as interfere with the functions of the central and peripheral nervous systems (Needleman, 2004). At high enough doses, it can result in brain edema and haemorrhage (Needleman, 2004).