Extracting the dental lead

Lead contamination in the black paper used to mask dental X-ray paper has been determined for the first time using atomic absorption spectroscopy. The worrying results suggest that the used material represents an environmental waste problem requiring pre-treatment before disposal.

According to Débora Guedes, Reginaldo Silva, Márcia da Veiga, and Jesus Pecora of the University of São Paulo, Brazil, dental waste management is a sector that needs to be entirely re-organized across the globe. The problem of infectious waste products is one aspect of this issue, but materials associated with dental X-rays is another because of the high lead content of various items used in protecting X-ray film and in masking the teeth and jaw during the X-ray procedure.

The black paper used to cover intraoral films is an almost ubiquitous material in dentistry but contains high levels of lead. "Intraoral dental film packaging and film packet components are a type of solid waste that is wrapped with a sheet of lead foil," the researchers explain, "this protects the film from backscattering and secondary irradiation." There are also outer vinyl covers, paper packet covers, and interior black paper stiffeners, all of which can be contaminated with lead. Despite the obvious safety risks associated with this heavy metal, lead-contaminated waste is often disposed of with normal waste and ends up in landfill where it becomes a serious environmental hazard.

The researchers have now collected samples of this black paper from the Radiology Clinics of the Dental School of Ribeirão Preto, at the University of São Paulo, with a view to quantifying the problem. For the sake of comparison they used four different analytical techniques to determine lead content in the samples, including flame atomic absorption spectrometry (FAAS) and inductively coupled plasma mass spectrometry (ICP-MS).

They also used several different preparation techniques to extract the lead content from their samples: microwave treatment, a standard waste extraction method using water (the DIN 38414eS4 test), and the US Environmental Protection Agency's Toxicity Characteristic Leaching Procedure (TCLP) method, which simulates landfill conditions.

Lead poisoning is a serious health problem with various names, including colica pictonium, saturnism, plumbism, Devon colic, or painter's colic, these are usually associated with a particular mode of ingestion or absorption. Fundamentally, increased levels of this element in the blood can lead to irreversible neurological damage, kidney disease, effects on the heart and damage to the reproductive system.

"The results revealed the presence of high lead levels, well above the maximum limit allowed by legislation," the team says. They also used scanning electron microscopy coupled with energy dispersive X-ray microanalysis (SEM-EDS) to confirm the presence of lead.

The team also simulated soil contamination with this waste product and found that levels could be high enough for this to be an urgent problem in need of addressing. "A preliminary treatment of black paper should be mandatory before it is disposed in the common trash," the team says. "The high lead content of this material makes its direct dumping into the environment unwise."