Emission testing and inhalational exposure-based risk assessment for candles having Pb metal wick cores

Segments of seven candles with wicks having a Pb metal core have been tested in a purpose-built combustion chamber to assess air Pb emissions. Emissions were collected on glass fibre filters that have been digested in concentrated HNO3 and analysed by flame atomic absorption spectroscopy (FAAS). Despite an indication of a bimodal distribution in Pb emission rates, and a range from 450 to 1130 micrograms Pb/h, the mean rate from the seven candles was 770 micrograms Pb/h. The 38-cm long candles are, on average, capable of emitting 104,000 micrograms of Pb into the air over approximately 127 h. A mean value of 20% of the Pb metal in the wick consumed by the candle is emitted into the air, the remainder appears to accumulate at the base of a molten wax-pool adjacent to the wick. Individual Pb-bearing particles from the combustion of candles were observed in a field emission scanning electron microscope (FESEM) to have a diameter of 1 micron or less. The emission from the candles has been analysed by X-ray diffraction (XRD) and identified as Sodium Lead Carbonate Hydroxide [NaPb2(CO3)2OH]. This compound, being a Pb carbonate, is likely to be easily absorbed in the lungs and gastrointestinal tract. Risks associated with inhalational exposure have been assessed after determining indoor lead in air (PbA) concentrations. Given a lack of information on the duration of use of candles, a range of scenarios from worst possible case to daily and weekly burning regimes are evaluated. Detailed evaluations of PbA are based on the emission from a single candle at rates of 500 and 1000 micrograms Pb/h, room volumes of 25 and 50 m3, durations of emission of 1.5, 3 and 6 h and air infiltration rates of 0, 0.25, 0.5, 0.75 and 1.0 air volume changes per hour (ACH). A candle burnt for 3 h at 1000 micrograms/h in a 50 m3 room having poor ventilation at 0.25 ACH is estimated to yield a 24-h average lead in air concentration of 9.9 micrograms/m3 with a peak PbA value of 42.1 micrograms/m3. Daily exposure to such candle burning where children spend 80% of their time indoors is likely to elevate PbB in children by a minimum of 24 to 40 micrograms/dl, according to the PbB:PbA relationship of Brunekreef, 1984 (The relationship between air lead and blood lead in children: a critical review). Estimating child Pb uptake from first principles using a range of exposure factors, a child would obtain some 85 to 127% of the provisional tolerable weekly Pb intake (PTWI) from such daily exposure. Child blood lead levels could readily exceed levels of 10 micrograms/dl, largely due to exposure to emissions from burning Pb wick core candles for several hours once per week. The regular burning of multiple candles in small, poorly ventilated spaces could readily be associated with clinical Pb poisonings and death. High levels of exposure could occur with Pb metal core wick candles in less developed countries where candles are used on a daily basis for indoor lighting purposes in small dwellings. Prolonged burning of candles may occur in religious and in ceremonial circumstances or restaurants where they may be of particular concern. On the basis of the limited investigation carried out, candles having a wick with a Pb metal core have the potential to present highly unacceptable and avoidable risks to human health.