ANN ARBOR---A University of Michigan School of Public Health study of candles purchased from stores in southeast Michigan shows that some candles on the market today are made with wicks that have either lead or lead cores that emit potentially dangerous levels of lead into the air.
The study is by Jerome Nriagu, a professor of environmental health sciences, who examined lead emissions from 15 different brands of candles made in the United States, Mexico and China. He also examined the concentration levels of lead that lingered in the air in an enclosed space, such as a room measuring 12 feet by 12 feet and 10 feet high, after one hour and then again for five hours.
Nriagu's study showed that lead emission rates for the candles ranged between 0.5 and 327 micrograms per hour. After burning the candle for one hour, the lead levels in the air of an enclosed space were estimated to range from 0.04 to 13.1 micrograms per cubic meter, which compares to the U.S. Environmental Protection Agency recommendation of 1.5 micrograms per cubic meter for ambient air. After one hour, five of the candles Nriagu tested emitted unsafe levels of lead into the air that measured greater than 1.5 micrograms per cubic meter.
After five hours, the lead levels in an enclosed space ranged from an estimated 0.21 to 65.3 micrograms per cubic meter. Candles produced in China and the United States released the highest levels of lead into the air.
Regular exposure to lead in this manner in confined spaces could pose health risks to people with weak immune systems, especially children and the elderly, Nriagu said.
"Lead poisoning remains one of the most serious environmental health diseases in this country and other parts of the world. It affects many organ systems and biochemical processes with the most serious sequelae often occurring in the central nervous, cardiovascular and blood systems," Nriagu said.
Nriagu's findings are consistent with an Australian study due to be published in the journal, Science of the Total Environment. In that study, Mike van Alphen of Lead Sense, an independent consultancy in Australia involved in environmental lead testing, lead exposure investigations and consumer product testing, examined a single brand of candle sold in Australia. The candle he examined released up to 1,130 micrograms of lead per hour.
Studies have shown that the central nervous system of children is particularly sensitive to lead. Some of the most damaging neuropsychological effects of lead poisoning of young children include learning disabilities, reduced psychometric intelligence and behavioral disorders. These effects have been associated with chronic low-level exposure to lead and are believed to be irreversible.
Nriagu's study measured the rate of lead emission in a laboratory setting using a flux chamber. The lead released as candle fume was collected in nitric acid and analyzed by means of an atomic absorption spectrometer. In addition to measuring emission rates, he calculated concentration levels of lead in the air in an enclosed space after one hour and then again, for five hours.
"The half-life of lead in air obviously would make a difference in terms of it being inhaled. A recent study has shown that particles emitted by candles during a normal burn are sub-micron in size and should remain suspended in the atmosphere for some time. Even if a particle is deposited after only a short trajectory through the atmosphere, it adds to the lead burden in the house dust. Airborne lead represents a hazard in more ways than one," Nriagu said.
House dust is widely recognized as a primary route of childhood lead exposure through hand-to-mouth activities.
"Assuming that only 50 percent of the lead released is deposited in an area measuring 12 feet by 15 feet (such as a living room), we estimate that the loading of the lead to house dust will exceed the U.S. EPA guideline of 100 micrograms per square meter by burning one of the Chinese candles for a few hours. Our data thus shows that burning leaded candles can result in extensive contamination of the air and house dust with lead," Nriagu said.
In general, Nriagu found that metal cores in Chinese candles were made of either pure lead or lead alloy while those made in the United States or Mexico consisted of zinc or lead-containing alloys. Lead was detected in small quantities in emissions from zinc-based wicks, suggesting that the lead may be a common contaminant in the zinc, wick or wax. The levels of lead were small, but still may represent a health risk over a long period of time.
Not all candles are made with wicks that have metallic cores. The practice is primarily used with candles that are needed to burn longer such as scented or ceremonial candles. A metal core is used to provide rigidity to the wick which provides an even and slower burn rate, and to reduce the mushrooming at the tip. Since lead and its alloys melt at relatively low temperature, a large fraction of the wick core material is volatilized as the candle is burned.
"Because it is costly and difficult to control lead once it is released to the environment and medical treatment does not fully reverse the health effects, the optimal strategy for minimizing the risk involves the reduction or elimination of exposure in various forms. This study shows that there are still other important domestic sources of lead exposure that have escaped public scrutiny and legislative control. Leaded candles were recently banned in Australia, and we recommend a similar action in this country," Nriagu said.