Scientific understanding of mercury content in fluorescent lamps

Foreword

With the promotion of high-efficiency lighting products by the national high-efficiency lighting product promotion project, energy-efficient energy-saving lamps have been recognized by consumers, but they are not aware of the harmful effects of mercury in fluorescent lamps. Many media are also very concerned about the mercury pollution of fluorescent lamps, and reported some data and claims. The National Electric Light Source Quality Supervision and Inspection Center (Beijing) has carried out research on the mercury content of fluorescent lamps and the mercury pollution problem of fluorescent lamps in the past six years. From the scientific point of view, we will analyze the harmful effects of mercury on the environment and human body in fluorescent lamps. Mercury-containing fluorescent lamps.

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Mercury is a heavy metal that exists widely in different forms in nature. According to a 2004 study by the Institute of Geophysical and Geochemical Exploration of the Chinese Academy of Geological Sciences, Qing Qinghua, mercury concentrations in various crusts, rocks and soil ranged from 6.9 ng/g to 60 ng/g [1]. There is evidence that the amount of mercury released into the atmosphere by natural processes on the surface may be much greater than the amount of mercury released directly into the atmosphere by human activities [2]. The amount of mercury that humans emit into the environment through mining, coal burning, and industrial emissions is estimated to be 2,000 tons per year [3].

Different forms of mercury have different characteristics, and are harmful to the environment and toxic to the human body.

Mercury-containing products in life

In daily life, the mercury-containing products that people can easily access include: a mercury thermometer containing about 1 gram of mercury, a benchtop mercury sphygmomanometer containing about 50 grams, a traditional filling tooth directly using amalgam fillings... and so on. An energy-saving lamp contains about 1-5 milligrams of mercury, just one thousandth of a mercury in a thermometer and one ten-thousandth of a mercury in a mercury sphygmomanometer. Therefore, mercury is not terrible. As long as you have mastered the knowledge of mercury characteristics, rational application, and proper treatment, you can avoid harm to the environment and human life.

Possible environmental pollution of mercury

Metallic mercury is insoluble in water, and its environmental impact is mainly caused by volatile mercury vapors polluting the air. The maximum allowable mercury concentration required by the Guangdong Provincial Local Standard DB44 27-2001 "Air Pollutant Emission Limits" is 0.010 mg/m3 (the national standard GB 16297-1996 "Integrated Emission Standard for Air Pollutants" The mercury concentration is 0.015 mg/m3), and if all 3mg metal mercury is volatilized, the volume of air that can be polluted is 300 m3, that is, the room area of ​​3 meters high is 100 square meters. Since the saturated vapor pressure of solid mercury at normal temperature and pressure is small, the volume of volatile and potentially contaminated air is only 1/5 to 1/10 of that of liquid mercury.

Inorganic mercury compounds are not volatile, but are water soluble, mainly contaminating soil and water. According to China's maximum mercury content limit requirements for different water bodies, 3 mg of inorganic mercury ions may contaminate water with 0.06 tons of discharged sewage (GB 8978-1996 Integrated Wastewater Discharge Standard) or 3 tons of drinking water (CJ 94-2005 Water quality standard for drinking water, GB 5749-2006 "Sanitary Standard for Drinking Water"), or 30 tons of surface water (GB 3838-2002 "Environmental Quality Standard for Surface Water"), or 60 tons of nature reserve water (GB/T) 14848-93 "Groundwater Quality Standards"). The current rumor that 0.5 mg of mercury contaminates 180 tons of water is not realistic.

Table 1 Characteristics and hazards of different forms of mercury

Possible harm of mercury to human health

If more than a safe level of mercury enters the human body, it will be mainly distributed in the kidney, liver, spleen, etc. Organic mercury can enter the brain. The mechanism of poisoning is that mercury ions can bind to proteins to degrade the protein, mainly through the kidneys. The absorption of metallic mercury in the digestive tract is very small, less than 0.01%. Generally, a single oral metal mercury does not cause poisoning. According to the latest research results of Tohoku University in 2012 [5], the half-life of mercury in blood is 57 ± 18 days, and the half-life in hair is 64 ± 22 days. Therefore, as long as it is not absorbed by long-term exposure, the trace amount of mercury in the safe level absorbed by the human body can be completely excreted by the body's own function. The US Environmental Protection Agency (EPA) sets a minimum level of safety for mercury consumption at 0.7 mg Hg/kg bw/week, and the World Health Organization (WHO) recommends 3.3 mg Hg/kg bw/week. In other words, for an average adult weighing 50 kg, it is safe to continuously absorb mercury no more than 35-165 mg in a week.

Mercury in fluorescent lamps

Fluorescent lamps rely on the ultraviolet light emitted by mercury vapor to excite the phosphor to emit light, so a small amount of metallic mercury must be injected into the tube.

How much mercury does an energy-saving lamp contain?

Depending on the volume of the lamp, for a typical 15W energy-saving lamp, the mercury vapor required in the lamp is only 0.01 mg when illuminated. Due to the needs of fluorescent lamp life, the actual fluorescent lamp will contain more mercury. At present, China's current effective mercury-containing mercury limit value standard is QBT2940-2008 "Limited Requirements for Toxic and Hazardous Substances in Lighting Electrical Products" issued in 2008, which stipulates that the maximum mercury content of the three primary color energy-saving lamps is 5mg. In 2011, the latest revised national standard for energy-saving lamps (GBT 17263 "Performance Requirements for Self-ballasted Fluorescent Lamps for General Lighting"), the mercury content of energy-saving lamps below 30W cannot exceed 2.5mg, and the mercury content of "low-mercury" energy-saving lamps cannot More than 1.5mg, "micro-mercury" energy-saving lamps should not contain more than 1.0mg of mercury. In 2008, the national first energy-saving lamp mercury content survey completed by the National Electric Light Source Quality Supervision and Inspection Center (Beijing), 62% of energy-saving lamps contain no more than 5mg of mercury. After that, the national high-efficiency lighting product promotion project also encouraged the use of low-mercury fluorescent lamps. In 2012, the promotion of energy-saving lamps has reached 1.5 mg or less of mercury. According to the long-term research on the mercury content of fluorescent lamps by the National Electric Light Source Quality Supervision and Inspection Center (Beijing), the average mercury content of energy-saving lamps in China should be 2-3mg. The above analysis of the environmental impact of mercury is based on this level of mercury. Suppose that 3 mg of mercury in an accidentally broken fluorescent lamp is volatilized into mercury vapor and is completely absorbed by a person weighing 50 kg through the respiratory tract, which is far below the internationally most stringent safety level limit of 35 mg/week.

Mercury for fluorescent lamps, elimination of liquid mercury fluorescent lamps

The mercury used in fluorescent lamps is atomic mercury. Past production processes use liquid mercury, but currently there are about 80-90% energy-saving lamps in the country and about 60-70% straight-tube fluorescent lamps use solid mercury. Mercury for fluorescent lamps is a homogeneous mixture or alloy of mercury and other metals, so that mercury exists as a solid at room temperature, which can effectively reduce mercury volatilization pollution during the production, use and recycling of fluorescent lamps, and reduce human health. Hazard. The lighting industry “The Self-Regulation to Stop the Use of Liquid Mercury in Fluorescent Lamp Production”, drafted by the China Lighting Association, has also begun to solicit comments in September 2012.

How much mercury is volatilized after the fluorescent tube is broken?

The promotion and use of mercury fixation greatly reduces the environmental impact of fluorescent tubes. The following are the changes in the mercury content of the air at different altitudes detected by two typical liquid mercury energy-saving lamps and mercury-fixing energy-saving lamps after the lamp is broken.

According to the requirements of China National Standard GBZ 2.1-2007 "Hospital exposure to occupational exposure limits for hazardous factors in workplace", the allowable concentration of short-term exposure in the workplace is 0.04mg/m3, and the time-weighted average allowable concentration (long-term exposure) is 0.02mg/m3. . In this test, when the energy-saving lamp was broken in a closed room, the mercury concentration near the ground was less than 0.04 mg/m3 after 5 minutes and less than 0.02 mg/m3 after 10 minutes (Fig. 1). Moreover, after opening the doors and windows to ventilate, the concentration of mercury vapor in the air will rapidly drop to the air background level (Table 2). The results of this test have been reported in the People's Daily's verification section on August 16, 2012 [6]. Most mercury-fixing lamps break the lamp in an unignited state and there is no mercury vapor concentration exceeding the standard.

Table 2 Changes in mercury vapor concentration of energy-saving lamp samples before and after ventilation (unit: microgram per cubic meter)

It can be seen that the trace mercury contained in the fluorescent lamp has a very limited influence on the surrounding environment after the lamp is broken. Just pay attention to the correct handling of the lamp fragments (recommended to collect the lamp fragments with a paper towel, put the paper towels together in a sealed plastic bag), and timely ventilation (15 minutes recommended) will not have a health impact on the user.

How big is the harmfulness of mercury in fluorescent lamps to the human body?

It is determined by the volume of the energy-saving lamp tube and the inherent characteristics of the metal mercury. At the moment of the energy-saving lamp tube breaking, only the vapor of less than 0.01 mg required for the light emission can be immediately volatilized (for the mercury-fixing energy-saving lamp, The amount of mercury vapor in the ignited state will be lower). These gaseous atomic mercury will diffuse rapidly under ventilated conditions and will be able to enter the body through the respiratory tract. This part of the atomic mercury that enters the bloodstream is converted into water-soluble divalent mercury ions (Hg2+), which are gradually discharged through the urine. The concentration is reduced by half in about 60 days and gradually discharged to complete discharge.

Therefore, as long as it is not a long-term, large-scale contact with broken fluorescent tubes, the effect of mercury in energy-saving lamps on the human body is almost negligible. Occasionally, an energy-saving lamp is broken in the family. As long as the treatment method is appropriate, it will not cause harm to the surrounding environment and human health.

What effect does fluorescent mercury have on the environment?

The environmental impact of mercury in fluorescent lamps is primarily a long-term, potential impact. By eliminating the use of liquid mercury and reducing the mercury content of a single lamp, the amount of mercury used in the fluorescent industry and the amount of mercury emitted to the environment can ultimately be reduced. According to the research of the Chemical Registration Center of the State Environmental Protection Administration, the total amount of mercury used in China in 2000 was 1,200 tons, and the amount of mercury used in the reagent and chemical industries was about 700-900 tons, accounting for more than 70% [7]. According to the statistics of China Lighting Association, the total amount of mercury used in China's fluorescent lamp industry in 2010 was about 56 tons. The person in charge of the Chemicals Division of the Pollution Prevention and Control Department of the Ministry of Environmental Protection once said that the amount of mercury used in the production of energy-saving lamps only accounts for about 2% of the total mercury used in China [6]. With the mature technology of low-mercury and micro-mercury fluorescent lamps, the amount of mercury used in the fluorescent lamp industry in China is expected to be reduced to 10 tons in three years, thanks to the active efforts of relevant government departments in the country, which is discharged into the environment through natural routes every year. In terms of thousands of tons of mercury, it can be said to be minimal.

High-efficiency lighting product promotion project to promote energy-saving lamps

The energy-saving lamps promoted in the high-efficiency lighting product promotion project are not concentrated in the end of the life but are scattered throughout the country. Calculated by containing 5mg of mercury per lamp of 150 million energy-saving lamps, it is scattered over the land area of ​​9.6 million square kilometers nationwide, equivalent to an average of 0.78mg mercury per square meter, calculated according to the average soil density of 2.65g/cm3 and 1m human activity depth. The average mercury concentration obtained was 0.29 ng/g, which is 0.5% of the average mercury background concentration in the soil of 60 ng/g [1]. Moreover, the mercury content of the newly promoted energy-saving lamps in the high-efficiency lighting product promotion project has been reduced to 1.5 mg, and the average mercury concentration discharged into the soil after 3 years is significantly reduced to 0.09 ng/g, which is higher than the average in the deep crust. The mercury concentration of 6.9 ng/g [1] is still two orders of magnitude lower. Therefore, the energy-saving lamps promoted by the high-efficiency lighting product promotion project will not have any adverse effects on the environment and people's health. If this part of the energy-saving lamps are completely recovered, the final amount of mercury recovered is only 0.225-0.75 tons, and according to the current energy-saving lamp recycling cost of 1.2 yuan/only, the funds to be invested during the period will be 180 million yuan. Such traces of mercury emissions and environmental impacts, whether it is worthwhile to invest in such huge amounts of recovery funds and other human and material inputs, require more in-depth research.

Conclusion

As an efficient lighting product, energy-saving lamps have made tremendous contributions to China's energy conservation and emission reduction in recent years under the background of the government's vigorous efforts to eliminate incandescent lamps and promote efficient lighting products. With the continuous deepening of research on the environmental impact of mercury in fluorescent lamps, it is necessary to comprehensively and scientifically understand the trace mercury contained in energy-saving lamps, so as to correctly evaluate and treat mercury-containing fluorescent lamps.

Reference material

[1] Chi Qinghua, Geochemistry, 2004, Vol.033, No.006, P641-648

[2] Feng Xinbin, Fu Xuewu, SOMMAR Jonas, LIN Jerry, Shang Lihai, Qiu Guangle, Journal of Ecology, 2011, Vol.030, No.005, P845-856

[3] UNEP, Global Mercury Assessment Report, 2002

[4] Beijing Global Village Environmental Education Center, compilation of basic information on mercury pollution and prevention, 2006

[5] Kozue Yaginuma-Sakurai; Katsuyuki Murata; Miyuki Iwai-Shimada; Kunihiko Nakai; Naoyuki Kurokawa; Nozomi Tatsuta; Hiroshi Satoh, The Journal of Toxicological Sciences, 2012, Vol.37, No.1, P123-130

[6] People's Daily, August 16, 2012