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Survey and health assessment of mercury in compact fluorescent lamps and straight fluorescent lamps 4 Health assessment of mercury vapours
Manufacturers/importers contacted in connection with the survey have stated that mercury used in compact and straight fluorescent lamps is either metallic mercury or mercury amalgam. If one or more compact or straight fluorescent lamps break in a home, mercury vapour may be released to the indoor air, as long as the residues have not been removed completely. Therefore, this health assessment has main focus on exposure to mercury vapour through inhalation. 4.1 Description of mercuryMercury (Hg) is a metallic element that may occur as the free metal or in inorganic and metal organic compounds. Furthermore, mercury can be mixed with other metals forming amalgams, for example with silver and copper for dental fillings. Inorganic compounds are found in the oxidation levels +1 and +2 as mercury(I) (mercurous, Hg2²+) and mercury(II) (mercuric, Hg²+) salts. Some salts readily dissolve in water, such as mercury(II) nitrate, and others such as mercury(II) sulfide are completely insoluble. Metal organic mercury compounds are insoluble in water, but dissolve in certain organic solvents. Mercury (Hg0) is the only metal that is liquid under normal pressure and temperature. It appears as a heavy, odour-free silvery liquid, which is practically insoluble in water and has a relatively high vapour pressure at room temperature. Occurrence of liquid mercury will therefore result in exposure to the invisible and odour-free mercury vapours. At room temperature air saturated with mercury will have a concentration of around 14 mg Hg/m³ or 500 times the current occupational threshold limit value. Mercury vapours are seven times heavier than air and will disperse along the floor in a room with insufficient ventilation (Clarkson et al., 2003). Identification
Physico-chemical data
Classification
4.2 Absorption and metabolism in human bodyAs described above liquid mercury is sparingly soluble and relatively inert. In case of ingestion of a few drops of mercury less than 0.01 % will be absorbed in the body through the gastrointestinal tract and this exposure will therefore not present an acute risk, but only add a minimal contribution to the mercury load (WHO 1980). Absorption of metallic mercury through undamaged skin is also assessed to be very limited. Even though it has not been studied quantitatively, absorption through intact skin for metallic mercury is assessed to be minimal due to the very low absorption rate of the gastrointestinal tract and the physical properties of metallic mercury (ATSDR, 1999). By contrast, mercury is readily absorbed through the respiratory tract (around 80 %) after inhalation of mercury vapours (WHO 1980). It has been estimated that upon exposure to mercury vapours 2.6 % of the mercury is absorbed through the skin and the remaining 97.4 % is absorbed through the respiratory tract (WHO, 2003). Mercury absorbed can be measured in the blood, where it is equally distributed in the plasma and the red blood cells. In the red blood cells extensive oxidation takes place of metallic mercury (Hg0) into mercury(II) ions (Hg²+), which may bind strongly to sulfurous proteins. Oxidation is catalysed by the enzyme catalase (Holmes et al., 2009). Mercury vapour is different from inorganic mercury compounds and reminds of methyl mercury in being transported easily and readily across the blood-brain barrier and the placental barrier, causing affects on the central nervous system and the unborn child. In the brain metallic mercury is transformed to inorganic mercury compounds as methyl mercury is (Holmes et al., 2009). A recent study with rats showed an interplay between mercury vapour and methyl mercury and the resulting level of mercury in the brain of offspring. Low dietary exposure to methyl mercury and parallel exposure to mercury vapour increased the level of mercury in the brain of offspring. Thus, the study concluded that human foetus exposed to both methyl mercury and mercury vapour has increased risk of impaired neurodevelopment compared with exposure to the two forms of mercury separately (Ishitobi et al., 2010). Body half-life of mercury after exposure to mercury vapour is 35-90 days (WHO 1980). Retention in the brain is however somewhat longer. Mercury is particularly long-term accumulated in the kidneys. Metallic mercury is excreted in exhaled air, sweat and saliva. After conversion to mercury(II) compounds these species may be excreted in urine through the kidneys (Berlin 1977). 4.3 Human intake of mercuryThe predominant route of exposure to mercury for the general public is through food, especially from fish and other seafood. The daily average intake through food is estimated at 2-3 μg mercury – almost exclusively in the form of methyl mercury (see Table 4-1). This is an organic form of mercury, which can be formed by micro-organisms in the aquatic environment, and which has a particular tendency to accumulate in aquatic food chains. Methyl mercury can just as mercury vapours be transported easily and readily across the blood-brain and the placental barriers – and is thereby similarly problematic. For methyl mercury a ”secure” limit value has been set at a daily intake of 0.1 μg Hg/kg body weight. (Clarkson et al., 2003). An additional contribution of mercury may origin from dental amalgam fillings, which contains around 50 % of mercury. It is estimated that 0.2 μg mercury is released from each amalgam filling per day (Richardson et al., 2009). WHO estimates that the ”intake” from dental fillings may amount to between 1.2 and 27 μg mercury per day (Holmes et al., 2009), but that the absorption in the gastrointestinal tract as mentioned above will be limited (see Table 4-1). WHO estimates that the daily average mercury intake by inhalation of ambient air is at 0.04-0.2 µg Hg per day, based on an air concentration of 0.002-0.01 μg Hg/m³ (Holmes et al., 2009). Mercury in the form of thiomersal – an ethyl mercury compound – is in some cases used as a preservative in vaccines. This use may also cause mercury loads. It has been calculated that children subject to an ordinary children’s vaccine programme with mercury preserved vaccine from birth and until the age of 6 months will be exposed to more than 0.1 μg Hg per day per kg of body weight (IPCS, 1980; Clarkson et al, 2003). Table 4-1 Estimated daily average intake of mercury in various forms for average population.
Source: WHO (2003, 2005). 4.4 Measurement of mercury exposureHuman mercury load can be measured by the content of mercury in blood, hair or urine. The blood-mercury level is a good indicator for recent exposure, since the half-life of mercury in blood is 3 days. Mercury in hair is a good indicator for long-term or historical (previous) exposure to mercury. In 1979 blood samples from 264 Danes – selected randomly among the Danish population – were analysed for mercury. Average concentration amounted to 1.5 μg Hg/L, and the highest concentration was 13 μg Hg/L. A slightly lower number of people had taken hair samples and here the average concentration amounted to 0.6 ppm Hg with a maximum of 3.1 ppm Hg. There was a clear correlation between contents in blood and hair (Bach, 1980). Intake of mercury contaminated fish may result in 5-10 times higher mercury concentrations in blood and hair than in the general population. Among residents from the Faroe Islands and Greenland, with a particularly large intake of fish and marine mammal, mercury in blood may even be more than 50 times higher than the background level (Grandjean et al., 1997). In the Bach (1980) study, mercury was not measured in urine, but other studies have shown that non-exposed persons excrete less than 0.5 μg Hg/L corresponding to around 1.5 μg Hg/g creatinine. Persons with amalgam fillings excrete slightly more - 2-4 μg Hg/L (ATSDR, 1999). Occupational mercury exposure can also be significant. Workers with a long-term exposure to mercury vapours had an average concentration of 10 μg Hg/L blood, while non-exposed persons only had 6.5 μg Hg/L in their blood. In urine concentrations were 11 and 2.3 μg Hg/g creatinine respectively. A significant correlation was seen between values in blood and urine and values in air and urine for these exposures (Berlin, 1977). The correlation between mercury in air and blood and between mercury in air and urine does not appear for ordinary people for whom the major part of mercury intake is in the form of methyl mercury in food. 4.5 Mercury toxicityIn most ordinary population studies for clarification of the health hazards of mercury, exposure to methyl mercury through food plays a predominant role. Therefore, it is difficult to determine the impact of an additional exposure to mercury vapours, unless that is very substantial, such as the levels occurring in the working environment in the past. An experimental study (Berlin, 1977) showed no observable effects in studies with dogs exposed to 0.1 mg Hg/m³ for 7 hours per day for 5 days per week for 83 weeks. This experimental no-observed-adverse-effect-level (NOAEL) of 0.1 mg Hg/m³ (100 µg/m³), however, did not take into account neurophysiological and psychological effects. Most data on health effects are derived from occupational exposures. At very high exposure levels for mercury vapours in the working environment the lungs are the target organs. These very high exposures cause irritation and corrosion of the respiratory tract, and after a few hours’ exposure to 1-3 mg Hg/m³ (1000-3000 µg/m³) acute fatal chemical pneumonia may occur (Milne et al., 1970, quoted from Berlin, 1977). Corresponding exposure of test animals for 8 hours daily for some months was also fatal (WHO, 1980). At prolonged high exposure to mercury vapours (>100 µg/m³ or > 0.1 mg/m³) the critical organ is the central nervous system where poisoning symptoms can occur such as tremor, insomnia, depression, mental unbalance, irritability, amnesia, abnormal shyness and gingivitis (Berlin, 1977, WHO, 1980). Slightly toxic effects in humans are to be expected from exposures corresponding to levels of 50 μg Hg/L of blood or 150 μg Hg/L of urine (Holmes et al., 2009). This probably corresponds to 0.025-0.050 mg/m³ (25-50 µg Hg/m³). Therefore a value of 0.025 mg/m³ (25 µg Hg/m³) is often used as the lowest-observed-adverse-effect level (LOAEL value). For long-term exposure to mercury vapour LOAEL has been determined at 0.014 mg/m³ (14 µg/m³). The effect was subtle neurological changes in the central nervous system and poor control of movements (Richardson et al., 2009). Exposure to mercury vapour is particularly risky for pregnant women since mercury vapours can penetrate the placental barrier and harm the unborn child. A study is available of a pregnant woman exposed for a long period of time to mercury vapours (0.020-0.060 mg Hg/m³ (20-60 µg Hg/m³)) from mercury spilled on a carpet in her home. She had no poisoning symptoms but the mercury level in urine was elevated (230 µg/L). The child was also born with elevated mercury levels, but an examination at the age of 2 showed normalised levels (Caravati et al., 2008). The no-effect-level (NOAEL) at long-term exposure has been estimated at 0.01 mg Hg/m³ (10 µg/m³) (Berlin, 1977). No information is available about the no-effect-level of mercury for short-term exposure of humans (Groth, 2008; TNO, 2008), but NIOSH states that there is immediate danger to life and health at exposure to 10 mg/m³ (10,000 µg/m³) – a value, which is relatively close to the saturated concentration at 20 oC of 14 mg/m³. A poisoning case has been described in the USA from exposure to mercury released from broken straight fluorescent lamps at a waste site near a nursery (Tunnessen et al., 1987). A child of 2 yrs acquired the mercury disease ”acrodynia”, which manifests itself, among other things, by strong pain, weight loss and skin changes such as blush and peeling. The entire family of five had elevated mercury levels in urine, with the mother showing the highest level, but only the 2 year old child - having the second highest concentration - acquired the disease. This may be because a child of that age plays near the ground and is more sensitive, but there are also indications that some people are genetically more sensitive to the harmful effects of mercury. 4.6 Limit valuesIn February 2010 FAO/WHO set a provisional tolerable weekly intake (PTWI) of inorganic mercury of 4 μg Hg/kg body weight (WHO 2010). This value replaces an older (1978) PTWI for total mercury of 5 μg Hg/kg body weight. The new PTWI for inorganic mercury is assessed to be useful for intake of mercury through other food than fish and shellfish. For fish and shellfish the PTWI from 2003 for methyl-mercury of 1.6 μg Hg/kg body weight still applies, corresponding to 0.23 μg Hg/kg body weight/day. FAO/WHO also assessed that the upper estimated limit for the average weekly intake of total mercury from food other than fish and shellfish of 1 µg/kg body weight for adults and 4 µg/kg body weight for children was below the new PTWI for inorganic mercury. The occupational threshold limit value (time-weighed average) for long-term exposure to metallic mercury and inorganic compounds is 0.025 mg Hg/m³ (25 µg Hg/m³) (AT, 2007). Present biological occupational limit values (BEI) are 35 μg Hg/g creatinine for urine before work and 15 μg Hg/L blood after work. For short-term exposure a limit value of 0.5 mg/m³ (500 µg/m³) has been recommended by WHO (WHO, 1980). Regarding harmful effects of long-term exposure to methyl mercury from marine food chains Danish-Faroese studies of Faroese children exposed, among others, for mercury in the embryonic stage, have been very important (Grandjean et al., 1997). Based on these studies USEPA recommended in 2001 a Reference Dose (RfD) for methyl mercury of 0.1 μg/kg/day (USEPA MeHg, 2009), or five times below a previous WHO threshold value for methyl mercury. Biomarkers in the Faroese study were mercury concentration in umbilical cord blood and the mother’s hair. The lowest concentration of methyl mercury in a mother’s hair, where statistically significant negative effects on the development of the central nervous system were observable in Faroese children, was 15 ppm. USEPA has set a Reference concentration (RfC) for mercury vapours of 0.0003 mg/m³ (0,3 µg/m³) (USEPA Hg, 2009). This value is based on (un)certainty factors (a total of 30) and a LOAEL of 0.025 mg Hg/m³ (25 µg Hg/m³) in the working environment during a normal workday/week. This LOAEL corresponds to the Danish occupational threshold limit value mentioned above. Corrected for long-term exposure[8] (from working environment to normal population) the LOAEL becomes 0.009 mg Hg/m³ (9 µg Hg/m³). These values are based on adverse effects such as tremor and memory loss. Agency for Toxic Substances Disease Registry (ATSDR) set in 1999 a minimum risk level (MRL) of 0.0002 mg Hg/m³ (0,2 µg Hg/m³). In addition, TSDR has recommended concentration limits after cleaning and spillage indoors (ATSDR, 1999). In 2005 EPA in California established a long-term Reference Exposure Level (REL) of 0.00003 mg Hg/m³ (0.03 µg Hg/m³) on the basis of a LOAEL of 0.025 mg Hg/m³ (25 µg Hg/m³) in the working environment (OEHHA, 2008). An adjustment to normal population exposure gave a LOAEL of 0.009 mg Hg/m³ (9 µg Hg/m³) (corresponds to USEPA above). This was converted to REL by using larger (un)certainty factors than those used by USEPA:
CalEPA has furthermore set a limit value of 0.0018 mg/m³ (1.8 µg/m³) for an exposure of one hour (Groth, 2008). A new Canadian assessment assumes a LOAEL value of 0.006 mg Hg/m³ (6 µg Hg/m³). With an (un)certainty factor of 100 for uncertainty and modifying factors the result is a REL of 0.00006 mg Hg/m³ (0,06 µg Hg/m³) (Richardson et al., 2009). A summary of information about limit values long-term mercury exposure is given in Table 4-2. Table 4-2 Limit values etc. for mercury exposure (Caravati et al., 2008; Richardson et al., 2009 a.o.).
IDLH = Immediately Dangerous to Life and Health. Represents maximum concentration for a substance for which you can avoid irreversible effects after 30 minutes’ exposure PEL = Permissible Exposure Limit determined by OSHA (US Occupational Safety and Health Administration). TWA = Time-weighed average concentration, limit value proposal from US National Institute for Occupational Safety and Health NIOSH. TLV = Threshold Limit Value is an occupational threshold limit value proposed by American Conference of Governmental Industrial Hygienists (ACGIH) GV = Limit value, Danish limit value for occupational health from the Danish Working Environment Authority RfC = Reference Concentration, developed by USEPA MRL = Minimum Risk Level, determined by ATSDR, Agency for Toxic Substances Disease Registry 4.7 SummaryUnder normal pressure and temperature mercury is a liquid metal that appear as a heavy, odour-free silvery liquid with a relatively high vapour pressure. Mercury vapours, which are seven times heavier than air, will disperse along the floor of a room with insufficient ventilation. At inhalation of mercury vapours about 80 % will be absorbed through the lungs, while the absorption of the sparingly soluble and inert metallic mercury through the skin is < 2 %, and the absorption in the gastrointestinal tract is < 0.01 %. In the general population the largest source of mercury is through intake by food especially fish. Daily average intake from food has been estimated at 2-3 μg of mercury, and almost exclusively in the form of methyl mercury. Among the population of the Faroe Islands and Greenland, who have a particularly high intake of fish and marine mammal, mercury in the blood can be more than 50 times higher than background loads. Similarly, people in particularly exposed jobs may have 10 times more mercury in their blood. Background exposure to mercury can also occur from dental amalgam, and WHO has assessed this to be between 1.2 and 27 μg mercury/day, but with limited absorption in the gastrointestinal tract (see Table 4-2). Mercury vapours are different from inorganic mercury compounds by readily penetrating the blood-brain and placental barriers, which may cause effects on the central nervous system and the unborn child. In the brain metallic mercury, like methyl mercury, is transformed to inorganic mercury (Hg²+). The biological half-life of mercury in the body after exposure to mercury vapours is 35-90 days. Retention time in the brain is, however, somewhat longer. Metallic mercury can be excreted with sweat and saliva and through exhalation. After oxidation into inorganic mercury it may be secreted with the urine through the kidneys. Excess mercury in the body is accumulated particularly in the kidneys. Mercury exposure of humans can be measured by analysing the content of mercury in blood, hair or urine. Average concentration of mercury in the blood of Danes was determined 30 years ago at 1.5 μg Hg/L, and the corresponding concentration in hair was 0.6 ppm Hg. There was a signifikant correlation between contents in blood and hair. Measurement of mercury in urine for non-exposed persons has shown that they excrete less than 0.5 μg Hg/L urine corresponding to around 1.5 μg Hg/g creatinine. People with amalgam fillings excrete slightly more (2-4 μg Hg/L) and people in particularly exposed jobs may have a ten times’ higher excretion. Most data on health effects from mercury vapours derive from occupational exposure. At very high exposures to mercury vapours in the working environment the lungs are the target organ. The respiratory tract is irritated and corroded, and after a few hours’ exposure fatal acute chemical pneumonia may occur. At an exposure to 10 mg Hg/m³ (10,000 µg Hg/m³) there is acute mortal danger. No information is available about no-effect-level of mercury in short-term exposure of humans. At prolonged high exposure to mercury vapours (>100 µg/m³ or > 0.1 mg/m³) the critical organ is the central nervous system, where poisoning symptoms such as tremor, insomnia, depression etc. may occur. Exposure to mercury vapour is particularly risky for pregnant women since mercury vapours can penetrate the placental barrier and harm the unborn child. At lower concentrations slightly toxic effects (e.g. hand tremors and memory loss) in humans are to be expected after long-term exposure to 0.025-0.050 mg Hg/m³ (25-50 µg Hg/m³). This 0.025 mg Hg/m³ (25 µg Hg/m³) level, which is identical to the present occupational threshold limit value, is often used as the LOAEL value. However, a recent study states a LOAEL of 0.014 mg Hg/m³ (14 µg Hg/m³) for prolonged exposure to mercury vapours; subtle neurologic changes of the central nervous system and poor control of movements have been described. Furthermore, 0.010 mg Hg/m³ (10 µg Hg/m³) has been proposed as NOAEL at long-term exposure. FAO/WHO has recommended a provisional tolerable weekly intake (PTWI) for inorganic mercury of 4 μg Hg/kg body weight/week and 1.6 μg Hg/kg body weight/week for methyl mercury. In comparison, daily average intake of methyl mercury is 2-3 μg Hg/day (corresponding to 0.2 – 0.3 μg Hg/kg body weight/week). A LOAEL of 0.025 mg Hg/m³ (25 µg/m³) has been established in the working environment for a normal workday/week. Corrected for permanent exposure[9] (from working environment to normal population) the LOAEL became 0.009 mg Hg/m³ (9 µg Hg/m³). This value has been used by USEPA (together with a certainty factor of 30 for particular sensitivity for children, variation between individuals and for sensitivity of nervous system under development) to set a reference concentration (RfC) for mercury vapours of 0.0003 mg/m³ (0.3 µg/m³). CalEPA used a further certainty factor of 10 since the basis was a LOAEL, not a NOAEL, and arrived at a long-term limit value of 0.00003 mg Hg/m³ or 0.03 µg Hg/m³. CalEPA has furthermore set a limit value of 0.0018 mg/m³ or 1.8 µg Hg/m³ for a one hour exposure. Agency for Toxic Substances Disease Registry (ATSDR) has set a minimum risk level (MRL) of 0.0002 mg Hg/m³ (0.2 µg Hg/m³) and recommends concentration limits after cleaning outdoors and spillage indoors of 0.03 and 0.001 mg Hg/m³ respectively (i.e. 30 and 1 µg Hg/m³ respectively). A Canadian assessment uses a LOAEL value of 0.006 mg Hg/m³ (6 µg Hg/m³) and a certainty factor of 100, setting a long-term exposure limit of 0.00006 mg Hg/m³ (0.006 µg Hg/m³). [8] I.e. multiplied by a factor 5/7 to take into account all seven days of the week and not only five workdays, and a factor 10/20 to take into account a respiratory volume of 10 m³ for a workday and 20 m³ for 24 hours. [9] I.e. multiplied by a factor 5/7 to take into account all seven days of the week and not only five workdays, and a factor 10/20 to take into account a respiratory volume of 10 m³ for a workday and 20 m³ for 24 hours.
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