Risk Analysis for Phenylmercuric Acetate in Indoor Latex House Paint

Chapter 26

Risk Analysis for Phenylmercuric Acetate in Indoor Latex House Paint

Downloaded by NORTH CAROLINA STATE UNIV on October 26, 2012 | http://pubs.acs.org Publication Date: February 18, 1993 | doi: 10.1021/bk-1993-0522.ch026

J. M . Blondell and S. M . Knott Health Effects Division (H7509C), Office of Pesticide Programs, U.S. Environmental Protection Agency, 401 M Street, SW, Washington, DC 20460

Respiratory exposure to elemental mercury vapor, resulting from the use of interior latex paint preserved with mercurial biocides, can pose a potential health hazard to humans, especially children. The review of mercury house paint was initiated after a Michigan child developed acrodynia, a rare form of mercury poisoning. Use of paint containing 200 ppm mercury has been shown to lead to air levels of mercury as high as 200 µg/m during application of the paint. Evidence for the risk of acrodynia was assessed from: case reports where liquid mercury had been spilled; studies involving mercury used in infant medicines and teething powder; and an incident where a mercury fungicide was used on diapers. Evidence from these studies suggested that infants displaying urinary levels above 50 µg mercury/g creatinine were atriskfor acrodynia. 3

Mercury-containing biocides have previously been added to approximately 25 to 30% of interior latex paints (1). The mercury biocide was added at low concentrations (200 ppm or less) to extend the shelf life of stored paints. It could also be added at higher concentrations to formulate a latex paint that would provide a mildew resistant coating. Recent evidence of mercury vaporization following application of indoor latex house paint raised questions about potential health effects. The recent occurrence of a childhood case of mercury-related disease brought to the attention of the U.S. Environmental Protection Agency the need to review potential exposure from previously unsuspected sources and estimate the dose and potential health effects. EPA's review resulted in voluntary cancellations of mercury containing biocides use in latex paints. BRIEF HISTORY OF ACRODYNIA Mercury-containing medicines and teething powders were often prescribed for young children during the first half of this century. During the sametimeperiod, hundreds of children developed a disease called acrodynia (meaning painful extremities) or pink disease (for the characteristic pink coloration of the hands and feet). Case series, with fatality This chapter not subject to U.S. copyright Published 1993 American Chemical Society

In Pesticides in Urban Environments; Racke, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


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PESTICIDES IN URBAN ENVIRONMENTS

rates of 3 to 17 percent, were reported in children in England, Australia, France, Switzerland, and the United States (2-7). Identification of causation was hampered by a delay of weeks or months from onset of exposure to onset of disease. One of the early clues that implicated mercury was the peak incidence in children under 2 years of age in England and Australia, where mercury was used most commonly in teething powder, and peak incidence in children more than 2 years old in France and Switzerland, where the most common source was from worm treatments often prescribed for children aged 3 to 10 (6). The first signs of disease are usually changes in personality, including increased irritability, marked swings in mood, and restlessness (8). The skin of the hands and feet become red or pink starting at the tips of the fingers and toes. The tip of the nose, ears and cheeks may display a similar discoloration. As the disease progresses, the hands and feet become swollen, itchy, and painful. The skin on the palms and soles starts to flake and shed as if sunburned. These symptoms are usually accompanied by heavy sweating, loss of appetite, hypertension, pain in joints, and muscle weakness. As weakness progresses, the muscles loss their tone and the child may be unable to stand or walk. Photophobia is common, the child is less active, cries excessively, and is unable to sleep. In cases that go untreated, there may be loss of nails on fingers and toes and loss of teeth from severe gingivitis. Once the causative connection was made, starting in the late 1940s, use of mercury-containing medicines and teething powders was banned. While appropriate treatment is now available for acrodynia, many of today's physicians would be unfamiliar with the symptomatology and might easily misdiagnose the disease. Modern pediatric texts often omit any discussion of acrodynia. EXPOSURE TO MERCURY FROM THE USE OF LATEX PAINTS The use of mercury-containing fungicides in latex house paints was not suspected of being a significant source of mercury exposure until Shalom Z. Hirschman, M.D., reported a case of acrodynia that coincided with the use of a paint containing phenylmercuric propionate (PMP) (9). Four months before the onset of symptoms, the five-year-old boy had helped his mother with the painting of two rooms in their home. The diagnosis of acrodynia was confirmed by the symptom complex and a measured urinary mercury concentration of 90 pg/L The upper limit of the normal range of urinary mercury excretion is 25 pg/1 (10). The concentration of mercury in the paint used was 0.02% or 0.036% phenylmercuric propionate (9). Ingestion of the paint and inhalation of its vapors were both considered as possible routes of exposure in this case. To estimate exposure, Hirschman et al. (1963) placed a panel, painted with the paint containing mercury, in a sealed jar with an air flow of 1 liter per minute through the jar (9). The mercury concentration of the air exiting the jar at the end of 30 minutes was 170 pg/m or a calculated average emission rate of 0.65 pg/min/ft . After 6 hours, the level fell to 100 pg/m yielding an average emission rate of 0.38 pg/min/ft . The authors concluded that, since it was possible to exceed 100 pg/m while using mercury-containing paints, inhalation exposure could have played a major role in the observed case of acrodynia. These conclusions have been the subject of considerable criticism. The strongest argument against the emphasis on the inhalation exposure is the fact that the acrodynia patient's parents and siblings had no detectable urinary mercury excretions (9). 3

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Risk Analysis for Phenylmercuric Acetate309

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Additional studies of the emission of mercuryfrompreserved latex paints evolved from the Hirschman et al. research and the resulting criticism. In the first of a series of experiments, Taylor formulated his own latex paints at low (0.02% Hg) and high (0.2% Hg) concentrations of phenylmercuric dodecenyl succinate (PMDS) that had been irradiated with neutrons to radiolabel the mercury (11). These paints then were applied to aluminum panels resulting in 200 pg of mercury on panels with the low concentration paint and 1000 pg on the panels with the high. The total loss of mercuryfromeach panel was measured at various time intervals using a Geiger counter. The data were corrected for background, decay of the Hg, and variations in the reference standard. Panels were tested under low and high humidity conditions. Using the emission rate data, Taylor estimated the air level that could be achieved on day 100 after painting under static conditions in a 50.7m room where the walls and ceiling (720 ft ) had been painted. Air concentration levels for the low paint were 16 and 28 pg/m in dry and wet air, respectively. The high mercury concentration paint resulted in levels of 140 and 250 pg/m in dry and wet air, respectively. Taylor concluded that the actual air concentrations that may be achieved during use of paints containing a mercury concentration of 0.02% would not pose a hazard to human health (11). He reached this conclusion because he believed that the scenario he used (i.e., static conditions in a small room) was unrealistic. Also, he believed that the neutron labeling may have resulted in decomposition of the PMDS leading to an unusually high proportion of the more volatile elemental mercury in the experimental paint. However, it may not be appropriate to make such a conclusion using air concentrations achieved on day 100 when other investigations demonstrated that maximum concentrations occur during andrightafter paint application. The information contained in the above described studies is not easily extrapolated to "real world" exposure situations. With this in mind, Jacobs and Goldwater (1965), collected mercury air concentration and human mercury excrétion data under a "real world" exposure scenario (12). In their study, latex paints containing 0.02% mercury (0.036% phenylmercuric acetate (PMA)) were applied by brush and roller to the walls and ceiling of a bedroom. A second room (control room) in the same house was painted concurrently with a mercury free latex paint A Beckman ultraviolet mercury vapor meter and an impinger method were used to assess air concentrations of mercury periodically. During painting, the house was ventilated in the usual manner (i.e., doors and windows open). Immediately after the completion of painting, mercury air concentrations as high as 210 pg/m were recorded. This corresponds to an average emission rate (assuming 1 air exchange per hour occurred in the bedroom) of 0.70 pg/min/ft , a value that compares well with the experimental value of 0.65 pg/min/ft obtained by Hirschman et al. However, 6 hours after the completion of painting, the mercury air concentration had declined to 52 pg/m . Levels of mercury were found in the control room indicating either method interferences or dissipation of mercuryfromother rooms in the house. One painter and one occupant of the house experienced increases in urinary mercury excretion to just above the upper limit of normal(25 pg/1). Due to the flaws in his 1965 study, Taylor conducted additional research in which the radiolabeled mercuric fungicide used (PMA) was manufactured using radioactive mercury ( Hg) (13). This deviation from the previous study avoided the decomposition observed during neutron labeling of the mercury containing biocide. The paints containing the PMA then were applied to glass panels, creating paint film thicknesses of 0.001 or 0.002 inches.


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The painted panels then were subjected to a variety of environmental conditions including: zero humidity, darkness, indoor ambient conditions, sunlight, temperature of 50°C., and outdoor conditions. Among the panels exposed to indoor conditions, those painted with a thin film (0.001 in.) of the low mercury paint (0.02% Hg) experienced an average loss of 61.4% after 236 days or an average emission rate of 0.0029 pg/min./ft. (13). This same group exhibited a mercury loss of approximately 42% after 100 days or an average emission rate over the 100 day period of 0.0046 pg/min./ft. , a level approximately 3timesthat determined in the earlier study using a paint with the same concentration of mercury but containing PMDS instead of PMA. Later study using both PMA and PMDS, under the same conditions, found only a 21% increase of emission from the PMA containing paint compared to the PMDS paint (14). Foote (1972) reported the results of a mercury air concentration survey conducted in homes and offices in the Dallas Texas area (15). Mercury measurements were conducted by passing air through a device that collects elemental mercury vapor on a fine mesh gold screen. The accumulated mercury then was transferred to a second gold screen before proceeding into the beam of a spectrometer for detection. It is believed that the paints used in the homes contained diphenylmercuric dodecenyl succinate. Levels of 0.07 pg/m mercury were detected in one home nearly 4 years after painting had occurred. Another home exhibited levels of around 0.15 pg/m approximately 5 months after painting. In each case, these levels were above that found in the control home (0.01 pg/m ). Additional "real world" monitoring data were collected by Sibbett et al. (16). In this study, mercury air concentrations were analyzed by passing air through a furnace containing a bed of hot (1200°F) cupric oxide to reduce any organic bound mercury to elemental vapor. The mercury vapor formed then was collected on a silver wire grid before being passed to an ultraviolet detector. A 57.8 m room was painted with paint containing 0.0047% mercury (specific compound not identified). One week after painting, mercury air concentrations in the room without ventilation were about 1.5 pg/m . On day 10, an emission of 100 pg/day was calculated. The authors concluded that "sufficient mercury remains (in the painted surface) to sustain this rate for about 7.5 years" (16). The discussion of mercury exposure has, thus far, focused on emissions from painted surfaces and their contributions to mercury air concentrations. The exposure scenario would not be complete without considering, where possible, the fate of the airborne mercury vapor. Spedding and Hamilton (1982) reported their findings in a study designed to measure the capacity of certain household materials to adsorb elemental mercury vapor (17). The study was conducted by placing various household materials in a chamber with approximately 300 pg/m of mercury. After 20 days of exposure, the household materials were analyzed. Of the materials tested, water-based paint films and PVC flooring materials tended to adsorb elemental mercury vapor at a higher rate. These materials may cover a large surface area in a normal home, adsorbing a significant quantity of mercury that may be released into the air later. However, Spedding and Hamilton concluded that, overall, mercury vapor was relatively unreactive toward surfaces. In the studies reviewed above, there is some disagreement about the form in which the airborne mercury is present. Hirschman et al. (1963) concluded that the mercury containing fungicide considered in his research (PMP) "decomposes to inorganic mercury, 2


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Risk Analysis for Phenylmercuric Acetate311

which is volatile" (9). Taylor and Tickle (1969) discussed observations of mercury loss from test panels on the basis of the volatility of the parent organo-mercury compound used (13), There is considerable evidence that the airborne mercury is present as elemental vapor and not as an organic derivative (18). In the paper industry in Sweden (where phenylmercuric compounds are used in the process as a fungicide), Lundgren and Swensson determined that the mercury in the atmosphere of the factory using phenyl-Hg or alkyl-Hg was metallic vapor resulting from decomposition of the organic compound (19). In the exposure studies reviewed above, the mercury vapor detectors used by Hirschman et a l , Jacobs and Gold water, and Foote were designed to measure only elemental mercury vapor. If it is accepted that the airborne mercury is elemental vapor resulting from decomposition of the parent compound in the paint, the next question is: what leads to the decomposition of the parent compound? Zepp et al. reported on the photodecomposition of phenylmercuric compounds by sunlight (20). They proposed that phenylmercuric salts, such as P M A , may dissociate, in the manner described in Figure 1, when dissolved in water. This dissociation could be expected to occur when these compounds are added to latex paints (many of which contain approximately 50% water). These studies indicated that phenylmercuric ion and phenylmercuric hydroxide photoreact to the same extent as the parent compound yielding elemental mercury. Michigan Case Report. In 1989, a four-year-old boy in Michigan was diagnosed as having acrodynia (21). The boy and the other four family members all had elevated mercury urine levels. The only significant source of mercury exposure identified by the Michigan Department of Public Health was from paint applied to the home's interior just 10 days before the onset of the child's illness (22). Measurements conducted three months later of the air inside the home found a level of 1.0 pg/m . Analysis of the paint that was used found it contained 930 ppm mercury in the form of phenylmercuric acetate (PMA). The four-year-old developed most of the typical poisoning symptoms including marked personality change, excessive sweating, itching, hypertension, gingivitis, headaches, insomnia, weakness in the shoulders and hips, inability to walk, and red, swollen palms and soles and tip of nose. The child had stayed with grandparents during the day while the house was being painted. He and his family slept in the house at night with all the windows kept closed and the air conditioning on. The child was hospitalized for four months and received repeated treatment to increase mercury excretion from the body, after which nearly all the symptoms abated and the child could walk again. 3

CDC Investigation. The Centers for Disease Control (CDC) set up an investigation to determine whether persons in other homes using the same type of paint had exposure to mercury (22). Nineteen exposed families were selected with 10 unexposed families. Data collected from each family included a questionnaire, first morning urine samples, indoor air mercury levels, and remaining paint samples. A total of 29 cans of paint were collected from the 19 exposed homes and found to contain a median level of 754 ppm mercury. Air samples taken from all the exposed homes had a median of 1.5 pg/m of mercury, with a range of undetectable to 10 pg/m . No mercury was detected in the air of nine of 10 unexposed homes that were tested. Statistical analysis of the data from exposed homes 3

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Risk Analysis for Phenylmercuric Acetate in Indoor Latex House Paint

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