Environ. Sci. Technol. 2000, 34, 3885-3889
Video Display Units: An Emission Source of the Contact Allergenic Flame Retardant Triphenyl Phosphate in the Indoor Environment HÅKAN CARLSSON, ULRIKA NILSSON, AND CONNY O ¨ STMAN* Department of Analytical Chemistry, Stockholm University, 106 91 Stockholm, Sweden
Triphenyl phosphate, an additive flame retardant with documented contact allergenic effects on humans, was identified in a computerized indoor office environment. The source of emission was found to be the computer video display units (VDUs). Eighteen VDUs were examined, and the outer covers were shown to contain triphenyl phosphate in levels up to 10% (w/w). When using this type of PC equipment with a brand-new VDU in a small office room, the air concentration of triphenyl phosphate raised to near 100 ng/ m3 after 1 day of operation. The measurements were performed in the breathing zone of an imaginary operator sitting in front of the computer. After 1 week of continuous operation, the concentration of triphenyl phosphate was reduced by half. Furthermore, a decrease to approximately 10 ng/m3 could be observed after 183 days, which corresponds to more than 2 yr of ordinary business hour operation.
Introduction Organophosphate esters, i.e., arylated, alkylated, or chloroalkylated phosphate esters whose general structure is shown in Figure 1, are used on a large scale in the developed countries as flame retarding agents and/or plasticizers in a variety of products. Plastic materials, rubbers, varnishes, lubricants, hydraulic fluids, electronic goods, such as TV sets and computers, often contain large quantities of added organophosphate esters. These additive flame retardant compounds are not covalently bound to the materials they are to protect. They are just mixed or dissolved in, for instance, the plastic polymer making up the outer cover of a computer VDU. Depending on its vapor pressure, the additive flame retardant may migrate out from the material and into the surrounding air. Organophosphate esters have been detected in indoor air (1-4). We have previously identified nine compounds of this class in common indoor environments, i.e., in school buildings, in a day care center, and in an office building (5). The compounds were found to originate from sources in the indoor environment. A wide range of biological effects of organophosphate esters has been reported (6-15). Triphenyl phosphate is widely used as a plasticizer and flame retardant in electronic equipment. This compound is a potent inhibitor of human * Corresponding author phone: +46 8 674 71 96; fax: +46 8 15 63 91; e-mail:
[email protected]. 10.1021/es990768n CCC: $19.00 Published on Web 08/18/2000
2000 American Chemical Society
FIGURE 1. General structure of organophosphate esters. R1-R3 are either similar or different arylated, alkylated, or chloro-alkylated substituents. blood monocyte carboxylesterase (16) and has shown hemolytic toxicity (17). Furthermore, it has been demonstrated to cause contact dermatitis in humans (18-20). In the developed countries, computers can nowadays be considered as basic equipment in a common occupational office environment. Thus, if computers contain and thereby emit organophosphate esters into the surrounding air, a large part of the population is consequently exposed to these compounds. In the present study, our aim was to investigate occupational related computerized environments with respect to the occurrence and emission of commonly used flame retardants and/or plasticizers.
Experimental Section Chemicals. Methanol (analytical grade, Merck, Darmstadt, Germany) was used without further purification, while acetone and dichloromethane were distilled in an all-glass apparatus prior to use. Triethyl, tri(n-propyl), tri(n-butyl), tri(2-chloroethyl), methyl diphenyl, triphenyl, tri(2-butoxyethyl), triethyl hexyl, and tritolyl phosphate were purchased from Aldrich Chemicals, Germany. Akzo Nobel, Sweden, kindly provided tri(chloropropyl) phosphate. A solution containing all 10 organophosphate esters was used as the external standard. Methyl diphenyl phosphate was used as an internal surrogate standard and was added to the samples prior to the extraction procedure. Prior to GC analysis tri(n-propyl) phosphate was added as an internal volumetric standard. All reference substances were of analytical grade (>98%), except for methyl diphenyl phosphate, which was of technical grade (80%). This chemical contained triphenyl phosphate as one of the impurities. By using semipreparative HPLC with an octadecylsilica column, it was possible to separate pure methyl diphenyl phosphate (99%) from the impurities. FTIR was used to ascertain that the obtained purified compound did not contain water. Cleaning Procedures. Our previous investigations have indicated that organophosphate esters are ubiquitous indoor air pollutants. We have also observed that all kind of laboratory utensils can be contaminated with organophosphate esters. Thus, before use, all glassware was soaked in a solution of 5% (w/w) sodium hydroxide in ethanol for at least 12 h and then extensively rinsed with water, ethanol, and finally acetone. The glass fiber filters were ultrasonicated for 20 min in methanol, acetone, and dichloromethane, respectively. The PUFs were first boiled in water for 4 h in order to eliminate compounds containing nitrogen, such as isocyanates. They were then washed with water, acetone, and dichloromethane and finally Soxhlet-extracted for 12 h in dichloromethane (5). Sampling, Extraction, and Analysis. Two studies were performed in indoor office environments, i.e., an intitial pilot VOL. 34, NO. 18, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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short-term emission study and a subsequent long-term emission study. In both cases, a personal exposure measurement equipment was used. Sampling Equipment. The sampler holder was made of anodized aluminum and equipped with a filter and two adsorbents in series (21). A 25-mm binder-free A/E borosilicate glass fiber filter (Gelman Sciences Inc., Ann Arbor, MI) was used to trap the particulate material. The adsorbents consisted of 15 × 15 mm cylindrical polyurethane foam (PUF) plugs (Specialplast AB, Gillinge, Sweden) and were used for collection of semivolatile compounds. The last PUF adsorbent was utilized as a marker of sampler break-through. Air was pumped through the sampler using a battery-operated personal sampler pump (224-PCXR7, SKC Inc., Eighty Four, PA). The flow rate was set to 3.0 L/min, and samples were collected for 700 min, yielding a total sampled air volume of 2.1 m3. Extraction of Air Samples. Prior to extraction of the air samples, methyl diphenyl phosphate was added to the filters and to the PUF adsorbents as an internal surrogate standard. Extraction was performed during 20 min in 5 mL of dichloromethane by use of a Bransonic 220 ultrasonic bath, with an output power of 50 W and a frequency of 48 kHz. The extraction was repeated once with fresh solvent. For all organophosphate esters studied, recoveries were higher than 95% (5). Extraction of Samples from Computer Equipment. VDU outer covers of 18 different computer equipments were analyzed with respect to organophosphate esters. Also the main unit outer cover and printed circuit board of the computer equipment used for the long-term study were analyzed. A piece of plastic material was taken from each component. By the aid of ultrasonication in dichloromethane, 5 mg of the material was extracted. Exhaustive extraction was performed, i.e., the procedure was repeated until no more material with NPD response could be obtained. The extracts were combined, and the internal surrogate standard was added. To determine the precision of the method, the analysis was repeated with five different plastic samples from one of the VDU units. The relative standard deviation was found to be less than 2%. After extraction, the air samples as well as the plastic samples from the PC components were filtered through a glass wool wad plugged in a Pasteur pipet. After filtration, the samples were evaporated at room temperature using a gentle stream of nitrogen. Tri(n-propyl) phosphate was added to the samples as an internal volumetric standard prior to GC analysis. GC-MS analysis was applied to ascertain the identity of the detected organophosphate esters. Pilot Short-Term Emission Study. An office module with an area of 21.4 m2 and a height of 2.7 m was used. It was fully enclosed with direct ventilation having both the inlet and outlet located in the room. The ventilation air flow was 201 m3/h yielding an air exchange rate in the room of 3.5 air changes/h. It was furnished with two desks, a table, six chairs, three bookcases, and three filing cabinets. Furthermore, it contained two old PC computers that had been used for more than 3 yr, a laser printer, and a telephone. A brandnew computer, consisting of a computer main unit, a VDU, a keyboard, and a mouse, was installed in the office. The plastic material in the VDU outer cover of this computer setup contained 8% (w/w) of triphenyl phosphate. Stationary air sampling was performed using the personal sampling equipment described above. Two samplers were placed in the middle of the room at a distance of 1.0 m from the computer and at a height of 1.0 m above the floor. The door was closed throughout the whole emission study. Long-Term Emission Study. In this case a smaller office module with an area of 9.6 m2 and a height of 2.7 m was used. This was also a fully enclosed room with direct 3886
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ventilation having both the ventilation inlet and outlet located in the room. During the whole emission study the door was closed, and the air exchange rate was 3.5 air changes/h as calculated from a ventilation air flow of 92 m3/h. The room was furnished with a chair, a desk, two bookcases, a filing cabinet, and a cupboard. All electronic equipment was removed from the room 8 weeks prior to the start of the emission measurements. A brand-new computer system consisting of a computer main unit, a VDU, a keyboard, and a mouse was installed in the office. All parts were placed side by side on a desk in front of an imaginary operator as in a normal operating situation. The plastic material in the VDU outer cover had a concentration of 10% triphenyl phosphate. Samples were collected at a distance of 0.50 m from the VDU in the breathing zone of an imaginary operator sitting in front of the computer. The sampling equipment described above was used. Before being switched on, the equipment was left standing in the room for 2 days, and samples were collected each day. After the inital 2 days, the computer equipment was switched on. The top of the VDU outer cover reached a temperature of 50 °C, while the central unit outer cover obtained ambient temperature, i.e., approximately 20 °C. The computer was then kept in continuous operation mode for 183 days. Instrumentation. GC-NPD. Quantitative GC analysis was performed using a Varian 3400 (Varian, Walnut Creek, CA) gas chromatograph equipped with a DB-5 column (J&W, 30m × 0.25 mm, 0.1 µm thickness of stationary phase), a nitrogenphosphorus detector (NPD) and a split/splitless injector. Nitrogen was used as carrier gas. The injector was kept at a temperature of 300 °C, with the split valve closed for 2 min during injection. Temperature programming of the GC oven was as follows: 35 °C for 2 min, followed by a linear temperature increase of 7 °C/min up to 300 °C. A PC computer-based laboratory data system (ELDS Win Pro, Chromatography Data System AB, Sweden) was used for registering, storing, and processing the detector signals. GC-MS. The gas chromatography-mass spectrometry (GC-MS) system consisted of a Varian 3400 GC and a Finnigan Incos 50 quadrupole mass spectrometer. The GC was equipped with a DB-5 column (equal to that used for the GC-NPD analyses), and helium was used as the carrier gas. Injections were made using a Varian septum-equipped programmable injector (SPI) and on-column technique. Temperature programming of the GC oven was the same as for the GC-NPD system. During injection, the injector temperature was held at 35 °C for 1 min and then programmed up to 295 °C with a rate of 180 °C/min. The temperature of the transfer line between the GC and the mass spectrometer was held at 310 °C. Analyses were made in electron ionization mode (EI) with an electron energy of 70 eV and a scan cycle from 35 to 500 Th in 1 s.
Results A total of 18 brand-new computer VDUs of 7 different models obtained from a large international manufacturing company was investigated with respect to their content of organophosphate esters. Triphenyl phosphate was identified as a component in the plastic material in 10 of the investigated VDU outer covers. This was the only compound in any of the VDU outer covers that exhibited a response using the NP detector. The concentrations of triphenyl phosphate in the outer cover of the VDUs were estimated to 8-10% (w/w) in four VDUs and 0.3-0.5% (w/w) in six VDUs. In the remaining eight VDUs, the concentrations were less than 0.02%. The concentration of triphenyl phosphate in the outer cover was shown to be related to the model of the VDU, i.e., the country in which the VDU had been manufactured. Both chassis and printed circuit board of the computer that was used for the long-term emission study were
investigated. The plastic material of the computer chassis was shown to contain a number of compounds exhibiting nitrogen and/or phosphorus response using the NP detector. However, none of these compounds were identified as organophosphate esters, neither were they detected in the air during the measurements. Analysis of the plastic from the computer printed circuit board revealed no significant NPD responses. Short-Term Pilot Emission Study. A computer was set up in an office described in the Experimental Section. Prior to installation of the brand-new computer, the concentration level of triphenyl phosphate in the air of the office was measured. The concentration was found to be 0.7 ng/m3 (CV ) 22%, n ) 3). After this measurement, the computer was installed in the room and switched on. It was left in continuous operation mode for 8 days. Two to four samples were collected simultaneously each day and analyzed with respect to triphenyl phosphate. The measurements showed that after 1 day of operation the air concentration of triphenyl phosphate in the office had increased from the background level up to 82 ng/m3 (CV ) 8%, n ) 4). After 8 days of continuous operation, the concentration in the air had decreased to 39 ng/m3 (n ) 2). This corresponds to 48% of the concentration obtained during the first day of operation. The result from this short-term pilot study clearly indicated that triphenyl phosphate was emitted from the VDU and that the air concentration, and thus the emission from the VDU, was declining with time. This initiated a longterm study of a single computer setup with a brand-new VDU in order to simulate the exposure of an operator to triphenyl phosphate and to further investigate the decline in emission during operation. Long-Term Emission Study. Organophosphate Esters in an Office without a Computer. To establish the back-ground levels of airborne organophosphate esters, air monitoring was performed in the office module used for the long-term emission study prior to installing the computer. Samples were collected during four consecutive days, with two samples collected simultaneously at each occasion with the sampler located at the same spot in the room as in the following measurements described below with the computer installed. More than 99% of the organophosphate material recovered from the sampler were present on the filter. Identification using mass spectrometry and reference substances showed that an isomer of tributyl phosphate with unknown structure, tri(n-butyl) phosphate, tri(2-chloroethyl) phosphate, three isomers of tri(chloropropyl) phosphate, triphenyl phosphate, and tri(2-butoxyethyl) phosphate were present in the office air. The concentration of triphenyl phosphate, the only organophosphate ester detected in the VDU outer covers, was 0.7 ng/m3 (n ) 8, CV ) 32%). The concentrations of the identified alkylated and chloro-alkylated phosphates are presented in Table 1. The most abundant compounds were the two tributyl phosphates with concentration levels of 10 and 17 ng/m3, respectively. Another five offices in the same hallway were also investigated with respect to organophosphate esters during the same time period. Computers with an operating age of more than three years were present in all of these rooms. They were switched off at least 1 day prior to measurement. The same background of organophosphate esters with similar concentrations was detected in these five rooms. Organophosphate Esters in an Office Containing a Computer. A computer with a VDU outer cover determined to contain 10% of triphenyl phosphate was installed in the office after the background level investigation was completed. When the equipment was left standing in the room for 2 days without being switched on, no significant difference in the concentrations of the identified organophosphates was observed in comparison to the background levels.
TABLE 1. Background Levels (in ng/m3) of Airborne Alkylated and Chloro-alkylated Organophosphate Esters in Investigated Office Rooma compound
concnb
CVc (%)
tributyl phosphate tri(n-butyl) phosphate tri(2-chloroethyl) phosphate tri(chloropropyl) phosphate:1 tri(chloropropyl) phosphate:2 tri(chloropropyl) phosphate:3 tri(2-butoxyethyl) phosphate
17 10 7.4 7.0 2.0 0.2 det.d
16 12 8 10 13 16
a The compunds were shown not to originate from the computer, i.e., the concentrations did not significantly vary over time during the 183 days of investigation. b Each value is the mean of eight measurements. c CV ) Coefficient of variation d det. )
