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METHYL PARATHION |
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| Method no.: | PV2112 |
| Control no.: | T-PV2112-01-8707-CH |
| Matrix: | Air |
| Target Concentration: | 0.2 mg/m3 ACGIH TLV. There is no OSHA PEL for methyl parathion. |
| Procedure: | Samples are collected by drawing known volumes of air through OSHA versatile sampler (OVS-2) tubes, containing a glass fiber filter and two sections of XAD-2 adsorbent. Samples are extracted with toluene and analyzed by gas chromatography (GC) using a flame photometric detector (FPD). |
| Recommended air volume and sampling rate: | 480 L and 1.0 L/min |
| Detection limit of the overall procedure (based on the recommended air volume): | 0.0015 mg/m3 |
| Status of method: | Stopgap method. This method has been only partially evaluated and is presented for information and trial use. |
| Date: July, 1987 |
Chemist: David B. Armitage |
Carcinogen and Pesticide Branch
OSHA Analytical
Laboratory
Salt Lake City, Utah
1. General Discussion
1.1 Background
1.1.1 History of procedure
This evaluation was undertaken to determine the effectiveness of the OVS-2 sampling tube as a sampling device for methyl parathion. It follows the procedure developed for several other organophosphorus pesticides. (Ref. 5.1)
It should be noted that in this evaluation for methyl parathion several other analytes were also present in the analytical procedure. These other analytes are not mentioned in this evaluation, but can be seen on the sample chromatogram.
1.1.2 Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy).
Organophosphorus pesticides act as irreversible inhibitors of cholinesterase, thereby allowing the accumulation of large amounts of acetylcholine. When a critical level of cholinesterase depletion is reached, usually about 20% of normal, symptoms and signs of acetylcholine accumulation poisoning become manifest. (Ref. 5.2)
These symptoms may include blurred vision, weakness, nausea, headache, abdominal cramps, chest discomfort, and diarrhea. Signs may include miosis, muscle twiching, salivation, sweating, tearing, cyanosis, convulsions, and coma. (Ref. 5.2)
Besides being absorbed following inhalation or ingestion, organophosphorus pesticides are readily abosrbed through the intact skin. (Ref. 5.2)
The acute oral LD50 of 0-25 mg/kg for male rats is similar to that of parathion (2 mg/kg, both sexes), however, methyl parathion is less toxic to female rats (LD50 of 24 mg/kg). The major difference in toxicity is found in the acute dermal LD50 for rats. It is 67 mg/kg for methyl parathion and 6.4 mg/kg for parathion. (Ref. 5.3)
By analogy to the similar, but more toxic parathion, methyl parathion has been given a TLV of 0.2 mg/m3 by the ACGIH. (Ref. 5.3)
1.1.3 Potential workplace exposure
No estimate of worker exposure to methyl parathion could be found. Methyl parathion is used as an insecticide. (Ref. 5.4)
1.1.4 Physical properties (Refs. 5.3-5.6)
Molecular weight: 263.23 Molecular formula C8H10NO5PS CAS #: 298-00-0 Melting point: 37-38°C Vapor Pressure: 0.5 mm Hg at 20°C Appearance: white, crystalline solid Solubility: practically insoluble in water soluble in most organic solvents Synonyms: Azophos, Cekumethion, devithion, dimethyl parathion, Folidol M, Metacide, metafos, Parton M, Wofatox Chemical name: O,O0-Dimethyl O-p-nitrophenyl phosphorothioate Structure: 1.2 Limit defining parameters
The detection limit of the analytical procedure is 0.5 ng per injection. This is the amount of analyte which will give a peak whose height is approximately five times the baseline noise.
2. Sampling procedure
2.1 Apparatus
2.1.1 Samples are collected by using a personal sampling pump that can be calibrated to within ±5% of the recommended flow rate with the sampling device in line.
2.1.2 Samples are collected with OVS-2 tubes, which are specially made 13-mm o.d. glass tubes that are tampered to 6-mm o.d.. These tubes are packed with a 140-mg backup section and a 270-mg sampling section of cleaned XAD-2. The backup section is retained by two foam plugs and the sampling section is between one foam plug and a 13-mm diameter glass fiber filter. The glass fiber filter is held next to the sampling section by a polytetrafluoroethylene (PTFE) retainer.
2.2 Reagents
No sampling reagents are required.
2.3 Sampling technique
2.3.1 Attach a small end of the OVS-2 sampling tube to the sampling pump with flexible, plastic tubing such that the large, front section of the sampling tube is exposed directly to the atmosphere. Do not place any tubing in front of the sampler. The sampler should be attached vertically (large end down) in the worker's breathing zone in such a manner that is does not impede work performance.
2.3.2 After sampling for the appropriate time, remove the sampling device and seal the tube with plastic enc caps.
2.3.3 Wrap each sample end-to-end with an OSHA seal (Form 21).
2.3.4 With each set of samples, submit at least one blank. The blank should be handled the same as the other samples except that no air is drawn through it.
2.3.5 Bulk samples should be submitted for analysis in a separate container. Do not ship with the air samples.
2.4 Extraction efficiency
Two 13-mm fiber filters were each liquid spiked with 95.91 µg of methyl parathion. The two filters, along with a blank filter, were each placed in separate 4-mL vials which also contained 270 mg of XAD adsorbent. These vials were stored overnight at room temperature, and then extracted with 2 mL of toluene.
The average extraction efficiency for these two filters (with the XAD-2 adsorbent present) was 91%.
2.5 Retention efficiency
Two OVS-2 tubes were each spiked with 95.91 µg of methyl parathion by liquid spiking the 13-mm glass fiber filter. Three hundred fifty liters of humid air were drawn through each tube. The two tubes were then extracted as in Section 3.4. No breakthrough to the backup section was observed.
The average retention efficiency for these two tubes was 91%.
2.6 Sample storage
Two OVS-2 tubes were each spiked with 95.91 µg of methyl parathion as above. Four hundred seventy liters of humid air were drawn through each tube. These two tubes were stored for ten days at ambient temperature in a drawer. They were then extracted as in Section 3.4. No methyl parathion was recovered from the backup section of these tubes.
The average recovery after ten days of storage was 97%.
2.7 Recommended air volume and sampling rate
2.7.1 The recommended air volume is 480 L.
2.7.2 The recommended flow rate is 1.0 L/min.
2.8 Interferences
It is not known if any compounds will interfere with the collection of methyl parathion. Suspected interferences should be reported to the laboratory with submitted samples.
2.9 Safety precautions
2.9.1 Attach the sampling equipment in such a manner that it will not interfere with work performance or employee safety.
2.9.2 Follow all safety practices that apply to the work area being sampled.
3. Analytical procedure
3.1 Apparatus
3.1.1 A GC equipped with an FPD detector operating in the phosphorus mode. A Hewlett-Packard 5730A GC fitted with an FPD was used in this evaluation. Injections were performed using a Hewlett-Packard 7671A automatic sampler.
3.1.2 A GC Column capable of resolving methyl parathion from any interference. A 30-m × 0.53-mm i.d. DB-210 Megabore GC column, 1.0-µm thick film, was used in this evaluation and is available from J&W Scientific, Inc., Rancho Cordova, CA.
3.1.3 An electronic integrator or other suitable means of measuring detector response. A Hewlett-Packard 3357 data system was used in this evaluation.
3.1.4 Vials, 2 and 4-mL glass with PTFE-lined septa.
3.1.5 Volumetric flasks, pipets, and syringes for preparing standards, making dilutions, and performing injections.
3.2 Reagents
3.2.1 Hydrogen, air, oxygen, and nitrogen, GC grade.
3.2.2 Toluene, Pesticide grade.
3.2.3 Methyl parathion, 99.9% pure (EPA).
3.3 Standard preparation
3.4.1 Transfer the 13-mm glass fiber filter and the 270-mg section of the sampling tube to a 4-mL vial. Place the first foam plug and the 140-mg section in a separate vial. A small glass funnel can be used to facilitate the transfer of the adsorbent. Discard the rear foam plug. Do not discard the glass sampling tube; it can be reused after it has been cleaned with surfactant or suitable solvent.
3.4.2 Add 2.0 mL of toluene to each vial.
3.4.3 Seal the vials with PTFE-lined septa and allow them to extract for one hour. The vials should be shaken by hand periodically during the one hour extraction time.
3.5 Analysis
3.5.1 GC conditions
Initial column temperature: 150°C Temperature program rate: 8°C/min Final column temperature: 200°C Injector temperature: 200°C Nitrogen flow rate: 5 mL/min Initial hold time: 0 min Final hold time: 4 min Injection volume: 1.3 µL GC column: 30 meter × 0.53 mm i.d. DB-210 Megabore, 1.0 µm thick film FPD conditions Hydrogen flow rate: 200 mL/min Oxygen flow rate: 60 mL/min Air flow rate: 30 mL/min Detector temperature: 300°C Retention time: 10.1 min 3.5.2 Chromatogram (See Figure 2)
3.6 Interferences
3.6.1 Any compound having a similar retention time to the analyte is a potential interference. Generally, chromatographic conditions can be altered to separate an interference from the analyte.
3.6.2 Retention time on a single column is not proof of chemical identity. Analysis by an alternate GC column, detection by an FPD in the sulfur mode for the sulfur containing pesticides, and confirmation by mass spectrometry are additional means of identification.
3.7 Calculations
3.7.1 A calibration curve is constructed by plotting detector response versus standard concentration.
3.7.2 The concentration of methyl parathion in a sample is determined from the calibration curve. If methyl parathion is found on the backup section, it is added to the amount found on the front section. Blank corrections for each section should be performed before adding the results together.
3.7.3 The air concentration is then determined by the following formula.
3.8 Safety precautions
3.8.1 Avoid exposure to all standards
3.8.2 Avoid exposure to all solvents.
3.8.3 Wear safety glasses at all times.
4. Recommendations for further study
This method should be fully validated.
5. References
5.1 Burright, D., Method #62, "Clorpyrifos, DDVP, Diazinon, Malathion, and Parathion", OSHA Analytical Laboratory, unpublished, 1986.
5.2 "OCCUPATIONAL DISEASES, A Guide to their Recognition", U.S. Department of Health, Education, and Welfare; Public Health Service, Public Health Service Publication No. 1097, U.S. government Printing Office, Washington, D.C., 1964.
5.3 "Documentation of the Threshold Limit Values and Biological Exposure Indices", American Conference of Governmental Industrial Hygienists Inc., fifth edition, 1986.
5.4 "Farm Chemicals Handbook", Meister Publishing Co., 1985.
5.5 Windholz, M., Ed. "Merck Index", 10th ed.; Merck and Co., Rahway, NJ,1983.
5.6 "Chemical Information File", U.S. Department of Labor, Occupational Safety and Health Administration, Directorate of Technical Support, June 14, 1985.
