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Related Information: Chemical Sampling -
||0.2 mg/m3 ACGIH TLV. There is no OSHA PEL for methyl parathion.
||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
|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):
|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
1. General Discussion
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
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.
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.
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)
||0.5 mm Hg at 20°C
||white, crystalline solid
||practically insoluble in water soluble
in most organic solvents
||Azophos, Cekumethion, devithion,
dimethyl parathion, Folidol M, Metacide, metafos, Parton M,
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
2.1.1 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.
3. Analytical procedure
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.
2.4 Extraction efficiency
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.
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.
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
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
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
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.
3.2.1 Hydrogen, air, oxygen, and nitrogen, GC grade.
3.3 Standard preparation
3.2.2 Toluene, Pesticide grade.
3.2.3 Methyl parathion, 99.9% pure (EPA).
Stock standard solutions are prepared by adding toluene to preweighed amounts of methyl parathion. Working range standard solutions are
prepared by diluting stock solutions with toluene. Stock and dilute standards are stored in a freezer.
3.4 Sample 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.
3.5.1 GC conditions
|Initial column temperature:
|Temperature program rate:
|Final column temperature:
|Nitrogen flow rate:
|Initial hold time:
|Final hold time:
||30 meter × 0.53 mm i.d. DB-210 Megabore,
1.0 µm thick film
|Hydrogen flow rate:
|Oxygen flow rate:
|Air flow rate:
3.5.2 Chromatogram (See Figure 2)
4. Recommendations for further study
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.
3.7.1 A calibration curve is constructed by plotting detector response
versus standard concentration.
3.8 Safety precautions
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
3.7.3 The air concentration is then determined by the following
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.
This method should be fully validated.
5.1 Burright, D., Method #62, "Clorpyrifos, DDVP, Diazinon,
Malathion, and Parathion", OSHA Analytical Laboratory, unpublished,
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.,
5.6 "Chemical Information File", U.S. Department of Labor,
Occupational Safety and Health Administration, Directorate of Technical
Support, June 14, 1985.