1.1  Background

1.1.1  History of procedure

This evaluation was undertaken to determine the effectiveness of the OVS-2 tube as a sampling device for coumaphos. It follows the procedure developed for several other organophosphorus pesticides. (Ref. 5.1)

1.1.2  Toxic effects  (This section is for information only and should not be taken as the basis of OSHA policy).

The following paragraph is excerpted from the book OCCUPATIONAL DISEASES, A Guide To Their Recognition. (Ref. 5.2)

The organic phosphorus compounds 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. Symptoms may include blurred vision, weakness, nausea, headache, abdominal cramps, chest discomfort, and diarrhea. Signs may include miosis, muscle twitching, salivation, sweating, tearing, cyanosis, convulsions, and coma.

Besides being absorbed following inhalation or ingestion, organophosphorus pesticides are readily absorbed through the intact skin (Ref. 5.2). When a particular pesticide has a low dermal LD₅₀,  a skin notation,should be added to the TLV or PEL.

Coumaphos has an acute oral LD₅₀ of 13 mg/kg for rats. Its acute dermal LD₅₀ is 850 mg/kg for rats (Ref. 5.3).

Due to these factors an arbitrary target concentration of 0.2 mg/m³, without a skin notation, was chosen for coumaphos.

1.1.3  Potential workplace exposure

No estimate of worker exposure to coumaphos could be found. Coumaphos is used as an insecticide and nematocide. (Ref. 5.4)

Physical properties (Ref. 5.4-5.6)
Molecular weight:	362.78
Molecular formula:	C14H16Cl05PS
CAS#:	56-72-4
IMIS#:	0736
Melting point:	91ºC
Vapor Pressure:	0.000013 Pa (0.0000001 mm Hg) at 25ºC
Appearance:	tan solid
Solubility:	1.5 ppm in water soluble in aromatic solvents somewhat soluble in alchohols and ketones
Synonyms:	Asuntol, Bay 21/199, Baymix, Co-Ral, Diolice, Meldane, Muscatox, Resistox, Umbethion
Chemical name:	0-(3-chloro-4-methyl-7-coumarinyl) 0,0 diethylphosphorothioate
Structure:

1.2  Limit defining parameters

The detection limit of the analytical procedure is 0.035 ng per injection. This is the amount of analyte which will give a peak whose height is approximately five times the baseline noise. This detection limit takes into account the split ratio of 13.4 to 1 used on the capillary GC.

2.1  Apparatus

2.1.1  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  OVS-2 tubes, which are specially made 13-mm o.d. glass tubes that are tapered to 6-mm o.d. They 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 polytetafluoroethylene (PTFE) retainer (See Figure 1.)

2.2  Reagents

No sampling reagents are required.

2.3  Sampling technique

2.3.1  Attach the 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.

2.3.2  Attach the sampler vertically (large end down) in the worker's breathing zone in such a manner that it does not impede work performance.

2.3.3  After sampling for the appropriate time, remove the sampling device and seal the tube with plastic end caps.

2.3.4  Wrap each sample end-to-end with an OSHA seal (Form 21).

2.3.5  Submit at least one blank with each set of samples. Handle the blank the same as the other samples, but do not draw air through it.

2.3.6  Submit any bulk samples in a separate container. Do not ship them with the air samples.

2.4  Desorption efficiency

A glass fiber filter and an amount of XAD-2 adsorbent equal to the sampling section (270 mg) of an OVS-2 tube were placed in each of six 4-mL vials. These vials were then sealed with
PTFE-lined septa.

Five of these vials were then each liquid spiked with 22 µL of a 4.46 mg/mL solution of coumaphos in toluene by injecting through the septum onto the glass fiber filter. After replacing the punctured septa, these vials were allowed to equilibrate overnight in a drawer at room temperature. They were then desorbed with 2.0 mL of toluene containing triphenyl phosphate (TPP) as an internal standard and analyzed as in Section 3.5.

 

Table 2.4 Desorption Study
Vial #	Amount spiked	Amount recovered	% Recovery
EX 1 EX 2 EX 3 EX 4 EX 5 EX 6	98.12 µg 98.12 µg 98.12 µg 98.12 µg 98.12 µg  0.00 µg	84.38 µg 91.35 µg 94.39 µg 92.92 µg 90.66 µg  0.00 µg	86.0 93.1 96.2 94.7 92.4 Blank
Average recovery is 92.5%

2.5  Retention efficiency

Six OVS-2 tubes were each liquid spiked with 22 µL of a 4.46
mg/mL solution of coumaphos in toluene by spiking the glass fiber
filter. These tubes were then sealed with plastic end caps and
stored in a drawer at room temperature. After overnight storage,
480 liters of humid air (approximately 70% relative humidity)
were drawn through each tube. Three of these tubes, along with a
blank tube, were then desorbed and analyzed as in Section 3. No
coumaphos was found on the backup sections of these tubes.

Table 2.5 Retention Efficiency Study
Tube #	Amount spiked	Amount recovered	% Recovery
RET 1 RET 2 RET 3 RET 4	98.12 µg 98.12 µg 98.12 µg 0.00  µg	93.41 µg 99.30 µg 98.22 µg 0.00  µg	95.2 101.2 100.1 Blank
Average recovery is 98.8%

2.6. Sample storage

The remaining three spiked tubes from Section 2.5. (and a blank tube) were stored for a total of 8 days in a drawer at room temperature. They were then desorbed and analyzed as in Section 3. No coumaphos was found in the backup sections of these tubes.

 

Table 2.6. Storage Study
Tube #	Amount spiked	Amount recovered	% Recovery
ST 1 ST 2 ST 3 ST 4	98.12 µg 98.12 µg 98.12 µg 0.00 µg	93.02 µg 94.78 µg 97.92 µg 0.00 µg	94.8 96.6 99.8 Blank
Average recovery is 97.1%

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 (sampling)

It is not known if any compounds will interfere with the collection of coumaphos. Suspected interferences should be reported to the laboratory with submitted samples.

2.9  Safety precautions (sampling)

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.

3.1  Apparatus

3.1.1  A GC equipped with an FPD. A Hewlett-Packard 5890A GC (capillary) equipped with both an FPD operating in the phosphorus mode and a Hewlett-Packard 7673A automatic sampler was used in this evaluation.

3.1.2  A GC column capable of separating coumaphos from any interferences. A 45 m x 0.2 mm i.d. SE-54 capillary column, 0.25 µm thick film, was used in this evaluation and is available from Supelco, Inc., Bellefonte, PA.

3.1.3  An electronic integrator or other suitable means of measuring detector response. A Hewlett-Packard 3392A Integrator and a Hewlett-Packard 3357 data system were used in this evaluation.

3.1.4  Vials, 4-mL and 2-mL glass with PTFE-lined septa.

3.1.5  Volumetric flasks, pipets, and syringes.

3.2  Reagents

3.2.1  Hydrogen, air, and nitrogen, GC grade.

3.2.2  Toluene, Pesticide grade.

3.2.3  Coumaphos. A 98+% pure standard from EPA was used in this evaluation.

3.2.4  Triphenyl phosphate (TPP), practical grade from J.T. Baker. If an internal standard method is used, the desorbing solution is prepared by adding the internal standard to the toluene. A 40 µg/mL solution of TPP was used as the internal standard in this evaluation.

3.3  Standard preparation

Prepare stock standards by adding either toluene or desorbing solution (if an internal standard is used) to preweighed amounts of coumaphos. Prepare working range standards by diluting stock solutions with either toluene or desorbing solution (if an internal standard is used). Store stock and dilute standards in a
freezer.

3.4  Sample preparation

3.4.1  Transfer the 13-mm glass fiber filter and the 270-mg sampling section of the tube to a 4-mL vial. Place the first foam plug and the 140-mg backup 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.

3.4.2  Add 2.0 mL of either toluene or desorbing solution (if an internal standard is used) to each vial.

3.4.3  Seal the vials with PTFE-lined septa and allow them to desorb for one hour. Shake the vials by hand periodically during this time.

3.4.4  If necessary, transfer aliquots of the samples to the vials used in GC analysis. In this evaluation, the samples were transferred to 2-mL glass vials, sealed with PTFE-lined septa and loaded on the automatic sampler.

3.5  Analysis

3.5.1  Analytical conditions (These conditions were developed for a series of organophosphorus pesticides, which was run in several groups. See Figure 2. for the group containing coumaphos.)

 

GC conditions
GC column:	45 m x 0.2 mm i.d. SE-54, 0.25 µm thick film
Carrier gas:	hydrogen
Flow rate:	2.05 mL/min at 220°C
Split ratio:	13.4 to 1 at 220°C
Retention time:	26.2 min
Injector conditions
Temperature:	250°C
Volume:	1 µL
Oven temperature program
Initial temperature:	160°C
Initial time:	5 min
Rate:	15°C/min
Final temperature:	260°C
Final time:	20 min
FPD conditions
Hydrogen flow rate:	75 mL/min
Air flow rate:	100 mL/min
Auxiliary gas:	nitrogen
Flow rate:	28 mL/min
Temperature:	250°C

3.5.2  Chromatogram (See Figure 2.)

3.6  Interferences (analytical)

3.6.1  Any compound having a retention time similar to that of the analyte is a potential interference. Generally, chromatographic conditions can be altered to separate interferences 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, detection by an electron capture detector (ECD) and confirmation by mass spectrometry are additional means of identification.

3.7  Calculations

3.7.1  Construct a calibration curve by plotting detector response versus standard concentration.

3.7.2  Determine the concentration of coumaphos in each sample from the calibration curve. If coumaphos is found on the backup section, make blank corrections for each section separately before adding the results together.

3.7.3  Determine the air concentration by the following formula.

 

	(µg/mL in sample)x(desorption volume, mL)
mg/m3 =
	(air volume, L)x(desorption efficiency, decimal)

3.8  Safety precautions (analytical)

3.8.1  Avoid exposure to all standards.

3.8.2  Avoid exposure to all solvents.

3.8.3  Year safety glasses at all times.

Figure 1.  OVS-2 Sampling Device

Figure 2.  Chromatogram of Coumaphos This chromatogram also contains TPP and other pesticides

5.1  Burright, D.; Method #62, "Chlorpyrifos, 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; p 245.

5.3  "Registry of Toxic Effects of CHemical Substances", 1985-86 ed.; U.S. Department of Health and Human Services (DHHS), Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health (NIOSH), DHHS (NIOSH) Publication No. 87-114, U.S. Government Printing Office; Washington, D.C., 1988; Vol. 2, pp 1679-80.

5.4  Windholz, M., Ed.; "Merch Index", 10th ed.; Merck and Co.: Rahway, NJ, 1983; p 366.

5.5  Ouellette, R.P. and King, J.A., Eds.; "Chemical Week Pesticides Register"; McGraw-Hill Book Co.; New York, NY, 1977; p 167.

5.6  "Farm Chemicals Handbook"; Meister Publishing Co.: Willoughby, OH, 1985; pp C64-C65.