1. General Discussion|
2. Sampling procedure
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 disulfoton. It follows the
procedure developed for several other organophosphorus pesticides. (Ref. 5.1)
1.2 Limit defining parameters
It should be noted that in this evaluation for disulfoton 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 acety1choline 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 twitching, salivation, sweating, tearing, cyanosis, convulsions, and coma. (Ref.
Besides being absorbed following inhalation or ingestion, organophosphorus pesticides are readily absorbed through, the intact skin. (Ref.
Disulfoton is a highly toxic chemical with an acute oral LD50 for male rats of
6.8 mg/kg and females rates of 2.3 mg/kg. The dermal LD50's are 25 and 6
mg/kg for male and female rats respectively. (Ref.5.3)
Due to these factors disulfoton has been given a TLV of 0.1 mg/m3 by the ACGIH
1.1.3 Potential workplace exposure
No estimate of worker exposure to disulfoton could be found. Disulfoton is
used as a systemic insecticide and acaricide.
1.1.4 Physical properties (Refs. 5.3-5.6)
||132-133°C at 1.5 mmHg
||0.00018 mmHg at 20°C
||colorless oily liquid
||insoluble in water soluble in most organic
|| Disyston, dithiodemeton, dithiosystox,
Disyston, dithiodemeton, dithios
|| O,O-Diethyl S-2-(ethylthio) ethyl
The detection limit of analytical
procedure is 0.6 ng per injection. This is the amount of analyte which
will give a peak whose height is approximately five times the baseline
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
2.1.2 Samples are
collected with OVS-2 tubes, which are specially made 13-mm o.d. glass
tubes, that are tapered to 6-mm o.d., packed with a 140-mg backup section and a 270-mg sampling section of cleaned XAD-2 and a 13-mm diameter glass fiber filter. The backup section is retained by two foam plugs and the sampling section is between one foam plug and the glass fiber filter. The
glass fiber filter is held next to the sampling section by a polytetrafluoroethylene
3. Analytical procedure
No sampling reagents are required.
2.3 Sampling technique
2.3.1 Attach the small tubing adapter of the 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 it 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 end 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 glass fiber filters were each spiked with 48.06 µg of disulfoton.
The two filters, along with a blank filter, were each extracted with 2 mL of
toluene in separate 4-mL vials which also contained 270 mg of XAD-2
The average extraction efficiency
for these two filters (with the XAD-2 adsorbent present, also) was 89%.
2.5 Retention efficiency
Two OVS-2 tubes were each spiked with 48.06 µg of disulfoton by spiking the 13 mm glass fiber filter in the tube with the analyte of interest.
350 liters of humid air was drawn through each filter. The two filters were then extracted as above.
The average retention efficiency for these two filters was 8O%.
2.6 Sample storage
Two OVS-2 tubes were each spiked with 48.06 µg of disulfoton as above. 470 liters of humid air was drawn through each filter. These two tubes were stored for ten days at ambient temperature in a drawer. They were then extracted as above.
The average recovery after ten days of storage was 77%.
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
disulfoton. 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
2.9.2 Follow all safety
practices that apply to the work area being sampled.
4. Recommendations for further study
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 disulfoton from any interference. A 30-m
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.
3.2.1 Hydrogen, air, oxygen, and nitrogen, GC grade.
3.2.2 Toluene. Pesticide grade.
3.3 Standard preparation
3.2.3 Disulfoton, 98.1% pure (Chem Services Inc.).
Stock standard solutions are prepared by adding toluene to preweighed amounts of disulfoton. 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. Shake the
vials by hand with vigorous force periodically during the one hour
3.5.1 GC conditions
Column temperature: (initial)
|Temperature program rate:
|Column temperature: (final)
|Nitrogen flow rate:
|Initial hold time:
|Final hold time:
||30-m × 0.53-mm i.d. DB-21
Megabore, 1.0-µm thick
|Hydrogen flow rate
|Oxygen flow rate:
|Air flow rate:
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
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
disulfoton in a sample is determined from the calibration curve. If
disulfoton 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.
||(mg/mL in sample) (desorption volume, mL)
||(air volume, L) (desorption efficiency,
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.
There appears to be some loss of disulfoton with increased sampling
time and/or storage time at ambient temperature. More statistically valid retention and storage studies should be done to clarify this loss of
analyte. This method should be fully validated.
5.1 Burright, D., Method #62, "Clorphyrifos, 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
Heath Service Publication No. 1097, U.S. Government Printing Office, Washington,
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 Science, Technology and Medicine, June 14, 1985.