Carcinogen And Pesticide Branch
1. General Discussion
The OSHA Analytical Laboratory received a set of samples requesting the analysis of methoxychlor and other pesticides. The samples had been collected on OVS-2 tubes. This report describes the analytical method developed for methoxychlor.
1.1.2. Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)
The oral LD50 of methoxychlor is 6000 mg/kg for rats. Animal studies have been done and the data did not provide evidence of being carcinogenic. The ACGIH has a threshold limit value (TLV) of 10 mg/kg because of the low toxicity of methoxychlor. This level will be adopted by OSHA. (Ref. 5.1. and 5.2.)
1.1.3. Potential workplace exposure
Methoxychlor is used as an insecticide. In the United States, a total of 2.5 million kg of methoxychlor was produced in 1975. The previous year 1.5 million kg of methoxychlor were used. (Ref. 5.2.) No information could be found on the number of workers exposed to methoxychlor.
1.1.4. Physical properties (Ref. 5.1. to 5.4.)
1.2. Limit defining parameters
The detection limit of the analytical procedure, including a 15:1 split ratio, is 0.006 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
2.1.2. 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, a 270-mg sampling section of cleaned XAD-2 adsorbent 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 (PTFE) retainer. (Figure 1.)
No sampling reagents are required.
2.3. Sampling technique
2.3.2. Attach the small end of the tube to the sampling pump with flexible tubing.
2.3.3. Attach the tube vertically in the employee's breathing zone in such a manner that it does not impede work performance.
2.3.4. After sampling for the appropriate time, rmove the tube and seal with plastic caps.
2.3.5. Wrap each sample end-to-end with an OSHA seal (Form 21).
2.3.6. Record the air volume for each sample, and list any possible interferences.
2.3.7. Submit at least one blank for each set of samples. Handle the blank in the same manner as the samples, except no air is drawn through it.
2.3.8. Submit bulk samples for analysis in a separate container. Do not ship with air samples.
2.4. Desorption efficiency (glass fiber filter and XAD-2 adsorbent)
Six vials each containing a 13-mm glass fiber filter and 270-mg of XAD-2 adsorbent were each liquid spiked on the glass fiber filter with 258.85 µg of methoxychlor and allowed to dry for 2 hours. These samples were each desorbed with 3.0 mL of acetonitrile, shaken for 30 min and analyzed as in Section 3. The results are listed in Table 2.4.
2.5. Retention efficiency
Eighteen OVS-2 tubes were each liquid spiked with 258.85 µg of methoxychlor on the glass fiber filter. These were allowed to dry for 2 hours and then 240 L of humid air (~80% relative humidity) were drawn through each tube at 1 L/min. Six of the tubes were each desorbed with 3.0 mL of acetonitrile, shaken for 30 min and then analyzed as in Section 3. The results are listed in Table 2.5. The remaining samples were stored, 6 in a drawer at ambient temperature and 6 in a freezer.
2.6. Sample storage
After 4 days of storage, 6 tubes, 3 from the ambient storage group and 3 from the freezer storage group, were each desorbed with 3.0 mL of acetonitrile, shaken for 30 min and then analyzed as in Section 3. The remaining tubes were desorbed and analyzed after 7 days of storage. The results are given in Tables 2.6.1. and 2.6.2.
2.7. Recommended air volume and sampling rate
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 methoxychlor. Any suspected interferences should be reported to the laboratory.
2.9. Safety precautions (sampling)
2.9.2. Follow all safety practices that apply to the work area being sampled.
3. Analytical Procedure
3.1.2. A mechanical shaker.
3.1.3. A GC equipped with an ECD. A Hewlett Packard (HP) 5890 equipped with an autosampler was used in this evaluation.
3.1.4. A GC column capable of separating methoxychlor from any interferences. A 15 m × 0.32 mm i.d. (1.0 µm film) DB-5 capillary column was used in this evaluation.
3.1.5. An electronic integrator, or some other suitable means for measuring detector response. The Hewlett-Packard 3357 Laboratory Data System was used in this evaluation.
3.1.6. Volumetric flasks and pipets.
3.1.7. Vials, 2-mL.
3.2.2. Methoxychlor, reagent grade. A standard obtained from EPA (EPA # 4541, 99.1% purity) was used in this evaluation.
3.3. Standard preparation
Prepare methoxychlor stock standards by weighing 10 to 15 mg of methoxychlor. Transfer the methoxychlor to separate 10-mL volumetric flasks, and add acetonitrile to the mark. Make working range standards of 0.5 to 150 µg/mL by pipet dilutions of the stock standards with acetonitrile. Store stock and dilute standards in a freezer.
3.4. Sample preparation
3.4.2. Add 3.0 mL of acetonitrile to each vial and seal with a Teflon-lined cap.
3.4.3. Shake the vials for 30 minutes on a mechanical shaker.
3.4.4. Transfer, if necessary, the samples to 2-mL vials for use on an HP autosampler.
3.5.2. Chromatogram (Figure 2.)
3.6. Interferences (analytical)
3.6.2. GC conditions may generally be varied to circumvent interferences.
3.6.3. Retention time on a single column is not proof of chemical identity. Analysis by an alternate GC column, high performance liquid chromatography (HPLC) and confirmation by mass spectrometry are additional means of identification.
3.7.2. Determine the µg/mL of methoxychlor in both sections of each sample and blank from the calibration curve.
3.7.3. Blank correct each section by subtracting the µg/mL found in the blank section from the µg/mL found in the sample section and then add the sections together.
3.7.4. Determine the air concentration by using the following formula.
3.8. Safety precautions (analytical)
3.8.2. Avoid skin contact with all solvents.
3.8.3. Wear safety glasses at all times.
4. Recommendation for Further Study
This method should be fully validated.
OVS-2 Sampling Tube
Chromatogram of Methoxychlor
5.2. Registry of Toxic Effects of Chemical Substances 1985-86 Edition; DHHS(NIOSH) Publication No. 87-114, U.S. Department of Health and Human Services: Cincinnati, OH, 1987; p 364.
5.3. Farm Chemicals Handbook; Berg, Gordon L. Ed.; Meister: Willoughby, Ohio, 1986; p C154.
5.4. Merck Index, 10th ed.; Windholz, Martha ED.; Merck: Rahway, N.J., 1983; p 861.