Methionine and cysteine-methionine compounds are widely used in research. At room temperature and above, small amounts of volatile S-35 decomposition products may be generated.
The manufacturers recommend venting the stock vials in a chemical fume hood prior to opening and before thawing. Pierce the septum with a cotton plugged needle or charcoal trap, taking care not to come into contact with the contents. Thaw at room temperature or in a 37-degrees-C water bath. Remove the needle or trap and discard in the radioactive waste sharps container.
When used for in-vivo labeling experiments, the following measures should be taken to reduce the levels of contamination that occur in water baths and incubators.
- Periodically assay the water in the bath for radioactive content. Count an aliquot of the bath water in a scintillation counter. Discard in the designated radioactive sink if S-35 is detected.
- When removing your samples, be careful not to drip water onto counters and floors.
- Place a shallow pan of activated charcoal or granulated carbon in the incubator at the same time as your cells. This will trap volatile S-35. Survey the charcoal with a GM survey meter and discard the charcoal as radioactive waste if any reading is detected. NOTE: The high humidity within the incubator will tend to reduce its effectiveness over time.
Several researchers report successful contamination control using plastic containers as mini-containment within the incubator. Two variations that are successfully used are:
- Placement of the culture dishes inside a larger (say, 14" x 10" x 3") plastic container with tight fitting lid. If the atmosphere is allowed to equilibrate before the lid goes on, the CO2 trapped within is adequate for several days of incubation time. The containers should be opened in a chemical fume hood.
- Placement of the culture dishes along with a pan of charcoal inside a larger plastic container with perforations in the lid. This allows full gas circulation but tends to localize the volatile S-35.
Periodically assay the water in the incubator drip pan for radioactive content. Count an aliquot of the bath water in a scintillation counter. Discard in the designated radioactive sink if S-35 is detected.
Take a smear of the incubator surfaces most likely to become contaminated. Pay special attention to the inner door, the door gasket, and the shelves. Decontaminate as necessary.