Commonly used MS-222 stock solutions for water bath or spray applications are prepared at 10 g/L. The working solution of MS-222 must be buffered (e.g., with sodium bicarbonate) to a pH as close as possible to system or environmental water. Each experimental protocol may differ slightly in procedure and use of MS-222, so there is no one single SOP for the use and preparation of MS-222. The IACUC office may be able to provide SOP examples upon request. MS-222 should be included within the lab safety plan to ensure all EHS requirements for safe handling and disposal are met.

MS-222 should be used the same day as preparation per vendor recommendations, if possible. When necessary, the stock solution can be stored away from light and either frozen or refrigerated. Stock and working solutions of  MS-222 must be labeled with the agent, concentration, date of preparation and date of expiration. 

When refrigerated, stock solution should be replaced after 30 days or sooner if  a change in color is observed.  Frozen stock MS-222 may be kept for up to 6 months at -20°C. The date of expiration of the original stock bottle must not be exceeded for any solution of MS-222 regardless of storage method.

It is the responsibility of the PI to ensure laboratory staff handling MS-222 are appropriately trained on safe handling and use. MS-222  has an oral rat LD50 of 5200mg/kg, which does not meet the OSHA classification of a toxic chemical.  OSHA classifies a chemical as toxic if the oral rat LD50 is less than 500 mg/kg.  The primary hazard of MS‐222 is that it is a respiratory irritant.

Personnel using MS-222 should be familiar with and have access to the safety data sheet (SDS). 

Because MS-22 is an irritant to the eyes, respiratory system and skin the following safety precautions are recommended during preparation: 

• Powder should be weighed in a fume hood or wearing an N95 mask in a well-ventilated area. 
• Use of a top loading balance with plastic wind/breeze guard to minimize dispersion of powder
• Minimize contact with skin when dissolved 
• For preparing solutions of MS‐222 in the laboratory, the following personal protective equipment should be worn: labcoat, gloves and safety glasses.
• When animals are immersed in an anesthetizing bath, there is a potential for splash and the following personal protective equipment should be worn:  labcoat, gloves and chemical splash goggles.
• Local exhaust ventilation (hood) is not required for typical applications in research labs or in the field, and air currents within the hood may make weighing the solid difficult.  As long as staff are careful to avoid aerosolization during the weighing of the solid, there is minimal potential for exposure to the pure MS‐222.
• Contact EHS to assist with proper disposal methods. 

The AVMA Guidelines for Euthanasia of Animals state the use of MS-222 is acceptable for euthanasia of fish and some amphibians and reptiles. A secondary method should be used to ensure death and any animal euthanized via this method must not be used as a food source. Please see the AVMA Guidelines reference below for further information. 

MS-222 use as an anesthetic varies widely between species and is affected by water temperature, hardness, and the size of the individual fish. Sedation and various rates of anesthetization are controlled by the concentration. The action of MS-222 anesthetic is slowed at cooler temperatures,  in extremely soft water and in larger fish. Manufacturers recommend that preliminary tests be done with anesthetic solutions in small numbers of fish to determine the desired rate of anesthesia and exposure times for specific lots of fish and the specific conditions. Animals may be revived from anesthesia by returning them to clean, untreated water preferably in their home tanks or environment.