Dear Flowers, Many thanks to everyone who answered my question about decontamination of the waste fluid form Propidium iodide. As I quickly discovered there are many options, from a cheap in house system using activated charcoal to more expensive ones using commercially available decontamination kit. PI can also be decontaminated using the same procedures employed for ethidium bromide. I enclose the response I received for those interested. Thanks again for all your help, Mara -------------------------------- The structure of propidium iodide is essentially the same as ethidium bromide - you should consider using cartridges (columns) designed for the disposal of DNA intercalators (Fluka #46136 - "Ethidium bromide/ SYBR green detoxification Kit" page 594, 1999/2000 catalog). -------------------------------- We treat Pi as we would ethidium bromide, the buffer is collected in a 25 litre carboy to which a HB-Et-Bag is added. When full, the carboy is allowed to stand overnight for all the dye to be absorbed into the bag, then the buffer is poured down the drain and the bag is sent for incineration. HB-Et-Bags from Helena Biosciences -------------------------------- For situations where we have high concentrations of PI we use the same method as for ethidium bromide solutions : 1. Add 100mg powdered activated charcoal for each 100ml solution. 2. Store the solution for 1 hour at room temp, intermittent shaking. 3. Filter solution through whatman No 1 filter and discard the filtrate. 4. Seal the filter and activated charcoal in a plastic bag, and dispose of as hazardous waste. (ours gets incinerated). Ethidium bromide (and PI) decomposes at 262c and is unlikely to be hazardous after incineration under standard conditions. Treatment of dilute solutions of ethidium bromide (PI ??) with hypochlorite (bleach) is not recommended as a method of decontamination. Such treatment reduces the mutagenic activity of ethidium bromide in the salmonella/microsome assay by about 1000-fold, but it converts the dye into a compound that is mutagenic in the absence of microsomes (Quillardet & Hofnung 1988). we recently had a mailshot from Merck, who now sell decontamination bags which are rather like Tea bags for getting rid of EB and PI from solution but they were very expensive so we stick to our charcoal for now. -------------------------------- Dilution is one way. We use PI for live/dead cell gating and its pretty dilute to start with. When I empty my waste tank, which has a mixture of bleach, saline and dead cells, into sink I will run a copious amount of water (guessing 4-5x tank volume)while I disposing. The same principle but only more of it could be applied as well if you are using higher amounts of PI for DNA content -------------------------------- The RETICS guide on hazardous chemicals reports that the minimum hazardous amount of PI is 150 mg. That translates to 3 liters of PI solution at 50 mg per liter or 50 micrograms per mL. You may flush it down the drain at quantities less than this. Of course, most people put some bleach in their waste containers. Bleach will oxidize PI to a harmless compound in less than 10 minutes. We therefore add 5% by volume of commercial bleach [Chlorox] for 10 minutes prior to flushing. -------------------------------- Several standard method for removal of ethidium bromide toxicity have been described in the classic 'Molecular Cloning' by Sambrook et al.. (pp. E.8-E.9). Since PI and EB have very similar structures I suppose these methods apply to both. The possibilities are: A. for concentrated solutions: 1. use of nitrite in acid solution 2. to use permanganate in acid solution (both methods are based on oxidation of the planar aromatic rings responsible for DNA intercalation) B. for diluted solutions: Use absorbent (e.g. activated charcoal) to remove the EtBr from the solution -------------------------------- I treat waste fluid (low level contaminated waste) with hypochlorit over night, neutralised with sodium thiosulfate the next morning. Highly concentrated solutions (e.g. sample tubes) are incinerated (chemical waster >1000oC) as wetting this waste with hypochlorit / oxidative destruction is not efficient --------------------------------
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