Mar 4, 2012 – Shelf Life

QUESTION:

How long can you keep chemicals on the shelf? How many months will they last?

ANSWER:

This is going to vary a great deal and it depends on several factors. One of these is the formulation itself. Dry products such as dusts and granules tend to change faster than liquid formulations, so take a look on the packages and note any dates or restrictions placed there by the manufacturer. Because synthetic active ingredients are subject to degradation over time, as opposed to the inorganic mineral actives such as boric acid, borates, or diatomaceous earth, you would be best off using the dry products within the first couple of years. This will also depend a lot on the conditions of that storage area, particularly dampness. If dry products are exposed to water they are going to degrade and become unusable very quickly. High humidity may even be a factor if the bags are not kept sealed properly. 

Temperature is another important factor, and virtually every pesticide label is going to state that it should be stored in a cool, dry environment. The higher the temperature the faster the molecules break apart and change and become something other than the original active ingredient. This may take years to happen for liquid products, but bit by bit they are changing and if you don't get around to using a product for 5 or 6 years after you bought it there may be a lot less active ingredient in it than you think is there. 

Another concern is physical changes in a liquid formulation. The active ingredients are often manufactured as a solid material, a crystalline material for example. This solid is then put into liquid form using solvents, and then it may further be diluted with water or other diluents to become the end use concentrate that you buy. Over time the original crystalline active ingredient is likely to re-crystallize and begin to settle out of the formulation, and getting it back into that homogenized and usable state may be impossible. If this occurs you now have toxic waste on your hands, and the legal disposal of toxic waste becomes very expensive. 

Aerosols are also not forever. If they sit on a shelf for years they can lose propellent, they may develop rust around the seams and ridges that eventually eat through the can, and contents also may separate inside the can and be impossible to get back into an even solution. I once visited a pest control company warehouse where several cases of methyl bromide in 1 lb. cans had been stored for many years - about 50 cans in all. ALL of these cans of fumigant had long since rusted through, releasing all of that methyl bromide into the warehouse and the nearby offices. 

It is important to have good control over your inventory and stocking procedures and to not buy more product than you know you will use in a reasonable time period. Use the FIFO concept of "first in, first out" so that products never sit at the back of the shelf and get forgotten. Another interesting incident was with an old pentachlorphenol product in large caulking tubes. Long after penta had been banned from use one company still had dozens of these tubes in their warehouse, and by that time the problem was that there was no way to legally use it, legally store it, or even legally dispose of it. 

So, it's hard to put firm numbers on this, but do check the containers themselves for "expiration" dates, keep your storage areas in good condition and cool, and use up product in a reasonable time  period. 


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