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| | | Junior Member
 
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| | Does anybody test their raw/seed for toxic substances? During a recent NELAC inspection we were asked if we ever test our raw/seed for toxic substances. Standard Methods does not specify what is meant by this. Do you run a set of dilutions? How often do you test for this?? Mark |
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Supreme Being
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| I would think that this would all fall into the SCF bottles that you set up with each batch. If those bottles deplete at the required amounts then everything is fine. But that is just my humble opinion. We are a commercial lab and don't have the luxury of having any kind of influent to use as seed.
David |
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| | I'll bite... What's an "SCF Bottle"? MLA |
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| Standard Methods doesn't do a good job on what is meant by "toxicity" or "toxic substances", Mark. They mention it when they say 'unless there is evidence of toxicity, average all bottles that meet the DO depletion and retention criteria' or words to that effect.
The toxic substances they are referring to are materials that interfere with the ability of the bacteria to do their thing. You test for that by running a series of dilutions as you suggested. If you observe increasing BOD as the bottles become more dilute, that could be evidence of toxicity. If your dilution series is only three bottles, it could also be nothing more than random differences.
As far as I know, there is no standardized procedure for proving toxicity. I recommend running a series of at least seven dilutions, with at least two of the bottles being pre-diluted by at least a factor of ten (don't forget to multiply the result by that extra dilution factor).
If you are treating only domestic waste, it is unlikely there would be any toxicity effect. If you are processing industrial waste, toxicity is more likely (the most recent case I observed involved a manufacturer of cardboard boxes...something in the adhesive they used). Septage is almost always toxic to the BOD test.
How often do you run it? And on what samples? What do you report if you "prove" toxicity? I have never known a regulator to require the test, but those are questions to pose to your regulator (permit manager?). Don't be surprised if they say, "What are you talking about?" I suspect that the NELAC assessor was just trying to impress you with his/her knowledge of the BOD test!
Perry |
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Supreme Being
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| MoscowLabAnalyst (4/18/2008)
I'll bite... What's an "SCF Bottle"? MLA SCF = Seed Control (or is it correction?) Factor. The bottle(s) you use to determine the amount you subtract out for your seed contribution to DO depletion. Our regulators require us to do bottles at 3, 4, and 5 times the volume of seed added to each sample. Each of those bottles that meets the 2:1 depletion rule is divided by the appropriate factor and then averaged together. This gives us our SCF value. We also have to set up one bottle with just the volume of seed added to samples in it. We were given no ± requirement to compare this to the average value from before, only that it has to be reasonably close. As you can guess everything we have set up has been 'reasonably close' 
David |
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| | Thanks for the information Perry. We will probably run this test once a quarter and retain the results for the next inspection. Mark |
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| Markaf (4/18/2008)
Does anybody test their raw/seed for toxic substances? During a recent NELAC inspection we were asked if we ever test our raw/seed for toxic substances. Standard Methods does not specify what is meant by this. Do you run a set of dilutions? How often do you test for this?? Mark To show whether or not toxicity is present in your raw samples you need to set up your bench sheets to show calculations for depletion in mg/ml. If there is more depletion at lower concentrations of sample than at higher concentrations then possible toxicity is indicated and needs to be resolved. We were asked that question by our inspectors some ten years ago and we had to rework our bench sheets to provide those calculations. Sometimes we have inhibition in our PE samples. ~Egadz |
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| | | Supreme Being
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| | I hate to do a "hit and run"!... but won't the GGA results let you know if the seed is toxic? Unusually low results COULD be due to toxic seed. The toxicity procedure outlined by Perry is a good diagnostic tool - IF GGA results are failing low consistently. However, I would make sure all other potential causes of low GGA results have been ruled out before performing a tox study. A lot of time can be wasted... |
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