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TNI Standards Guidance

Disclaimer: This material represents the opinion of its authors. It is intended solely as guidance and does not include any mandatory requirements except where such requirements are referenced. This guidance does not establish expectations of being implemented universally, exclusively, in whole, or in part.

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Module: Microbiology


Subject: Sample Receipt

Question 1

Does the temperature of samples at the time of sample acceptance apply to presence/absence tests such as SM 9223-a chromogenic substrate test? The LOD is 1cfu and if the result of a test is present, it does not matter whether there is one or thousands of bacteria present.

SM 9223 (B) can also be run under quantitative most probable number and multiple well technologies and not just for presence-absence purposes.  If compliance with US EPA's Clean Water Act is needed, the Microbiology sample arrival temperature needs to be <10 degrees Celsius.  Thus, the temperature of the incoming Microbiology samples must be checked, regardless of the test method to be used.  Even if regulatory compliance is not required, the laboratory should consider the condition of any and all received samples, and it should question the validity of any samples where the arrival times, temperatures, and preservations are such that the sample as received at the laboratory may not be representative of the sample as collected in the field.

Question 2

If purchased vessels are used which contain the required amount of sodium thiosulfate, is a test for chlorine residual done in the field sufficient?

No, it is not sufficient.  Please see TNI Volume 1, Module 5, Section 1.7.5(b).  The "required" amount of sodium thiosulfate cannot be verified unless the laboratory tests one or more containers from each lot to verify that the enclosed preservative can remove 5 mg/L or 15 mg/L chlorine, as appropriate.  Also, it is presumed that all Microbiology samples will arrive exclusively in those containers supplied by the laboratory.  If the samples arrive in client-supplied containers, the laboratory needs to check each such sample to verify validity for Microbiological testing, namely, absence of chlorine.



References:

2009 TNI V1M5 Section 1.7.5

Sample Handling
a)   Samples that require thermal preservation shall be considered acceptable if the arrival temperature of a representative sample container meets the method or mandated temperature requirement.
i)    Samples that are delivered to the laboratory on the same day they are collected may not meet the requirements of Section 1.7.5.a). In these cases, the samples shall be considered acceptable if the samples were received on ice.
ii)   If sample analysis is begun within fifteen (15) minutes of collection, thermal preservation is not required.
iii) Thermal preservation is not required in the field if the laboratory receives the sample and either begins the analysis or refrigerates the sample within fifteen (15) minutes of collection.
b)   Microbiological samples from known chlorinated sources (such as wastewater effluent), unknown sources where chlorine usage is suspected (such a new client or a new source) and all potable water sources (including source water) shall be checked for absence of chlorine residual. Laboratories that receive samples from potable water sources (including source water) that have a demonstrated history of acceptable preservation may check a sample from each source at a frequency of once per month if:
i)    the laboratory can show that the received sample containers are from their laboratory;
ii)   sufficient sodium thiosulfate was in each container before sample collection to neutralize at minimum 5 mg/l of chlorine for drinking water and 15 mg/l of chlorine for wastewater samples;
iii) one container from each batch of laboratory prepared containers or lot of purchased ready-to-use containers is checked to ensure efficacy of the sodium thiosulfate to 5 mg/l chlorine or 15 mg/l chlorine as appropriate and the check is documented;
iv) chlorine residual is checked in the field and actual concentration is documented with sample submission.