AS 4276.23:2016 – Water microbiology Method 23: Soils, sediments, sludges, slurries and bio-solids-Procedures for sample preparation.
The sampling plan shall be in accordance with end-user requirements. Sterile resistant-glass or plastic bottles shall be used to collect samples for analysis, provided that thc material in suspension does not adhere to container walls. Containers should be capable of being tightly scaled. Sterile or disinfected sampling cquipmcnl shall be used such that thc sampling surfaces in contact with sample are sterilized or disinfected betcen samples (example: sampling-surfaces of a soil auger; inner surfaces of a push- or piston-corer; spatulas, corers, trowels, shovels). If the end-user requirements in terms of sampling equipment are more stringent, these shall be followed.
To optimize the recovery of the target microorganisms, transportation conditions and holding times should be in accordance with AS 2031, unless end-user requirements are more stringent. Sample storage conditions prior to analysis should be those indicated in the applicable analytical procedure utilizing the homogenate produced in this method. Analysis shall commence as soon as possible after collection, with samples being brought to room temperature before commencing the analysis.
I Scc references 131, 151 and 161 for additional guidance on sampling.
2 Samples are generally classified as liquid when they contain approximately <7% total solids. N PROCEIRRES X.l MIsing Sub-sampling for analysis is a process by which an analytical unit is obtained from a sample. Samples shall be well mixed prior to obtaining subsamples for processing. It is essential to ensure that any subsainples are representative. When assessing the homogeneity of a sample, bear in mind that this will vary depending on the matrix. hich can be solid. semi-solid or high-particulate-liquid in nature. Liquid and semi-liquid samples shall be mixed thoroughly by shaking, stirring or mechanical agitation/mixing in order to re-suspend any settled or floating material. It may be iiecessar to transfer the sample to a larger. or more suitable container. Visually assess the resultant sample for homogeneity. Some liquid samples may contain aggregates or other material capable of being disrupted. If such samples cannot be adequately mixed by the shaking. stirring or mechanical agitation/mixing, then stomaching should be used. Wet sludges may bc mixed by stirring the entire sample thoroughly with a sterilized spatula. Alternatively, a blender may be used. For solid samples, such as caked, thickened or thermally dried sludges and compoats. a variety of measures may be needed to ensure that adequate mixing is achieved. These sludges vary in nature, with some being relatively moist and others being hard and unyielding. Coniposts are usually moist and friable, however some may contain hard maicriak such as rocks, twigs. and other plant matter. For semi-solid and hardcaked sludges and composts, it is particularly important for the sample to be well mixed. Soft caked sludges and soft composts may be transferred to a stomacher bag placed inside a second blender bag. This can be crushed or ground using a suitable heavy object to aid the mixing process. Hard caked sludges. pressed sheet sludges and granules and pellets may ticed to be aseptically maccrated, crushed or ground to facilitate mixing. If using a laboratory mill, the manufacturer’s instructions should be followed to ensure that microorganisms are not damaged due to mechanical action. 8.2 SubsampIln and homogenIzatIon 8.2.1 Gc,wrc,I If results are to be reported on a dry weight basis, the percent solids o subsamples from the thoroughly mixed sample shall be determined as per the procedure in Appendix D. The homogenization procedure. including p11 ncutraliiation. should be performed in less than 60 mm, and the homogenate diluted and/or placed directly into growth media within this time period. This does not include the time required for treating difficult matrices so that they are in a suitable condition for complete homogenization. For example, particularly hard matrices requiring soaking and very low moisture content matrices which are difficult to wet. If a non-selectise medium is used in the applicable method, the receptacle used in homogenization shall he sterile rather than disinfcctcd. Spiking of samplc with positive control microorganisms shall occur after pH neutralization, 8.2.2 LIquid xampk.s (upprox. 7% solids) An adequate degree of homogenization of liquid samples should have been achieved in the initial mixing step. If not, a subsample is homogenized using stomaching or blending. The minimum subsample volume required for a liquid sample is 300 mL. Check the p11 of homogenized liquid samples.