Best Practices for Sample Storage and Handling in Environmental Studies

The reliability of any environmental study ultimately depends not just on how samples are collected in the field, but on what happens to them afterward. A perfectly collected soil core or water sample can yield meaningless data if it degrades, gets contaminated, or is mislabeled before reaching the laboratory. According to the U.S. EPA, sample integrity begins the moment collection ends – making proper storage and handling a non-negotiable part of environmental monitoring protocols.

Soil sample preparation: drying, sieving, and storage
Drying the sample
Sieving for uniformity
Choosing the right storage container
Handling air and water samples: transport and storage protocols
Water samples
Air samples
Avoiding cross-contamination: decontamination and labeling
Equipment decontamination procedures
Labeling and chain of custody
Quality control samples
Holding times and storage monitoring

Soil sample preparation: drying, sieving, and storage

Preparing soil samples for laboratory analysis involves a clear sequence of steps. Skipping or rushing any one of them introduces error into the entire dataset.

Drying the sample

The first step after field collection is drying. For most chemical and physical analyses, air-drying is the preferred method – it removes excess moisture without the risk of heat-induced chemical changes that come with oven drying. Samples are spread in thin layers on clean, non-reactive trays and left at room temperature until they reach a stable dry weight. When testing for volatile organic compounds (VOCs), however, air-drying is not appropriate. The EPA’s soil sampling protocol specifies that VOC samples must be immediately placed in pre-preserved vials and kept cold, since any drying step would cause the very compounds you’re trying to measure to evaporate.

Sieving for uniformity

Once dried, soil must be sieved to achieve a consistent particle size for analysis. The FAO’s standard operating procedure for soil analysis recommends passing samples through a 2 mm sieve to separate the fine earth fraction from stones, root fragments, and coarse organic debris. Stainless steel or nylon sieves are preferred over other metals to avoid introducing trace metal contamination. Crucially, sieves must be thoroughly cleaned between each sample – ideally rinsed with distilled water and an appropriate solvent – to prevent carryover from one sample to the next. When processing multiple samples in sequence, work from the least to the most contaminated.

Choosing the right storage container

Research-backed guidelines from CGIAR recommend storing prepared soil samples in airtight containers at low temperature, low humidity, and in darkness to minimize chemical alteration such as oxidation. Glass containers are generally preferred for most analyses. Plastic containers can leach organic compounds and are unsuitable when testing for organics. For long-term storage or when microbial activity is a concern, vacuum-sealed bags or containers offer an additional layer of protection. Each container must be clearly labeled with the sample ID, collection location, depth, date, and the analysis it is intended for.

Handling air and water samples: transport and storage protocols

Air and water samples present different challenges compared to soil. They are inherently more dynamic – chemical reactions continue after collection, and volatile compounds can be lost within hours. Strict temperature control and airtight handling are essential from the moment of collection.

Water samples

Water samples must be transported in containers appropriate to the target analyte. The U.S. Geological Survey’s National Field Manual specifies that trace metal samples require acid-washed plastic or glass containers, while organic compound analyses demand containers that will not leach interfering substances. The standard storage temperature for most water samples is 4°C, maintained using insulated coolers with ice packs during transport. Water samples should never be frozen unless the specific method requires it, as freezing can fracture glass containers and alter chemical equilibria.

Chemical preservation is often necessary to extend hold times and prevent degradation. For metal analysis, samples are typically acidified with nitric acid to bring the pH below 2. For samples from chlorinated municipal water, sodium thiosulfate is added to neutralize residual chlorine that would otherwise continue reacting with organic analytes. Texas Commission on Environmental Quality guidelines advise that labeling information should never be written directly on sample containers – instead, write on the bag holding the container to avoid chemical contamination from ink or adhesive.

Air samples

Air samples collected on particulate filters must be stored in clean petri dishes or filter holders, wrapped in aluminum foil to block light degradation, and refrigerated until analysis. Whole air samples collected in stainless steel canisters must be pressurized correctly and stored upright to prevent condensation from affecting results. EPA ambient air monitoring quality assurance guidelines require that canister pressures be checked regularly during transport and that chain-of-custody documentation accompany all air samples. Because air samples are invisible and cannot be visually inspected for tampering or loss, documentation becomes the primary safeguard of their integrity.

When collecting air samples near running vehicles or generators in the field, Minnesota Pollution Control Agency field protocols recommend filling sample containers upwind from any exhaust sources and shielding collection points from wind-borne dust under dusty conditions.

Avoiding cross-contamination: decontamination and labeling

Cross-contamination – where residues from one sample transfer to another – is one of the most common and consequential errors in environmental sampling. It can produce false positives, skew concentration readings, and invalidate entire data sets. Preventing it requires structured decontamination routines, disciplined labeling, and careful sample sequencing.

Equipment decontamination procedures

The USGS National Field Manual for water-quality sampling describes a systematic “Clean Hands/Dirty Hands” (CH/DH) protocol in which one team member handles only clean, sample-contact surfaces while another manages all other field tasks. This separation prevents contamination from coins, food, vehicle surfaces, or other common field items from reaching sample containers. The same principle applies to soil sampling – tools such as trowels, augers, and split spoons must be cleaned between every sample using a standard sequence: wash with laboratory-grade detergent, rinse with tap water, rinse with distilled water, and finish with an appropriate solvent rinse if organic compounds are being analyzed.

When moving between multiple sampling sites, always follow the order of least to most contaminated. USGS guidelines note that sampling the cleanest sites first prevents contaminated residues on equipment from masking true background concentrations at pristine locations.

Labeling and chain of custody

Every sample container must be labeled at the point of collection – not later in the laboratory. A complete label includes the sample ID, collection location, depth or height of collection, date and time, collector’s name, and the analysis type intended. EPA air monitoring protocols require that transport containers themselves carry unique identification codes, and that all samples be sealed with tamper-evident custody tape before leaving the field. Chain-of-custody (COC) forms must be signed by every person who handles the sample, creating a continuous record from collection to laboratory receipt.

Quality control samples

Blank samples are an essential tool for detecting contamination that might otherwise go unnoticed. USGS field collection protocols distinguish between field blanks (distilled water subjected to the same field handling as environmental samples), equipment blanks (distilled water passed through all sampling tools after cleaning), and trip blanks (sealed containers of clean water or soil that travel with samples throughout transport and storage). Each type of blank targets a different potential contamination pathway. If a blank shows contamination, any results from samples collected alongside it must be flagged and investigated before being reported or used in environmental decision-making.

Holding times and storage monitoring

Even perfectly collected and preserved samples have a finite shelf life. Every analyte has a maximum allowable holding time between collection and analysis – after which chemical or biological changes render results unreliable. For example, Minnesota PCA soil sampling guidelines specify that VOC samples must be extracted within 7 days of collection and fully analyzed within 40 days. Water samples for organic compounds generally have holding times measured in days, not weeks.

Storage areas should be monitored with temperature loggers, and any deviation from required conditions must be documented. Many regulatory programs require this temperature record as part of data quality defense. A first-in, first-out inventory system ensures older samples are analyzed before newer ones, reducing the risk of holding time violations. Regular inventory checks also help identify samples approaching their deadline, giving laboratory staff time to prioritize analysis before data is lost.

What do you think? Given that a single labeling error or missed decontamination step can compromise an entire set of samples, where do you think the greatest risk of error lies in field sampling – during collection, transport, or laboratory handoff? And how might digital chain-of-custody systems change the reliability of environmental monitoring programs compared to paper-based records?

References

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Table of Contents

Soil sample preparation: drying, sieving, and storage 🔗

Drying the sample 🔗

Sieving for uniformity 🔗

Choosing the right storage container 🔗

Handling air and water samples: transport and storage protocols 🔗

Water samples 🔗

Air samples 🔗

Avoiding cross-contamination: decontamination and labeling 🔗

Equipment decontamination procedures 🔗

Labeling and chain of custody 🔗

Quality control samples 🔗

Holding times and storage monitoring 🔗