Scrubber Water Testing: Compliance Starts in the Sample Bottle
A scrubber-water test can fail before it reaches the laboratory. Reliable results depend on correct sampling, preservation and handling from the moment the bottle is filled.
By Varuna Marine Services B.V. · 7 September 2026Sources: IMO MEPC.340(77), US EPA 2013 VGP, 40 CFR 136, EPA Methods 200.8, 353.2 and 625.1
pH and residual oxidants are field tests. They must be measured onboard within 15 minutes of sampling.
Dissolved metals are filtered at collection, then acidified to pH <2. Total-recoverable metals are not filtered.
Nitrate or nitrite measured separately under EPA 353.2. Preserved combined nitrate-nitrite may be held 28 days.
PAH samples must be extracted within 7 days of collection, then analysed within 40 days of extraction.
VGP first-year analytical monitoring: two sampling events at least 14 days apart, then at least once per calendar year.
Evidence starts onboard
A scrubber-water test report should do more than present a set of results. It should provide reliable evidence of what the vessel discharged, under identifiable operating conditions, using samples collected and handled correctly.
That evidence starts onboard — not when the samples arrive at the laboratory. The bottle, sampling point, filtration, preservation, storage conditions and time elapsed before analysis all matter. A laboratory can analyse what it receives; it cannot retrospectively correct every mistake made before receipt.
At VMS, our position is clear: where the applicable method requires preservation, it must be part of the sampling plan — not an assumption about how quickly a courier will deliver the samples. That is why we align sampling procedures, vessel operations, laboratory capability and reporting requirements before the sample is collected.
A fast laboratory turnaround is not a sampling strategy
Consider a sample collected while the vessel is underway. It remains onboard until the next port, passes to an agent, clears the necessary formalities and travels to the laboratory. A promise to test it quickly after arrival addresses only the final stage of that journey.
The risk in a fragmented testing chain is that each party completes its own task while nobody checks the whole process. The crew fills the bottles, the agent arranges collection, the courier delivers the package and the laboratory issues a report. Those individual steps do not, by themselves, establish that sample integrity was maintained.
US EPA's vessel-sampling guidance recommends that laboratory arrangements, transport conditions and holding-time requirements are considered during the planning stage, so that sample integrity is maintained from collection to analysis. The sampling window should therefore be planned around the actual vessel itinerary and laboratory capabilities, rather than an ideal delivery scenario. IMO Resolution MEPC.340(77) likewise sets out recommendations on preservatives, analytical methods and sampling conditions for scrubber discharge water.
The holding-time clock does not restart at the laboratory door. It starts the moment the sample is collected and runs until the required preservation, extraction and analysis steps are completed within the specified timeframe.
Preservation is essential — but the sequence matters
Metals testing illustrates why the details cannot be left to chance. EPA Method 200.8 distinguishes between dissolved and total-recoverable metals. Dissolved analysis requires a filtered sample, while total-recoverable analysis uses an unfiltered sample with the specified preparation procedure. These represent different measurements and are not interchangeable.
- Dissolved metals: filter through a 0.45 µm membrane at the time of collection, or as soon as practically possible, then acidify the filtrate to pH <2.
- Total-recoverable metals: do not filter; acidify to pH <2 in accordance with the method requirements.
However, metals are only one part of scrubber-water testing. PAHs, nitrate/nitrite and hydrocarbon or oil-related analyses have their own preservation, storage and holding-time requirements. A single preservation approach cannot be applied to every bottle collected during a sampling campaign. The correct container, preservative, storage condition and analytical timeline must be defined for each parameter.
One scrubber sample does not mean one handling procedure
Preservation is broader than adding acid. Each parameter needs the handling specified by its method, and the most demanding deadline may determine the entire sampling plan.
Polycyclic aromatic hydrocarbons (PAHs) show why parameter-specific handling matters. Under EPA Method 625.1 — and its SW-846 counterpart, Method 8270 — aqueous samples are kept cool and in the dark, dechlorinated where residual chlorine is present, extracted within 7 days of collection and analysed within 40 days of extraction. Those windows must be managed as part of the sampling plan, taking the vessel schedule, transport arrangements and laboratory capability into account. They are separate requirements — not an allowance to delay proper handling after collection.
Nutrient testing also needs a precise scope. EPA Method 353.2 allows acid-preserved, cooled combined nitrate-nitrite samples to be held for up to 28 days. Nitrate or nitrite measured separately must be cooled and analysed within 48 hours. A generic label such as “nitrates” is not enough to establish the correct handling route.
Field measurements cannot be deferred to a distant laboratory. For scrubber-water pH, VMS specifies field testing within 15 minutes of sampling. That measurement must be taken separately from an acid-preserved metals sample.
| Parameter | Method | Where | Handling requirement |
|---|---|---|---|
| pH | SM 4500-H+ B | Field | Measure onboard within 15 minutes of sampling |
| Total residual oxidants / chlorine | EPA 330.5 · ISO 7393-2 | Field | Field test within 15 minutes; result decides whether PAH bottles need dechlorination |
| Turbidity | EPA 180.1 · ISO 7027 | Lab | Cool ≤6 °C; analyse within 48 hours |
| PAHs (16 VGP compounds) | EPA 610 · 625.1 · 8270 · 8310 | Lab | Amber glass; cool ≤6 °C, dark; sodium thiosulfate if residual chlorine present; extract within 7 days, analyse within 40 days of extraction |
| Nitrate + nitrite | EPA 353.2 | Lab | H₂SO₄ to pH <2, cool; 28 days combined. Separate nitrate or nitrite: 48 hours, unpreserved |
| Total metals — As, Cd, Cr, Cu, Pb, Ni, Se, Tl, V, Zn | EPA 200.8 · 200.9 | Lab | Do not filter; HNO₃ to pH <2 (acid may be added on receipt, at least 24 h before analysis); 6 months |
| Dissolved metals — same ten elements | EPA 200.8 · 200.9 | Lab | Filter 0.45 µm at collection (40 CFR 136: within 15 minutes), then HNO₃ to pH <2; 6 months |
| Hydrocarbon oil index (IMO scope) | ISO 9377-2 | Lab | Glass; acidify, cool; 28 days |
Table 1. Analytical scope as offered in the VMS Environmental Service Brochure Rev. 1.1 (§3.2 and §3.3(E)), with the handling each method imposes. Indicative; the laboratory's bottle instructions govern.
Sample the operating scrubber — not the convenient port call
A convenient collection time is not necessarily a representative sampling time. The system's operating condition must match the purpose of the test. IMO Resolution MEPC.340(77), Appendix 3, recommends sampling with the exhaust gas cleaning system operating above 50% of maximum exhaust-gas flow, with the water flow and engine load steady before and during sampling. The applicable approval documents and sampling purpose must also be checked.
Sampling points need equal care. The US Vessel General Permit (VGP) specifies inlet water, water after the scrubber but before any treatment system, and discharge water. IMO Appendix 3 places its intermediate point after treatment, where applicable, but before any dilution, and its final point after treatment and dilution. Depending on the installation, those are different locations.
For a combined testing campaign, map the required points on the vessel's piping diagram rather than assuming that three bottles labelled “inlet, outlet and overboard” cover both scopes. Link each sample to the operating mode, load and collection time.
Be precise about the compliance claim
“IMO and US EPA testing” should describe a defined scope, not a generic certificate. IMO Appendix 3 provides recommended discharge-water data collection; the US VGP establishes mandatory analytical monitoring for applicable vessels. They should not be presented as identical obligations.
Under VGP section 2.2.26.2.2, two sampling events at least 14 days apart are required in the first year of permit coverage or scrubber operation, whichever comes first, followed by sampling at least once per calendar year. Periodic laboratory testing does not replace the permit's continuous-monitoring requirements. EPA continues to identify the 2013 VGP as the interim framework until both EPA and US Coast Guard regulations under the Vessel Incidental Discharge Act (VIDA) are final, effective and enforceable.
Analytical suitability matters as well. The VGP specifically flags matrix interference for arsenic and selenium in saltwater samples and strongly recommends interference-controlled techniques such as collision or reaction cell ICP-MS or hydride generation. Ask the laboratory to demonstrate suitable interference control and reporting sensitivity for the actual sample — not merely quote a method number.
How VMS builds sample integrity into the service
Our scrubber-water testing service brings the sampling materials, vessel records and laboratory coordination together. We provide bottles and preservatives, sampling procedures, chain-of-custody forms and engine-performance recording forms, with filtration items and cooling arrangements included in the relevant service scope.
We select partner laboratories with the required analysis, location and holding-time constraints in mind. This aligns the sampling event with a workable route to the laboratory, rather than trying to solve those constraints after the samples have been collected.
Our reporting framework links vessel identity and sampling location to collection date and time, field measurements, preservation used, shipment and receipt details, analytical methods and results. These records help owners explain how the evidence was produced — not simply present the final numbers.
The value is not the presence of a preservative bottle on a packing list. It is a coordinated process that helps the crew collect the right sample, preserve it correctly and retain the information needed to assess the result.
What owners should require before the next test
We recommend asking four questions before approving a scrubber-water testing proposal:
- Question 01
Is the scope explicit?
Confirm the applicable requirements, sampling points, operating conditions, analytes and total or dissolved fractions.
- Question 02
Is every bottle accounted for?
Obtain the container, filtration, preservative, fill-volume and storage instructions for each test, including any permitted laboratory-preservation route.
- Question 03
Can the real itinerary meet every deadline?
Include onboard storage, agent handling, transport, laboratory receipt, extraction and analysis — not just courier transit.
- Question 04
Will the sample history withstand review?
Agree what will be recorded, how deviations will be reported and when qualification or resampling will be necessary.
A missed method requirement can undermine a result's suitability as compliance evidence. It does not automatically prove that a discharge limit was exceeded, but a reassuring number cannot compensate for an invalid sampling process. Where a problem is identified, our recommendation is to obtain the laboratory's underlying records, assess the affected results and arrange representative resampling where needed.
A practical first step
Start with one recent report from your fleet. Request the complete sample history and check it against the stated method. That is a practical way to identify gaps before the next sampling event.
The industry should compete on the quality of its compliance evidence — not simply the speed of issuing a report. Contact Varuna Marine Services to plan your scrubber-water sampling, preservation and laboratory route at info@varunamarine.eu. Reliable compliance evidence starts with the sample.
- [1]IMO, Resolution MEPC.340(77), 2021 Guidelines for Exhaust Gas Cleaning Systems, Appendix 3 (Discharge water data collection). IMO resolution (PDF)
- [2]US EPA, 2013 Vessel General Permit (VGP), Part 2.2.26 (Exhaust Gas Scrubber Washwater Discharge), sections 2.2.26.2.1–2.2.26.2.3. 2013 VGP (PDF)
- [3]40 CFR 136.3, Table II — Required containers, preservation techniques, and holding times, including footnotes 2, 4, 7 and 19. eCFR § 136.3
- [4]US EPA, Method 200.8, Revision 5.4 — Determination of trace elements in waters and wastes by ICP-MS, sections 3.3, 3.16 and 8.1–8.3. Method 200.8 (PDF)
- [5]US EPA, Method 625.1 (2016) — Base/neutrals and acids by GC/MS, section 9: Sample collection, preservation, and handling; SW-846 Chapter Four, Table 4-1, for the equivalent aqueous holding times under Method 8270. Method 625.1 (PDF)SW-846 Chapter Four (PDF)
- [6]US EPA, Method 353.2, Revision 2.0 — Determination of nitrate-nitrite nitrogen by automated colorimetry, sections 8.2–8.4. Method 353.2 (PDF)
- [7]US EPA, Vessel Discharge Sample Collection and Analytical Monitoring: A How-To Reference for EPA's 2013 Vessel General Permit, EPA 800-B-14-001, September 2014. How-to reference (PDF)
- [8]US EPA, Vessel Incidental Discharge Act (VIDA) — status of the 2013 VGP as interim requirements. Regulatory status reviewed 7 September 2026. 2013 VGP and interim requirementsVIDA overview
- [9]Varuna Marine Services B.V., Environmental Service Brochure, Rev. 1.1, 6 June 2026: sections 3.2, 3.3(E), 6.0 and Annex A. Brochure (PDF)