The Unlisted Screen: Why Pesticide Residues Need Their Own Line on a UK CBD Certificate

A certificate of analysis for a UK CBD product often arrives as a neat sequence of tables. Cannabinoid potency sits at the top, followed by heavy metals, perhaps microbial results, and a conclusion that reads, in effect, compliant. For a buyer trying to make a sensible decision, those heavy-metal figures can be quietly reassuring. Lead, arsenic, cadmium and mercury are familiar contaminants, and a clean result suggests that someone has considered what might be in the soil or the process. Yet that reassurance covers a defined question. It does not answer a neighbouring one: whether the hemp was screened for pesticide residues.

The distinction is not a technicality. Heavy metals and pesticides belong to different contaminant families, arise from different routes, and require different analytical methods. A certificate that is strong on one can be entirely silent on the other. For UK buyers, the practical task is to notice that silence and to know what a proper pesticide screen should contain.

Two Contaminant Families, Two Different Questions

Heavy metals are elements. They can be measured with techniques such as inductively coupled plasma mass spectrometry, and the result is expressed in milligrams per kilogram or parts per billion. Pesticides are a much broader group of organic active substances, along with their metabolites and breakdown products. They are typically measured by chromatographic methods coupled to mass spectrometry, often split between liquid chromatography and gas chromatography depending on the chemistry of the compounds concerned.

That difference matters because one test cannot act as a proxy for the other. A low lead result says nothing about whether a grower used a plant protection product late in the season, whether a neighbouring field drifted, or whether a stored batch was treated during handling. Nor does a full cannabinoid profile settle the question. Potency testing describes the desired constituents; it does not survey unwanted ones.

A COA can therefore be accurate, well presented and genuinely reassuring on metals while leaving the pesticide question open. The absence of a pesticide section is not proof of a problem. It is, however, an evidence gap.

What a Pesticide Screen Actually Looks Like

A credible pesticide screen is usually a multi-residue panel. Rather than testing for one substance, the laboratory looks for a defined list of active substances and, in some cases, their metabolites. The list might run to dozens or several hundred compounds. The exact scope depends on the laboratory, the method and the commodity being tested.

This is where a single word such as ‘pass’ can mislead. A pass only means that the analytes on that particular panel were below the agreed reporting criteria. It does not mean that every pesticide ever registered, withdrawn or used elsewhere in the world has been excluded. Targeted analysis is powerful, but it is targeted. A buyer should therefore look for the scope of the panel, not simply its conclusion.

The method also matters. Modern multi-residue work often uses tandem mass spectrometry, with liquid chromatography for polar or thermally fragile compounds and gas chromatography for more volatile ones. Sample preparation is equally important. A dried flower sample and a finished oil extract are different matrices, and an extraction step can concentrate residues as well as cannabinoids. A result obtained on one does not automatically describe the other.

The Difference Between ‘Not Detected’ and ‘Not Tested’

Certificates frequently use shorthand. ‘ND’ may stand for not detected. ‘<LOQ’ means below the limit of quantification. Neither phrase means zero. They mean that the instrument did not find the analyte at or above the stated reporting threshold. The size of that threshold is central to how much the result proves.

For pesticide residues in food, UK maximum residue levels are set under retained legislation, with default levels applying where no specific MRL exists for a commodity. A laboratory’s limit of quantification should sit at or below the relevant limit if the result is to support a compliance statement. A report that says only ‘below 0.05 mg/kg’ is less informative than one that lists the individual limits of quantification and shows that they are fit for the intended purpose. A result below a relatively high threshold may tell a buyer very little about whether the batch meets a much lower default level.

Buyers should also distinguish between a summary line and the underlying data. A sentence such as ‘pesticides: compliant’ is a conclusion. The useful evidence is the analyte list, the limits of detection and quantification, the units, the sample identity and the date of analysis. Without those, the conclusion is difficult to audit.

Why Hemp Is Not Automatically Low-Risk

It is sometimes assumed that hemp is a robust crop that needs little intervention. Hemp can indeed grow vigorously, but it is not immune to pests and diseases. Aphids, mites, moulds and other pressures can affect a crop, particularly in a damp UK season or in protected environments. Growers may use integrated pest management, biological controls and authorised plant protection products. The relevant question is not whether hemp is a ‘natural’ crop, but whether the specific batch was produced under a system that controlled residues and whether that control was verified.

Outdoor cultivation brings its own variables: neighbouring land, drift, shared equipment and water sources. Indoor or protected production may reduce some exposures while introducing others, such as recirculated air, shared irrigation and close plant spacing. None of these factors can be inferred from a heavy-metal panel. They belong to the pesticide and production-history conversation.

Sensitivity, Scope and Accreditation

When a pesticide section does appear, a few details deserve attention. Is the laboratory accredited to ISO/IEC 17025 for the specific method and matrix? Is the method named or referenced? Are the limits of detection and quantification stated per analyte? Is the sample clearly identified as flower, extract, oil or finished product, and does its batch code match the bottle? Is the analysis date recent enough to describe the batch in question?

Accreditation is not a guarantee of perfection, but it provides a framework for competence and traceability. Matrix effects are another consideration. Hemp extracts can be complex, and a laboratory should be able to explain how it handled interference and recovery for the matrix tested. A buyer does not need to interpret the raw chromatography, but the producer should be able to supply the underlying report on request.

Practical Questions for a UK Hemp Producer

A short, direct set of questions will usually reveal whether the pesticide evidence is substantive:

• Which laboratory carried out the pesticide screen, and is it accredited for this matrix?
• Which analytical method was used, and what is the full list of analytes covered?
• What were the limits of detection and quantification for each analyte, and how do they compare with the applicable UK limits?
• Was the sample dried flower, crude extract or finished oil, and how does that relate to the product being sold?
• Does the batch code on the certificate match the batch code on the bottle?
• Were any analytes detected above the limit of quantification, and if so, what action was taken?
• Does the producer operate a documented pesticide policy, including integrated pest management and supplier declarations for any inputs?

These questions are not adversarial. They are the normal due diligence of a buyer who understands that a certificate is a map of what was tested, not a guarantee of everything that was not.

A Balanced Reading of the Certificate

Heavy-metal testing remains valuable. It addresses a real route of contamination and should not be dismissed. The point is that it occupies its own lane. Pesticide residues need a separate, scoped and sufficiently sensitive screen, reported with enough detail for a buyer to see what was covered and what the limits were.

At CBD Produce, the editorial position is straightforward: a COA should be read as a set of specific claims, each with a method, a limit and a batch behind it. If the pesticide line is missing, the appropriate response is not to assume contamination. It is to ask for the missing evidence. A producer who can supply a clear multi-residue panel, with accredited methods and meaningful limits, has given the buyer something more useful than reassurance. They have given them a record they can examine.