Cannabis cultivation entails a number of variables including soil, moisture, fertilization, and lighting, among other considerations. Cultivation practices involving fertilizers and other additives may contribute to the presence of naturally-occurring ground contaminants such as heavy metals - arsenic, cadmium, lead, and mercury - which are present at varying levels in soil. As a “metal accumulator” cannabis plants can absorb and concentrate these metals, representing a significant health concern in raw material consumption. As well, downstream processing can further concentrate and even introduce new sources of these contaminants into manufactured consumables.
For these reasons, it is paramount to test for heavy metal contamination in raw cannabis materials and cannabis products, and many states have enacted regulations regarding test parameters and acceptance levels. The FDA and US Pharmacopeia, which dictate the testing methodologies and acceptance criteria associated with food, drug, cosmetic/personal care and dietary supplements, have recently moved away from traditional “wet chemistry” techniques, in favor of “greener” methods with higher sensitivity and specificity for target contaminants.
Atomic absorption (AA) and other atomic spectrometry techniques can readily identify heavy metals in solid materials and liquids. High-performance inductively coupled plasma mass spectrometry (ICP-MS) and variations thereof have quickly become the state-of-the-art testing technologies, producing the highest sensitivity and specificity for metals analysis. These technologies are very likely to see increased and perhaps universal adoption as the industry continues to grow and regulations evolve.
Inductively coupled plasma is plasma that has been ionized through inductively heating gas with an electromagnetic coil.
The key with ICP is the use of a plasma temperature that produces a significant proportion of ions formed through loss of single electrons (singly charged ions), without significant generation of multiply-charged low energy ions. ICP serves to produce ionized species from challenging samples, suitable for downstream measurement.
ICP can be coupled with a mass spectrometer to measure high-resolution masses of charged sample ions.
An advantage of ICP-MS is the ability to acquire high-resolution absolute quantitation over a wide range of sample ions, limited only by the mass range of the MS instrument. The robustness, sensitivity, and accuracy of the technique supports it’s use as a superior method for metals analysis in cannabis.
ICP-OES differs from ICP-MS in that the technique utilizes ICP in combination with measurements of electromagnetic radiation at wavelengths characteristic of specific elements (metals) in the sample.
Wavelengths can be measured simultaneously across a broad range, limited only by the system. In this regard, ICP-OES can analyze a large number of ions and samples very quickly and efficiently. An advantage over ICP-MS is a relatively straightforward workflow without the requirements for complex MS instrumentation. Disadvantages include lower resolution and quantitative power along with potential loss of some species identification.
Although the use of a specific technique (AA, ICP-MS, ICP-OES, or other) may vary with the scope and scale of the cannabis operation, tightening state regulations and eventual federal mandates may dictate the use of a standard high-performance platform for metals analysis.
Visit the LabX Cannabis Laboratory application page for product listings and further resources
Updated August 2021