Traces of several contaminants dangerous to human health, including heavy metals and pesticides, were found in cannabis sold in Dutch coffee shops, according to a recent report.
The Netherlands is known for its coffee shops, where the sale of the drug for personal consumption, in small quantities, is tolerated by authorities.
However, cultivation and delivery are still prohibited, which can lead to varying standards as shops are forced to buy from illegal suppliers.
A new study by the Trimbos Institute, the Netherlands' research centre on the use of alcohol, tobacco and drugs, has investigated the quality of over-the-counter cannabis in the country.
"Cannabis is always harmful, especially if you combine it with tobacco," Pieter Oomen, researcher of Drugs at the Institute, said. "In our study, we also found contaminants in cannabis. So extra vigilance is needed."
The research will be used by several Dutch ministries launched the Closed Coffee Shop Chain Experiment (EGC), in which shops in 10 municipalities will sell cannabis produced by licensed growers. As part of this project, the cannabis was subjected to limits on contaminants.
Lead, pesticides and fungi
The Trimbos Institute's research focused on the presence of heavy metals, pesticides, microbiological contaminants and aflatoxins (a family of toxins produced by certain fungi).
A total of 105 samples were randomly purchased from coffee shops: about half of the samples involved hashish, the other half weed.
About a third of the samples contained pesticides which will not be allowed under the EGC rules. "However, the amount of these substances you would ingest if you were to smoke every day remains well below the amount considered harmful."
A man smokes cannabis at a shop in Amsterdam. Credit: Belga
One of the 50 hash samples tested contained an excess of the permitted amount of lead, a heavy metal that can be very harmful to humans. "The health impact of the concentration found is probably limited, but it does give reason to be alert for this type of contamination."
Six cannabis samples contained high levels of the potentially harmful Staphylococcus aureus bacteria.
This can be an indicator of inadequate sanitary conditions under which the cannabis in question was grown, trimmed, packaged or sold. "However, whether these contaminants lead to disease also strongly depends on the health of the user."
None of the cannabis samples had a concentration of aflatoxins that exceeded the limits that will be set by the EGC.
The study noted that, with this knowledge, most contaminants do not pose additional health risks to otherwise healthy people. "More research on consumers' intake of contaminants from (smoked) cannabis and its specific effects is needed to better identify its harmfulness."
Users were also warned that while contaminants fall below the permissible limits, alertness is still required, especially where heavy metals are concerned. "The EGC offers the chance to minimise risks from cannabis contaminants by making quality requirements central to cultivation," it concluded.
