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Lead, pesticides and potentially harmful bacteria were among the contaminants found during an investigation into cannabis sold in semi-legal “coffee shops” in the Netherlands.
The research, which aimed to establish a “baseline” level of typical contamination , was carried out by the Netherlands Institute of Mental Health and Addiction (Trimbos Institute). It will be used to inform a trial starting in April in which shops in 10 municipalities will sell cannabis that is produced by licensed growers and subject to limits on contaminants.
The researchers tested 50 cannabis samples, both resin and weed, bought from randomly selected sellers. One in five of the samples contained “microbiological transgressions” such as Staphylococcus aureus bacteria or fungal residue, and pesticide traces were found in about one-third. One hashish sample contained almost six times the amount of lead (28.5mg/kg) that will be allowed in the cannabis sold during the trial.
“Yes, there are contaminants in the cannabis,” said Pieter Oomen, an analytical chemist and researcher on the Dutch drug market. “We found multiple pesticides, multiple instances of microbiological contamination and one sample that contains lead.”
Although tourists flock to the Netherlands under the impression that cannabis is fully legal, since 1976 a tolerance policy has simply meant the sale of hash and marijuana is permitted in regulated “coffee shops”. However, since growing more than five plants is illegal, shops must buy from illegal suppliers, raising concerns about encouraging criminality.
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The regulated cannabis trial aims to cut out the criminal circuit and reduce contamination. Ten growers have gone through criminal checks and will be licensed to supply cannabis to the coffee shops taking part in the trial; four are now ready to supply. Their produce will be tested to make sure it does not exceed limits for contaminants including heavy metals, micro-organisms, pesticides and harmful aflatoxins produced by fungi.
In the research, potentially harmful Staphylococcus aureus bacteria were an indication of inadequate hygiene levels at any stage of growing, trimming, packaging or selling cannabis.
Oomen said the small study was “exploratory” and did not mean all cannabis in the Netherlands was contaminated. The study concluded that the harm was likely to be relatively minimal compared with the health impact of smoking a joint in the first place, especially when combined with tobacco.
“It’s hard to interpret any of the microbiological contaminants we found, because the impact very much depends on the immune system of the person consuming the cannabis,” he said.
“We do not expect that the contaminants that we found will add significantly to the risks that somebody runs already, just from using the cannabis itself. The acute effects can range from anxiety and panic, issues with attention that can potentially lead to accidents in traffic, to addiction, basically … Cannabis is a drug. If you don’t want to run any risks regarding your health, don’t use drugs.”
