Cannabis radioactivity
Abstract
Cannabis (Cannabis sativa L.) is the most widely used illicit drug of abuse in the world. Burning marijuana produces hundreds of chemicals, including over a hundred different cannabinoids. The most important is delta-9-tetrahydrocannabinol (Δ9-THC), which is responsible for psychoactive effects such as euphoria and relaxation, but also for potential psychotic effects, which are linked to cannabinoid receptors in the brain (mainly CB1). The compounds in cannabis smoke and tobacco smoke are similar, differences being the presence of cannabinoids and nicotine, respectively. The common constituents of tobacco smoke are mainly carbon monoxide, ammonia, hydrogen cyanide, isoprene, acetaldehyde, formaldehyde, acrolein, phenols, polycyclic aromatic hydrocarbons (benzopyrene) and heavy metals (cadmium, mercury, and lead) which can cause diseases affecting the respiratory system and other organs in the body. Recently, the presence of Polonium-210 (Po-210), an alpha radioactive substance in all cannabis products (smoked cannabis, hashish,) in various and different concentrations, has been identified in cannabis, as well as in tobacco, smoke as well. Awareness of the presence of this highly radioactive and carcinogenic heavy metal may be an extra motivational boost, both for not starting to experiment cannabis and for current smokers to cease cannabis use.
Introduction
The amount of radiation received by humans comes from naturally occurring uranium series unearthed in Nature. Over the last 80 years, this natural radioactive amount has been enriched by radionuclides caused by nuclear tests and accidents at nuclear reactors for the production of nuclear energy. Characteristics of nuclear fission radioisotopes, such as cesium-137 and strontium-90, which have seeped into the environment, polluting ecosystems, can become more concentrated as they enter the food chain, which could cause serious threats to human health [1-3].
In particular, Polonium (Po-210) and its precursor, Lead (Pb-210), alpha-emitting radionuclides, with a physical half-life of 138.4 days and 22.4 years, respectively, penetrate and accumulate in the body, through various entrances [1-4]. Polonium is readily absorbed by organisms [5, 6] and it is estimated that the internal radiation of natural Po-210 obtained by food ingestion, through the food chain, contributes about 7% of the total human harm dose [7].
The dominant source of Po-210 and Pb-210 in the atmosphere is the decay of Radon (Rn-222) from the Earth’s crust [8, 9]. Radionuclides fall with atmospheric precipitation (rain, snow and dust) and can be deposited on soil, including on crop plants and water surfaces.
The atmospheric deposition of 210Po and 210Pb is measurable in a wide range of 0.05 to 0.5 kBq·m2.y-1 [10, 11]. Polonium uptake by plants occurs indirectly through the root system and directly from atmospheric fallout on plants [12] and polyphosphate fertilizers [13-15].
Cannabis plants (Cannabis sativa L.), like tobacco plants, receive direct deposition of Po-210 and Pb-210 on the surface of their leaves, which have the particularity of being rich in trichomes, a sort of glandular pores capable of storing heavy metals [16, 17]. A certain proportion of these radioactive isotopes may come from phosphate fertilizers [18-23].
A characteristic of Cannabis sativa L. is that it belongs to the Rosales family [24, 25], a family known for absorbing wet and dry deposition on leaves and other parts of the plant [20]. These properties are likely related to the leaf structure, which is characterized by a dense network of trichomes capable of retaining heavy metals.
Not surprisingly, due to its properties such as short vegetation time and rapid growth rate, this plant is often used as a medium in the Phyto-extraction of toxic metals from the soil [26]. Under industrial cultivation conditions, Cannabis sativa L. is grown in large fields, and this affects the structure of the plant itself. Cannabis grows up to reach the hight of 3, (depending on the species and weather conditions), and has reduced lower layers of leaves. This can have an impact because the lower leaves during high growth have less access to airborne dust which is one of the main sources of polonium in the plant. A very similar mechanism is present in tobacco plants. However, there are also factors that increase the accumulation of nuclides in some parts of the plant compared to others.
One of these for the lower leaves is, on the one hand, their long exposure to weather conditions and dry and wet precipitation; on the other hand, these leaves often become wilted and there is no transport of substances in them; this can affect the level of accumulation of Po-210 and Pb-210 radionuclides as well. During 4-5 months of growth, plants require a significant amount of water and soil rich in organic carbon, phosphorus, and nitrogen. As a result, the fields are highly fertilized, especially with nitrogen and polyphosphate-based fertilizers. The latter, being extracted from uranium rocks containing apatite, enrich the culture media of radium, uranium, and its decay products such as Po-210 and Pb-210 [19-22, 27]. Thanks to the rhizosphere and root absorption, these radioisotopes increase the alpha radioactive presence of the cannabis plant, similar to the tobacco plant.
Cannabis products
There are several types of cannabis products, generally available, for both legal and illegal trade. Three products stand out in particular: dried Cannabis sativa L. (cannabis), hashish and cannabis infusion or herbal tea.
In the clandestine trade, there are various types of hashish that depend on the type of cannabis used. Hashish Afghan-type is black, Moroccan type green to creamy green, Dutch type is green, Nepalese type is dark brown, Indian type is brownish and greenish with white veins, Lebanese type is red or yellow. The colour of hashish also depends on the growing conditions and the type of plant from which it is produced [28].
Cannabis: from soil to plant
Cannabis sativa L. (where “L.” stands for Linnaeus, the scientist who first classified it in 1735) appears to possess the capacity to regenerate ecosystems, particularly those with high radioactive contamination and elevated concentrations of heavy metals. Similar to the tobacco plant, cannabis can significantly reduce the concentrations of various heavy metals and anthropogenic toxic substances, such as lead-210, polonium-210, and strontium-90, through phytodegradation in the rhizosphere and the absorption of radiation via its stems and leaves.
Cannabis plantations have been employed to aid in the remediation of land contaminated by radiation, such as certain areas affected by the nuclear disaster at Chernobyl [21, 29, 30]. However, it must be noted that while the plant’s capabilities facilitate detoxification, they also result in the depletion of macronutrients in the soil where it is cultivated.
Furthermore, it is critical to ensure that these crops, intended for land regeneration, are incinerated in dedicated facilities capable of handling radioactive ash as hazardous waste. This would prevent their diversion into illicit markets, where unscrupulous individuals might exploit them.
Finally, it is important to clarify that consumers of cannabis, in any form, may inadvertently ingest toxic substances accumulated by the plant, thereby exposing themselves to potentially serious health risks.
Radioactive pharmacotoxicology of cannabis
Burning cannabis produces thousands of chemicals, both in the gas phase and in the tar phase. In particular, in the study of Wieczorek et al. the concentrations of Po-210 and Pb-210 were determined in 44 cannabis samples, 20 hashish and 8 cannabis tea samples, as well as in 3 types of cannabis plants (higher parts of the mature hemp plant Phenola, Fedora, and Futura) [29]. Each of the sample names indicates a different type and cross of Cannabis sativa L. Since they are numerous, they are recognized on the market by these names. Effective doses were calculated and compared with doses of other combustion products, such as tobacco. In the case of c