As more US states legalize recreational and medicinal cannabis use, legal market cannabis products present a new and growing potential source of heavy metal exposure. Currently, most states with legal markets only require testing for the big four heavy metals: arsenic, lead, cadmium, and mercury. However, cannabis and hemp plants are known hyperaccumulators of heavy metals from soil and water and may be subject to a much broader array of contaminants. Heavy metal exposure is associated with a wide array of negative health impacts, including cardiovascular and respiratory system damage, making appropriate regulatory limits in consumer products a public health priority. The goal of this study was to characterize levels of 20 heavy metals in Colorado market cannabis flower using newly validated laboratory methods. Flower samples were anonymized and randomly selected from within the inventory of a laboratory that conducts state regulatory testing of cannabis and hemp in Colorado. Flower samples were analyzed using inductively coupled plasma-mass spectrometry. Heavy metal concentrations were generally within previously established ranges for tobacco and cannabis products, with some heavy metals at markedly lower levels than what has been observed in tobacco products. Flower samples that failed state regulatory testing for one of the big four heavy metals had higher levels of chromium and lower levels of beryllium than samples that did not fail for any of the big four heavy metals. Flower samples from indoor grow operations had lower levels of barium, lithium, and selenium than samples from outdoor grow operations. These findings highlight the need for more research into the levels of heavy metal contaminants in consumer cannabis products in Colorado and other US legal markets.

The increasing impact of global climate change has resulted in adversity stresses, like salt and drought, gradually becoming the main factors that limit crop growth. Hemp, which contains numerous medicinal active components and multiple bioactive functions, is widely used in the agricultural, industrial, and medical fields, hence promoting the rapid development of related industries. Arbuscular mycorrhizal fungi (AMF) can establish a symbiotic relationship with 80% of vascular plants. This symbiosis promotes host plant growth, regulates plant physiology and biochemistry, facilitates secondary metabolite synthesis, and enhances resistance to abiotic stresses. However, the effects of salt stress, drought stress, and AMF interaction in hemp are not well understood. In this study, to investigate this, we performed a study where we cultured hemp that was either inoculated or uninoculated with Funneliformis mosseae and determined changes in effective colonization rate, growth, soluble substances, photosynthesis, fluorescence, ions, and secondary metabolites by cultivating hemp under different concentrations of NaCl (0 mM, 100 mM, and 200 mM) and different soil moisture content (45%, 25%, and 15%). The results showed that salt, drought stress, or salt-drought interaction stress all inhibited colonization rate after stress, plant growth, mainly due to ion toxicity and oxidative damage. Inoculation with F. mosseae effectively alleviated plant growth inhibition under 100 mM NaCl salt stress, drought stress, and salt-drought interaction stress conditions. It also improved osmoregulation, photosynthetic properties, fluorescence properties, and ion homeostasis, and promoted the accumulation of secondary metabolites. However, under 200 mM NaCl salt stress conditions, inoculation with F. mosseae negatively affected plant physiology, biochemistry, and secondary metabolite synthesis, although it did alleviate growth inhibition. The results demonstrate that there are different effects of salt-drought interaction stress versus single stress (salt or drought stress) on plant growth physiology. In addition, we provide new insights about the positive effects of AMF on host plants under such stress conditions and the effects of AMF on plants under high salt stress.