The [64Cu]-NP-uptake and accumulation amounts observed within lettuce seedlings were reasonable and comparable to others reports in the literature, reaching the same general conclusions that NP transport and accumulation in plants is species and size dependent.Smaller NPs have been demonstrated to have higher accumulation in plants than larger NPs. For example, Ni-NPs had very high NP uptake ranging from ∼13 200−38 983 μg/g in mesquite.The amount found in the leaves varied from 400 to 803 μg/g of mesquite with most the NPs remaining in the roots ranging from 12 835 to 38 183 μg/g.Another study using small CeO2-NPs exhibited NP accumulation ranging from 300 to 6000 μg/g of plant and indicated that NP accumulation was plant species dependent.NP sizes above active transport ranging from 14 to 40 nm had a large variation in uptake ranging from 0.25 to 3750 μg/g of plant, but typically had accumulation ranging from ∼1−1100 μg/g of plant again with the majority of the NPs contained within the root and with 0.5−183 μg/g in the leaves.NPs , had accumulation in mung bean of 8 μg/g and in wheat of 32 μg/ g.When comparing the accumulation of two similarly sized TiO2-NPs of different crystalline structure [22 nm and 25 nm ] in wheat different accumulation amounts were observed,vertical grow tables suggesting size was not the only limiting factor for transportation into a plant.In another study using radioactive NPs, Zhang et al.generated 141Ce by neutron bombardment of CeO2NPs synthesized via a precipitation method.
The fabrication of [ 141Ce]CeO2-NPs could make controlling the size distribution very difficult and the exact size of the radioactive [141Ce]CeO2- NPs was never determined. In addition, free radioactive 141Cemetal could dissolute and be transported into the plant, making it appear as if the intact-NPs were in the plant because possible leaching of radioactivity was not explored. We aimed to avoid complications of NP-fabrication in which the exact size distribution during the study could not be determined and to improve upon prior radio labeling methods, which gave low specific activity of 2.7 μCi/mg of NP.We were able to generate stable radioactive [ 64Cu]-NPs with high radio chemical purity and a specific activity of 2.2 mCi/mg of NP with a tight size distribution . Zhang et al.’s work also demonstrated a concentration and size dependence of the [141Ce]CeO2-NPs on plant accumulation in cucumber.These uptake differences may be attributed to the use of a different species and/or the NP solution administered had 2.4-times higher concentration . Autoradiography images showed [ 141Ce]CeO2-NPs movement to the leaves, implying that once NPs entered into the vascular cylinder, they move along with water flow. This was in good agreement with our study. In contrast, we saw no concentration dependence for either sized [ 64Cu]-NP using 48, 96, and 144 mg L−1 over a 2 h period with approximately the same accumulation amount at all concentrations . Similarly, another study using CuO-NPs administered two concentrations 10 mg L−1 and 100 mg L−1 for a period of 14 days in maize also observed no concentration dependence.
The use of NPs tagged with radioactivity and tracked by autoradiography and PET/CT has provided a noninvasive analytical tool to spatially visualize and quantify NP uptake and accumulation in plants. We investigated the fate of [64Cu]-NP transport into plants at the largely unexplored early time points, which would prevent dissolution events. Stability studies concluded that the [64Cu]-NPs were stable during the imaging and quantification time frame from 0.25 to 24 h resulting in intact NP-transport into lettuce seedlings. We further demonstrated that the transport of [64Cu]-NPs into lettuce was not concentration dependent but was size dependent with the 20 nm [64Cu]-NPs reaching a plateau with accumulation at ∼5.7 μg/g of lettuce and the smaller 10 nm NPs accumulation increasing linearly with the maximum amount at 24 h being ∼7.6 μg/g of lettuce.With the numerous factors that may dictate NP uptake and accumulation, further studies are warranted to fully understand the molecular mechanism of NP transport into plants.Legalization of cannabis production in 2017 has generated demands for state regulatory, research and extension agencies, including UC, to address the ecological, social and agricultural aspects of this crop, which has an estimated retail value of over $10 billion . Despite its enormous value and importance to California’s agricultural economy, remarkably little is known about how the crop is cultivated. While general information exists on cannabis cultivation, such as plant density, growing conditions, and nutrient, pest and disease management , only a few studies have attempted to measure or characterize some more specific aspects of cannabis production, such as yield per plant and regional changes in total production area . These data represent only a very small fraction of domestic or global activity and are likely skewed since they were largely derived not from field studies but indirectly from police seizure data or aerial imagery . In California, where approximately 66% of U.S. marijuana is grown , knowledge of the specific practices across the wide range of conditions under which it is produced is almost nonexistent.
Currently, 30 U.S. states have legalized cannabis production, sales and/or use, but strict regulations remain in place at the federal level, where it is classified as a Schedule I controlled substance. As a land-grant institution, UC receives federal support; were UC to engage in work that directly supports or enhances marijuana production or profitability, it would be inviolation of federal law and risk losing federal support. As a result, UC research on California cannabis production has been limited and focused on the geography of production and its environmental impacts . These studies have documented the negative effects of production on waterways, natural habitats and wildlife. While such effects are not unique to cannabis agriculture per se, they do present a significant threat to environmental quality and sensitive species in the watersheds where cannabis is grown . Science-based best management practices to mitigate or avoid impacts have not been developed for cannabis. Because information on cannabis production practices is so limited, it is currently not possible to identify key points of intervention to address the potential negative impacts of production. As a first step toward understanding cannabis production practices, we developed a statewide survey on cultivation techniques, pest and disease management, water use, labor and regulatory compliance. The objective was to provide a starting point from which UC scientists could build research and extension programs that promote best management practices — which are allowable as long as their intended purpose is not to improve yields, quality or profitability. Survey results also establish a baseline for documenting changes in cultivation practices over time as legal cannabis production evolves in California. To characterize key aspects of cannabis production in California,hydroponic growing systems we developed an anonymous online survey using Qualtrics survey software . A web-based survey that masked participants’ identity was determined to be the most suitable approach given that in-person interviews were limited by legal restrictions on UC researchers visiting cannabis farms, and mail or telephone surveys were constrained by the lack of any readily available mailing address or telephone contact information for most cannabis growers, who are understandably discrete with this information. An online survey was also the most cost-effective means of reaching a large number of cannabis growers. Survey questions focused on operational features , pest and water management, labor, farm revenue and grower demographics. Two draft surveys were reviewed by a subset of cannabis growers to improve the relevance of the questions and terminology. A consistent critique was that the survey was too long and asked for too much detail, taking up to 2 hours to complete, and that such a large time commitment would significantly reduce the response. We therefore made the survey more concise by eliminating or rephrasing many detailed questions across various aspects of cannabis production. The final survey included 37 questions: 12 openended and 25 structured . Structured questions presented either a list of answer choices or a text box to fill in with a number. Each list of answer choices included an “Other” option with a box for growers to enter text. Open-ended questions had a text entry box with no character limit. Condensing the survey to capture more respondents resulted in less detailed data, but the overall nature of the survey remained the same — a survey to broadly characterize multiple aspects of cannabis production in California. Data from the survey has supported and contextualized research by other scientists on specific aspects of cannabis production, such as water use , permitting , law enforcement , testing requirements , crop prices and perceptions of cannabis cultivation in the broader community . Recruitment of survey participants leveraged networks of California cannabis growers who had organized themselves for various economic and political purposes . These were a combination of county, regional and large statewide organizations, with many growers affiliating with multiple groups.
We identified the organizations through online searches and social media and sent recruitment emails to their membership list-serves. The emails contained an explanation of the survey goals, a link to the survey website and a message from the grower organization that endorsed the survey and encouraged members to participate. The emails were sent in July 2018 to approximately 17,500 email addresses, although not all members of these organizations necessarily cultivated cannabis, and the organizations noted that their mailing lists somewhat overlapped the lists of other groups that we contacted. For these reasons, the survey population was certainly less than 17,500 individual cannabis growers, but because we were not able to view mailing lists nor contact growers directly, and because there are no comprehensive surveys of the number of cannabis farms in California, we could not calculate a response rate or evaluate the representativeness of the sample. Respondents were given until Aug. 15, 2018, to complete the survey. All survey participants remained anonymous, and response data did not include any specific participant identifiers.In total, 101 surveys were either partially or fully completed. Responses to open-ended questions were coded before summary. Since incomplete surveys were included in this summary, the number of responses varied between questions. Each response was considered a unique grower and farm operation. As noted, survey response rate was difficult to quantify, and participants were self-selecting, which introduces bias. The survey data should be taken only as a starting point to guide more detailed evaluations of specific practices in the future, not as a basis for developing recommendations for production practices or policies.Survey respondents operated farms primarily in Humboldt , Mendocino and Nevada counties, but survey responses also came from Trinity , Santa Cruz , Sonoma , San Luis Obispo , Sacramento , Butte , Calaveras , Fresno , Los Angeles , San Diego , San Mateo and Siskiyou counties and Josephine County, Oregon . In line with California regulatory guidelines, small farms were defined as those of 10,000 sq ft or less, medium farms 10,001 to 22,000 sq ft and large farms 22,001 sq ft or more. Accordingly, 74% of farms were small, 16% were medium and 8% were large . For those growers who reported on their land use in 2013 , most farmed on land that was previously used entirely or in part for cannabis production . The other 22% indicated that the land was used in 2013 for agricultural crops, ranching, open space or “other” land uses.For this survey, we differentiated between outdoor , greenhouse and indoor farming . The most common ways to farm were all outdoors , combined outdoor and greenhouse and greenhouse only . This was followed by various combinations of greenhouse and indoor , greenhouse and other , outdoor and other , outdoor and indoor , all indoor and other . When measured by total plants, farms with combined outdoor and greenhouse facilities were responsible for 41% of crop production, followed by outdoor and other , greenhouse only , outdoor only , greenhouse and other , outdoor and indoor , greenhouse and indoor and other . A majority of survey respondents grew their cannabis crop in raised beds , native soil and/or grow bags , followed by hydroponic systems and plastic pots .Most growers reported groundwater as their primary water source for irrigation , with some growers reporting use of multiple water sources. Those using groundwater extracted 87% of annual volume between June and October. Of those storing water, most stored exclusively well or spring water, though some stored municipal water or rainwater .