Throughout time, our country has had many pollutants in our soil throughout time. Some are natural, but as we look closer to the industrial revolution, many are man-made. As this began, we realized many plants were not surviving near rivers and streams that were highly polluted, they also did not survive well near mines, because of the high amount of metals, or what other things were being mined (Denchak, 2019). Due to all of these pollutants, there is a lot of interest in how to reduce the amount of these pollutants in the soil, water, and air. For my focus, we will be focusing on ways to remove pollutants from soil, and we will be using common pollutants. We will be particularly focusing on a plant known for being able to remove some pollutants from the soil. We will be focusing on the plant known as hemp (Cannabis sativa L.), which is not marijuana. We will be focusing on the effects of three main heavy metal pollutants found in soil which are arsenic, copper, and zinc. Hemp is known to be able to absorb some amount, so I will be testing 3 different amounts, none, a little bit, and then a lot of the metal. I will be observing how different amounts of the metal will affect the plant growth (height, grow time, root length and width, number of branches). In addition, I will also potentially measure the soil composition once the experiment is over to see how much metal has been absorbed by the hemp plants.
In Penn State's Extension, I found some background on how hemp works, and the many uses of the plant as well. Hemp has been found as one of few plants who can survive in heavily polluted soils (Linger et al., 2001). There have been quite a few studies on how plants use phytoremediation to help clean soil and waters, and hemp is one of the few plants that has been used successfully in these studies. In a study completed at University of Florence in Italy, there was an experiment completed on uptake of cadmium, lead, and thallium. The experiment showed that growth was slightly stunted but the plants still grew just fine (Candilo et al., 2004). The presence of hemp in all experiments, not just for the one done in Florence, greatly decreased the heavy metal content greatly and the plant absorbed the metals in its leaves and stems (Linger et al., 2001; Candilo et al., 2004; Husain et al., 2019; Dizikes, 2010).
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It is also important to note that hemp is used in a variety of industries: medicine, retail uses, etc. (Etter, 2019). Hemp is used medicinally when the CBD or cannabidiol is extracted from the plant and given orally or absorbed through the skin. It can help with inflammation, seizures, anxiety, and insomnia (Grinspoon, 2019). These are the main scientifically proven treatments that do work. It mainly is used medicinally for chronic pain, but, there are some side effects. They are not bad, but they can be annoying to some. Retail use is the main and most common use for hemp. Each part of the plant has different industrial uses, the fibers, leaves, oil, and seeds. The fibers are used for clothing, shoes, paper; leaves for mulch and compost; oil for well, oil, beauty products, and moisturizer; and seeds are used for flour and seed cake (Harper et al., 2020). However, there is a downside to the phytoremediation of hemp. The metals, pesticides, and other pollutants that are absorbed by the hemp plant, can produce contaminated products (Etter, 2019). The pollutants that get condensed into the oil and the seeds that are harvested, can contain condensed amounts of pollutants which can be toxic when ingested (Etter, 2019).
While there hasn't been much research done on hemp and phytoremediation, as it is still a new idea and new research topic, what has been found is that hemp is a plant that is very good at removing contaminants from soil and water (Linger et al., 2001; Candilo et al., 2004; Husain et al., 2019). There have been other studies and articles showing that plants can purify water (Dizikes, 2010; Stone, 2019; Linger et al., 2001; Candilo et al., 2004; Husain et al., 2019). There hasn’t been a lot of research conducted on how larger or smaller amounts of pollutants affect plant growth. With a study conducted on this, researchers and scientists may be able to decide how close they can place these plants to a contaminated area without killing it and absorbing the maximum amount of the pollutant.
Hemp plants can are usually diploid plants, which means they are single sex, but sometimes they can be hermaphroditic. Hemp plants come from the Cannabinaceae family, which is separated into 11 different genera, with cannabis, humulus, and celtis being the most commonly known. Within the genus cannabis there are hundreds of subspecies, the main three subspecies being Cannabis sativa, Cannabis indica, and Cannabis ruderalis (Halawa, 2018). Cannabis sativa is the more socially potent version of the three as it gives a head high and is more used recreationally. Cannabis indica gives more of a body high and can soothe aches and pains. Cannabis ruderalis does not have a high THC content, but it has a higher CBD content typically, so it is more used medicinally rather than to get high ('Understanding Cannabis', 2019). Humulus is more commonly known as hops, found in beer. Growing these plants is fairly similar for sativa and indica strains as they both grow indoors, but sativa takes longer to flower and grow. Ruderalis flowers on an internal timer, regardless of season they will always flower when they are ready. Hemp comes from the Cannabis genus, and is known scientifically as Cannabis Sativa L. The growing conditions for these plants are all fairly similar as they need specific conditions, water, etc.
In our suggestion to examine this plant and the relationship between heavy metal pollutants and plant growth, my team and I plan to gain a better understanding of plant biology, and to be more specific, the way hemp plants absorb the heavy metals without it killing them. While completing our research, our focus will be on familiarizing ourselves with the scientific method as well as gain personal experience with how the method works. In our study, we will be focusing primarily on how much of heavy metals hemp plants can absorb without dying. This is a topic of interest because our planet is becoming so polluted and our soil, groundwater, and surface water are all becoming affected with different pollutants running through them. By studying how much pollutant these plants can absorb, researchers may be able to plant them in heavily contaminated areas to help absorb the chemicals so other plants can grow there.
Based on our publication and article review and concerns surrounding soil and groundwater pollution, our hypothesis statement is the following: If certain plants are able to absorb pollutants in soil and we plant hemp in soils with varying concentrations of heavy metals such as zinc, copper, and arsenic then we should observe that the overall growth (eg. height, growth time, etc) of the hemp plant will not be affected. We will measure the plants characteristics (eg. height, grow time, root length/width, and number of branches) in the hemp plants and we will be observing how they will be possibly responding to the heavy metal amount placed in the soil. By simulating the heavy metals, arsenic, copper, and zinc, in different concentrations in our soil: no metal, low metal, and high metal amounts, we believe we will be able to create a highly useful study that will allow conclusions to be drawn about our explanatory variables.
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