Essay on How Heavy Metals Are Taken Up by Plants Where They Are Retained

Abstract

The necessary micronutrients for plants are manganese, copper, iron, zinc, nickel, and molybdenum. A large amount of them can affect the plant or degrade harvested plant products. In addition, plants do not require other heavy metals such as cadmium, lead, and mercury, which are considered contaminants. When it comes to distribution in aerial plant parts, it’s all about the absorption into the roots, stacking into the xylem, and the redistribution in the phloem. This study examines the long-distance transfer of heavy metals via phloem and xylem, as well as the interconnections between the two transportation networks. Phloem movement is the foundation for transfer within the shoot as well as development in fruits and seeds. Nickel is a highly phloem-mobile metal that is directed to plant sections that are growing and developing.

Keywords: micronutrients; heavy metals; transport; pollutants; phloem; xylem; redistribution.

Instrument/Technique

An experiment can be done to determine the effect of heavy metals on seeds during germination when exposed to different concentrations. Nickel, copper, cadmium, and nickel will be used as the test metals in this experiment. The seeds to be used in this test are mung seed and winter wheat. The seeds will be exposed to heavy metals for 96 hours. After that, they will be tested to see whether early seed development has happened throughout the germination phase. In addition to the type of metal used, the plants and seeds’ physiology and biomechanics have a major role in germination’s responsiveness. A small amount of lead, for example, does not affect growth and development but may be extremely damaging to the environment when exposed at even low levels. Seed germination will be affected by heavy metal toxicity. Toxic metals impair plant growth, particularly in its early stages. To conduct the experiment, copper and cobalt will be used (Fan et al., 2018). To sustain and control cellular and metabolic activities within the body, critical metals have a role in health and growth. Cadmium is a non-essential metal utilized in this experiment (Sevik et al., 2020). Even at low levels, it does not help the plant and has more detrimental than beneficial effects. It has been determined that cadmium is a human carcinogen and may cause a variety of cancers.

When evaluating the exchangeable percentage of elements in soil, single extractions are employed most often. There is much metal pollution in the environment, but heavy metal contamination in agricultural soils poses a serious problem. Heavy metals, which plants absorb, can enter the food chain in large quantities. Consumption of vegetables cultivated in soils with high metal concentrations might result in severe health effects for individuals (Bhatti et al., 2018). Humans consume roughly half of their lead from food, with plants accounting for the majority. The metals most concerned are cadmium and lead due to their potential for toxicity or aggregation in plants and animals. According to the Environmental Protection Agency, it is clear that lead is the most frequent heavy metal pollutant in the environment, and it may be hazardous to organisms even in low amounts (Bhatti et al., 2018). Therefore, a national facility will be better for researching the heavy metals in plants and coming up with ways to reduce or eliminate the metals in the soil in which human and animal consumed crops grow.

Science Case

The statistics will show that the percentage of germination falls as the concentration increases when it comes to germination. In general, heavy metal toxicity will inhibit plant development; however, germination rates may vary depending on the kind of metal and the type of seed. The germination rates of mung beans will be higher than those of winter wheat seeds. There will be a clear difference between nickel and cadmium and copper and cobalt when it comes to heavy metal toxicity in seeds, especially mung beans. It is possible that the measuring method is not precise. Since seedlings’ root and shoot lengths are so short, averaging will help eliminate mistakes in variability (Rodríguez-Bocanegra et al., 2018). Toxic metals will harm seeds and plants if this test is done in the field because of pH and soil conditions.

Plants and seeds are more vulnerable to harmful metals when the pH falls. Cadmium and other heavy metals such as lead and arsenic fight free H+ ions to diffuse in the soil, increasing their solubility (Sevik et al., 2020). Due to an increase in metal content, plants and seeds would most likely increase the absorption of highly concentrated metals in soil, which will enhance plant toxicity. Due to farming, mining, and other human-induced activities that may include heavy metals that may affect plant growth, the soil can significantly impact toxic reactions in plants. In this experiment, seeds exposed to low quantities of certain metals, such as nickel and copper, perform better (Rodríguez-Bocanegra et al., 2018). As a vital metal, copper stimulates growth and development in plants while also regulating cellular processes. This is especially true for the free-reactive metal form, which may be harmful to plants at high concentrations and dosages.

Human activities and anthropogenic sources contribute to the presence of heavy metals in soils. Most heavy metals have a very long residence period in soils. Heavy metals can enhance the formation of reactive oxygen species (ROS) within plants while also assisting in their enzymatic detoxification; in addition, stress can lead to a buildup of reactive oxygen species (ROS) and ROS-damaged cells (Sevik et al., 2020). The xylem transports heavy metals from the roots to the transpiring shoot sections. There, they’ve transported up the root’s xylem, either free or bound to an anion chelator. Heavy metal concentrations in the transpiration stream are affected by xylem stacking in the roots, contacts with cell membranes during acropetal transfer, and selective removal from xylem sap. The heavy metals would concentrate predominantly in photosynthetically active (transpiring) leaves if there were no additional redistribution. Heavy metals like nickel and cadmium can limit development by reducing nutrient absorption or increasing oxygen-induced stress, respectively (Bhatti et al., 2018).

As the concentration increases, it is expected that the percentage of germination inhibition will also increase. At a nickel concentration of 1.5 mM in a plant, however, the germination percentage will be higher than the control, hence showing help to the seed’s development (Bhatti et al., 2018). The bioavailable fraction of heavy metals is the proportion that can be easily mobilized in the soil environment and absorbed by plant roots. A chemical’s “bioavailability” is defined as the amount to which it is absorbed by a live creature and circulates in its bloodstream throughout the organism (Bhatti et al., 2018). This means that bioavailability and total metal concentrations in soil are not always related. The extent to which heavy metals are bioavailable relies on physical and chemical variables in soil. An extract that replicates plant-available heavy metals from polluted soil is essential for assessing the bioavailability of the metal to crops. A wide range of extracts has been used for single and sequential extractions in the past few decades.

References

Bhatti, S. S., Kumar, V., Sambyal, V., Singh, J., & Nagpal, A. K. (2018). Comparative analysis of tissue compartmentalized heavy metal uptake by common forage crop: a field experiment. Catena, 160, 185-193.

Fan, Y., Li, Y., Li, H., & Cheng, F. (2018). Evaluating heavy metal accumulation and potential risks in soil-plant systems applied with magnesium slag-based fertilizer. Chemosphere, 197, 382-388.

Rodríguez-Bocanegra, J., Roca, N., Febrero, A., & Bort, J. (2018). Assessment of heavy metal tolerance in two plant species growing in experimental disturbed polluted urban soil. Journal of Soils and Sediments, 18(6), 2305-2317.

Sevik, H., Cetin, M., Ozel, H. B., Ozel, S., & Cetin, I. Z. (2020). Changes in heavy metal accumulation in some edible landscape plants depending on traffic density. Environmental monitoring and assessment, 192(2), 1-9.