| | Category | EV | P17 | Heavy Metal Veggies: The Effect of Soil pH on the |
| | Phytoaccumulation of Lead |
| | Abstract | Lead is found naturally in the environment. However, high concentrations |
| | of lead, particularly in foods, can be harmful to human health. Oftentimes, |
| | vegetables and other edible plants are grown inadvertently in soils of high |
| | lead content. Through phtyoaccumulation (a specific form of |
| | bioaccumulation in which plants absorb substances from the |
| | environment), lead present in soil can be collected in the edible tissues of |
| | these plants. Many possible solutions may remedy this common problem of |
| | lead phytoaccumulation; one of which is the increase of soil pH to |
| | immobilize lead ions thus preventing the uptake of lead particles by plants. |
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| | In the experiment, the effect of soil pH on the bioaccumulation of lead in |
| | plants is analyzed. To contaminate, a large sample of neutral soil was |
| | treated with a lead(II) nitrate solution to achieve a lead level of 700 ppm by |
| | mass; this is considered unsafe for use in gardening and vegetable |
| | growing. (Rosen) The soil was then separated into 18 groups and each |
| | group was individually treated with unique solutions of aluminum sulfate |
| | and calcium carbonate to vary soil pH. Each of the 18 soil samples was |
| | then placed into an individually labeled soil tray, and another two soil trays |
| | were filled with neutral, unmodified soil. The twenty soil trays were then |
| | separated into two sets: the spinach set and the mustard set. Each set |
| | contained 9 contaminated soil trays of varying pH: 5.0, 5.5, 6.0, 6.5, 7.0, |
| | 7.5, 8.0, 8.5, and 9.0 and a final neutral, uncontaminated soil tray. 25 |
| | spinach (Spinacia oleracea) seeds were planted in each of the soil trays |
| | of the spinach set and 25 mustard (Brassica juncea) seeds were planted |
| | in each of the soil trays of the mustard set. After a growing period of 50 |
| | days, various tissues of the plants, namely the leaves, stems, and |
| | rootstalks, of each soil tray were harvested. The collected samples were |
| | then desiccated, powdered, weighed and suspended in individual |
| | solutions of water. Enzyme solutions were then added to the solution |
| | samples to digest and break down organic matter. After filtration to remove |
| | organic debris, a solution of potassium iodide was then added to each of |
| | the solutions to produce a precipitate of lead(II) iodide. The precipitate was |
| | then isolated, dried, and weighed to obtain the mass of lead(II) ion present |
| | in each of the plant samples. With this mass of lead(II) ion and the mass of |
| | the dried plant sample powders, the amount of lead accumulated by each |
| | group was calculated in parts per million. |
| | |
| | According to the World Health Organization, ingestion of more than 254 |
| | micrograms of lead per day can be dangerous for adults (Bassuk) and |
| | even less for small children. High concentrations of lead that collect in |
| | produce through phytoaccumulation poses a serious health hazard. The |
| | amounts of lead calculated in the experiment indicate trends of lead levels |
| | in edible foods grown in contaminated soils as soil pH changes. |
| | Bibliography | Chaney, Rufus L. “Phytoremediation: Using Plants to Clean Up Soils.” |
| | Agricultural Research June 2000: n. pag. General OneFile. Web. 22 Nov. |
| | 2009. |