The Effects of Different Lead Concentration Levels in Soil on the Growth of Brassica Rapa

The Effects of Different Lead Concentration Levels in Soil on the Growth of Brassica rapa

Stephen Won and Sierra Eady

Biology Department

Birmingham-Southern College

BI 115

Abstract

        The City of Birmingham is affected by toxic metal contamination in the soils due to its past history of massive steel production and the byproducts that resulted from the industrial revolution. The effects of lead poisoning can be lethal in many organisms including humans. In this experiment, Brassica rapa seeds were planted in lead contaminated soil samples ranging between 0 and 2000 Pb mg/kg of soil to determine the effects of lead exposure on the plant’s growth and viability. The plant heights were measured over a 21-day period. The overall trend in the data showed that there were no statistical significant differences in the plants height using a t-test to determine if p was less than 0.05. Due to its high immunity against toxic metals, it can be concluded that the genus Brassica could be efficiently used for phytoremediation.

Introduction

        The city of Birmingham, Alabama, was reliant on the steel industry, which was prevalent here because the three essential ingredients (coal, iron ore and limestone) needed for steel production existed in such close proximity of each other. The steel industry was the main source of economic gains for Birmingham and it was the second largest steel producing city in the United States. Most steel mills are closed today, but unfortunately, the byproducts of steel production are still present in the air, water and soils of low-income families’ residential areas due to the city’s history of segregated residential zoning. Lead is one of the byproducts that is derived from steel production and it has many negative effects on both plants and humans if exposed to it.

        Lead contamination in the soil affects all organisms either directly or indirectly. The roots of the plants can uptake lead in their roots and incorporate it into their tissue and if the plant is edible, wildlife animals and humans can be affected by consuming lead contaminated vegetables. Lead exposure is known to affect humans in many negative ways: childhood exposure to lead alters the expression of micro-RNA that targets proteins associated with Alzheimer’s disease (Masoud et al., 2016), it induces telomere instability in adults (Pottier et al., 2013), it damages the central nervous system, causes severe developmental delays, causes anemia, and disrupts reproductive function (Feleafel et al., 2013). Humans aren't the only victims of lead exposure. Plants can uptake metal ions such as lead with their roots and its effects are apparent. It decreases the rate of cell division, reduces chlorophyll and protein synthesis, and decreases nutrient uptake, which all lead to stunted growth rate (Feleafel et al., 2013). The genus Brassica (mustards, radishes, cabbages) is one of many essential vegetable crops on earth (Siddiqui et al., 2014). This genus provides humanity with crops that produce oil, vegetables, and spices that provide essential nutrients such as fiber and vitamin C along with other healthy beneficial nutrients (Cho et al., 2015).

        The objective of this experiment is to analyze the effects of lead contamination on plant growth and viability using a dose response bioassay (if there is an indirect relationship between concentration of lead in soil and the growth/height of plants). Also, this leads to the idea of phytoremediation, which is the use of living plants to remove contaminants in the soil. Phytoremediation is a low cost, solar-energy driven cleanup technique and is an efficient way to get rid of unwanted contaminants in the soil. Brassica rapa was used in this study because of the genus’s involvement in our diet and its ability to grow quickly in a relatively controlled setting. This experiment was carried out over a 21-day period with different lead concentrations of soil to see what the cumulative effects of various concentrations of lead in soil have on B. rapa. After 21 days of this experiment, there will be an indirect relationship between lead contamination and the growth of B. rapa that the soils with higher lead concentration will produce plants with lower height than the control.

Materials and Methods

Preparation (Before Planting)

To avoid lead exposure and cross-contamination, nylon gloves and different tools were used for each assorted lead contaminated soil samples. A styrofoam quad with eight different cells was prepared by labeling each cell with ascending levels of mg Pb/kg of dry soil: unknown, 0, 100, 250, 500, 1000, 2000 mg Pb/kg of dry soil. Wicks were put through the holes at the bottom of the cells so about half an inch of it would be poking through the bottom to absorb water from the reservoir and keep the soil moist. Seven cells were filled about half-way with soils with the corresponding lead contaminated concentrations (with different spoons to avoid cross contamination). Two to three fertilizer pellets were added with two B. rapa seeds that were picked up from the wet end of the skewer. The cells were topped off with each levels of soil samples. The cells were saturated with water by a pipette and they were placed about five to eight centimeters under a light source with a water reservoir with a water mat under the styrofoam quad. The water reservoir contained copper sulfate solution to prevent potential algae growth.

Analysis (After Planting)

        The cells were watered with a pipette for the first three days. The reservoirs were checked daily to keep them full of water. Consistency was important for accurate plant growth data. The temperature of the greenhouse was measured in Celsius before each plant height measurements (the mean temperature was calculated at the end of data collection). Plant height measurements were taken on days 7, 9, 12, 14 and 21. The height measurements were measured from the site of cotyledon buds to the tip of the apical bud using millimeter as the unit of measurement. All the measurements were recorded in the lab manual. The measurements were submitted into Microsoft Excel to create figures and tables with the class data set. T-tests were determined with an alpha level of 0.05 using Microsoft Excel based on the data from day 21.