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

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Results

Figures

Figure 1: Lead contamination’s effect on Brassica rapa’s growth after 21 days. This figure shows the mean growth of B. rapa in mm after 21 days in soils containing different concentrations of lead. Error bars represent the standard deviation. (n=23-32 plants in each treatment group).[pic 1]

[pic 2]

Figure 2: The effect different lead contaminations have on the height of Brassica rapa over 21 days. B. rapa seeds that were plants in soils with unknown, 0, 100, 250, 500, 1000, 2000 mg/kg of lead were measured on the days 7, 9, 12, 14 and 21. This figure represents the mean height change at each soil concentrations over 21 days. (n=23-32 plants in each treatment group).

Comparison

Df

p

0 to 100 mg/kg

31

0.122787906

0 to 250 mg/kg

28

0.278021844

0 to 500 mg/kg

27

0.368403874

0 to 1000 mg/kg

23

0.182848395

0 to 2000 mg/kg

29

0.194421013

0 to unknown mg/kg

22

0.291020654

Table 1: Results of t-tests comparing Brassica rapa contaminated with various amounts of lead in soil samples over a 21-day period to control plants that contained no lead (0 mg/ kg of soil). There were no p values that showed statistically significant differences.

Figure 1 and 2 show that there is no major trend in the data. There isn’t a general decrease or increase in plant height as the lead concentrations increase. Figure 1 shows that the soil sample with 100 Pb mg/ kg of soil produced the tallest plant after 21 days. However, there are two groups that the standard deviation is similar: 100, 1000, 2000 Pb mg/ kg of soil and 0, 250, 500, unknown. Figure 2 is consistent with the data from Figure 1, but it shows that there is a dramatic increase in the rate of growth after day 14.

The numerical data of the t-test done between the control (0 Pb mg/ kg of soil) and different levels of lead contaminated soils are shown in Table 1. The results of the t-test showed that there were no statistically significant differences between any of the soil samples. Although there are no differences, 0 to 100 Pb mg/ kg of soil had the closest value that satisfies p

Discussion

The results obtained from this experiment do not support the argument that lead contamination affect the growth and the height of the plants. The initial hypothesis stated that increasing the lead concentration in the soil would decrease the growth of B. rapa. The t-test proved the hypothesis to be wrong since there were no statistically significant differences. The closest value that would satisfy pB. rapa.

There were two experimental errors that contributed to the results being slightly inaccurate. Human errors, such as not watering the plants at the right time and not using precise measurement techniques when measuring the plant heights, caused results to deviate from. Also, the temperature inconsistency in the greenhouse would affect the plant growth/seed germination regardless of placing them underneath a light source and watering them properly. For future experiments, improvements can be made to decrease the range of standard deviation by increasing the period of experiment longer than 21 days and collecting data from a larger data pool than just BSC students. Even with those experimental errors, the results prove to be consistent with other research done with B. rapa.

Siddiqui et al. (2014) experimented on Brassica rapa seeds coated with cadmium, chromium and lead contaminated aqueous solution as well as a control solution (distilled water). The seed germination rate decreased, but the germination rate for the lead contaminated solution was the least affected group. As it turned out, the toxicity of cadmium and chromium was far more toxic than lead. Lead had the least effect on the growth/germination of B. rapa compared to other toxic metals. Similarly, Mourato et al. (2015) experimented with multiple Brassica species on phytoremediation. Since Brassica plants developed a defense mechanism against heavy metal uptake in the roots, they are able to take in more toxic metals than other plants without being affected by it negatively. This study proves that the Brassica genus can be efficiently used to extract toxic metal from the soil.

However, this does not mean B. rapa is immune to toxic metal exposure. It does decrease the chlorophyll activity and slows down cell division rate, but it does not have severe negative effects that affect the health of the plant. There are many studies being done to cross pollinate specific Brassica species to maximize their metal uptake to use for phytoremediation. If this study turns out to be successful, it would be a huge advancement in the study of phytoremediation.

Acknowledgements

I would like to thank my lab partner, Sierra Eady, and TA, Dania Yazbak, for aiding my peers and myself in our research.

Literature Cited

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Feleafel, M.N. and Z. M. Mirdad. 2013. Hazard and Effects of Pollution by Lead on Vegetable Crops. J Agric Environ Ethics (2013) 26:547-567

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Mourato M.P., I.N.Moreira, I. Leitao, F.R. Pinto, J.R. Sales, L.L. Martins. 2015. Effects of Heavy Metals of the Genus Brassica.