Scientific Journal Review: Enhancing Phytoremediation of cadmium-contaminated agricultural soils using Solanum nigrum L

In this post, I will discuss the use of a cadmium-hyperaccumulator plant to remove cadmium in soils. I have found a scientific journal article (see Reference) by (Ji et. al., 2010) discussing this and it would be interesting to share with you readers.

The research article recommends the use of Solanum nigrum L., or black nightshade (refer to Image 1 below), for phytoremediation of cadmium-contaminated soil. The plant was selected as it has a relatively higher biomass as compared to other hyperaccumulators, such as T. caerulescens and A. halleri. Assessing cadmium uptake of nightshade is applicable for Japan soil countermeasures as the plant grows in Japan too. 

Image 1: Solanum nigrum L (Source: Lee, n.d.)

An experiment using black nightshade was conducted in China at Shenyang Zhangshi Irrigation Area. The farmland at the area has been contaminated by cadmium, with 10 mg Cd/ kg in surface soil. Various planting and harvesting methods was tested to see which is most effective method to enhance phytoremediation.

Results showed that plant biomass was the most critical determinant of cadmium accumulation. The larger the plant roots, the greater its biomass. Planting density will have no effect as the plant biomass depends on its genetic predisposition and the contamination level in soils. One way to increase the biomass is then to conduct double harvesting (harvesting twice per year). This can only be achieved when the plant is cut correctly. Mild cutting, cutting the plant at 50cm above the soil during harvest, was found to achieve the highest biomass. It is advised that harvest is done during the flowering period as cadmium accumulates most in the stems and leaves. Understanding the cutting position and period to harvest the plant is thus beneficial in enhancing the phytoremediation efficiency.

Another conclusive finding is that fertilization is unnecessary, as it did not increase the plant biomass. In fact, phosphate fertilizers reduce the solubility and mobility of cadmium due to formation of metal-phosphates. Cadmium accumulation in black nightshade plant is thus inhibited.

From the article, we understand more about phytoremediation and its relevance to farming. This reminds me of my classmate, Heng Sulli, blog about farming techniques. Maybe this would be a good topic for her to write about, on the impact of hyperaccumulators in heavy metals uptake in plants. When correct farming techniques is adopted, phytoremediation will be enhanced and polluted soils can recover faster. In my opinion, I would urge the Japan government to pump in more funding for such research and the experiment results shared with small-scale farmers. Involvement of small-scale farmers is important in my opinion as they are major stakeholders and regulators of the environment. If farmers are able to preserve the health of their soils, heavy metal concentration in food crops will be reduced and heavy metal poisoning in humans can be prevented. 

References

Ji, P., Sun, T., Song, Y., Ackland, M. L., & Liu, Y. (2011). Strategies for enhancing the phytoremediation of cadmium-contaminated agricultural soils by Solanum nigrum L. Environmental pollution, 159(3), 762-768.

Lee Yu S. (n.d.). Photo taken from http://www.agroatlas.ru/en/content/weeds/Solanum_nigrum/. Web.