Heavy Metals and Crop Contamination

Implementing a sustainable framework for agriculture to promote food security and produce safe food is a facet of goal two within the UN’s 17 Sustainable Development Goals (United Nations, 2022). However, as the world becomes increasingly industrialized, environmental contaminants are released from more and more anthropogenic sources, particularly from the fields of agriculture and industry, threatening the UN’s objective (Rai et al., 2019). These practices include smelting, the use of fertilizers and pesticides, and the burning of fossil fuels (Alengebawy et al., 2021). These contaminants include heavy metals and metalloids such as mercury, arsenic, lead, and cadmium (Rai et al., 2019). This issue and the risks it poses have become an urgent concern for the environment as contaminants accumulate in the soil and make their way into the food chain (França et al., 2017).

The soil, an integral part of crop development, can be contaminated through pollution from a single point-source, such as coal mines and thermal power plants or a variety of non-point sources, such as agricultural runoff from several crop fields (Rai et al., 2019). The accumulation of heavy metals in the soil has been shown to have consequences on both abiotic and biotic ecosystem components (Gall, Boyd and Rajakaruna, 2015). These metals affect the properties and fertility of the soil, such as the pH, salinity, cation exchange capacity, and texture. Additionally, interactions between multiple heavy metals can affect the quantity of compounds accessible for uptake in the soil (Alengebawy et al., 2021). However, their most pronounced effect on the soil is their destruction of microbial and soil-microbial interactions, as heavy metals denature microbial cell membranes (Rai et al., 2019; Xie et al., 2016).

These alterations in the soil can cause plants to have biochemical and mineral deficiencies (Shahid et al., 2011). In addition, heavy metals can cause elevated levels of reactive oxygen species (ROS) within the plant. The plant can not keep up with this increase, and the resulting oxidative stress causes molecular damage to structures like proteins and nucleic acids. This deterioration causes physiological issues such as inhibited enzymatic activities and can ultimately lead to necrosis (Alengebawy et al., 2021). The route heavy metals take from accumulation in the soil to the plant, and the negative impacts they cause are depicted in Figure 1.

Figure 1: Heavy metals cause soil to change properties which then affects what is taken up by the plants. Damage is done to the plant’s protein, nucleic acids, lipids, and enzymes as there is an excess of highly reactive free radicals, which have an unpaired electron. The free radicals formed from oxygen are called reactive oxygen species (ROS) and can cause oxidative stress (Alengebawy et al., 2021).

While these heavy metals are critical toxins for the soil and plants, they also have detrimental effects on human health. Humans are constantly exposed to these pollutants through ingestion and inhalation (Rai et al., 2019). These pollutants can accumulate in organs such as the kidney, liver, and bone causing damage to vital body systems (endocrine, reproductive, immune, circulatory, etc.). Several diseases are also associated with heavy metal toxicity, such as several types of cancer, osteoporosis, neurodegenerative disorders, diabetes, and hypertension (Alengebawy et al., 2021). There are many additional health risks as each metal compound has different diseases associated with it, and added adverse health effects arise from accumulated heavy metals interacting in the body (Rai et al., 2019; Alengebawy et al., 2021).

Action must be taken to remediate the number of heavy metals released into the environment. There are environment-based solutions, such as growing hyperaccumulator crops like Alyssum murale, to extract the heavy metals from the soil through phytoremediation (Wiszniewska et al., 2016). There are also human-based solutions to remove heavy metals from the body through specific diets and supplements, like spirulina and ginseng (Zhai, Narbad and Chen, 2014). Ultimately, humans must recognize the disruption of ecosystems caused by these contaminants and stop the unsustainable production of products polluting the planet.

Resources

Alengebawy, A., Abdelkhalek, S.T., Qureshi, S.R. and Wang, M.-Q., 2021. Heavy Metals and Pesticides Toxicity in Agricultural Soil and Plants: Ecological Risks and Human Health Implications. Toxics, 9(3), p.42. https://doi.org/10.3390/toxics9030042.

França, F.C.S.S., Albuuerque, A.M.A., Almeida, A.C., Silveira, P.B., Filho, C.A., Hazin, C.A. and Honorato, E.V., 2017. Heavy metals deposited in the culture of lettuce (Lactuca sativa L.) by the influence of vehicular traffic in Pernambuco, Brazil. Food Chemistry, 215, pp.171–176. https://doi.org/10.1016/j.foodchem.2016.07.168.

Gall, J.E., Boyd, R.S. and Rajakaruna, N., 2015. Transfer of heavy metals through terrestrial food webs: a review. Environmental Monitoring and Assessment, 187(4), p.201. https://doi.org/10.1007/s10661-015-4436-3.

Rai, P.K., Lee, S.S., Zhang, M., Tsang, Y.F. and Kim, K.-H., 2019. Heavy metals in food crops: Health risks, fate, mechanisms, and management. Environment International, 125, pp.365–385. https://doi.org/10.1016/j.envint.2019.01.067.

Shahid, M., Pinelli, E., Pourrut, B., Silvestre, J. and Dumat, C., 2011. Lead-induced genotoxicity to Vicia faba L. roots in relation with metal cell uptake and initial speciation. Ecotoxicology and Environmental Safety, 74(1), pp.78–84. https://doi.org/10.1016/j.ecoenv.2010.08.037.

United Nations, 2022. Food security and nutrition and sustainable agriculture .:. Sustainable Development Knowledge Platform. [online] Available at: <https://sustainabledevelopment.un.org/topics/foodagriculture> [Accessed 20 October 2022].

Wiszniewska, A., Hanus-fajerska, E., Muszyńska, E. and Ciarkowska, K., 2016. Natural Organic Amendments for Improved Phytoremediation of Polluted Soils: A Review of Recent Progress. Pedosphere, 26(1), pp.1–12. https://doi.org/10.1016/S1002-0160(15)60017-0.

Xie, Y., Fan, J., Zhu, W., Amombo, E., Lou, Y., Chen, L. and Fu, J., 2016. Effect of Heavy Metals Pollution on Soil Microbial Diversity and Bermudagrass Genetic Variation. Frontiers in Plant Science, [online] 7. Available at: <https://www.frontiersin.org/articles/10.3389/fpls.2016.00755>.

Zhai, Q., Narbad, A. and Chen, W., 2014. Dietary Strategies for the Treatment of Cadmium and Lead Toxicity. Nutrients, 7(1), pp.552–571. https://doi.org/10.3390/nu7010552.


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