Dr. Philipp Lengsfeld
Primary source paper: Chromium Pollution: A Threat to Environment: A Review – 2014
Heavy metals can be found naturally in the earth’s crust, however the rise in the use of heavy metals has resulted in its increase in terrestrial and aquatic ecosystems. The contamination of soil and water by heavy metals is now an important global environmental issue. Heavy metal contamination resulting majorly from anthropogenic activities is highlighted as a key problem in regions around the world such as USA, China, Europe, and India (Davis et al., 2009; Dotaniya et al., 2014a). Industries involved in metal mining, electroplating, leather tanning, steel production, textile production, and wood preservation all contribute to the introduction of heavy metals into the environment, necessitating the need for remediation measures (Briffa et al., 2020).
In this outline, we focus on an example of a toxic heavy metal – Chromium (Cr). Using excerpts from a primary source paper, we highlight the sources and effects of Chromium pollution, concluding with possible remediation techniques.
Sources and availability
“Chromium is one of the toxic heavy metal for ecosystem as well as survival of human beings on earth. It is the 21st most abundant element in the earth’s crust (Eliopoulos et al., 2013). It occurs in nature in bound forms that constitute 0.1-0.3 mgkg -1 of the earth’s crust. The principal manmade sources of Cr are industrial point sources, i.e. mines, foundries and smelters, and diffuse sources such as combustion by-products and traffic etc.
Chromium availability in soil
The total Cr concentration levels in igneous and sedimentary rocks are usually in the range of up to about 100 µgg-1. For most of soils the Cr concentration is in the range of 15 to 100 µgg-1 soil and increase with the proportion in clay (Baize, 1997). However, soil derived from serpentine may contain several percent of Cr. Soil Cr is largely unavailable to plants because it occurs in relatively insoluble compounds such as chromite FeCr2O4 in mixed oxides of Cr, Al and Fe, or in silicate lattice. In addition Cr3+ binds tenaciously to negatively charged sites on clays and organic matter. For this reason the translocation of Cr from soils into plants is generally insignificant (Juste and Mench, 1992). Chromates (hexavalent Cr) in soils are relatively rare and only stable in alkaline oxidizing conditions. It is supported that Cr3+ and CrO4 2- are taken up by two different mechanisms. The uptake of CrO4 2- is depressed by SO4 2- (Shenbagavalli and Mahimairaja, 2012).
Effects of chromium pollution
Excessive metal accumulation in contaminated soils can result in decreased soil microbial activities, soil fertility, and overall soil quality which may lead to reduction in yield. The entry of toxic materials into food chain can cause many diseases in human and animals. Very high levels of Cr (VI) contamination (14,600 mgkg-1 in ground water and 25,900 mgkg-1 in soil) were reported at the United Chrome Products site in Corvallis, Oregon (Krishnamurthy and Wilkens, 1994). The critical concentration of chromium in plant varies according to species but generally 1-2 mgkg-1 of plant biomass was found to be growth limiting and maximum allowable limit in soil is 100 mgkg-1 (Purakastha and Chhonkar, 2010).
Symptoms of Cr phytotoxicity include inhibition of seed germination, seedling development, reduction of root growth, leaf chlorosis and depressed biomass (Dotaniya et al., 2014b). Many studies were conducted to evaluate the Cr toxicity in crop plants shows chromium significantly affects the metabolism of plants such as barley, citrullus, cauliflower, wheat and maize (Shanker et al., 2005). The sub-cellular localization of Cr as found by electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) suggested that Cr is accumulated mainly in the cell wall and vacuoles (Zou et al., 2006).
Effects of chromium on human health
Chromium is used in metal alloys and pigments for paints, cement, paper, rubber, and other materials. Low level exposure can irritate the skin and cause ulceration. Long term exposure can cause kidney and liver damage and damage too circulatory and nerve tissue. It often accumulates in aquatic life, adding to the danger of eating fish that may have been exposed to high levels of chromium. However, human activities have drastically altered the biochemical and geochemical cycles and balance of some heavy metals.
Cr contamination is steeply increasing in the environment. It can be remediated by chemical, physical and biological approaches. In biological approach, it can be separated into phytoremediation as well as bioremediation (microorganism). Among the all remediation technologies, phytoremediation is cheaper and eco-friendly in nature (Dotaniya and Lata, 2012).
So many chemical, physical and biological technologies are in practice nowadays; cheaper and effective technologies are needed to protect the precious natural resources and biological lives. As countries around the world are struggling to arrive at an effective regulatory regime to control the discharge of industrial effluents into their ecosystems, use of modern and traditional approaches can diverse our land use system in new horizon.”
References and Sources
Primary source paper – Dotaniya, M. L., Thakur, J. K., Meena, V. D., Jojoria, D. K., Rathor, G. (2014a). “CHROMIUM POLLUTION: A THREAT TO ENVIRONMENT - A REVIEW.” Agricultural Reviews, vol. 35, no. 2, pp. 153–157.
Baize, D. (1997). Total Contents of Metallic Trace Elements in Soils. INRA Paris.
Briffa, J., Sinagra, E., Blundell, R. (2020). Heavy metal pollution in the environment and their toxicological effects on humans, Heliyon, Volume 6, Issue 9.
Davis, H.T., Aelion, C.M., McDermott, S., Lawson, A.B. (2009). Identifying natural and anthropogenic sources of metals in urban and rural soils using GIS-based data, PCA, and spatial interpolation. Environmental Pollution 157: 2378–2385.
Dotaniya M. L., Das, H. and Meena, V. D. (2014b). Assessment of chromium efficacy on germination, root elongation, and coleoptile growth of wheat (Triticum aestivum L.) at different growth periods. Environ. Monit. Assess. 186:2957-2963.
Dotaniya, M. L. and Lata M. (2012).Cleaning soils with phytoremediation. GeoGraphy You. 12 (73): 18-21.
Eliopoulos, E. M., Megremi, I., Cathy, A., Theodoratou, C. and Vasilatos, C. (2013). Spatial evolution of the chromium contamination in soils from the Assopos to Thiva Basin and C. Evia (Greece) and potential source(s): Anthropogenic versus natural processes. Geosci. 3(2): 140-158.
Juste, C. and Mench, M. (1992). Long-term application of sewage sludge and its effects on metal uptake by crops. In: Adriano DC (eds.) Biogeochemistry of trace metals, Lewis Publishers, Boca Raton, pp 159–193.
Krishnamurthy, S. and Wilkens, M. M. (1994). Environmental chemistry of Cr. Northeastern Geol. 16: 14–17.
Purakastha, T. J. and Chhonkar, P. (2010). Phytoremediation of heavy metal contaminated soils. Soil Biol. 19: 389-429.
Shanker, A. K., Cervantes, C. Tavera, H. L. and Avudainayagam, S. (2005). Chromium toxicity in plants. Environ. Int. 31:739-753.
Shenbagavalli, S. and Mahimairaja, S. (2012). Biotransformation and bioavailability of chromium contaminated soil and the effect of poultry manure and pseudomonas. Int. J. Plant, Animal Environ. Sci. 2 (1):190-196.
Zou, J., Wang, M., Jiang, W. and Liu, D. (2006). Chromium accumulation and its effects on other mineral elements in Amaranthus viridis L. Acta Biol Cracoviensia Series Bot. 48 (1): 7–12.