1. Chromium exists in several oxidation states with Cr(VI) being the most toxic form to plants. Cr(VI) toxicity negatively impacts seed germination, root growth, photosynthesis, nutrient uptake, and water relations in plants. 2. Various remediation techniques exist to remove chromium from contaminated soils including physical, chemical, and biological methods. Promising biological methods include phytoremediation using hyperaccumulator plants and bioremediation using chromium reducing bacteria. 3. Chelating agents such as citric acid, oxalic acid, and EDTA can form soluble complexes with chromium, enhancing phytoextraction of chromium from soils by plants. Further research is being done to develop effective phytore

1. Welcome

2. EffectofChromiumToxicityonPlantsandRemediationofChromiumContaminated
Soil
Supervisor
Dr. Pramod Kumar Sharma
Prof. Dept. of SSAC IAS
BHU Varanasi
Speaker
Sarvajeet
M.Sc.(Ag.)SSAC Final Year
Id no. 17412SAC014
Enroll. No. 397628

3. INTRODUCTION
CHROMIUM
 Atomic Number: 24
Atomic Weight: 51.9961
Melting Point: 2180 K (1907°C or 3465°F)
Boiling Point: 2944 K (2671°C or 4840°F)
Density: 7.15 g/cm3
Phase at Room Temperature: Solid
Element Classification: Metal
Period Number: 4 Group Number: 6

4. Piece of chromium metal.
Source: http://images-of-elements.com/chromium.bhp
 This element was discovered in
1798 and was initially used as a
pigment.
 The name of the element is
derived from the
Greek word “chroma” meaning color.
 Carcinogen according to the
International Agency for Research on
Cancer (IARC, 1987) and the National
Toxicology Program.

5.  7th ranked among the top 20 hazardous
substances by the Agency for Toxic
Substances and Disease Registry (Oh
et al., 2007).
 Chromium (Cr) is the second most
common metal contaminant in ground
water, soil, and sediments due to its
wide industrial application.
 Chromium has several oxidation
states(-2 to +6).

6. PRODUCTION SCENARIO
 Chromium is mined as chromite (FeCr2O4) ore.
Source: U.S. Geological Survey, Mineral Commodity Summaries, January 2015

7. Table1 : World Mine Production and Reserves
Country Mine production (thousand tons) Reserves
(shipping grade)2017 2018
United States — — 620
India 3,500 3,500 100,000
Kazakhstan 4,580 4600 230,000
South Africa 16,500 16,000 200,000
Turkey 6,500 6,500 26,000
Other countries 4,580 4,500 NA
World total (rounded) 35,700 36,000 560,000
Source : U.S. Geological Survey, Mineral Commodity Summaries, February 2019

8. Annual world mine production of Cr (USGS, 2016). World production trend of chromium (in million tons per
year)

9.  93 per cent of the resources are
in ODISHA. [ Sukinda valley in Cuttack and
Jajapur ]
 Minor deposits are spread over Manipur,
Nagaland, Jharkhand, Maharashtra, TN &
AP.
 Karnataka is the second largest producer.
Chromite ore distribution in India

10. Percentage use of chromium in different industries.
Source: B. Dhal et al. / Journal of Hazardous Materials 250– 251 (2013) 272– 291

11. Sources of Chromium
www.seacoastventures.net
Sources
Sewage
Sludges
Wood
preservative
Coal and fly
ash disposalLeather tanning
Cement
industry

12. Table2 . Chemical species of Cr in the environment
Source: Katz and Salem (1994).

13. Biogeochemical behavior of Cr in soil-plant system.
Source: Shahid, M., et. al.,(2017).

14. CHROMIUM TOXICITY
 Chromium (VI) is the most toxic to form of Cr, which usually occurs associated
with oxygen as CrO4
2- or Cr2 O7.
 Cr(III) in the forms of oxides, hydroxides, and sulphates is less toxic as it is
relatively insoluble in water.
Figure . Eh-pH diagram for aqueous Chromium species in a chromium H2O system (Palmer and Wittbrodt, 1991).

15. TOXICITY OF CHROMIUM TO PLANTS
Curled and discolored leaves
Stunted growth
Leaf chlorosis
Poorly developed root
system
Yield reduction
Toxicity
symptoms

16. Levels of Cr in soil and plant tissue toxic to plants:-
Plant Soil Cr concentration toxic Reference
species to plants (mg kg−1)
Pea 30 Parr (1982)
Wheat 50 Sullivan (1969)
Bus beans 100 Wallace et al. (1976)
Rye grass(L. perenne)
500 Breeze (1973)
Table3 : Soil Cr concentrations reported to be toxic to plants in soil experiments
Source : Zayed, A. M., & Terry, N. (2003).

17. Plant species Cr concentration in plant tissues Reference
(mg kg−1)
Corn 5.9 Chang et al. (1992)
4–8 Kabata-Pendias and Pendias (1992)
Tobacco 18–24 Kabata-Pendias and Pendias (1992)
Barley 10 Kabata-Pendias and Pendias (1992)
Rice 10–100 Kabata-Pendias and Pendias (1992)
Cabbage 27 Hara and Sonoda (1979)
Table4 . Leaf tissue chromium concentration that is phytotoxic to plants
 The critical leaf Cr concentration in most plants seems to fall
between 1 and 10 mg kg−1(DW).
Source: Zayed, A. M., & Terry, N. (2003).

18. EFFECT OF Cr (VI) ON PLANT GROWTH
Figure : Toxic effects of Cr(VI) on plants Source: Stambulska, U. Y. et al,

19. Effect on seed germination
 Reduction of 23% in the seeds of Lucerne with 40 ppm Cr
(Peralta et al.,2001).
 Reductions of 32-57% in sugarcane bud germination with 20
and 80 ppm Cr, respectively (Jain et al., 2000).
 Reduction of 48% in the Phaseolus vulgaris with 500 ppm Cr
(Parr and Taylor,1982).

20. Medda, S., & Mondal, N. K. (2017).

21. Effect on photosynthesis
 Chromium stress is one of the important factors that affect photosynthesis in terms of CO2
fixation, electron transport, photophosphorylation and enzyme activities(Clijsters and Van
Assche, 1985).
 The more pronounced effect of Cr(VI) on PS I than on PS II activity in isolated chloroplast
has been reported by Bishnoi et al. (1993) in peas.
 Cr (VI) has high oxidative potential and can reduce photosynthesis by producing ROS as an
alternative sink for electrons via oxygen reduction.

22. Figure . Schematic diagram of sites of Cr inhibition of photosynthetic electron transport in
isolated chloroplasts.
Source: Pandey et al, (2013)
Effect on photosynthetic electron transport

23. Effect on Nutrient uptake
 Nutrient solution with Cr(VI) decreased the uptake of K, Mg, P,
Fe and Mn in roots of soybean (Turner and Rust, 1971).
 Excess Cr interfered with the uptake of Fe, Mo, P and N
(Adriano, 1986).
 Greatly reduce the uptake of Fe, Ca, Mg, Cu, Mn, and Zn in
sugarcane.

24. Effect on Water uptake
 Wilting of various crops and plant species due to Cr toxicity has been reported (Turner and
Rust, 1971).
 Decrease in leaf water potential in Cr treated bean plants (Barcelo et al. (1985).
 Excess Cr decreased the water potential and transpiration rates and increased diffusive
resistance and relative water content in leaves of cauliflower (Chatterjee and Chatterjee, 2000).
 The significantly higher toxic effect of Cr(VI) in declining the stomatal conductance could be
due to the high oxidative potential of Cr(VI).
 Toxic levels of Cr in beans were found to decrease tracheary vessel diameter, thereby reducing
longitudinal water movement (Vazques et al., 1987).
 Decreased turgor and plasmolysis was observed in epidermal and cortical cells of bush bean
plants exposed to Cr (Vazques et al., 1987).

25. Soil Remediation Technologies
Physical
• Electro kinetics
• Vitrification
• Capping/ soil
covering
• Pyrometallurgical
Biological
• Phytoremediation
• Bioremediation
Chemical
Mobilization Immobilization
• Chelating agent
• Organic matter
• Phosphate compound
• Liming material
• Organic matter
• Minerals
• Biochar
REMEDIATION TECHNOLOGY

26. Electro-kinetics:-
 Ions and small charged particles, in addition to water, are transported between the electrode.
 Anions moves towards the positive electrode and cations towards the negative.
Source: Mulligan, et al, (2001)Fig. diagram showing electrokinetic processes

27. Vitrification:
-
 Vitrification is a solidification process
requiring thermal energy.
Fig. diagram showing steps in the vitrification process.
 This processes are suitable for
contamination in shallow depth and of
large volume.
 It involves insertion of electrodes into the
soil which must be able to carry a
current, and then to solidify, as it cools.
Source: Mulligan, et al, (2001)

28. Soil flushing:-
 Extracting solutions are infiltrated into soil
using surface flooding, sprinklers, leach
fields, basin infiltration system, surface
trenches, horizontal drains or vertical drains.
 The efficiency of the extraction depends on
the hydraulic conductivity of the soil.
 High permeability gives better results
(greater than 1×10-3 cm/s).
 Chemical enhanced flushing with addition of
organic and inorganic acid, complexing
agents such as EDTA.
Fig. diagram of soil flushing process using injection of water
or solution containing chemicals .
Source: Mulligan, et al, (2001)

29. Application of chelating agents:-
 Chelating agents such as low molecular weight organic acids (LMWOAs), e.g.,
citric acid, oxalic acid, tartaric acid, etc., and synthetic chelators
(ethylenediaminetetraacetic acid, EDTA and diethylene triamine Penta acetic
acid, DTPA) are the amendments most commonly applied for chemically
assisted phytoextraction of metals from soils (Nascimento et al. 2006).
 Mohanty and Patra (2011) observed that total chlorophyll content in the rice
(Oryza sativa L.) seedlings treated with Cr(VI)–EDTA (10 μM) solution was
more as compared to the untreated.

30. Effect of chelating compounds on growth of maize and mustard in chromium contaminated soil
Source: Suryakant et al, 2018

31. Source: Suryakant et al, 2018

32. Bioremediation:-
 Microbes, especially bacteria capable of Chromium (VI)
reduction.
 Bacterial chromate reductases can convert soluble and toxic
chromate to the insoluble and less toxic Cr(III).
 Under aerobic, field-moist conditions, soil rich in organic
matter reduced 96% of Cr(VI).

33. Mechanisms of Cr(VI) reduction to Cr(III) by Bacteria.
Source: Joutey, N. T. et. al., (2015).
Fig. diagram showing to reduction of Cr(VI) in aerobic and anaerobic condition

34. Fig. Effects of Cr(IV) exposure alone and in combination with nodule rhizobacteria on selected growth
parameters and ROS homeostasis in P. sativum plants.
Source: Stambulska, U. Y. et al, (2018).
Inoculation of rhizobium decrease the toxicity of Cr(VI) on Pea

35. Phytoremediation:-
I. Phytoextraction.
III. Rhizofiltration.
IV. Phytostimulation.
VI. Phytodegradation.
II. Phytostabilization.
V. Phytovolatilization.
Fig. Schematic showing possible fates of chromium during the
phytoremediation processes.
Source: V. Sinha et al., (2018)

36. Table : List of Cr hyperaccumulators with a potential for use in phytoremediation studies.
Source: Singh, H. P. et al, 2013

37. Source: Singh, H. P. et al, 2013
Cont.

38. PHYTOREMEDIATION OF CHROMIUM CONTAMINATED SOILS BY CYPERUS ROTUNDUS L.
Subhashini, V., & Swamy, A. V. (2014).

39. Remediation Of Phytotoxic Effect Of Chromium By Different Amendments In Rice-wheat Sequence
Parmar, J. K., & Patel, K. P. (2015)

40. Parmar, J. K., & Patel, K. P. (2015)

41. Conclusion
 Despite known toxicity of Cr to plants, there are several plants that hyper accumulate this
metal contributing to its removal from soil/water, showing good potential for application in
Cr phytoremediation strategies.
 Cr affects several processes in plants, namely, seed germination, root growth, yield and also
physiological processes as photosynthesis impairment and nutrient and oxidative imbalances.
 The toxic properties of Cr(VI) originate from the action of this form itself as an oxidizing
agent, as well as from the formation of free radicals during the reduction of Cr(VI) to Cr(III)
occurring inside the cell.
 Natural (CA and OA) and Synthetic chelating agents, ethylene diamine tetra acetic acid
(EDTA) and diethylene triamine Penta acetic acid (DTPA) are commonly used as they are
efficient in complexing metals(Cr).