A heavy metal is toxic when relatively it is dense metal or metalloid that is noted for its potential toxicity, especially in environmental contexts. Heavy metal toxicity means excess of required concentration or it is unwanted which were found naturally on the earth, and become concentrated as a result of human caused activities. Then enter in plant, animal and human tissues via inhalation, diet and manual handling, and can bind to, and interfere with the functioning of vital cellular components.

1. EFFECT OF HEAVY METALS ON
PLANTS : AN OVERVIEW
Malik Ghulam Asghar
M.Sc. (Hons) Agronomy
DEPARTMENT OF AGRONOMY
Faculty of Agricultural Sciences and Technology
Bahauddin Zakariya University Multan Pakistan

2. •A heavy metal is toxic when relatively it is dense metal or
metalloid that is noted for its potential toxicity, especially in
environmental contexts.
•Heavy metal toxicity means excess of required concentration or
it is unwanted which were found naturally on the earth, and
become concentrated as a result of human caused activities.
•Then enter in plant, animal and human tissues via inhalation, diet
and manual handling, and can bind to, and interfere with the
functioning of vital cellular components.
Introduction

3. Heavy metals are group of metals and metalloids with atomic
density greater than 4 g/cm3, including:
 Copper (Cu)
 Manganese (Mn)
 Lead (Pb)
 Cadmium (Cd)
 Nickel (Ni)
 Cobalt (Co)
 Iron (Fe)
 Zinc (Zn)
 Chromium (Cr)
 Iron (Fe)
 Arsenic (As)
Introduction

4. Essential heavy metals
•Heavy metals are natural components cannot be degraded or
destroyed biologically.
•Some of heavy metals (Fe, Cu and Zn) are essential for plants
and animals
•Their availability in medium varies, and metals such as Cu, Zn,
Fe, Mn, Mo, Ni and Co are essential micronutrients.
•Their uptake in excess to the plant requirements result in toxic
effects.
Introduction

5. Range of a few important heavy metals in plants like :(µg g-1 dry
wt.)
As 0.02-7 (µgg -1) Cd 0.1-2.4 (µgg -1)
Hg 0.005-0.02 (µgg -1) Pb 1-13 (µgg -1)
Sb 0.02-0.06 (µgg -1) Co 0.05-0.5 (µgg -1)
Cr 0.2-1 (µgg -1) Cu 4 -15 (µgg -1)
Fe 140 (µgg -1) Mn 15-100 (µgg -1)
Mo 1-10 (µgg -1) Ni 1 (µgg -1)
Sr 0.30 (µgg -1) Zn 8-100 (µgg -1)
Introduction

6. Effects of Copper on Plants
Functions of Copper
1) Copper is an essential metal for normal plant growth and
development,
2) It is also potentially toxic in excess.
3) Copper (Cu) is considered as a micronutrient for plants.
4) It plays important role in CO2 assimilation and ATP synthesis.
5) Essential component of various proteins of photosynthetic
system.
Copper dust has adverse effect on various photosynthesis
pigmentation secretions in species leaves.

7. Enhanced industrial and mining activities have contributed to the
increasing occurrence of Cu in ecosystems.
Cu is also added to soils from different human activities including
mining.
Toxic Effects
1) Excess of Cu in soil plays a cytotoxic role.
2) Induces stress and causes injury to plants.
3) This leads to plant growth retardation and leaf chlorosis.
4) Excess Cu generates oxidative stress and ROS.
5) Copper reduces the root growth.
6) Reduces biomass and seed production.
Effects of Copper on Plants

8. • Cu toxicity leads plant growth retardation and leaf chlorosis.
• Copper reduces the root growth.
Effects of Copper on Plants

9. •The function of zinc is to help a plant to produce chlorophyll.
Deficiency of Zn
1) Stunted plant growth
2) Leaves get discolor
3) Chlorosis of tissues
4) Veins turn yellow
•Chlorosis appears on the lower leaves first, and then gradually
moves up to the plant.
•In severe cases, the upper leaves become chlorotic and the
lower leaves turn brown or purple and die.
Effects of Zinc on Plants

10. Toxic Effects
Typical effect of Zn toxicity is the appearance of a purplish red
color in leaves.
1) Decrease in growth and development
2) Induction of oxidative stress
3) Alternation of catalytic efficiency of enzymes
4) Inhibit plant metabolic functions
5) Causes senescence
6) Give rise to manganese (Mn) and copper (Cu) deficiencies
Effects of Zinc on Plants

11. Purplish red color especially near veins on older leaves.
Effects of Zinc on Plants

12. •The permissible limit of cadmium (Cd) in agricultural soil is 100
mg/kg soil.
Toxic Effects
1) Chlorosis.
2) Growth inhibition.
3) Browning of root tips.
4) Reduces absorption of nitrate.
5) Affect the plasma membrane permeability.
6) Causes a reduction in water content.
Effects of Cadmium on Plants

13. • Chlorosis and Growth inhibition.
• Causes a reduction in water content. (Soybean Leaves)
Effects of Cadmium on Plants

14. Contamination of soils by Hg is often due to the addition of this
heavy metal as part of fertilizers, lime, sludge's, and manures.
Toxic Effects
1) High level of Hg+2 is strongly phytotoxic to plant cells.
2) Toxic level of Hg+2 can induce physiological disorders.
3) High level of Hg+2 reduces germination and seedlings stand.
4) Induces oxidative stress by triggering the generation of ROS.
Effects of Mercury on Plants

15. High level of Hg+2 reduces germination and seedlings stand.
(Methylmercury--MeHg)
Effects of Mercury on Plants

16. Chromium is known to be a toxic metal that can cause serve
damage to plant.
Toxic Effects
1) Induces oxidative stress
2) Severs damage to cell membranes
3) Degradation of photosynthetic pigments
4) Decline in growth
High levels (500 ppm) of hexavalent Cr in soil reduced
germination up to 48%.
Effects of Chromium on Plants

17. Plants on land tend to absorb lead from the soil and retain most of
this in their roots.
There is some evidence that plant foliage may also take up lead.
Toxic Effects
1) Reduces the uptake of Calcium and Phosphorus
2) Exerts adverse effect on morphology and growth
3) Reduces photosynthetic activity
4) Inhibit root and stem elongation and leaf expansion
Effects of Lead on Plants

18. Cobalt, a transition element, is an essential component of several
enzymes and co-enzymes.
Toxic Effects
1) Excess of Co has adverse effect on shoot growth and biomass
2) Restrict the concentration of Fe, chlorophyll, protein
3) Reduces the catalase activity in leaves
4) High level of Co also affect the translocation of P, S, Mn, Zn
5) Restrict the transport of assimilates
6) Decrease plant sugar
Effects of Cobalt on Plants

19. •Nickel is an essential nutrient for plants.
•Amount of Ni required for normal growth of plants is very low.
•Ni+2 concentration is increasing in certain areas by human
activities such as:
1) Mining works
2) Emission of smelters
3) Burning of coal and oil
4) Sewage
5) Phosphate fertilizers
6) Pesticides
Effects of Nickel on Plants

20. Toxic Effects
• Diverse toxicity symptoms such as chlorosis and necrosis
• Nickel decreases chlorophyll content
Effects of Nickel on Plants

21. Functions
 Iron is mainly involved in the process of plant photosynthesis.
Important biological roles in the processes as:
 Photosynthesis
Chloroplast development
Chlorophyll biosynthesis.
Effects of Iron on Plants

22. Toxic Effects
Iron toxicity symptoms in Rice.
Effects of Iron on Plants

23. Manganese is an essential plant mineral nutrient
Play a key role in photosynthesis.
Manganese deficiency most often occurring in:
1) Sandy soils.
2) Organic soils.
3) Heavily weathered Soils.
4) Tropical soils.
Effects of Manganese on Plants

24. • Necrotic brown spotting on leaves, petioles and stems.
• It is also associated with chlorosis and browning of these tissues.
• Another common symptom is known as ‘‘crinkle leaf’’.
Effects of Manganese on Plants

25. Toxic Effects
1) Reduces seed germination
2) Decreases seedling height
3) Stunted growth
4) Causes Chlorosis and Wilting
5) Decreases Leaf fresh weight
6) Reduces dry matter production
7) Reduces Yield
Effects of Arsenic on Plants

26. • Reduces seed germination
• Decreases seedling root length
Effects of Arsenic on Plants

27. Heavy metal polluted soils leads to reduction in growth due to
changes in physiological and biochemical activities.
There are two aspects on the interaction of plants and heavy
metals:
1. Heavy metals show negative effects on plants.
2. Plants have their own resistance mechanisms against toxic
effects and for detoxifying heavy metal pollution.
The toxicity of heavy metals can be removed bioremediation or
phytoremediation.
Phyto-extraction is the most common method of phyto-
remediation used for treatment of heavy metal polluted soils.
Conclusion

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References

29. Thank you
For your kind attention!