FACTORS AFFECTING PLANT SENSTIVITY TO AIR POLLUTANTS

Pollutant	Factor	Sensitivity	Comment
C2H4 pollution	Tissue age	Epinasty in immature leaves. Other symptoms on oldest leaves first.	Tissues with high natural C2H4 are more sensitive.
C2H4 pollution	High temperature	Sensitivity increased
C2H4 pollution	Other pollutants	Effects inhibited by high levels of SO2 or CO2
Cl2 pollution	Bright sunshine	Sensitivity increased
Cl2 pollution	Tissue age	Little effect; in conifers, current year’s needles most sensitive	Immature leaves tolerant in some species.
Cl2 pollution	Wet leaves	No effect
Cl2 pollution	Drought	Sensitivity decreased
Cl2 pollution	Low temperature	Sensitivity decreased in pines	Symptoms take longer to develop.
Cl2 pollution	Plat age	Seedling less sensitive than oleder plants
HCl pollution	Tissue age	Young, fully expanded leaves most sensitive	Immature leaves tolerant.
HCl pollution	Plant age	Seedlings less sensitive than mature plants	Older plants become more tolerant.
HCl pollution	High relat. Humidity	Sensitivity increased
HCl pollution	Ca-deficit	Sensitivity decreased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Ca-excess	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Cl-deficit	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Cl-excess	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Mg-deficit	Sensitivity increased
NH3 pollution	Concentration	Variable	Some conifers sensitive at moderate but tolerant at high levels.
NH3 pollution	Tissue age	Little effect
NH3 pollution	Darkness	Variable
NH3 pollution	Drought	Sensitivity decreased
NH3 pollution	Wet leaves	Sensitivity increased	Symptoms develop faster.
NOx pollution	Ca-excess	Sensitivity decreased	Opposite effect in some species.
NOx pollution	Tissue age	Immature leaves/needles most sensitive
NOx pollution	Cultivar	Highly variable; especially in gladiolus & tomato	In gladiolus, sensitivity related to flower colour
NOx pollution	High relat. humidity	Sensitivity increased
NOx pollution	Low temperature	Sensitivity decreased; symptom expression delayed
NOx pollution	Drought	Sensitivity decreased; symptoms induced in conifers needles previously exposed.	Sensitivity increased in some fruit trees.
NOx pollution	N-deficit	Sensitivity decreased	Opposite effect in some species.
NOx pollution	Ca-deficit	Sensitivity decreased	Opposite effect in some species.
NOx pollution	N-excess	Sensitivity decreased	Opposite effect in some species.
NOx pollution	P-excess	Sensitivity increased	Opposite effect in some species.
NOx pollution	Other pollutants	Interaction with SO2, NO2, O2 & hydrocarbons	Response varies with concentrations and relative proportions.
NOx pollution	K-deficit	Sensitivity increased	Opposite effect in some species.
O3 pollution	K-excess	Variable sensitivity
O3 pollution	N-excess	Variable sensitivity
O3 pollution	Plant age	Young plants most sensitive
O3 pollution	Tissue age	Intermediate leaves usually most sensitive
O3 pollution	Darkness	Sensitivity decreased	Plants grown in low light are more sensitive. High light during exposure increases injury.
O3 pollution	Wet leaves	Variable sensitivity
O3 pollution	Drought	Sensitivity decreased
O3 pollution	Other pollutants	Interactions with SO2, NO2, PAN & heavy metals	Response varies with species, concentration & relative proportions
O3 pollution	High soil salinity	Sensitivity decreased
O3 pollution	High relat. Humidity	Sensitivity increased
O3 pollution	S-excess	Sensitivity decreased
O3 pollution	N-deficit	Variable sensitivity
O3 pollution	P-deficit	Sensitivity decreased
O3 pollution	Low temperature	Sensitivity decreased	Sensitivity decreases again above 30 degree C. Response varies according to dose.
O3 pollution	K-deficit	Variable sensitivity
PAN pollution	High relat. Humidity	No effect
PAN pollution	Tissue age	Young, rapidly expanding leaves most sensitive	Sensitivity strongly affected by physiological age, results in bands of damage.
PAN pollution	Other pollutants	Interactions with O3 & SO2	Response varies with concentrations & pollutant.
PAN pollution	Drought	Sensitivity decreased
PAN pollution	Time of day	Sensitivity more in morning than after noon
PAN pollution	Darkness	Injury eliminated. Sensitivity increases with increased light intensity	Presence of light before, during and after exposure must for injury to occur.
PAN pollution	Low temperature	Injury decreased
PAN pollution	Plant age	Young plants more sensitive
SO2 pollution	Other pollutant	Interaction with O3, NO2, HF	Response varies with concentrations and relative proportions.
SO2 pollution	Time of day	More sensitivity when sugar content low	In many plants in the morning.
SO2 pollution	High relat. Humidity	Sensitivity increased
SO2 pollution	Drought	Sensitivity decreased
SO2 pollution	High wind	Sensitivity increased
SO2 pollution	Wet leaves	Variable; may increase
SO2 pollution	Darkness	Sensitivity decreased	Some plants e.g. Potato not closing stomata at night may be unaffected.
SO2 pollution	Low temperature	Sensitivity decreased	Susceptibility to frost injury increased by SO2 exposure
SO2 pollution	Plant age	Seedlings more sensitive than older plants
SO2 pollution	Season	Grasses more sensitive in winter; conifers more in April/May than in July/August	Not vry important for very short exposures.
SO2 pollution	N-deficit	Sensitivity decreased
SO2 pollution	S-deficit	Sensitivity decreased
SO2 pollution	P-deficit	Sensitivity decreased
SO2 pollution	N-excess	Sensitivity decreased
SO2 pollution	K-deficit	Sensitivity increased
SO2 pollution	S-excess	Sensitivity increased
SO2 pollution	Tissue age	Most in young, fully expanded leaves
SO2 pollution	Ca-deficit	Sensitivity increased

HABITAT AND PLANT RESPONSE

Cause	Common name	Botanical name	Plant part	Symptom
Cold area	Pea	Pisum sativum	Leaf	Bronzing
Cold area	Bean	Phaseolus vulgaris	Leaf	Bronzing
Cold area	Spinach	Spinacea oleracea	Leaf	Bronzing
Dry area	Pine	Pinus sp.	Needle	Tip burn; sharp boundaary between necrotic and healthy tissue
Dry area	Spruce	Picea sp.	Needle	Tip burn; sharp boundaary between necrotic and healthy tissue
Dry area	Fir	Abies sp.	Needle	Tip burn; sharp boundaary between necrotic and healthy tissue
Dry area	Aspen	Populus tremula	Leaf	Tip necrosis with sharp boundary
Dry area	Plum	Prunus domestica	Leaf	Marginal/interveinal necrosis, boundary chlorotic & diffuse
Dry area	Wych elm	Ulmus glabra	Leaf	Tip necrosis with sharp boundary
Dry area	Willow	Salix sp.	Leaf	Tip necrosis with sharp boundary
Dry area	Cherry	Prunus avium	Leaf	Marginal/interveinal necrosis, boundary chlorotic & diffuse
Dry area	Oak	Quercus rubur (Q. pedunculata)	Leaf	Interveinal brown/bronzed lesions
Dry area	Apple	Malus sylvestris	Fruit	Dark lesions
Dry area	Cherry	Prunus avium	Fruit	Brown/black depression at tip
Dry area	Pear	Pyrus communis	Fruit	Brown/black depression at tip
Dry area	Tomato	Lycopersicum esculentum	Fruit	Blossom end rot
Water logged area	Lucerne (alfalfa)	Medicago sativa	Leaf	White stipple
Hot area	Onion	Allium cepa	Leaf	Tip necrosis; white/grey stipple
Hot area	Horse chestnut	Aesculus hippocastanum	Leaf	Marginal necrosis
Hot area	Lettuce	Lectuca sativa	Leaf	Brown stipple of veins
Hot area	Lucerne (alfalfa)	Medicago sativa	Leaf	White stipple
Cold area	Lucerne (alfalfa)	Medicago sativa	Leaf	Necrotic stipple
Cold area	Potato	Solanum tuberosum	Leaf	Black discolouration; necrotic stipple

NUTRIENT DEFICIENCY SYMPTOMS IN PLANTS

Cause	Common name	Botanical name	Plant part	Symptom
K-deficit	Pear	Pyrus communis	Leaf	Upward curling
K-deficit	Pea	Pisum sativum	Leaf	Brown stipple
K-deficit	Potato	Solanum tuberosum	Leaf	Bronzing of lower surface; marginal, later interveinal necrosis
K-deficit	Tomato	Lycopersicum esculentum	Leaf	Marginal, later interveinal necrosis
K-deficit	Lucerne (alfalfa)	Medicago sativa	Leaf	Marginal, later interveinal necrosis
P-deficit	Cabbage	Brassica oleracea var. capitata	Leaf	Red/purple discolouration
P-deficit	Lucerne (alfalfa)	Medicago sativa	Leaf	Red/purple discolouration
P-deficit	Potato	Solanum tuberosum	Leaf	Curling or rolling
S-deficit	Tomato	Lycopersicum esculentum	Leaf	Very pale new leaf; Bleached old leaf
Ca-deficit	Tulip	Tulipa gesneriana	Leaf	Necrosis
Ca-deficit	Tulip	Tulipa gesneriana	Plant	Wilting
Mg-deficit	Pear	Pyrus communis	Leaf	Black necrosis
Mg-deficit	Potato	Solanum tuberosum	Leaf	Brown stipple
Mg-deficit	Tomato	Lycopersicum esculentum	Leaf	Curling & brittleness
Mn-deficit	Oats	Avena sativa	Leaf	Grey discolouration
Mn-deficit	Wheat	Triticum vulgare	Leaf	White dashes
Mn-deficit	Wheat	Triticum vulgare	Plant	Pale floppy appearance
Mn-deficit	Barley	Hordeum vulgare	Plant	Pale floppy appearance
Mn-deficit	Barley	Hordeum vulgare	Leaf	White dashes
Zn-deficit	Lucerne (alfalfa)	Medicago sativa	Leaf	White stipple on lower & Bronzing of upper surface
Zn-deficit	Tomato	Lycopersicum esculentum	Leaf	Interveinal chlorosis, later necrosis
Mn-excess	Cauliflower	Brassica oleracea var. botrytis	Leaf	Brown/purple stipple
Mn-excess	Potato	Solanum tuberosum	Leaf/stem	Black stipple or streaks

MINIMUM EXPOSURE TO AIR POLLUTANTS FOR PLANT INJURY

Plant name	Pollutant	ppm	hours	tolerance
Alder	HCl	6.00	4.00	Middle
Aster	HCl	9.00	0.40	Low
Barley	HCl	7.00	0.40	Very low
Bean	HCl	4.00	0.40	Very low
Beech	HCl	1000.00	1.00	Very high
Cherry	HCl	9.00	4.00	High
Chrysanthemum	HCl	9.00	3.00	High
Cornflower	HCl	20.00	0.40	Middle
Cosmos	HCl	9.00	0.40	Low
Douglas fir	HCl	10.00	4.00	High
Marigold	HCl	9.00	0.40	Low
Nasturtium	HCl	9.00	0.40	Low
Norway maple	HCl	7.00	4.00	High
Norway spruce	HCl	19.00	4.00	Very high
Oak	HCl	1000.00	1.00	Very high
Tomato	HCl	5.00	2.00	Low
Tulip tree	HCl	3.00	4.00	Low
Weymouth pine	HCl	8.00	4.00	High
Zinnia	HCl	9.00	0.40	Low
Annual poa	NH3	12.00	4.00	Middle
Buckwheat	NH3	16.60	4.00	Middle
Chickweed	NH3	12.00	4.00	Middle
Dandelion	NH3	12.00	4.00	Middle
Apple	SO2	0.40	6.00	Middle
Aspen	SO2	0.40	3.00	Middle
Barley	SO2	1.30	1.00	Very low
Bean	SO2	0.80	3.00	Low
Begonia	SO2	0.30	1.00	Very low
Broad bean	SO2	2.00	4.00	High
Broccoli	SO2	0.30	4.00	Low
Buckwheat	SO2	0.70	1.00	Very low
Cabbage	SO2	1.00	4.00	Low
Chrysanthemum	SO2	2.50	3.00	Very high
Cocksfoot	SO2	3.10	6.00	Very high
Cucumber	SO2	0.80	4.00	Low
Dandelion	SO2	2.00	4.00	High
Douglas fir	SO2	0.70	4.50	Middle
French marigold	SO2	2.00	2.00	High
Geranium	SO2	2.00	2.00	High
Ginkgo	SO2	2.80	3.00	Very high
Gladiolus	SO2	0.50	8.00	Middle
Iris	SO2	0.50	8.00	Middle
Italian ryegrass	SO2	1.90	6.00	High
Larch	SO2	0.30	8.00	Low
Lettuce	SO2	1.00	2.00	Low
Locust tree	SO2	2.00	4.00	High
Lucerne	SO2	0.10	4.00	Low
Lilac	SO2	0.30	6.00	Middle
Tomato	NH3	8.30	5.00	Low
White clover	NH3	100.00	0.10	Middle
African marigold	C2H4	0.01	20.00	Low
Cattleya orchid	C2H4	0.00	24.00	Very low
Aspen	O3	0.15	2.00	Low
Bean	O3	0.06	8.00	Low
Begonia	O3	0.13	3.00	Low
Bindweed	O3	0.20	4.00	Low
Apple	C2H4	0.01	48.00	Middle
Buckwheat	C2H4	0.05	48.00	Middle
Carnation	C2H4	0.10	6.00	Low
Chrysanthemum	C2H4	1.00	9.00	High
Cucumber	C2H4	100.00	6.00	Very high
Fat hen	C2H4	0.05	48.00	Middle
Forsythia	C2H4	0.70	20.00	High
Narcissus	C2H4	0.40	1.00	Very low
Pepper	C2H4	0.10	8.00	Low
Rose	C2H4	10.00	24.00	Very high
Snapdragon	C2H4	0.50	1.00	Very low
Strawberry	C2H4	1.00	24.00	High
Sunflower	C2H4	0.05	48.00	Middle
Tomato	C2H4	1.00	24.00	Middle
Tulip	C2H4	0.40	1.00	Very low
Norway maple	SO2	2.50	3.00	High
Oats	SO2	1.00	1.00	Low
Onion	SO2	1.00	4.00	Low
Pea	SO2	1.00	1.00	Low
Petunia	SO2	2.00	4.00	High
Pine	SO2	0.30	2.00	Low
Plantain	SO2	0.80	6.00	Middle
Poplar	SO2	2.00	4.00	High
Potato	SO2	4.20	1.00	Middle
Radish	SO2	0.50	1.00	Low
Red fescue	SO2	1.20	6.00	Middle
Rose	SO2	0.70	6.00	Middle
Rye	SO2	0.70	3.00	Low
Ryegrass	SO2	1.00	6.00	Low
Fat hen	NH3	12.00	4.00	Middle
Lettuce	NH3	2.00	24.00	Low
Ryegrass	NH3	100.00	0.20	Middle
Smooth-stalk meadow grass	NH3	12.00	4.00	Middle
Silver birch	SO2	0.90	2.00	Low
Smooth-stalk meadow grass	SO2	0.20	2.00	Low
Snapdragon	SO2	4.00	2.00	High
Spruce	SO2	3.00	6.00	Very high
Spinach	SO2	1.00	4.00	Low
Sweet pea	SO2	0.80	3.00	Low
Swiss chard	SO2	1.00	1.00	Low
Timothy	SO2	0.80	1.00	Low
Tomato	SO2	0.50	4.00	Low
Turnip	SO2	1.00	2.00	Low
Wheat	SO2	0.80	1.00	Low
Annual poa	HF	0.10	4.00	Low
Apple	HF	0.40	4.50	Middle
Azalea	HF	0.10	48.00	High
Bean	HF	0.70	2.30	Middle
Buckwheat	HF	0.70	2.30	Middle
Celery	HF	0.10	48.00	High
Chickweed	HF	0.10	4.00	Low
Corn	HF	0.10	4.00	Low
Dandelion	HF	0.10	4.00	Low
Dock	HF	0.50	8.00	High
Fat hen	HF	0.10	4.00	Low
Gladiolus	HF	0.06	6.00	Very low
Iris	HF	0.50	8.00	High
Lucerne	HF	0.10	48.00	High
Nettle-leaved goosefoot	HF	0.10	4.00	Low
Norway spruce	HF	0.20	5.80	Low
Pine	HF	0.07	4.00	Very low
Polygonum	HF	0.50	8.00	High
Rose	HF	0.50	8.00	High
Smoot-stalk meadow grass	HF	0.10	4.00	Low
Sunflower	HF	0.10	4.00	Low
Tomato	HF	0.30	3.00	Low
Tulip	HF	0.50	8.00	High
Azalea	Nox	13.00	1.00	Middle
Awnless brome	Nox	4.00	0.50	Very low
Bean	Nox	6.00	2.00	Low
Beet	Nox	30.00	1.00	High
Begonia	Nox	16.00	0.50	Middle
Broccoli	Nox	16.00	0.50	Middle
Buckwheat	Nox	4.00	4.00	Low
Chrysanthemum	Nox	4.00	0.50	Very low
Corn	Nox	4.00	0.50	Very low
Cocksfoot	Nox	4.70	6.00	Low
Cucumber	Nox	6.00	2.00	Low
Erica heather	Nox	1000.00	1.00	Very high
Sunflower	NH3	3.00	4.00	Very low
Italian ryegrass	Nox	4.70	6.00	Low
Lettuce	Nox	30.00	1.00	High
Lucerne	Nox	6.00	8.00	Low
Oats	Nox	4.00	0.50	Very low
Pea	Nox	6.00	4.00	Low
Plantain	Nox	3.30	6.00	Low
Potato	Nox	30.00	1.00	High
Radish	Nox	4.00	0.50	Very low
Rape	Nox	30.00	1.00	High
Rye	Nox	30.00	1.00	High
Ryegrass	Nox	4.70	6.00	Low
Red fescue	Nox	4.70	6.00	Low
Smooth-stalk meadow grass	Nox	4.70	6.00	Low
Spinach	Nox	6.00	2.00	Low
Swiss chard	Nox	1.00	1.00	Very low
Timothy	Nox	4.70	6.00	Low
Tomato	Nox	8.00	1.00	Low
Wheat	Nox	5.00	0.50	Very low
Azalea	Cl2	0.80	4.00	Low
Azalea	Cl2	0.80	4.00	Middle
Bean	Cl2	1.30	0.50	Low
Begonia	Cl2	1.00	4.00	High
Buckwheat	Cl2	0.50	1.00	Low
Carnation	Cl2	0.50	4.00	Middle
Clover	Cl2	35.00	2.00	Middle
Corn	Cl2	0.10	4.00	Very low
Cucumber	Cl2	0.50	4.00	Middle
Dahlia	Cl2	0.50	4.00	Middle
Dandelion	Cl2	0.50	4.00	Middle
Fat hen	Cl2	1.00	4.00	High
Geranium	Cl2	0.80	4.00	High
Lucerne	Cl2	0.10	2.00	Very low
Maple	Cl2	0.10	4.00	Very low
Nasturtium	Cl2	0.50	4.00	Middle
Onion	Cl2	0.80	4.00	High
Petunia	Cl2	0.10	4.00	Very low
Pine	Cl2	1.00	3.00	High
Polygonum	Cl2	1.00	4.00	High
Radish	Cl2	0.10	2.00	Very low
Rose	Cl2	1.00	0.50	Low
Ryegrass	Cl2	35.00	0.20	Middle
Squash	Cl2	0.80	4.00	High
Sunflower	Cl2	0.10	2.00	Very low
Tomato	Cl2	0.50	4.00	Middle
Zinnia	Cl2	0.10	4.00	Low
Buttercup	O3	0.20	4.00	Low
Chrysanthemum	O3	0.26	3.00	Low
Corn	O3	0.10	2.00	Low
Corsican pine	O3	0.25	4.00	Low
European larch	O3	0.25	4.00	Low
Grape	O3	0.40	4.00	Middle
Lettuce	O3	0.15	2.00	Low
Lucerne	O3	0.15	4.00	Low
Oats	O3	0.10	2.00	Very low
Pea	O3	0.10	2.00	Very low
Poplar	O3	0.18	4.00	Low
Radish	O3	0.08	2.00	Very low
Red clover	O3	0.15	4.00	Low
Scots pine	O3	0.25	8.00	Middle
Smooth-stalk meadow grass	O3	0.10	17.50	Very high
Spinach	O3	0.13	3.00	Low
Tobacco	O3	0.05	5.00	Very low
Common vetch	O3	0.20	4.00	Low
Weymouth pine	O3	0.07	4.00	Very low
Wheat	O3	0.23	3.00	Low
White clover	O3	0.15	4.00	Low
Bean	PAN	0.05	4.00	Low
Petunia	PAN	0.01	8.00	Low
Tomato	PAN	0.01	4.00	Low
Lettuce	PAN	0.05	12.00	High
Small nettle	PAN	0.05	35.00	Very high
Annual poa	PAN	0.05	42.00	Very high
Phalaenopsis orchid	C2H4	0.00	24.00	Very low

AIR POLLUTANTS AND PLANT RESPONSES

Cause	Common name	Botanical name	Plant part	Symptom
Acid mist pollution	Begonia	Begonia sp.	Leaf	Necrotic spots on upper surface at point of contact
	Swiss chard	Beta vulgaris var. cicla	Leaf	Shot holing
Boron pollution	Honeysuckle	Lonicera periclymenum	Leaf	Brown marginal necrosis; interveinal necrosis; cupping & distortion
	Norway maple	Acer platanoides	Leaf	Brown marginal necrosis; interveinal necrosis;necrotic stipple; abscission
	Silver maple	Acer saccharinum	Leaf	Brown marginal necrosis, interveinal necrosis; cupping & distortion
	Spiraea	Spiraea sp.	Leaf	Abscission
Br2 pollution	Bean	Phaseolus vulgaris	Leaf	Marginal necrosis
	Beech	Fagus sylvatica	Leaf	Black spots, later whole leaf black/brown
	Corn	Zea mays	Leaf	Yellow tip, later necrotic
	Dahlia	Dahlia pinnata	Leaf	Brown discolouration; marginal necrosis
	Fir	Abies sp.	Needle	Red/brown discolouration, later grey/brown
	Larch	Larix decidua	Needle	Yellow/white tip
	Pea	Pisum sativum	Leaf	Marginal necrosis
	Pea	Pisum sativum	Tendril	Necrosis
	Rose	Rosa sp.	Leaf	Brown discolouration
	Rye	Secale cereale	Leaf	Yellow tip, later necrotic
C2H4 pollution	Apple	Malus sylvestris	Flower	Intumescence formation
	Apple	Malus sylvestris	Bark	Hypertrphy, especially around lenticels
	Azalea	Rhododendron sp.	Flower	Necrosis
	Beet	Beta vulgaris	Old leaf	Red/purple discolouration
	Carnation	Dianthus caryophyllus	Flower	Closing of flowers; ’sleepiness’
	Cattleya orchid	Cattleya sp.	Sepal	Drying/bleaching from tip to base
	Cucumber	Cucumis sativus	Flower	Conversion of male into female
	Daffodil	Narcissus pseudonarcissus	Leaf	Inwards roll, curl or twist
	Hibiscus	Hibiscus sp.	Stem	Hypertrophy of lenticels
	Hyacinth	Hyacinthus sp.	Flower	Delayed opening; abnormal colour
	Hyacinth	Hyacinthus sp.	Leaf	Inwards roll, curl or twist; abscission
	Lettuce	Lectuca sativa	Young leaf	Dark green colouration
	Lilac	Syringa vulgaris	Bark	Hypertrphy, especially around lenticels
	Lily	Lilium sp.	Leaf	Inwards roll, curl or twist; abscission
	Marigold	Tagetus sp.	Stem	Root induction
	Pea	Pisum sativum	Young leaf	Dark green colouration
	Petunia	Petunia hybrida	Flower	Flowering inhibition
	Phalaenopsis orchid	Phalaenopsis sp.	Sepal	Drying/bleaching from tip to base
	Poplar	Populus sp.	Bark	Hypertrphy, especially around lenticels
	Radish	Raphanus sativus	Old leaf	Red/purple discolouration
	Radish	Raphanus sativus	Young leaf	Dark green colouration
	Rose	Rosa sp.	Flower	Premature opening
	Rose	Rosa sp.	Old leaf	Chlorosis, later necrosis
	Rose	Rosa sp.	Young leaf	Dark green colouration
	Snapdragon	Antirrhinum majas	Flower	Loss of petals
	Tomato	Lycopersicum esculentum	Stem	Root induction
	Tulip	Tulipa gesneriana	Leaf	Inwards roll, curl or twist; abscission
	Tulip	Tulipa gesneriana	New leaf	Continued folding
	Willow	Salix sp.	Bark	Hypertrphy, especially around lenticels
	Wych elm	Ulmus glabra	Bark	Loss of bark
Cement pollution	Bean	Phaseolus vulgaris	Leaf	Margin rolling; interveinal necrosis; growth inhibition
	Oats	Avena sativa	Leaf	Yellow spots
Cl2 pollution	Apple	Malus sylvestris	Leaf	Abscission; marginal necrosis
	Azalea	Rhododendron sp.	Leaf	Necrotic margins
	Barberry	Berberis vulgaris	Leaf	Marginal cholrosis
	Cherry	Prunus avium	Leaf	Necrotic stipple; abscission
	Chrysanthemum	Chrysanthemum sp.	Leaf	Necrotic stipple
	Dahlia	Dahlia pinnata	Leaf	Black marginal discolouration
	Dandelion	Taraxacum officinale	Leaf	Red discolouration
	Douglas fir	Pseudotsuga menziesii	Needle	Necrosis
	Fir	Abies sp.	Needle	Red/brown necrosis; narrow band of necrotic stipple between necrotic and healthy tissue
	Ginkgo	Ginkgo biloba	Leaf	Necrotic stipple
	Hibiscus	Hibiscus sp.	Leaf	Marginal cholrosis
	Horse chestnut	Aesculus hippocastanum	Leaf	White stipple
	Horse chestnut	Aesculus hippocastanum	Leaf	Marginal necrosis
	Larch	Larix decidua	Needle	Chlorotic mottle
	Lettuce	Lectuca sativa	Leaf	Necrotic margins; bronzing of lower surface
	Lucerne (alfalfa)	Medicago sativa	Leaf	Necrotic margins
	Oak	Quercus rubur (Q. pedunculata)	Leaf	Necrotic stipple; bronzing
	Onion	Allium cepa	Leaf	Tip necrosis
	Pear	Pyrus communis	Leaf	Black necrosis
	Peony	Paeonia sp.	Leaf	Necrotic margins
	Pine	Pinus sp.	Needle	Dull grey/green, later necrotic; orange necrosis; chlorotic mottle; narrow band of necrotic stipple between necrotic and healthy tissue
	Plum	Prunus domestica	Leaf	Necrotic stipple; marginal necrosis
	Rhododendron	Rhododendron	Leaf	Dark stipple, more on upper surface
	Rose	Rosa sp.	Leaf	Dark stipple, more on upper surface
	Spruce	Picea sp.	Needle	Red/brown necrosis; narrow band of necrotic stipple between necrotic and healthy tissue
	Squash	Cucurbita	Leaf	Cupping
	Sycamore	Acer pseudoplatanus	Leaf	Marginal necrosis
	Sycamore	Acer pseudoplatanus	Leaf	Black necrosis
	Tomato	Lycopersicum esculentum	Leaf	Cupping; epinasty
	Tulip	Tulipa gesneriana	Leaf	Bleached lower surface
	Wych elm	Ulmus glabra	Leaf	Marginal necrosis
	Yew	Taxus baccata	Needle	Black necorsis
Fluoride pollution	Apple	Malus sylvestris	Leaf	Interveinal necrotic stipple; red/brown necrosis
	Bilberry	Vaccinium sp.	Leaf	Red tip & margin discolouration
	Buckwheat	Fagopyrum esculentum	Leaf	Leaf cupping
	Cherry	Prunus avium	Fruit	Necrosis of stylar end
	Colorado spruce	Picea pungens	Young needle	Purple necrosis
	Corn	Zea mays	Leaf	Marginal chlorotic mottle; necrotic stipple, later necrotic streaks
	Cyclamen	Cyclamen	Sepals & petals	Marginal necrosis
	Dahlia	Dahlia pinnata	Leaf	Black necrosis
	Dandelion	Taraxacum officinale	Leaf	Ivory necrosis
	Gladiolus	Gladiolus sp.	Leaf	Glazed upper surface; red/brown necrosis
	Lilac	Syringa vulgaris	Leaf	Necrotic bands; red margin discolouration
	Lucerne (alfalfa)	Medicago sativa	Leaf	Marginal necrosis
	Oats	Avena sativa	Leaf	Ivory necrosis
	Peach	Prunus persica	Fruit	Premature ripening & suture rotting
	Pear	Pyrus communis	Fruit	Necrosis of stylar end
	Petunia	Petunia hybrida	Sepals & petals	Marginal necrosis
	Pine	Pinus sp.	Young needle	Reddish necrotic bands
	Poplar	Populus sp.	Leaf	Ivory necrosis; tip notching
	St. Johns Wort	Hypericum perforatum	Leaf	Red/brown necrosis
	Sunflower	Helianthus annuus	Leaf	Brown necrosis
	Tomato	Lycopersicum esculentum	Leaf	Edge curling; ivory necrosis
	Tulip	Tulipa gesneriana	Leaf	Glazed upper surface
	Wheat	Triticum vulgare	Leaf	Bleached tip; ivory necrosis
H2S pollution	Aster	Callistephus chinensis	Flower	Necrosis of bracts
	Buckwheat	Fagopyrum esculentum	Leaf	Upward rolling
	Sunflower	Helianthus annuus	Leaf	Distortion; orange interveinal necrosis
HCl pollution	Aspen	Populus tremula	Leaf	Chlorotic mottle
	Aster	Callistephus chinensis	Leaf	Bronzing/glazing of lower surface
	Bean	Phaseolus vulgaris	Leaf	Ivory necrosis; bronzing/glazing of lower surface; upward curling or rolling
	Beech	Fagus sylvatica	Leaf	Interveinal bleaching; necrotic stipple
	Cherry	Prunus avium	Leaf	Chlorotic mottle
	Cornflower	Centaurea cyanus	Leaf	Necrotic stipple; upward curling or rolling
	Cosmos	Cosmos bipinnatus	Sepal	Tip burn
	Cosmos	Cosmos bipinnatus	Leaf	Upward curling or rolling
	Cosmos	Cosmos bipinnatus	Petal	Discolouration
	Dahlia	Dahlia pinnata	Leaf	Black marginal discolourationg; black necrosis
	Maple	Acer sp.	Leaf	Necrotic stipple
	Marigold	Tagetus sp.	Sepal	Tip burn
	Nasturtium	Tropeolum majas	Leaf	Necrotic stipple; bleaching
	Oak	Quercus rubur (Q. pedunculata)	Leaf	Interveinal bleaching
	Pear	Pyrus communis	Leaf	Marginal necrosis
	Rose	Rosa sp.	Leaf	Black marginal discolourationg; marginal necrosis
	Silver birch	Betula pendula	Leaf	Marginal necrosis
	Tomato	Lycopersicum esculentum	Leaf	Bronzing/glazing of lower surface; bifacial bronzing, later necrotic
	Zinnia	Zinnia angustifolia	Leaf	Bronzing/glazing of lower surface; upward curling or rolling
	Zinnia	Zinnia angustifolia	Petal	Necrotic stipple
Hg pollution	Privet	Ligustrum sp.	Leaf	Browning of interveinal tissue
	Rose	Rosa sp.	Petal	Colour loss, later brown at margins
	Rose	Rosa sp.	Stamen/pistil	Black
	Rose	Rosa sp.	Bud	Remain closed, later necrosis
	Rose	Rosa sp.	Peduncle	Brown/black
	Rose	Rosa sp.	Flower	Abscission
NH3 pollution	Apple	Malus sylvestris	Fruit	Purple/black/brown discolouration around lenticels
	Azalea	Rhododendron sp.	Leaf	Brown/black necrosis
	Azalea	Rhododendron sp.	Flower	Brown & white marks on white and red flowers respectively
	Barley	Hordeum vulgare	Leaf	Bleaching
	Bean	Phaseolus vulgaris	Leaf	Red discolouration; red/brown/purple margins of necrotic areas
	Beech	Fagus sylvatica	Leaf	Bronzing/glazing of upper surface
	Broad bean	Vicia faba	Leaf	Yellow discolouration; later black
	Buttercup	Ranunculus sp.	Leaf	Yellow discolouration; later black
	Carrot	Daucus carota	Leaf	Brown/black necrosis
	Cauliflower	Brassica oleracea var. botrytis	Leaf	Ivory necrosis; black spots on lower surface
	Celery	Apium graveolens	Leaf	Red discolouration
	Clover	Trifolium sp.	Leaf	Red/brown/purple margins of necrotic areas
	Cocksfoot	Dactylis glomerata	Leaf	Ivory necrosis
	Cotoneaster	Cotoneaster sp.	Leaf	Yellow discolouration
	Dandelion	Taraxacum officinale	Leaf	Brown/black necrosis; red discolouration
	Forsythia	Forsythia intermedia	Leaf	Dark pigmented spots spreading & coalescing untill leaf becomes dark green/brown/black
	Gladiolus	Gladiolus sp.	Leaf	Ivory necrosis
	Hawthorn	Crataegus monogyna	Twig	Dieback
	Horse chestnut	Aesculus hippocastanum	Leaf	Dark pigmented spots spreading & coalescing untill leaf becomes dark green/brown/black
	Iris	Iris sp.	Leaf	Yellow discolouration
	Leek	Allium porrum	Leaf	Glazing; ivory necrosis
	Onion	Allium cepa	Leaf	Glazing; ivory necrosis
	Parsley	Petroselinum crispum	Leaf	Ivory necrosis
	Pea	Pisum sativum	Leaf	Purple/black/brown discolouration around lenticels
	Pear	Pyrus communis	Leaf	Dark pigmented spots spreading & coalescing untill leaf becomes dark green/brown/black
	Poplar	Populus sp.	Leaf	Bronzing/glazing of upper surface
	Potato	Solanum tuberosum	Leaf	Ivory necrosis
	Rhubarb	Rheum rhaponticum	Leaf	Red/brown/purple margins of necrotic areas; reddish necrosis
	Rye	Secale cereale	Leaf	Reddish necrosis
	Sorrel	Rumex acetosa	Leaf	Red/brown/purple margins of necrotic areas
	Sprouts	Brassica oleracea var. gemisera	Leaf	Black spots on lower surface
	Spruce	Picea sp.	Young needle	Red/yellow discolouration
	Spruce	Picea sp.	Needle	Pale green, becoming white and then red
	Stinging nettle	Urtica dioica	Leaf	Brown/black necrosis
	Strawberry	Fragaria vesca	Leaf	Red discolouration
	Sycamore	Acer pseudoplatanus	Leaf	Dark pigmented spots spreading & coalescing untill leaf becomes dark green/brown/black; yellow discolouration
	Wheat	Triticum vulgare	Leaf	Ivory necrosis
	Willow	Salix sp.	Leaf	Bronzing/glazing of upper surface
Nox pollution	Alder	Alnus glutinosa	Leaf	Red/brown necrosis
	Annual poa	Poa annua	Leaf	Glazing
	Apple	Malus sylvestris	Leaf	Red/brown necrosis
	Apple	Malus sylvestris	Leaf	Herringbone necrosis
	Aspen	Populus tremula	Leaf	Ivory necrosis, often with dark brown border
	Aster	Callistephus chinensis	Leaf	Orange/brown necrosis
	Azalea	Rhododendron sp.	Leaf	Orange/brown necrosis
	Barley	Hordeum vulgare	Awn	Tip necrosis
	Bean	Phaseolus vulgaris	Leaf	Marginal necrosis
	Beech	Fagus sylvatica	Leaf	Red/brown necrosis
	Beech	Fagus sylvatica	Leaf	Herringbone necrosis
	Begonia	Begonia sp.	Leaf	Shot holing with coloured margin
	Cabbage	Brassica oleracea var. capitata	Leaf	Necrotic stipple; bronzing/glazing
	Carnation	Dianthus caryophyllus	Leaf	Tip necrosis
	Carrot	Daucus carota	Leaf	Tip necrosis
	Clover	Trifolium sp.	Leaf	Marginal necrosis
	Cocksfoot	Dactylis glomerata	Leaf	Yellow/orange necrosis
	Dahlia	Dahlia pinnata	Leaf	Orange/brown necrosis
	Fir	Abies sp.	Old needle	Abscission after several months; sharp red/brown band between necrotic and healthy tissue
	Gooseberry	Ribes uva-crispa	Leaf	Tip necrosis
	Hazel	Corylus avellana	Leaf	Ivory necrosis, often with dark brown border; herringbone necrosis
	Kohlrabi	Brassica oleracea var. gongylodes	Leaf	Necrotic stipple
	Larch	Larix decidua	Old needle	Abscission after several months
	Lettuce	Lectuca sativa	Leaf	Necrotic stipple; ivory necrosis; shot holing with coloured margin
	Lucerne (alfalfa)	Medicago sativa	Leaf	Marginal necrosis
	Lupin	Lupinus angustifolium	Leaf	Marginal necrosis
	Maple	Acer sp.	Leaf	Red/brown necrosis
	Oak	Quercus rubur (Q. pedunculata)	Leaf	Red/brown necrosis; marginal necrosis; ivory necrosis, often with dark brown border
	Ox-eye daisy	Chrysanthemum leucanthemum	Leaf	Orange/brown necrosis
	Parsley	Petroselinum crispum	Leaf	Tip necrosis
	Pea	Pisum sativum	Leaf	Marginal necrosis
	Pear	Pyrus communis	Leaf	Black necrosis
	Pine	Pinus sp.	Old needle	Abscission after several months
	Pine	Pinus sp.	Old needle	Bleaching, later necrosis
	Pine	Pinus sp.	Old needle	Ring of white spots close to base
	Pine	Pinus sp.	Old needle	Sharp red/brown band between necrotic and healthy tissue
	Plantain	Plantago sp.	Leaf	Ivory necrosis; bronzing/glazing
	Potato	Solanum tuberosum	Leaf	Black marginal stipple
	Rhododendron	Rhododendron	Leaf	Necrotic stipple
	Rye	Secale cereale	Awn	Tip necrosis
	Silver birch	Betula pendula	Leaf	Ivory necrosis, often with dark brown border
	Spinach	Spinacea oleracea	Leaf	Bronzing/glazing; shot holing with coloured margin
	Spruce	Picea sp.	Old needle	Immediate abscission
	Sweet William	Dianthus barbatus	Bracts	Tip necrosis
	Sweet William	Dianthus barbatus	Sepals	Tip necrosis
	Timothy	Phleum pratense	Leaf	Basal necrosis
	Tulip	Tulipa gesneriana	Leaf	Basal necrosis
O3 pollution	Apple	Malus sylvestris	Fruit	Tissue collapse around lenticels
	Apple	Malus sylvestris	Leaf	Bronzing by very dense small lesions, mostly on upper surface
	Ash	Fraxinus excelsior	Leaf	Dense to sparse purple/reddish stipple of upper surface, bounded by smallest veins
	Barley	Hordeum vulgare	Leaf	Fine chlorotic/white/tan streaks between large veins, more at leaf bendings & seedling tips/margins
	Bean	Phaseolus vulgaris	Leaf	Brown necrotic lesions on upper surface, darker on first trifoliate leaf
	Bean	Phaseolus vulgaris	Fruit	Rows of necrotic lesions
	Citrus	Citrus sp.	Fruit	Premature drop
	Corn	Zea mays	Leaf	Light tan/white bifacial irregular necrotic streaks severe on margins occurring at tips in young leaf pregressively downwards on old leaf; bands of small silver grey/light tan necrotic steaks
	Grape	Vitis vinifera	Leaf	Dense to sparse purple/reddish stipple of upper surface, bounded by smallest veins
	Lilac	Syringa vulgaris	Leaf	Curling with drying of tip & margin
	Lime	Tilia cordia	Leaf	Bronzing by very dense small lesions, mostly on upper surface
	Lucerne (alfalfa)	Medicago sativa	Leaf	White/light yellow-green/silvergrey/tan variable necrosis on all or limited area
	Maple	Acer sp.	Leaf	Dense to sparse purple/reddish stipple of upper surface, bounded by smallest veins
	Oats	Avena sativa	Leaf	Fine chlorotic/white/tan streaks between large veins, more at leaf bendings & seedling tips/margins
	Onion	Allium cepa	Leaf	White fleck, later brown tips
	Pea	Pisum sativum	Leaf	Fawn lesions
	Pine	Pinus sp.	Needle	Chlorotic mottling, later tip burn
	Plane	Platanus sp.	Leaf	Dense to sparse purple/reddish stipple of upper surface, bounded by smallest veins
	Poplar	Populus sp.	Leaf	Dark brown bifacial necrotic lesions
	Silver birch	Betula pendula	Leaf	Bleaching of upper surface except at margins
	Snowberry	Symphoricarpos albus	Leaf	Bleaching of upper surface except at margins
	Spinach	Spinacea oleracea	Leaf	Dull white/tan lesions; large bifacial necrosis
	Tobacco	Nicotiana tobacum	Leaf	Numerous small white/tan bifacial lesions on upper surface, larger and more on more sensitive varieties
	Weymouth pine	Pinus strobus	Needle	Chlorotic flecks, later pink lesions and then orange-red tip necrosis
	Wheat	Triticum vulgare	Leaf	Fine chlorotic/white/tan streaks between large veins, more at leaf bendings & seedling tips/margins
Salts pollution	Hawthorn	Crataegus monogyna	Branch	Tip-dieback
	Maple	Acer sp.	Leaf	Yellow necrosis
	Poplar	Populus sp.	Leaf	Abscission
	Willow	Salix sp.	Leaf	Brown necrosis
So2 pollution	Apple	Malus sylvestris	Leaf	Reddish necrosis; red discolouraion
	Azalea	Rhododendron sp.	Leaf	Reddish necrosis
	Beech	Fagus sylvatica	Leaf	Brown/orange necrosis; red discolouraion; necrotic stipple
	Begonia	Begonia sp.	Leaf	Shot holing
	Blackberry	Rubus fruticosus	Leaf	Brown necrosis
	Bracken	Pteridium aquilinum	Frond	Orange/red marginal necrosis
	Broad bean	Vicia faba	Leaf	Black necrosis
	Cabbage	Brassica oleracea var. capitata	Leaf	Red discolouration around necrotic areas
	Carrot	Daucus carota	Leaf	Tip necrosis
	Cherry	Prunus avium	Leaf	Red discolouraion
	Chrysanthemum	Chrysanthemum sp.	Leaf	Brown necrosis
	Corn	Zea mays	Leaf	Red discolouration
	Daffodil	Narcissus pseudonarcissus	Leaf	Light brown necrosis; sharp band between necrotic and healthy tissue
	Dandelion	Taraxacum officinale	Leaf	Brown necrosis
	Fir	Abies sp.	Old needle	Immediate abscission
	Fir	Abies sp.	Middle age needle	Sharp boundry between necrotic and healthy tissue ater 3 wks of exposure
	Fir	Abies sp.	Young shoot	Twist
	Fuschia	Fuschia hybrida	Leaf	Distortion, puckering, curling
	Geranium	Pelargonium sp.	Leaf	Distortion, puckering, curling; grey necrosis
	Gladiolus	Gladiolus sp.	Sepal	Tip necrosis
	Gooseberry	Ribes uva-crispa	Leaf	Red stipple on upper surface; tip necrosis
	Hazel	Corylus avellana	Leaf	Brown/orange necrosis
	Hydrangea	Hydrangea macrophylla	Leaf	Red discolouration around necrotic areas
	Larch	Larix decidua	Middle age needle	Necrosis
	Lettuce	Lectuca sativa	Leaf	Dark spots on lower surface; shot holing
	Lily of the Valley	Convallaria majalis	Leaf	Sharp band between necrotic and healthy tissue
	Lime	Tilia cordia	Leaf	Brown/orange necrosis
	Lucerne (alfalfa)	Medicago sativa	Leaf	Bronzing of lower surface
	Lucerne (alfalfa)	Medicago sativa	Leaf	Ivory necrosis
	Maple	Acer sp.	Leaf	Distortion, puckering, curling
	Marigold	Tagetus sp.	Sepal	Tip necrosis before leaf injury
	Marigold	Tagetus sp.	Leaf	Large, bifacial necrotic spots on margin; distortion, puckering, curling
	Oak	Quercus rubur (Q. pedunculata)	Leaf	Ivory necrosis
	Oats	Avena sativa	Leaf	Ivory necrosis
	Parsley	Petroselinum crispum	Leaf	Tip necrosis
	Pea	Pisum sativum	Leaf	Ivory necrosis
	Pear	Pyrus communis	Leaf	Black necrosis
	Pine	Pinus sp.	Terminal bud	Necrosis
	Pine	Pinus sp.	Young needle	Chlorosis
	Pine	Pinus sp.	Middle age needle	Sharp boundry between necrotic and healthy tissue ater 3 wks of exposure
	Pine	Pinus sp.	Old needle	Abscission after several months
	Pine	Pinus sp.	Young shoot	Necrosis
	Poplar	Populus sp.	Leaf	Reddish necrosis
	Raspberry	Rubus idaeus	Leaf	Marginal necrosis
	Red currant	Ribes rubrum	Leaf	Red stipple on upper surface
	Rose	Rosa sp.	Leaf	Red stipple on upper surface
	Rowan	Sorbus aucuparia	Leaf	Ivory necrosis
	Silver birch	Betula pendula	Leaf	Distortion, puckering, curling
	Silver birch	Betula pendula	Leaf	Ivory necrosis
	Spinach	Spinacea oleracea	Leaf	Shot holing
	Spruce	Picea sp.	Middle age needle	Necrosis
	Strawberry	Fragaria vesca	Leaf	Red discolouration around necrotic areas; brown necrosis
	Sweet William	Dianthus barbatus	Leaf	Tip necrosis
	Tulip	Tulipa gesneriana	Leaf	Ivory necrosis
	Violet	Viola sp.	Leaf	Ivory necrosis
	Wheat	Triticum vulgare	Leaf	Red discolouration
	Willow	Salix sp.	Leaf	Ivory necrosis
	Zinnia	Zinnia angustifolia	Leaf	Ivory necrosis

PLANTS AS AMELIORATORS (MITIGATORS) OF POLLUTION

Many types of higher and lower plants and microorganisms have the capability to tolerate and absorb large amounts of gaseous, liquid and solid pollutants from the environment and decompose them into harmless substances. This ability of such organisms can be usefully exploited in the control of environmental pollution.

Plants cover about one third of the land area as forests and grasslands and another one third as agricultural crops. Large surface area of ponds, lakes, rivers and sea coasts is also covered with aquatic flora. All this vegetation provides huge surface area that can be gainfully used to trap pollutants from the environment. In this large vegetational cover, those plant species that can absorb large quantities of pollutants and accumulate them in their tissues without damage (tolerant-accumulator species) provide natural storehouses or sinks of various pollutants without any cost. Such plants are very important resource materials in environmental pollution control strategies. Generally, woody plants absorb more pollutants than herbaceous plants. Actively growing tissue of wood absorbs larger amounts of pollutants than dormant tissues. Therefore, trees are comparatively more useful than herbaceous plants in pollution control.

Use of tolerant-accumulator plats in the control of air and soil pollution involves:

1. Identification of pollutant(s) present in the area,
2. Identification of tolerant-accumulator plant species suitable for the climate and the pollution problem of the area and then
3. Plantation of identified plant species in the area on available bare lands, fallow lands, community lands, waste lands, along roads, railway lines, canal banks as well as green belts, shelter belts, wind breaks, city forests, parks etc.

Trees reduce the velocity of air passing through them thus facilitating the absorption of pollutants by the foliage. Establishment of tolerant-accumulator epiphytic mosses and lichens on the trees may also help in absorption of pollutants. Many microorganisms that can degrade pollutants to harmless substances are also established on the leaves as phyllosphere. Many plants absorb pollutants from the soil and thus check their runoff into water bodies or their leaching into the groundwater.

Use of plants in the control of water pollution mostly involves treatment of sewage an industrial effluents before their release into lakes or rivers and treatment of polluted water bodies. Introduction and maintenance of accumulator aquatic plants like Eichhornia, Azolla, Cladophora, Fontinalis squamosa etc. in the ponds is very effective in cleaning polluted water and keeping them free of organic, chemical and metal pollution. Most important sewage and effluent treatment systems using plants are:

Peat moss treatment systems: Many types of systems have been designed to treat urban sewage and industrial effluents using Sphagnum moss. These can treat upto 91,000 litres of effluent per day. Effluents are passed through columns containing the moss, which absorbs metals and the used up moss is then destroyed. Pre-treatment of moss with CaCO₃ increases the metal absorption.

Eichhornia treatment systems: Diluted sewage or industrial effluent is passed through a zig-zag system of ponds and canals in which Eichhornia plants are grown. These plants asorb pollutants and retain them in their rhizomes. Plants from these hyacinth lagoons are regularly harvested and can be used to produce biogas in suitable digesters or after extraction of absorbed metals, can be used in making paper, boards etc. In the lagoons, the growth and death rates of plants are continuously monitored and managed by regulating the dissolved oxygen, biological oxygen demand and chemical oxygen demand, pH, turbidity and conductivity of the water at different stages of cleaning.

Microbial treatment/biogas systems: Treatment systems for organic sewage use suitable aerobic/anaerobic decomposer bacteria, ammnifying and sulphur bacteria in anaerobic lagoons. The organic matter in he polluted water is decomposed producing methane and carbon dioxide. In such systems, combination of decomposer bacteria and algae like Spirulina, Scendesmus, Clorella etc. can also be used. The decomposed organic matter is used up by algal growth. These protein-rich algal cultures can be regularly harvested and used as cattle feed. In the biogas systems, anaerobic bacterial decomposition of organic matter produces combustible gas. The freed metals and other pollutants are removed and clean effluent is used as rich fertilizer.

Many bacteria can absorb metals (e.g. Thiobacillus ferrooxidans and T. thiooxidans absorb copper), degrade petroleum oil (Pseudomonas sp.) or other chemicals. Genetic engineering is being applied to create new and more efficient strains of bacteria for use in mining and industries to control metal pollution, to clean oil spills, to degrade herbicides and pesticides in the soil and to absorb SO₂ from chimney gases before their release into the atmosphere. Pseodomonas, Staphylococcus and a cornybacterium that accumulate metal bearing particles like silver, Aspergillus and Penicilium that concentrate uranium and phosphate are examples of such useful bacteria. Sulphur bacteria like Chlorobium, Chromatium and Thiospirillum may be helpful in control of SO₂ pollution of air.

PLANTS AS INDICATORS AND MONITORS OF POLLUTION

Plants can effectively be used as cheap and naturally available monitoring systems or bioassays of the level and type of air, soil and water pollution in an area. The type and concentration of a pollutant can be reliably found out by various characteristics damage symptoms produced in the plants because such damage symptoms are pollutant specific as well as concentration specific. For example, in young needles of Pinus, chlorois indicates SO₂ pollution, necrosis indicates HF pollution, beaching indicates NO₂ pollution while chlorotic mottle indicates Cl₂ pollution in the atmosphere. These characteristic symptoms of damage in young pine needles appear only when concentration is 0.3 ppm for SO₂, 0.07 ppm for HF and 1.0 ppm for Cl₂. Similarly, browning in moss leaves due to fluoride accumulation is 5% in 65 ppm dry weight accumulation but rises to 90% in 4500 ppm dry weight accumulation. However, certain precautions have to be taken while using plants as pollution indicators.

Precautions in use of plants as pollution indicators

1. The damage symptoms in plants should preferably be studied in the local native species. Cultivated and introduced species should be avoided.

2. The species sensitive to pollutants should be first identified in the local flora and then used for pollution monitoring. Tolerant species should be identified and avoided in such work.

3. Damage symptoms for a particular pollutant should be studied in different species sensitive to that pollutant so that presence of the pollutant in the area may be cross-checked. For example, grey necrosis in Geranium, ivory necrosis in Zinnia, brown necrosis in Chrysanthemum and reddish necrosis in Azalea indicates absolutely certain presence of SO₂ pollution in the area.

4. Many types of damage symptoms viz. morphological, anatomical, ultra-structural physiological, biochemical etc. should be studied in one or more sensitive plant species to ascertain the presence of a particular pollutant in the area.

5. Samples should be taken from as many different sites in the area as possible. From such data the extent of pollution can be determined and the possibility of symptoms being due to some pathogen is also excluded because the intensity of damage symptoms due to pollution varies in different sites according to the distance from the source of pollution while it is same in all sites in case of a pathogenic disease.

6. The possibility of damage symptoms in plants occurring due to some cause other than pollution e.g. due to pathogen, environmental condition or nutritional deficiency/excess should be thoroughly checked and ruled out.

Important characteristics of plant species used in pollution monitoring

The plant species used to monitor pollution in an area should have certain important features for the success of such programme. Most important such features are:

1. Species should be easy to identify in the field and easy to handle for damage analysis.

2. Species should have a wide range of distribution so that it can be used in different areas.

3. Species should be sensitive to many types of pollutants so that it can be used to monitor different types of pollutants in the area.

4. Species should produce highly specific damage symptoms in response to particular types and concentrations of pollutants.

Plants commonly used as pollution indicators

Though all types of sensitive species can be used in monitoring pollution, most useful and commonly used plants include sensitive species of lichens, mosses, plankton algae, aquatic ferns and angiosperms, other ferns, conifers oaks and many crop plants. Mosses, lichens, ferns algae and aquatic plants are generally more useful in pollution monitoring because their range of pollutant specificity is usually much higher than that of higher vascular plants. Examples of some common types of plants useful as pollution monitors are given below.

Plant type	Plants
AIR & SOIL POLLUTION