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6.2 Sources of Soil Pollutants 215

6.2.12.7 Metal Hyperaccumulator Plants

Some metal-tolerant plants are characterized by the ability to accumulate very
high concentrations of metals, far in excess of normal physiological requirements
(if any) and far in excess of the levels found in the majority of other species tolerant
of metals. These plants are known as metal “hyperaccumulator” plants. The term

hyperaccumulation was first applied by Jaffre et al. ( 1976 ) for nickel concentrations
in the New Caledonian tree species Sebertia acuminata . According to Reeves
( 1992 ), a hyperaccumulator of Ni is a plant in which a Ni concentration of at least
−1
1,000 mg kg has been recorded in the dry matter of any aboveground tissue in at
−1
least one specimen growing in its natural habitat. Later, 1,000 mg kg criterion was
−1
also taken for hyperaccumulation of Cu, Co, and Pb. A concentration >10,000 mg kg
is applied to Mn and Zn hyperaccumulation. Many plants have been identifi ed as
metal hyperaccumulators. However, a list of some important metal hyperaccumulator
plants obtained from Reeves and Baker ( 2000 ) is given below.

Metal Hyperaccumulator plants
Chromium Alyxia rubricaulis , Maytenus bureaviana , M . pancheriana , M . sebertiana ,
Garcinia amplexicaulis , Austromyrtus bidwillii , Eugenia clusioides , Eugenia
sp., Beaupreopsis paniculata , Macadamia angustifolia , M. neurophylla ,
Astragalus stanleya , Haplopappus , Machaeranthera
Cobalt and Pandiaka metallorum , Anisopappus davyi , Cyanotis longifolia , Ascolepis
copper metallorum , Bulbostylis pseudoperennis , Phyllanthus williamioides ,
Crotalaria cobalticola , Vigna dolomitica , Aeollanthus subacaulis var.
linearis , Haumaniastrum robertii , Eragrostis racemosa , Actiniopteris sp.,
Buchnera henriquesii , Sopubia neptunii , Triumfetta dekindtiana , T.
welwitschii var. descampii , Xerophyta retinervis var. equisetoides
Cadmium, lead Arabidopsis halleri , Thlaspi caerulescens , T. caerulescens , T. brachypetalum ,
and zinc T. caerulescens , T. ochroleucum , T. cepaeifolium , T. praecox , T. stenop-
terum , T. tatrensinuartia verna , Polycarpaea synandra , Dichapetalum
gelonioides , Armeria maritima , Agrostis tenuis , Arrhenatherum elatius ,
Festuca ovina , Rumex acetosa , Viola calaminaria
Manganese Vaccinium myrtillus , Austromyrtus bidwillii
Nickel Berkheya coddii , Pentacalia (10 species), Senecio (9 species), Alyssum
(52 taxa), Bornmuellera (6 taxa), Cochlearia aucheri , Peltaria emarginata ,
Streptanthus polygaloides , Thlaspi (23 taxa)

−1
A concentration higher than 100 mg kg is taken for Cd hyperaccumulation
(Reeves and Baker 2000 ). Some hyperaccumulator plants accumulate very high
amounts of heavy metals. For example, Thlaspi calaminare and Phyllanthus
serpentinus were reported to accumulate 39,600 mg kg Zn and 38,100 mg kg Ni,
−1
−1
respectively, in their leaves (Siegel 2002 ).
Study Questions

1. What do you mean soil pollution? How do polluted soils affect water and air

quality?