heavy metal contamination of soil and vegetation

7/30/2019 Heavy Metal Contamination of Soil and Vegetation

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Presented

By

Riyadul Islam


2/13

The investigation was made to understand the

heavy metal contamination of soil andvegetation in the vicinity of industries aroundDhaka city.

The concentration of total Cd,Cu,Mn,Ni,Pb andZn ranged from 0.1-1.8,28-217,106-577,25-

112,17-99 and 53-477 mg/kg soil respectivelyamong the industrial sides.

The concentration of total Cu,Mn,Ni,Pb and Zn isdecreased with increasing distance from thedisposal point.

The concentration of most heavy metals werehigher in the soil and vegetable samples oftannery area.


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Industrial effluents and municipal waste containhigh amount of heavy metals such asAs,Cd,Cr,Cu,Fe,Hg,Mn,Ni,Pb and Zn.

Some heavy metals are essential in trace

amounts for plants and animal(Zn,Cu,Fe,Mn,Ni).

But.higher concentration of these metal in theecosystems can be toxic to plants and causehealth problem to us.

In Bangladesh,untreated industrial wastes andeffluents dischare in the vicinity of industriespollute soils,surface water and ground water.


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four sampling sites were selected at the vicinityof different types of industry.

Tannery industrial area at hazaribagh,ceramic andtextile dying industries at Tongi and sulphuric acidproducing industrial area at Rupgonj.

The common agricultural practice in thesurrounding areas is paddy cultivation.Alsograsses,water hyacinth and arum were seen.

Total 53 samples were collected from the depth of

0-5 and 5-15cm around the four industrial sites. 10 samples were collected from 5-15cm depth of

3 industrial sites to see Anthropogenic sources ofheavy metal contamination(mixing of heavy metalin the deeper soil by agricultural practice).


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Soil samples were collected from excavation pitand Plant samples were collected within 5sq.m of

soil sampling area.Industrial area

NO. Ofsamples

pHrange

OC%range

CECcmol/kg

Type ofplantsample

Tannery 12 soil,9

plant

5.2-7.6 2.0-4.9 9.6-38.9 Grass,hya

cinth,rice

Ceramic 14 soil,6plant

4.8-7.6 0.87-2.97 12.2-24.1 Rice atfloweringstage

Textiledying 14 soil,6plant 5.2-7.7 1.36-7.99 11.9-23.1 Arum,grass

Sulphuricacid plant

16 soil,5plant

4.6-7.2 0.79-1.70 11.5-4.8 Rice atfloweringstage


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After processing the samples soil pH,EC,soil OC,cation

exchange capacity(CEC) and exchangeablecations(Ca,Mg,K) were determined using standardmethods.

The total concentration of Cd,Cu,Mn,Ni,Pb and Zn ofsoils were measured after digestion with conc.HNO3-

HClO4

(5:1) acid.The available Cd,Cu,Mn,Ni,Pb and Zn content of soils

were extracted by 0.005 M DTPA-extractent.

In case of determining plant content of heavymetal,wet oxidation of the samples was made with

HNO3-H2SO4-HClO4(10:4:1)Statistical analysis of the results(correlation

coefficient,regression analyses,etc) was done byMinitab program.


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The highest concentration of total and DTPA

extractable Cd,Mn,Ni,Pb and Zn were found insoils of tannery area and the lowest concentrationwere found in ceramic indutrial area.

this might be due to discharging liquidwaste,flocculated sludges and other solids with

excessive heavy metals coming from differenttanning processes. The highest concentration of Pb in the tannery

area may cause Pb poisoning to 20,000 slumliving people and children who live around wastedischarging channel.

The highest concentration of total andextractable Cu found in the textile industrial areawhich is due to the effluents and solid wastes ofdying industries.


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Metals

name

Tannery

ind. area

Ceramic

ind. area

Textile

dying ind.area

Sulphuric

acid ind.area

soil vegetation

soil vegetation

soil vegetation

soil vegetation

Cd 0.87-

1.80

0.58-

0.83

0.11-

0.58

0.45-

0.70

0.24-

0.58

0.38-

0.58

0.42-

0.64

0.50-

0.68Cu 35-

2175.5-15.2

28-56

7.9-15.4

29-357

10.8-16.9

41-74

4.5-5.5

Mn 218-577

164-229

106-268

88-186

143-473

72-270

241-341

127-194

Ni 47-112

6.90-13.8

25-90

7.3-10.6

37-65

7.2-9.2

59-104

7.6-11.3

Pb 20.5-89.7

13.3-44.7

17.1-39.4

12.8-19.6

33.0-89.6

10.1-15.9

27.4-40.8

17.1-20.6

Zn 73-

477

98-

244

106-

465

35.9-

84.0

53-

354

32.7-

97.6

102-

147

31.9-

50.0


9/13

Concentration of total Cd,Cu,Ni,Pb and Zn were

found above the natural background level in allindustrial sites with few exceptions in the ceramicindustrial sites.

Cd content was found in the group of tolerable level

in all industrial sites(


10/13

Total concentrati of Cd,Cu,Mn and Zn in the soilsof tannery and textile dying area were found to

decrease with the increasing distance from thedisposal point.

This means.metals have been accumulating inthe soil through these industrial operations.

Butdecreasing tendency of concentration withdistance was not noticeable in soils of ceramicand H2SO4 producing industries.

The metal content in the sulphuric acid producingindustrial area is due to discharging of waste

materials in the land and localized acid rain. Low pH value in the soils of sulphuric acid

producing area increase the solubility of metalwhich lead to incresed availability of the heavymetals for plant uptake and cause metal toxicity.


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The Cd contents in vegetations ranged from

0.38-0.83 mg/kg among the industrial sites.Cu concentration among the sites were similar

except the H2SO4 producing industrial site.The highest concentration of Mn,Pb,Zn and Ni was

found in the vegetation sample of the tannery

area.Concentration of Zn(98-244mg/kg) and Pb(13.28-

44.7mg/kg) in the vegetations of tannery area isin the range oftolerable to above the toxic limit.

Higher concentrations of Cd,Cu,Ni and Zn in the

grass and water hyacinth in tannery area may bedue to the exposure of these plants to the heavymetals for longer period

.or there might be different mechanism ofabsorbtion of heavy metals by these plants.


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A number of metals were observed were

significantly(p


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heavy metal contamination of soil and vegetation

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