Heavy Metals

HEAVY METAL Contaminants

METAL • An element whose atoms are packed closely together by strong forces of attraction with free electrons moving around • Physical Properties: - Good conductor of electricity - High melting point - High thermal conductivity - High density - Malleable - Ductile

P er io d

Periodic Table

Group** 1 IA 1A

       

  2 IIA 2A

1

1

H 1.008 3

2 3 4 5 6 7

4

Li

Be

6.941

9.012

11

12

Na

Mg

22.99

24.31

19

20

K

Ca

39.10

40.08

37

38

Rb

Sr

85.47

87.62

55

56

Cs

Ba

132.9

137.3

87

88

Fr

Ra

(223)

(226)

 

 

Lanthanide Series* Actinide Series~

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

13 IIIA 3A

14 IVA 4A

15 VA 5A

16 VIA 6A

17 VII A 9 7A

He

F

Ne

19.0 0 17

20.1 8 18

5

 

 

 

 

 

 

 

 

6 VIB 6B

7 VII B 7B

8

9

10

3 IIIB 3B

4 IVB 4B

5 VB 5B

21

22

23

Sc

Ti

V

44.9 6 39

47.8 8 40

50.9 4 41

Y

Zr

Nb

Mo

88.9 57 1

91.2 2 72

92.9 1 73

95.9 4 74

Hf

Ta

178. 5 104

180. 9 105

La *

138. 89 9

Ac ~

24

25

Cr

Mn

52.00 42

54.94 43

------- VIII ------8 -------28 26------- 27

 

 

11 IB 1B

12 IIB 2B

29

N

O

14.0 1 15

16.0 0 16

P

S

Cl

Ar

30

32.0 7 34

35.4 5 35

39.9 5 36

Zn

Ga

Ge

As

Se

Br

Kr

69.7 2 49

72.5 9 50

74.9 2 51

78.9 6 52

79.9 0 53

83.8 0 54

Co

Ni

55.8 5 44

58.4 7 45

58.6 9 46

63.55 47

65.3 9 48

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

(98) 75

101. 1 76

102. 9 77

106. 4 78

107. 9 79

112. 4 80

114. 8 81

118. 7 82

121. 8 83

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

127. 6 84

126. 9 85

131. 3 86

183. 9 106

186. 2 107

190. 2 108

190. 2 109

195. 1 110

197. 0 111

200. 5 112

204. 4

207. 2 114

209. 0

Tc

Sg

Bh

Hs

Mt

---

---

---

(263)

(262)

(265)

(266)

()

()

()

 

 

 

 

 

 

 

 

 

59

60

61

Ce

Pr

Nd

140. 1 90

140. 9 91

144. 2 92

(147) 93

150. 4 94

Pa

U

Np

Pu

(231)

(238)

(237)

(242)

232. 0

C 12.0 1 14

30.9 7 33

Db

Th

B 10.8 1 13

4.00 3 10

Si

(260)

58

8

28.0 9 32

Rf

 

7

Al

(257)

(227)

6

26.9 8 31

Fe

Cu

18 VIII A 8A 2

62

Pm Sm

     

63

64

65

66

67

Eu

Gd

Tb

Dy

Ho

Er

152. 0 95

157. 3 96

158. 9 97

162. 5 98

164. 9 99

167. 3 100

Bk

Cf

Es

(247)

(249)

(254)

Am Cm (243)

(247)

68

Fm (253)

---

 

()

  69

Tm 168. 101 9

Md (256)

Po

At

Rn

(210)

(210)

(222)

116

---

 

118

---

()

 

 

70

71

Yb

Lu

173. 0 102

175. 0 103

No

Lr

(254)

(257)

()

 

 

 

 

 

 

Heavy Metal • Refer to several elements beginning with beryllium & actinides • Generally having an atomic numbers 22 to 92 in all groups from period 3 to 7 in the periodic table • MARC definition – metals of atomic weight higher than sodium and having a specific gravity of more than 5g/cm3 • Over 70 metallic elements

Toxicity • Cause catastrophic effect on normal metabolic function even when present in small amounts • Change biological structures & systems, leading to deformity or finally death • Almost all metals are toxic at higher concentrations & some are lethal even at low concentrations

Why are heavy metals toxic???

• Have a great affinity for sulphur attack, e.g –SH bonds in enzymes, thereby immobilising it • Attack protein carboxylic acid groups (-COOH) & amino groups (-NH2) • Involve binding to the metabolically active groups such as amino-, sulphydryl-, carboxyl-, phenolic- or phosphoryl• Progressive accumulation of metals through food chain, causing biomagnification, especially in fish

Toxicity to Humans & Aquatic Organisms Meta l

Toxicity To Huma n

Fish

Invertebrat Plant e

Cd

VeryHigh Medium

VeryHigh Medium

Pb

High

Medium

Medium

Hg

High

High

Variable

As

Variable High

Variabl e LowMediu m LowMediu m High

Arsenic (As) • Best known of the toxic trace metals • No known biological function & is highly toxic • Exists in organic & inorganic forms • Inorganic forms are more harmful but there are great differences in toxicity of different arsenic compounds • Common effects: skin cancer & dermatitis

Toxicity of As • Depends on: - valence states (0, +3 & +5) - organic & inorganic forms - physical aspects (absorption & elimination) • Inorganic arsenic & +3 arsenic are more toxic than organic & zero-valent or +5 arsenic • Under Food Act, the limit of As presence for fish, crustaceans & molluscs should be

Presence of As • Widely distributed in nature in number of minerals • Industrial sources: by-product in the smelting of copper, lead & nickel ores • Methylated arsenic exists due to conversion of As by microorganism • Organic As is the predominant form accumulated in aquatic species • As compounds (pesticide, herbicides) used in agricultural purposes get wash into the marine environment

As poisoning • Black food disease cause by the chronic ingestion of inorganic As • Incidence of massive As poisoning: nearly 50 million in Bangladesh are reported to be victims of the poisoning due to the drinking water that had been found with 80% contaminated with As beyond the safe limit

Cadmium (Cd) • No essential biological functions • Extremely toxic to human due to the absence of homeostatic control for the metal in the body • Common effects: Bronchitis, Kidney damage, skeletal damage, carcinogenic, affects heart & liver

Toxicity of Cd • Inhibition of various enzyme systems e.g. inactivating enzymes containing sulphydryl groups • Can compete with other metals such as Zn & Se for inclusion into metallo-enzymes as well as Ca for binding sites for regulatory proteins

Presence of Cd • Widely distributed in the earth crust • Released from volcanic activity • Widespread use in the metal plating & smelting of nonferrous metal ores • Commonly found in metallic form as sulphites & sulphates • Contamination arises from mine drainage water, waste water from processing of ores leading to pollution of aquatic environment

Cd Poisoning • “Itai-itai” disease (“ouch-ouch”) caused by chronic ingestion of Cd • Incidence of massive Cd poisoning: In 1965, Japan reported ~100 deaths by consuming rice contaminated with Cd for several years

Lead (Pb) • An element of particular interest to the food analyst as it is highly toxic • A bluish or silvery-grey soft metal • Exist in both organic & inorganic forms • Organic lead is more poisonous than inorganic lead • Common effects: anaemia, cardiac disease, kidney damage, reduced antibody synthesis optical atrophy, tremors & wrist drop.

Toxicity of Pb • Elemental Pb & inorganic Pb are absorbed by ingestion or inhalation while organic Pb is absorbed by skin contact • Has an affinity for cell membranes, affecting sodium, potassium & calcium ATP-ase pumps, impairing enzyme protein kinase C in the brain & also altering gene expression • Under Food Act, the limit of Pb presence for fish, crustaceans & molluscs should be

Flow Diagram of the effects of lead in the body Entry of lead into the body Enters the blood & is absorbed rapidly into the blood plasma. Progressively  taken up by red blood cells where it binds to haemoglobin & other molecules Equilibrates rapidly with extra-cellular fluid Crosses membranes in the body including the blood-brain barrier & the  placents / accumulates in soft & hard tissue especially in calcium sites Obstructing the utilisation of oxygen & glucose for life sustaining  energy production, causing kidney dysfunction & brain damage /  replacing calcium in bones

Presence of Pb • Occurs through releases (directly or through atmospheric deposition) from smelting & refining of Pb, the burning of petroleum fuels containing lead additives • Metallic lead deriving from shotgun cartridges, storage battery, solder, pipe, brass or used as fishing weights thus washing into the aquatic environment

Mecury (Hg) • Extremely toxic trace metal • Exist in 3 oxidation states (0, +1, +2) • Exists in inorganic & organic forms • Organic Hg is more toxic, particularly in the form of methyl mercury • Common effects: loss of vision, hearing & intellectual abilities & nervous disorders

Toxicity of Hg • A potent inhibitor of some enzymes & blocks the transport of potassium into cells & the transport of sugars • Vapour Hg is easily absorbed by the lungs • Inorganic Hg can be absorbed through the GI tract & also through the skin • Organic Hg undergo pulmonary absorption & are well absorbed by ingestion • Long-term effect: accumulation in the kidney & brain for years

Presence of Hg • Natural Hg arises from the degassing of the earth’s crust through volcanic gases & by evaporation from the oceans • Atmospheric poluution from industrial production, water pollution by mine tailings, burning of fossil fuels, chloralkali & wood pulping industry & as fungicides in agriculture • Dissolved Hg has a strong affinity for organic matter & suspended sediment. Hg can undergo methylation to produce methylmecury

Hg poisoning • Ingestion of mercuric chloride (in disinfectant) & from contaminated illegal drugs eg, amphetamines • Industrial accidents in which Hg vapour was inhaled • Environmental discharge of industrial waste thus contaminating the marine lives • Incidences of massive poisoning: - “Minimata disease” - In 1953, 52 persons in Japan were killed by chronic poisoning after consuming shellfish contaminated with Hg containing effluent from a nearby plastic industry - In 1972, 450 Iraqi villagers died after consuming grain treated with Hg containing pesticides

Internationally accepted safe levels of exposure to metals

Metal

Standard

Reference

Inorganic As Cd

15ug/kg body weight per week

WHO 1989

7ug/kg body weight per week

WHO 1989

Pb

25ug/kg body weight per week

WHO 1998

Hg

5ug/kg body weight per week WHO 1972 Reference dose of 0.1ug/kg of body USEPA weight per day 1995

Methodology • A lot of methods for quantification or qualification of heavy metals • Qualification – Wet Chemistry • Quantification – Atomic Spectroscopy (Flame AAS, Furnace AAS, ICP-OES and ICP-MS) • In Marine Fisheries Research Department, accredited methods under ISO/IEC 17025 were adopted for the determination of the four heavy metals

Analysis of Total Hg Sample Preparation

Dried Fish Sample

Wet Digestion Conc HNO3 + H2SO4

NaBH4

Hg Vapour Analysis

Flow injection AAS

Analysis of Total As Sample Preparation Dried Fish Sample

Wet Digestion Conc HNO3 + H2SO4 + HClO4

Pre-Reduction ( Conc HCl + KI + Ascorbic Acid) NaBH4

AsH Vapour Analysis

Flow injection AAS

Flow Injection Atomic Absorption Spectrometer

Analysis of Total Pb & Cd Dried Fish Sample Ashing

1st Ashing 450oC/ 16hrs

2nd

Conc HNO3 (450oC/ 2hrs) 6M HCl + 0.1M HNO3 Sample Solution

Analysis Matrix Modifier Graphite Furnace AAS

Graphite Furnace Atomic Absorption Spectrometer

Conclusion • Stop Marine Pollution • Maintain a well-balanced diet to avoid excessive exposure to contaminants from a small range of food items

Thank You