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