ABSTRACT
The research work analysed levels of lead, chromium and cobalt in five samples of water-based paints sold in Zaria. Water-based paints, also known as emulsion, are made with water as the primary solvent instead of oil. The paint samples were dried then digested in HNO3 and HCl which was repeated two more times and concentration of the heavy metals is determined using Atomic Absorption Spectroscopy. The level of lead in the whole sample is found to be below the permissible limit of 90 ppm while the level of chromium in all the samples is found to be below the permissible limit of 75 ppm and the level for cobalt in the whole sample is found to be below the permissible limit of 90 ppm. Since all the concentrations of the paint samples where below the standard limit, therefore they are safe for usage.
TABLE OF CONTENT
DECLARATION ii
CERTIFICATION iii
DEDICATION iv
ACKNOWLEDGEMENT v
ABSTRACT vi
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background Information 1
1.1.1 Lead (Pb) 2
1.1.2 Chromium (Cr) 2
1.1.3 Cobalt (Co) 2
1.2. Problem statement 3
1.3. Justification 3
1.4 Aim(s) and Objective 4
1.4.1 Objectives 4
1.5 Scope of the Study 4
CHAPTER ONE
2.0 LITERATURE REVIEW
2.1 History of Paints 5
2.2 Paints Classifications According to the Kind of Solvent and Binder 9
2.2.1 Oil- based Binders 9
2.2.2 Acrylic, Vinyl Acrylic and PVA Binders 10
2.2.3 Other Binders Used in Water-based Paints 10
2.2.4 More About Water-based Acrylic Paints 11
2.3 Paint Classification According to the Application 12
2.3.1 Architectural Paint 12
2.3.2 Industrial Paints 12
2.4 Components of Paints 13
2.4.1 Pigments 14
2.4.2 Binders 14
2.4.3 Solvents 15
2.4.4 Additives 16
2.5 Heavy Metals 17
2.5.1 Lead and it’s Poisoning 19
2.5.2 Chromium and it’s Poisoning 23
2.5.3 Cobalt and its Poisoning 26
2.7 Atomic Absorption Spectroscopy 29
2.7.1 Instrumentation 30
CHAPTER THREE
3.1 Sampling 32
3.2 Laboratory Procedures 32
3.2.1 Glassware and Plastic Containers 32
3.3 Sample Preparation 32
3.3.1 Acid Digestion 33
3.4 The Atomic Absorption Spectrometry (AAS) Analysis 33
3.5 Data Analysis 34
CHAPTER FOUR
4.0 RESULTS AND DISCUSSIONS
4.1 Results: 35
4.2 Discussion 37
4.2.1 Concentrations of Pb, Cr and Co Samples by Manufacturers. 37
CHAPTER FIVE
5.1 CONCLUSION AND RECOMMENDATIONS
5.2 Conclusions 38
5.3 Recommendations 38
LIST OF TABLES
Table 3.1; AAS instrument parameters …………………………. 34
Table 4.1; Lead concentrations in paint samples ………………... 35
Table 4.2; Chromium concentrations in paint samples …………... 36
Table 4.3; Cobalt Concentrations in paint samples ………………. 36
LIST OF FIGURES
Fig 2.1; Systematic diagram of AAS Equipment …………………….... 31
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background Information
Paint is any liquid, liquefiable or mastic composition of a homogeneous mixture of three major ingredients namely binders, pigments, VOC (Volatile Organic Compounds) and additives which when applied on the surface as a thin layer forms a solid dry film after oxidation, evaporation or polymerization used for decorative and protective purposes.
Paints are prepared by mixing different components in proper proportions. These are some essential components of paints: pigments, binders, solvents, additives, fillers and driers. A good paint has to be easy to apply, have high resistance, high opacity, dries quickly, good hiding power, etc.
Paints are classified into industrial and decorative paints. Industrial paints are used in automobile and marine coating and steel industries. Decorative paints are divided into water and oil-based paints which are primarily used for exterior and interior decoration of buildings and homes. Some examples of paint brands are Dulux, Berger, Horse, etc.
Inorganic pigment of paints contains metals which play a vital role in the ability of the paint to perform its function. Metal content or pigment compounds produces colour and also contribute to the chemical and physical properties of paint such as durability and rust inhibitive characteristics. However, lead, chromium and cobalt are present in organic pigments which are toxic elements (Kameti, 2013).
1.1.1 Lead (Pb)
Lead is a poison and a persistent environmental pollutant when it's higher than its acceptable limit. It affects the developing brain and nervous system; it can also result in mental retardation of young children. Lead can damage the kidneys, brain function, basic cellular processes, liver, red blood cells and reproductive systems of men and women. Some symptoms of effects of lead toxicity includes dizziness, muscle weakness, hallucination, anaemia, irritability, renal damage, headache and insomnia (Fu et al., 2011). It also accumulates in the skeleton which then affects the foetus and breast-fed infants due to its mobilization in bones during pregnancy and then lactation (Yurdakok, 2015; Agrawal, 2012).
1.1.2 Chromium (Cr)
Chromium compounds are added to paints and primers to provide corrosion protection and reflective properties. When chromium concentration is low it is used for medical purposes, and it is also involved in natural human lipid and protein metabolism. However, at high concentrations, especially hexavalent chromium, it is toxic and carcinogenic. Chromium is an element that occurs in food products of both plants and animals. It is known as an essential trace element present in humans and animals and takes part in various metabolic processes. Chromium, as essential elements are usually present in food in the trivalent form; the hexavalent form of chromium is toxic and not normally found in food (Rêczajska et al., 2005).
1.1.3 Cobalt (Co)
Cobalt is among the d-block elements on the periodic table, it has a bluish colour. With other constituents of cobalt are used in technology industries e.g. rechargeable batteries, catalyst, super alloys, etc. It can also be used to make magnets. Some ores often associated with cobalt are Ag, Cu, Fe, Mn, Ni, Pb and are mostly obtained as by-products (Gunn, 2014). Cobalt also forms a number of minerals e.g. cobaltite (CoAsS), Spherocobaltite (CoCO3), Heterogenite(CoO(OH)). It also occurs naturally in air, soil, plants and water. Cobalt deficiency affects nodule development, function, and nitrogen fixation. Cobalamin, also called vitamin B-12, is essential for human and animal health, nutrition, and growth. High and frequent Co exposures can affect the nervous system and cause an axonopathy (Flora, 2014). High exposure to Co dust can lead to diffuse-inflammatory reactions of the bronchial mucosa and chronic respiratory tract disorder (Banza et al., 2009; Cheyns et al., 2014).
1.2. Problem statement
In as much as heavy metals help in providing durability, pigmentation, rust inhibitive characteristics, they are as well not good if their required content level is exceeded. They are toxic to the health of humans and the environment causing brain damage, kidney damage, carcinogenic effects amongst others. Therefore because of this usefulness and challenges coming from heavy metals in paints we will look at the presence and the quantity of some of these heavy metals namely Lead, Chromium and Cobalt in paints sold in Zaria, Kaduna State, Nigeria.
1.3. Justification
Water based paints are mostly used in homes and buildings in Zaria since they are economically friendly. In Zaria, so many constructions, renovations or even re-modelling of old buildings that take place now are being painted with decorative paints. Apart from buildings; furniture, playground equipment in children's schools and other materials which children come in contact with are also painted. Information on the concentration of lead in paints has been reported in many parts of the world, even in Lagos State, Nigeria. But little or no information is known on paints sold Kaduna State. Also, little or no information is known about the concentration of Cr and Co. Lead, Chromium and Cobalt have specific residue limits but are not seriously enforced in Nigeria.
1.4 Aim(s) and Objective
This study work seeks to determine the presence and quantity of heavy metals - Lead (Pb), Chromium (Cr) and Cobalt (Co) in water-based paints sold in Zaria metropolis, Kaduna State, Nigeria.
1.4.1 Objectives
● To identify and collect paint samples sold in Zaria, Kaduna State, Nigeria.
● To determine the presence of Lead (Pb), Chromium (Cr) and Cobalt (Co) in selected paint samples sold in Zaria.
● To determine the quantity of Lead (Pb), Chromium (Cr) and Cobalt (Co) in selected paint samples sold in Zaria.
● To compare the levels of these metals in paints with the standard limits.
● To determine if the paint samples are safe for usage
1.5 Scope of the Study
Five paint samples are analyzed for three (3) heavy metals - Lead (Pb), Chromium (Cr) and Cobalt (Co) in water-based paints sold in Zaria metropolis, Kaduna State, Nigeria.
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