s effective as polychlorinated biphenyls (PCBs) may be in achieving thermal stability as coolant in transformer oils; spills, decommissioning and poor handling of these transformer oils often results to contamination of PCBs on the environment. The attendant adverse effect of PCBs on the environment and humans has been of serious concerns. The residue levels of PCBs in soil of selected transformer maintenance workshops in Kaduna and Zaria metropolis, Kaduna State, Nigeria was determined. Two soil samples per site, one top-soil (0 – 5 cm) and one sub-soil (20- 30 cm), totalling fourteen (14) soil samples were collected in four (4) and three (3) different locations in Kaduna and Zaria metropolis respectively. Some soil physico-chemical properties such as particle size (sand, silt and clay) and total organic carbon (TOC) in the soil that may influence the dynamics of the pollutants was determined. In addition, the soil samples were analysed for residues of PCBs using the technique of gas chromatography-mass spectrometry (GC-MS). PCB concentrations were correlated (PEARSON) with the particle size and total organic carbon (TOC). The coefficient of variation of percent TOC was 45. The concentration of the PCBs measured showed significant correlation (P< 0.05) with TOC. PCB congeners CB 28, CB 52, CB 101, CB 153, CB 138 and CB 180 were detected at varied concentrations, occurring most frequently with highest sum PCB congeners of 8209.50 μg/kg at Arewa Metal Containers (AMECO) Kaduna, lowest sum PCB congeners of 0.81 μg/kg at Ahmadu Bello University (ABU) Main Campus, Samaru- Zaria, and absent at farmland near National Research Institute for Chemical Technology (NARICT), Zaria that serve as control. CB 153, CB 138 and CB 180 (hex- and hepta- chlorinated biphenyls) were dominant species in all the soil samples, accounting for more than 82 % and 68 % of total PCBs in the soil samples from Kaduna and Zaria respectively. The sum PCB congeners‘ residue levels down the soils in all the sites decreases due to soil binding effect and other weathering process. The percent hexa- and hepta- chlorinated biphenyls increased from top-soil to sub- soil except in AMECO. This finding reveals that higher molecular weight PCBs percolates down the soil which might offer an insight for ground water contamination. The measured Relative Retention Factors of all the samples were within the 6-11 percent (%) standard deviation retention time of the referenced standard PCB congeners, and was found satisfactory. The percent (%) recoveries of PCBs in topsoil and subsoil of AMECO, topsoil and subsoil of Mando are in the ranges of 83-145 % and 53-86 %, 52-92 % and 71-143 % respectively. The PCB residue levels in all the samples complied with the United Nations Environmental Programme (UNEP) set maximum limit of 50 ppm (50,000 μg/kg).
TABLE OF CONTENTS
Title Page iii
Table of Contents ix
List of Figures xii
List of Tables xiii
Abbreviations and Symbols xiv
1.0 Introduction 1
1.1 Background of Study 1
1.2 Justification of Study 7
1.3 Aim and Objectives of Study 7
1.3.1 Aim of the Study 7
1.3.2 Objectives of the Study 7
2.0 Literature Review 9
2.1 History of PCB of PCBs 9
2.2 Physical and chemical properties of PCBs 9
2.3 Uses and application of PCBs 10
2.4 Health effects of PCBs 12
2.5 Extraction and clean up 14
2.6 Microbial destruction of PCBs 16
2.7 PCBs as biomarkers in environmental risk assessment (ERA) 17
3.0 Materials and Methods 19
3.1 Materials 19
3.1.1 Apparatus and Equipment 19
3.1.2 Reagents 20
3.2 Methods 22
3.2.1 Sample Collection 22
3.2.2 Sample Pre-treatment for Analysis 22
3.3 Determination of Physico-chemical Properties 24
3.3.1 Determination of Soil Particles Size 24
3.3.2 Method 24
3.4 Determination of Total Organic Carbon (TOC) 25
3.5 Sample Extraction 25
3.6 Clean-up 26
3.7 Gas Chromatography-Mass Spectrometry 27
3.7.1 Calibration 28
3.7.2 GC-MS Analytical Conditions 30
3.8 Quantification 31
3.8.1 Preparation of PCB Standard 31
3.8.2 Calibration of analytes PCBs 31
3.8.3 Acceptance Criteria and Sample Quality Control Measures 32
3.8.3a Relative Retention Factors (RRFs) 33
3.8.3b PCB Quantification 33
4.0 Results 34
4.1 Physico-chemical Properties of Soil Sample 34
4.1.1 Texture of Soil 34
4.1.2 Total Organic Carbon 35
4.2 Range and Mean of Physico-chemical Characteristics of Soil Samples 35
4.3 PCBs Residues Level or Contents 37
4.3.1 PCBs in Kaduna and Zaria metropolis 37
4.4 Pearson Correlation (r) of Soil Physico-chemical Properties with
Total PCBs Residues Concentrations 40
4.5 Percent (%) of Hexa-and-Hepta-biphenyls in Total PCBs Concentrations. 42
4.6 Relative Response Factor (RRF) and % Recovery of PCBs in Soil Samples 44
5.0 Discussion 48
5.1 Physico-chemical Property Analysis 48
5.2 PCB Congeners‘ Residue Levels or Content Analysis 48
5.3 Correlation Analysis 50
6.0 Summary, Conclusion and Recommendation 52
6.1 Summary 52
6.2 Conclusion 53
6.3 Recommendations 54
1.1 Background of the Study
Polychlorinated biphenyls (PCBs) are a subset of synthetic organic chemicals known as chlorinated hydrocarbon that is to a large degree, chemically inert. PCBs have been produced in high volume by the chemical industry and used as additives to oils in electrical equipment, hydraulic machinery, and other applications where chemical stability has been required. These organic compounds can be transported for long distances, and have been detected in the furthest corners of the globe, including places far from where they are manufactured or used. Since PCBs exhibit a high degree of chemical and biological stability and also lipid solubility, they tend to accumulate in the food chains and have been detected in animal and human tissues ( Breivik et al., 2007).
Commercial formulations of polychlorinated biphenyls (PCBs), such as Aroclor mixtures, were widely used in the past in transformers, capacitors, hydraulic fluids and as plasticizers in paints, plastics and sealants. It has been estimated that globally 1.3 million tonnes of PCB compounds have been produced (Breivik et al., 2007).
Historically the main sources of PCBs in the marine environment include energy production, combustion Industries, production processes, and waste (landfill, incineration, waste treatment, and disposal). Due to concerns about the environmental impact of PCBs, production in Western Europe and North America ceased in the late 1970s and in Eastern Europe and Russia in the early 1990s. PCBs can still enter the marine environment following the destruction and disposal of industrial plants and
equipment or from emissions from construction materials (Kohler et al., 2005) and old electrical equipment (for example from landfill sites). PCBs are included in the Stockholm Convention (UNEP, 2009) due to their persistence, bioaccumulation, and toxicity (PBT).
Theoretically 209 individual PCB congeners can be produced, depending on the number and position of chlorine that is substituted onto the biphenyl moiety. Individual congeners are generally named according to the short-hand system developed by Ballschmiter and Zell (1980) for PCB congeners. For this naming system a number from 1 to 209, often prefixed with ―CB‖, was applied to each congener after the congeners had been sorted on the basis of their structural names by Mills et al., (2007). The molecular weight (g/molecule) of PCB ranges from 188.7 for monochlorobiphenyl to 498.7 for decachlorobiphenyl.
The seven ICES (International Council for the Exploration of the Sea) PCBs (CB28, 52, 101, 118, 153, 138, and 180) were recommended for monitoring by the European Union Community Bureau of Reference; these PCBs were selected as indicators due to their relatively high concentrations in technical mixtures and their wide chlorination range (3–7 chlorine atoms per molecule). The ICES-7 PCBs have been part of the OSPAR Co-ordinated Environmental Monitoring Programme (CEMP) since 1998 (Webster et al., 2013). Of the 209 PCB congeners, the most toxic are the so-called ‗dioxin-like‘ PCBs (DL-PCBs). The DL- PCBs are the four non-ortho (CB77, 81, 126, and 169) and eight mono-ortho (CB105, 114, 118, 123, 156, 157, 167, and 189) PCBs that also have chlorines in both para and at least two meta positions. The non-ortho PCBs can obtain a planar configuration and the mono-ortho PCBs can obtain a near planar configuration. As
a result, the twelve DL-PCBs are stereo chemically similar to 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and therefore have similar toxic and biological responses to those of dioxins (Safe et al., 1985; Kannan et al., 1989).
Chemical structures and physical properties of selected PCBs are well documented (Mackay et al., 2006). Protection of human health and the environment requires that PCBs be disposed off in such a way that they do not enter the environment. The important step in the environmental management of PCBs is to identify their sources and develop strategies for reducing or eliminating their release to the environment (UNEP, 1999).
UNEP‘s Council in February 1997 and Stockholm Convention included PCBs among the 12 POPs identified for International action due to their persistence, bioaccumulation and toxicity (PBT) (UNEP, 2009).
Article 7 of the Stockholm convention requires National implementation plans (NIPs) to be developed by signatory Countries, with Nigeria being a signatory in 2002 (UNEP, 2001).
The empirical formula for PCBs is C12H(10-n)Cln, where n is a number of chlorine atoms within the range of 1-10. Theoretically, a total of 209 possible PCB congeners exist, but only about 130 of these are likely to occur in commercial products. These commercial PCBs are mixtures of PCB congener (Neumeier, 1998). Twelve of the 209 congeners: PCB 77, 81, 105, 114, 118, 123,126, 156,157,167, 169 and 189 are known to show toxic responses similar to those caused by 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) toxic dioxins and furans (Keon et al., 2007; Lynda et al., 2013).
Figure 1.1: PCB molecular structure
PCB bio accumulate in the fatty tissues of exposed animals and humans (Fiedler, 1997) and this exposure is believed to be responsible for a wide variety of health effects, which includes skin rashes, eye irritation, disturbances in liver function and immune system, fatigue, impotence, depression, memory loss and possibly cancer. The US Department of Health and Human services as well as the International Agency for Research on Cancer (IARC) consider PCBs to be probable carcinogens in humans (IARC, 1987; ATSDR, 1989).
Many countries have developed classification and regulation for PCBs –containing fluids and materials. The benchmark level for PCB is considered as 50 mg/kg (or 50 ppm) as maximum permissible limit for regulation in many countries (UNEP, 1999).
Increasing awareness about the health and environmental effects associated with PCB exposure has resulted in a gradual withdrawal of use and an increase in production restrictions. Despite these efforts, PCBs continue to enter the environment. This is true
for developing nations like Nigeria that may have large quantities of PCB- containing electrical equipment still in service.
The various persistent cycles and pathways that led to widespread distribution of PCBs in the environment is represented in Figure 1.2, which may be a useful tool in the identification of specific focal areas for management or clean-up of PCBs (UNEP, 1999).
Figure 1.2: Distribution cycles and pathways of PCBs in the environment; Source: UNEP, 1999
1.2 Justification of the Study
PCBs bio magnifies in the food chain and the health effects are numerous, such as tumours, cancer, liver damage, memory loss, impotence, reproduction and developmental effects. PCBs persistence once released into the environment, and its likely continual use means that PCBs could pose a threat for decade to come. Therefore, National action plan is required for the monitoring and management of PCBs towards Nigeria‘s obligation to the Stockholm convention on POPs (UNEP, 2001). Closed systems such as power transformers and transistors contain PCBs as dielectric coolant for electricity transmission. Maintenance/repairs of these transformers by Power Holding Company of Nigeria (PHCN) and their approved clients whenever technical malfunction arises often results to spills, accidental discharge or improper disposal of the spent PCBs transformer oils to the environment (UNEP, 1999).
1.3 Aim and Objectives of the Study
1.3.1 Aim of the Study
The aim of this study is to determine residue levels of PCBs in soils of selected transformer maintenance workshops in Kaduna and Zaria metropolis.
1.3.2 Objectives of the Study
The aim would be achieved by the following objectives:
i. Determine the soil particle size, and total organic carbon (TOC) content of the soil sample.
ii. Determine Polychlorinated biphenyls (PCBs) using Gas Chromatography/Mass Spectrometer (GC-MS).
iii. Determine relative response factor (RRF) and recovery (%) of PCBs in the soil samples.
iv. Correlation of results obtained at different sites with UNEP regulatory framework. This research work focuses on chemical monitoring for Environmental Risk Assessment (ERA). The chemical monitoring of PCB residue levels in soils at the designated sampled sites in Kaduna and Zaria metropolis will serve as lead for further studies to link the bio availability of the measured PCBs with their concentrations at target organs and intrinsic toxicity.
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