Journal of Occupational

Introduction

Lead (Pb) is a ubiquitous natural-occurring heavy metal found in many occupational processes or activities in inorganic and organic forms [1, 2]. Human exposure occurs through activities, including fossil fuel burning, mining, and manufacturing [3]. Though the use of Pb is as old as humankind, its poisoning reached an epidemic dimension by the 19^th and 20^th centuries, influenced by industrialization and its uncontrolled use in pure or alloyed forms [4, 5]. Lead poisoning was known to be toxic in high doses, and the burden of toxicity was greatly underestimated since mostly the poisoning was clinically overt [3]. However, from the 20^th century to the present, most developed countries have halted Pb poisoning by restricting it in industry and using unleaded gasoline, except chronic exposures at lower levels. The reverse is the case in developing countries, where there are non-existent biomonitoring programs [6, 7]. Lead enters the body through inhalation of dust and fumes, ingestion, and absorption by the skin [8 –10]. Pb poisoning effects are of respective target organs, e.g., haematologic, neurobehavioral, cardiotoxic, nephrotoxic, reproductive, and gastrointestinal effects [1, 11]. They occur in severe clinical and subclinical/asymptomatic forms [4].
Panel beaters are part of automobile technicians whose occupational activities of vehicle body repairs, cutting, soldering, and spray painting expose them to lead poisoning [12]. This occupational group operates in different forms and organizations. Some are observed along the roadsides with no safety rules, while others work in a formal sector governed by safety rules. [13] This setup may result in different occupational Pb exposure levels and haematoxicity effects.
The haematological effects of Pb poisoning occur following acute or chronic lead exposure interfering in the enzymatic steps in haeme synthesis pathway with a consequent reduction in red blood cells [1, 7, 14]. The impairment of haeme biosynthesis is first by inhibition of delta–aminolaevulinic acid dehydratase (ALA–D) with an elevation of protoporphyrin in the erythrocytes. This is dose-related, noted initially at a blood lead concentration of 10–20µg|dl and completed at levels of 70–90µg|dl. It is second by inhibition of ferrochelatase, causing increased excretion of coproporphyrin and aminolevulinic acid (ALA) in the urine. This begins to rise at a blood lead concentration of 25–30µg|dl [1, 15], confirmed by marked reductions in blood haemoglobin and haematocrit levels and other erythrocytes after Pb exposure [16]. Other haematologic effects are direct toxic action of lead on leucopoiesis in lymphoid organs with an increase in total leucocytes, basophils, eosinophils, and lymphocytes, as well as lead inhibition of platelets aggregation in the bone marrow with an increase in platelet and platelet distribution width [15, 17].
The commonest outcome of lead haematopoietic toxicity is anaemia. At acute high-level exposure, lead poisoning causes haemolytic anaemia, while at chronic low-level exposure, it causes frank anaemia [11]. According to the Agency for Toxic Substances and Disease Registry (ATSDR-1999), children and adults with lead levels of ≥70µg|dl and ≥ 80µg|dl, respectively, are anaemic. Also, Schwartz et al. (1990) noted that 20% of children with blood lead above 60µg|dl were anaemic [18]. A study in Iran found that the prevalence of anaemia among children at blood lead level <5µg|dl was 40%, while another study in Egypt found 63.3% of children with blood lead ≥10µg|dl [19, 20].
Few studies have been performed in Nigeria and other low-income countries on occupational Pb-induced haematoxicity, none of which has compared the haemtoxicity effects of Pb exposure between occupational groups with different organizational structures affecting exposure. Available studies have assessed the occupational Pb exposure at higher thresholds [5]. The present study helps occupational health physicians understand the relationship between lead exposure and haematological parameters (HP) at varying levels of exposure for early intervention. Further, it can add to existing local knowledge and data. It can also help ascertain differences, if any, among workers with different organizational structures and occupational health practices. Therefore, this study aims at assessing the relationship between haematological parameters and lead exposure among roadside and organized panel beaters in Enugu Metropolis, Nigeria.
 
Materials and Methods
The study area is the Enugu metropolis, the capital of Enugu State in the southeast geo-political zone of Nigeria. The metropolis is constituted by three Local Government Areas (LGA) in Enugu State, including Enugu North, Enugu South, and Enugu East, and inhabited mostly by the Igbo ethnic group [21]. The panel beaters in this part of the state do not have a centralized garage, i.e., mechanic village. The roadside (informal) panel beaters are observed mainly in the streets; some are on streets close to spare parts markets. The organized (formal) panel beaters are those under government rules governed by factory, labor law, and workman compensation acts. They have an organizational structure that promotes safety precautions.
This was a comparative cross-sectional study of roadside and organized panel beaters in the Enugu metropolis. In this research, panel beaters and trainees who were 18 years and above, spent over one year with an exposure time of 8 hours and above, not involved in another job, and interested in participating in the study were included, while those with chronic diseases were excluded.
The minimum sample size for the study was determined using the formula for comparing two independent proportions [22], as well as 14.3% representing the proportion of Nigerian adults with blood lead levels >20ug|dl [23]. Standard normal deviate (Zα) of 1.96% and 80% power (Zβ) were included. A minimum sample size of 214 per sector was obtained after correcting the non-response rate, giving a sample size of 428.
A multistage sampling technique was used for both roadside and organized panel beaters in this study. For the roadside panel beaters, the first stage was the selection of Enugu North among the three local government areas by simple random sampling as a zone using the balloting method. The second was the selection of one division out of the 5 in Enugu North LGA by simple random sampling using the balloting method. The third was the selection of 10 branches out of the 13 in Enugu North LGA by simple random sampling using the balloting method. Lastly, stratification and proportionate allocation of panel beaters from all the workshops within the selected branches were performed, and a total of 228 panel beaters were selected.
For the organized panel beaters, the first phase was the selection of Enugu North among the three local government areas by simple random sampling as a zone using the balloting method. The second was the proportionate allocation of government and private-owned company workers. There were a total of 70 and 220 panel beaters in government and private workshops, respectively. Using a ratio of 1:3, 56 panel beaters from government-owned workshops were selected out of 70 by simple random sampling using the balloting method. From the private-owned workshops, 170 panel beaters were selected. A total of 226 panel beaters were selected from the organized panel beaters considering missed and incomplete responses.
Data and sample were collected using research assistants who were three resident doctors and three phlebotomists. They were trained for two days, two hours per day, on sample collection procedures. Blood for the lead was collected under an aseptic procedure and analyzed using the standard lead stock solution at Project Development Agency (PRODA) Enugu. Blood sample collection was done in an enclosed and well-screened place. The venipuncture system was used to perform venipuncture, and the desired blood of 2–3mls was emptied into Ethylenediaminetetraacetic acid (EDTA) vacutainer bottles for blood lead estimation and complete blood count. The EDTA bottles containing the required amount of blood were gently shaken to
ensure the samples not to be clotted. The samples for lead estimation were transported immediately to the laboratories using the Gio-style cold box after each day, accompanied by 5 and 10ml syringes, bleach, and gloves for maintenance of universal precautions. The blood samples were diluted to 10ml using deionized water because of accompanying cations and anions. The diluted samples were aspirated by the Buck Scientific Model 210 VGP Atomic Absorption Spectrometer (AAS) via a capillary tube at a wavelength of 283.3nm for Pb analysis. The blood samples for complete count were taken to Community Medicine Department Laboratory UNTH Ituku Ozalla for analysis using Mindray Auto Haematology Analyzer. The results of analyses were entered into a proforma or spreadsheet for the blood lead levels and HP.
Data were analyzed using Statistical Package for Social Science (SPSS) version 25. Categorical variables were summarized using frequencies and proportions, while continuous variables were summarized using mean, standard deviation, median, and inter-quartile range for skewed data. The lead levels in blood were categorized using a cut-off of 10µg|dl and above as Pb poisoning [24]. Prevalence of Pb poisoning was noted as a proportion of panel beaters with blood lead of 10µg|dl and above. Haematological parameters were categorized into normal and abnormal using reference values. Comparison of variables was managed using Man Whitney U- (MHU) test, Chi-square test, and T-test. The relationship between blood lead (BPb) and HP was determined using correlation analyses. The level of significance was set at P< 0.05.
Ethical approval was obtained from the Health Research Ethics Committee of the University of Nigeria Teaching Hospital, Ituku Ozalla (No. NHREC/05/01/200BB–FWA00002458–IRB00002323).  Permission was obtained from :union:s of roadside and organized panel beaters in Enugu State. Informed consent was obtained from participants.
 
Results
The median Pb levels were 3.0µg|dl and 16.0µg|dl among roadside and organized panel beaters, respectively. About two-third and one-third of roadside and organized panel beaters, respectively, had Pb level <10µg|dl, while 79 (36.4%) and 138 (63.6%) of roadside and organized panel, respectively, had abnormal levels of Pb. The differences between the two sectors were found to be significant (P< 0.0001) (Table 1).

All the HP on both sectors of panel beaters had mean values within the normal reference values. The mean differences in MCHC, RDWc (%), Neutro (%), Lymph, Lymph (%), Mono (%), and PDWc (%) between the two sectors were found to be significant. Very few respondents among roadside and organized sectors had abnormal HP, 7 (3.3%) of respondents on both sectors had abnormal haemoglobin, 3 (1.4%) of roadside and 12 (5.6%) of organized sector respondents had abnormal RBCs, 4 (1.9%) of roadside and 3 (1.4%) of organized sector respondents had abnormal WBC, and 11 (5.1%) of roadside and 7 (3.3%) of organized sector respondents had abnormal platelets (Tables 2 and 3).

 
Fig.1. A scatter plot showing the correlation between blood lead levels and haemoglobin among roadside panel beaters

Fig. 2. A scatter plot showing the correlation between blood lead levels and red blood cells among roadside panel beaters
 
Fig. 3. A scatter plot showing the correlation between blood lead levels and White blood cells among roadside panel beaters

Fig. 4. A scatter plot showing the correlation between blood lead levels and platelets among roadside panel beaters

Fig. 5. A scatter plot showing the correlation between blood lead levels and haemoglobin among organized panel beaters

Fig. 6. A scatter plot showing the correlation between blood lead levels and red blood cells among organized panel beaters

Fig. 7. A scatter plot showing the correlation between blood lead levels and white blood cells among organized panel beaters

Fig. 8. A scatter plot showing the correlation between blood lead levels and platelets among organized panel beaters