HEAVY METAL CONTENTS
The results of heavy metal analysis are presented in Table 1. The values for lead (Pb) ranged from 0.001 to 0.034 mg/kg. Control samples had the highest concentration of lead while fried and smoked samples did not differ significantly (p>0.05) from each other and they have the lowest concentration. Control sample had higher lead than the processed samples which revealed the impact of processing in the reduction of lead in chicken meat. The levels of lead reported in this study are below the maximum limit (0.10 mg/kg) set by the ATSDR (1995). Liu et al. (2014) reported a value of 0.20 to 0.45 (mg/kg) for smoked meat, Fredrick et al. (2015) reported a value of 0.410 to 0.70 mg/kg in grilled guinea fowl meat, Kayode et al. (2015) reported a value of 13.2 mg/kg in smoked chicken meat while Iwegbue et al. (2008) recorded a value of 0.01 to 4.60 mg/kg in smoked Nigerian chicken meat. These values were higher than the values obtained in this study. High values of lead may over time, induce bioaccumulation in the tissues following constant consumption and causes toxicity complications for consumers such as adverse effects on the cardiovascular, renal, endocrine, gastrointestinal, immune, and reproductive systems (Adamolekun and Adamolekun, 2012; Bas et al., 2016; Dolores and Doyle, 2011). Lead concentrations in poultry meat originate mainly from contaminated feeds, water and soil (Adamolekun and Adamolekun, 2012; Angelides et al., 2016). Difference in levels of lead contamination in chicken meat are related to variations in exposure levels and their concentration in animal tissues (Fredrick et al., 2015) which explains the variation of values obtained in this study in comparison to other studies.
Table 1: Heavy metal composition of processed chicken samples (μg/g).
| Samples | Pb | Hg | As |
| Boiled | 0.002a±0.00 | 0.361b±0.01 | 0.696a±0.01 |
| Fried | 0.001b±0.00 | 0.441a±0.01 | 0.631b±0.01 |
| Smoked | 0.001b±0.00 | 0.321c±0.01 | 0.427c±0.01 |
| Control | 0.034±0.00 | 0.01±0.00 | 0.03±0.00 |
a-c: Values are means ± s.d of duplicate determination. Mean value in the same column but with different superscript are significantly different (P<0.05). Pb= Lead. Cd= Cadmium. Hg = Mercury. Ar=Arsenic.
Although the values recorded in this study are substantially low but according to Sahu and Saxena (2014) there is no threshold value for the level of lead below which it would not have a toxic effect. lead is classified as possibly carcinogenic for humans (Group 2B) by MFDS (2020). Therefore, all measures must be taken to reduce their contamination in the environment.
Mercury concentration ranged from 0.010 to 0.441 mg/kg. Control sample had the lowest mercury content compared to processed samples. The values were significantly (p<0.05) different from each other which portrayed the influence of each processing method. Fried samples had the highest mercury concentration while smoked samples had the lowest. Just like cadmium, mercury is toxic even at low concentrations (Fazayeli-Rad et al., 2014). Mercury is very toxic and exceedingly bioaccumulative. Major sources of mercury pollution include anthropogenic activities such as agriculture, municipal wastewater discharges, mining, incineration, and discharges of industrial wastewater (Eduzor et al., 2016). Like other commonly known heavy metals like lead and arsenic, mercury contents in chicken meat increases with subject to processing methods such as frying, grilling, smoking, roasting etc (Cardinale et al., 2015). This phenomenon was observed in the present study such that processed samples had higher mercury content than the unprocessed sample which is the control. High amount of mercury can impair any organ and lead to malfunctioning of nerves, kidneys and muscles. It can cause disruption to the membrane potential and interrupt with intracellular calcium homeostasis (Quinto et al., 2019). The values obtained in this study are lower than the tolerable intake limits of 1.6 mg/kg (EFSA, 2017) and may not impact negatively on the health of consumers. However, the highest concentration recorded for fried chicken meat samples suggest the dangers associated with chicken meat when fried relative to mercury concentration.
Arsenic is prominently toxic and carcinogenic, and is extensively available in the form of oxides or sulfides or as a salt of iron, sodium, calcium, copper, etc. (Singh et al., 2007). Its consumption may cause acute poisoning (Mathew, 2016). The concentration of arsenic obtained in this study ranged from 0.03 to 0.696 mg/kg. control samples had lower concentration than processed samples. Among the processed samples, arsenic concentration increased with boiling but lower concentrations were recorded when the chicken meat samples were fried (0.631 mg/kg) and smoked (0.427 mg/kg). JECFA provisional daily intake is 0.002 mg/kg (Tang and Yu 2020). The concentration obtained in this study exceeded the recommended daily intake for all processing methods. The high concentration may be attributed to the feed of the animal, drinking of contaminated water by the livestock, environment etc