DETERMINATION OF HEAVY METALS LEVELS IN COMMON SPICES IN SOUTHEASTERN NIGERIA

ABSTRACT

In this study, the degree of contamination with selected heavy metals were determined in fifty common food spices in Southeastern Nigeria.Samples were purchased from three major markets namely, Nkwo market Nnewi, Ose market Onitsha and Ogbete main market Enugu. Two grams of dried ground spice samples were digested using 2:1 HNO₃/HClO₄, mixture and analysis of metals were carried out using a GBC Avanta ver. 2.02 atomic absorption spectrophotometer. Results (in µg/g) show that the range of detectable values of the fruits, vegetables, and other natural spices were Cd (0.02 –3.1), Co (0.009 –12.25), Cu (0.06 –15.08), Cr (0.14-23.43), Fe (0.40-472.33), Mn (0.098-182.00), Ni (0.15-11.05), Pb (0.08-125.77). Other metals in mg/g are Na (0.0056-6.75), K (0.053-481.91), Ca (0.18-3.497), Mg (0.068-1.641). Values obtained for the processed spice samples  in µg/g were Cd (0.03-93.28), Co (0.132-20.19), Cu (0.020-11.38), Cr (1.27-27.64), Fe (1.26-395.27), Mn (1.28-74.55), Ni (0.58-9.72), Pb (0.122-60.24). Others in mg/g are Na (0.011-7.15), K (0.017-4.69), Ca (0.006-0.127) and Mg (0.021-0.907). The natural spice samples from Onitsha contained the highest concentrations of Cd, Fe and Pb, those from Nnewi contained the highest concentrations of Co, Mn, Ni, Na, K, and Mg while Enugu samples contained the highest concentrations of Cu,Cr and Ca. Mean concentrations of Cd, Pb, Na, K and Mg were above international maximum permissible levels in some of the natural samples while the Mean concentrations of Cd, Na, K and Mg were within international maximum permissible levels in some of the processed samples. One way  analysis of variance showed no significant difference in levels of Cd, Co, Cu, Cr, Ni, Pb, Na, K and Mg in the natural and processed spice samples (P>0.05) while Fe, Mn and Ca showed significant difference (P<0.05). However, Fe and Ca showed significant difference (P<0.05) in the processed smaples. Cd, Fe and Ca accumulated mostly in smaples from Onitsha; Co, Cu, Na, Cr, Ni and Mg accumulated mostly in samples from Enugu while Mn and K accumulated mostly in samples from Nnewi. Smaples of natural spices from Onitsha had the lowest concentrations of Co, Cu, Cr, Mn, Ni, Na and Pb. Those from Nnewi contained the lowest concentrations of Cd, K and Mg while those from Enugu contained the lowest concentrations of Fe and Ca. These show peculiarities in geochemistry and contamination levels of the areas studied. The concentration of heavy metals determined in this study when compared with the Food and Agriculture Organization (FAO) dietary guideline values were found to be within safe levels. From previous survey, the levels of consumption of natural and processed spices of our people were quite low, therefore the consumption of heavy metals from the sources studied would not pose any danger to the consumers if the level of consumption of spices is maintained as previously reported.

CHAPTER ONE

1.0 INTRODUCTION

Since the 1980s, the use of spices and culinary herbs has increased tremendously in most regions of the world, including Europe and North America, mainly because of their medicinal values. For instance, during this period, herbal medication in the USA has grown into an industry worth yielding an average of $1.5 billion per year, with projected annual growth of 15% (Abebe, 2006). Many common spices have outstanding antimicrobial effects. However, the process of preparation and handling can make them a source of food poisoning (Sherman et al., 1998). With the current emphasis on eating more healthy diets that are low in fat and salt, people are turning to various herbs and spices to flavor their food. The culinary herbs and spices that are used to enhance the flavor of food, soup, stir-fry, and pasta dishes can be derived from the bark, buds, flowers, leaves, fruits, seeds, rhizomes, or roots of plants. The presence of essential elements like iron, copper, nickel, sodium, potassium, calcium, magnesium and zinc are very useful for the healthy growth of the body, though very high levels are intolerable. Metals like mercury, lead and cadmium  are toxic at very low concentrations and are are always checked in foods. Frequent use of spices that may have been contaminated with heavy metals as a habit may result in accumulation of these toxic metals in human organs and could pose different health challenges (Al-Eed, et al., 1997). These metals may contaminate vegetables, fruits and canned foods through air, water and soil and during industrial processing and packaging (Ozores-Hampton et al., 1997). Food spices sold in Nigerian markets are often exposed to diversity of conditions and environments before they reach the consumers. There is no doubt that along the route from the producer to the users, as well as during processing, these commodities, could become contaminated with sand and grit, dust, smoke, particulates, pathogens and heavy toxic metals.

The study of heavy metals in the environment and organisms is crucial because they have potential hazardous effects on human. Although, they are generally present in agricultural soils at low levels (Ozkutlu, et al., 2006), monitoring the levels of heavy metals in spices would help ascertain the health impacts of consuming these spices, and provide relevant data on heavy metals content of spices. Regulatory bodies such as National Agency for Food and Drug Administration and Control (NAFDAC) would be aided or informed of the safety or otherwise of the use and circulation of these spices especially the processed ones. Metallic elements are of significance in daily diets because of the nutritional value of some and possible harmful effects of others. Metals like iron, copper, chromium, nikel, zinc, cobalt and manganese are essential elements since they play important roles in biological systems; whereas mercury, lead and cadmium, are non-essential and toxic even in trace amount (Reilly, 1991; Skuvikhin, 1993; Iyengar, 1989). However, these elements can also have harmful effects when their intake significantly exceeds the recommended values. Spices are important sources of nutrition and flavoring for humans (Somer, 1974; Graham et al., 1976; Prasad, 1976).  Some are parts of plants which have been used as diet components are often used to improve color, aroma, palatability and acceptability of food. They consist of rhizomes, barks, leaves, fruits, seeds and other parts of the plant (Sattar, et al., 1989). Most of these are fragrant, aromatic and pungent. The bulk of dry material of spices contains carbohydrate, and organic compounds having diverse functional groups.

1.1 Food Spices and their Uses

Food spices as opposed to herbs have strong, zesty, pungent, and fiery fragrance which when added to food gives a dish an exotic and exciting taste. Whereas herbs are enjoyed fresh, spices are nearly always dried and either used whole or ground into a powder. Whole spices such as whole cloves, usually last much longer than the pre-ground form, even up to several years longer. It is best to buy spices, in small quantity as they loose their aroma and flavor over time. Although it may be cheaper to buy in bulk, for a well spiced and flavorsome meal, it is worth using the freshest spices available and renew them within six months if possible.  Always store spices in an airtight container and place them in a dark space such as a cupboard or pantry, a spice rack above the cooker may look very pretty, however, spices should be kept away from moisture, sunlight and sources of heat all of which damage the spices. Most spices are added towards the end of cooking time, otherwise, they may turn bitter and lose their flavor or other give out too much flavor.

Many spices have been known for hundreds and even thousands of years. They are used as cosmetics, medicine, dye, form of money and also to mask the flavor of meat that have bad oduor or irritating smell. Spices such as black pepper were held in high regard and in some places were even worth the same as gold. For health reasons some people substitute spices for salt in their foods (Scully, 1995).

1.2 Importance of Spices and Culinary Herbs

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