Determination of Heavy Metals Levels in Common Spices in Southeastern Nigeria

Determination of Heavy Metals Levels in Common Spices in Southeastern Nigeria

CHAPTER ONE

Aim and Objectives of the Study

The aim of the study is to examine the levels of contamination by some metals in fifty common spices purchased from each of the three major markets in southeastern Nigeria.

The objectives are to:

Determine the levels of cadmium, cobalt, copper, chromium, iron, manganese, nickel, lead, sodium, potassium, calcium and magnesium in the fifty food spices from each market
Estimate the safety of these spices with respect to heavy metal contamination.
Provide current levels of the selected heavy metals in the food spices.

CHAPTER TWO

LITERATURE REVIEW

Contamination of Processed Food Spices

There are many sources through which processed food spices can be contaminated. These ranges from absorption by the plants, air and environmental conditions affecting the plants, the method of handling, processing and cooking of the products. For instance, the concentrations of some metal such as copper, cobalt, cadmium, calcium, sodium, potassium, nickel, chromium, manganese, magnesium, and lead, depends on the soil in which the plants are grown and will therefore vary significantly in finished products or from one area to another (Bani and Preda 1985). During processing, the wearing of machine parts occurs. This may lead to unavoidable addition of some trace elements to finished products. Excess of these mineral contaminants would constitute health hazards to human beings. This is why it is necessary to monitor the levels of toxic metals concentration in processed food items.

The major sources of elemental contaminants in soil include the natural constituents of the soil and pollutants from agrochemicals. Iron contaminates food products through adulteration of processed food spices by merchants who add different type of ferrous materials like nail and coins to fraudulently increase the weight of the processed food spices. When the processed spices are produced through machine, the wearing of machine parts into the material being processed contribute significantly to contamination of processed food spices with iron.

Copper contaminates food spices as residue of copper sulphate fungicide, through alloys in machine parts and through adulteration with copper products (Bani and Preda, 1985).

Occurrence and Characteristic of Some Metals in Environment.

Heavy metals are extremely persistent in the environment. They are non – biodegradable and non-thermodegradable and thus readily accumulate to toxic levels (Rajesh et al., 2007). Heavy metals can remain in the air for varying lengths of time determined by the size of the particle, the prevailing relative humidity and precipitation. Under high humidity small particles may sometimes combine to form larger particles and fall to the ground. While suspended in air, these metals may be inhaled by humans and animals and subsequently absorbed into their blood streams. Heavy metals absorbed by plants from the atmosphere may reach the soil through mineralization of plant litters.

Lead

Once lead gets into the atmosphere, it may travel long distances if the lead particles are very small. Lead is removed from the air by rain and by particles falling to land or into surface water. Once lead enters the soil, it sticks strongly to soil particles and remains in the upper layer of soil, small amount of lead may enter rivers, lake, and steams when soil particles are moved by rainwater. Small amount of lead from lead pipe or solder may be released into water when water is acidic or “soft”. Lead may remain stuck to soil particles or sediment in water for many years. Movement of lead from soil particles into groundwater is unlikely unless the rain falling on the soil is acidic or “soft”. Movement of lead from soil will also depend on the type of lead salt. However, elemental lead cannot be broken down. The levels may build up in plants and animals in areas where air, water or soil are contaminated with lead (Gerbeding, 2005a).

Human exposure to lead can result in a wide range of biological effects, depending on the level and duration of exposure. Developing foetus and infants are more sensitive than adult to lead effects (Lenntech, 2002). High level of exposure may result in toxic biochemical effects in humans which in turn cause problems in the synthesis of haemoglobin, kidney, gastrointestinal tract, joints and reproductive system, and acute or chronic damage to the central nervous system (CNS) (Mwakio, 2003). Soil Pb-species are insoluble in the digestive tract of young children and adult women (Ilya et al., 2003).

Cadmium

This is the 67^lh most abundant element in the earth’s crust. Solid salts of cadmium with strong acids are readily soluble in water. Less soluble compounds are the sulphide, carbonate, fluoride and hydroxide. Cadmium can enter the air and travel a long way before settling on earth as dust, or in water or snow. The cadmium metal itself does not break down in the environment, but it can change into different forms. Most forms of cadmium stay for a long time in the same place where they first entered the environment. Some forms of the cadmium that goes into the water will bind to soil, but some will remain in the water. Some forms of cadmium in soil can enter water or be taken up by plants. Fish, plants and animals can take some forms of cadmium into their bodies from air, water, or food (Koplan, 1999).

Cadmium is biopersistent that is, it can remain resident in an organism that absorbs it for many years, and over decades for humans (Lenntech, 2002), although it is eventually excreted. In humans, long-term exposure is associated with renal disfunction. High exposure can lead to obstructive lung disease and has been linked to lung cancer (Lenntech, 2002). Cadmium may also produce bone defects such as osteomelacia, osteoporosis in humans and other animals. In addition, cadmium affects the kidney and is linked to increased blood pressure (Lenntech, 2002)

CHAPTER THREE

EXPERIMENTAL

Sample collection and identification:

Fresh vegetables, other spices of plant origin and processed spices were purchased from Ose Market Onitsha, Ogbete main market, Enugu and Nkwo Market Nnewi in Southeastern Nigeria, fifty from each market giving a total of one hundred and fifty samples. They were identified and classified according to their common and botanical names by the Department of Plant Science and Environmental Biology, University of Nigeria Nsukka and are shown in Table 3.1.

Washing of glass wares

Beakers and watch glass (for digesting samples) polythene bottles for solution as well as standard flasks (20 mL, 50 mL, 500 mL) were properly washed with detergent and rinsed several times with water. The glass wares and bottles were later rinsed once with distilled water, once with a mixture consisting of 500 mL deionised water, 200 mL concentrated HCl and 80 mL H₂O₂(Sharief et al., 2005).

CHAPTER FOUR

RESULTS

Tables 4.1, 4.2 and 4.3 show the concentration of Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Na, K, Ca, and Mg in fruits, vegetables and other natural spices in Southeastern Nigeria (µg/g). Tables 4.4, 4.5 and 4.6 show the Concentration of Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Na, K, Ca, and Mg in Processed spices in Southeastern Nigeria (µg/g). Tables 4.7, 4.8, 4.9 and 4.10 show the mean concentrations (n = 3) of trace metals in all samples [fruits, vegetables and other natural spices (dry weight) (µg/g)] from the various markets. Tables 4.11 and 4.12 show the mean concentrations of trace metals (µg/g) (dry weight) in processed spices. Table 4.13 shows the variation in values of metals in natural spices in various markets. Table 4.14 show the variation in values of metals in processed spices. Table 4.15 shows the comparism between the present work and reported literature values (µg/g). Tables 4.16 and 4.17 shows the daily intake (g/person/day) of trace metals and essential metals (DIM) through consumption of contaminated fruits, vegetable and other natural spices. Tables 4.18 and table 4.19 shows the daily intake (g/person/day) of trace metals and essential metals (DIM) through consumption of contaminated processed spices.

CHAPTER FIVE

Discussion and Conclusion

Quality Assurance

Sample preparation consists of several operations such as grinding, drying, homogenization, digestion and dissolution. Each of these stages may be a source of contamination, thus, a great attention was paid to preserve the original chemical constitution of the samples. This was done by washing all laboratory wares and subsequent leaching of the glasswares with acid; drying of the food spices in a watch-glass, grinding the dried samples with wooden mortar and pestle, carring out wet digestion at low temperature to avoid loss of volatile metals; acidifying the standard solutions and use of high purity reagent and de-ionized water. The choice of digestion mixture (2:1v/v of HNO₃/HClO₄) was made as a result of information from literature ^[266]. The chemicals are purely of analytical grade. For digestion of biological materials, mixtures of acid could be used for instace HNO₃-H₂SO₄, HNO₃-HClO₄ or H₂SO₄-HNO₃-HClO₄– HNO₃-H₂SO₄ is used for biological materials of plant origin, HNO₃-HClO₄ mixture is recommended for foods containing proteins and carbohydrates and no fat. Concentrated trioxonitrate(V) acid enables the metals to form nitrates. The use is advantageous because the metals form nitrates and all nitrates are soluble in aqueous solution (Pomeranz et al., 1994).

Conclusion

The results reported here confirm that the food spices obtained from the three major markets in Southeastern Nigeria contained metals at acceptable levels according to WHO/FAO guideline levels. The values obtained compared favourably with the findings of the earlier researchers from other parts of the world (Shaibu, 2002). Furthermore, the levels of Cd, Co, Cu, Fe, Cr, Pb, Mn, Ni, K, Na and Mg obtained do not appear to pose any serious health hazard problem of concern yet. No risk from daily intake of the spices under study for hazardous Pb, Cd, Co and Cr if the human take about 20 g of spices per day. Whereas the human needs from spices is very few grams per day there is no risk from using the studied species in the food. Levels of the metals are found to be within the safe limits prescribed by FAO/WHO. This is an important result as human health is directly affected by consumption of food. There is indication of mild or little increase of the concentration of these metals in the spices. This is attributed to the continuous increase in the concentration of these metals over the years, but it is okay, there is no danger in the consumption of these metals.

Recommendations

We recommended that

People living in contaminated areas should not consume large quantities of natural and processed spices to avoid excess accumulation of heavy metals in the body. Dietary intake of food results in long-term low level body accumulation of heavy metals and the detrimental impact becomes apparent only after several years of exposure.
Regular monitoring of these toxic heavy metals from fruits, vegetables and other natural spices is essential to prevent excessive build up in the food chain and as the spice samples are transported from different sources.
Foods spices should be hygienically safeguarded or packaged.
There should be thorough control over imported food stuff which do not meet FAO/WHO recommendations and tolerable daily intake limits for heavy metals.

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