Heavy Metal Composition of Some Imported Canned Fruit Drinks in Nigeria

MATERIALS AND METHODS

Six brand or types of imported canned fruit drink (6 to 8 in each brand or types) were obtained from local markets in Warri and Agbor, Nigeria. The selection was specially made to reflect the popular brands consumed by different income groups and also influenced by availability at the time of purchase. The samples were stored at almost identical conditions similar to those of retail shops. 300 mL of the liquid samples was heated in evaporating dish on a regulated hot plate until caramelous mass was formed. The caramelous mass was formed in most cases was than digested with a mixture of perchloric and nitric acid. The digest was diluted to 25 mL mark using 1 M nitric acid. The sample solutions were subsequently analyzed for the metals using a graphite furnace atomic absorption spectrophotometer (GBC scientific equipment XAA1175, Australia) equipped with D₂ background correction devices.

Appropriate quality assurance procedures and precautions were carried out to ensure reliability of the results. Samples were generally carefully handled to avoid contamination. Glassware was soaked in 1 M nitric acid for 48 h and rinsed with ultra pure water. The reagents (nitric acid, perchloric and distilled water) were of analytical grades. Reagent blank determination was used to correct the instrument reading. Calibration standard were made by dilution of high purity commercial BDH metal standards for atomic absorption analysis. A recovery test of the total analytical procedure was carried for the metals by spiking analyzed samples with aliquots of metal standards and then reanalyzing the samples. The results of recovery studies for the elements were 92.5. 93.4, 96.4, 90, 95, 94 and 89.9% for Fe, Cu, Cr, Pb, Ni, Mn, Zn and Cd, respectively.

RESULTS AND DISCUSSION

Table 1 present the means concentrations of heavy metals while Table 2 presents the range of the levels of heavy metal in the samples. Analysis of variance (p>0.05) showed that there is significant variability in the concentration of the studied metals within a brand except for Zn and Pb in the orange brand. However, apparent and significant variation exists when the brands are compared.

Fe had the highest mean levels amongst the metals studied. The levels of Fe in the fruit drinks exceeded the local standard and limits for iron in Nigeria except for mixed fruits and guava brands. The highest level of iron was found in the pineapple brand (Table 1). Contreraslopez et al. (1987) reported 15.0 ppm in fruit juice in Spain. The mean levels of Fe this study is comparable to that of Contreraslopez et al. (1987). Al-Swaidan (1988) analyzed the levels of Fe in fruit drink using ICP-MS. The author reported concentration range of iron to be 4.49-8.25 ppm. 56% of the total samples have iron concentration within the range reported by Al-Swaidan (1988).

Copper is an essential element for growth, although emetic in large doses, but when present in some beverages such as milk products and fruit juices tends to impair the shelf life or keeping quality of such products, so it expected that fruit juice and milk products should contain relatively low levels of copper. Paolo and Maurizio (1978) reported concentration range of 0.87-0.97 ppm in fruit drink in Italy while Contreraslopez et al. (1987) reported mean levels of 5.00 ppm for Spain. The levels of Cu found in this study are higher than that of Paolo and Maurizio (1978) but are comparable to the levels reported by Contreraslopez et al. (1987). However, the guava and apple brands have mean levels exceeding Contreraslopez et al. (1987).

Table 1:	Mean±SD of heavy metals (ppm) characteristic of canned fruit drinks

Table 2:	Range of heavy metals in canned fruit drinks (ppm)
nd = Below detection limit. The detection limit = 0.001 ppm

The concentration of lead in the fruit drink follows the order: Apple > Guava > orange >mixed fruit > pineapple> mango brands. The levels of Pb report in this study are above the guideline value for Pb in foods drinking water except for mango brands. The major source of Pb in canned fruits drinks is the leaching of Pb from the canning. Pb toxicity causes many sign and symptoms such as abdominal pains, anemia, anoxia, bone pair, brain damage, convulsion, dizziness, inability to concentrate etc. (Kocak et al., 2005).

Adraiano (1984) reported Pb levels of 0.01 ppm for beverage drink in Canada. Paolo and Maurizio (1978) reported mean levels of 0.38 ppm Pb for fruit drinks while Contreraslopez et al. (1987) reported 0.15 ppm Pb in fruit drinks in Spain. The mean levels of Pb in the various brands were above the levels reported by these investigators except for the mango brands. However, some samples have levels comparable to levels reported by these authors.

The mango brand had the highest concentrations of Ni compared to another other brand. Most of the brands have elevated Ni levels. The mean levels of Ni reported in this study are higher than mean values reported by for fruit drink by Onianwa et al. (1999).

The level of manganese found in this study is generally low compared to any other metal examined. The highest concentration of Mn was found in the mixed fruits while the apple brands have the lowest concentration of Mn. The order of concentration of Mn in the various brands of fruit drinks follow the order: mixed fruits>orange>pineapple>guava>mango>apple brands. The levels of manganese found in this study is are below permissible limits food and drinking water. Hence, Mn do not constitute contamination hazard in the brands of fruits drinks. The highest mean levels of cadmium were found in mango. Apart from the pineapple brand, all other brand have mean concentrations of Cd exceeding the WHO permissible limit for drinking water (WHO, 1984). Adraiano (1984) reported 0.003 ppm Cd in beverage drinks in Canada. The level of cadmium found in the various brands was higher than the value reported by Adraiano (1984), except for the pineapple brand.

The concentration pattern of zinc follows the order: orange> mixed fruits >pineapple > apple guava> mango brand. Contreraslopez et al. (1987) reported 5.0 ppm Zn in fruit juice in Spain while Paolo and Maurizio (1978) reported 0.41 ppm Zn in fruit in Italy. The levels of zinc found in this study were less than mean levels reported by Contreraslopez et al. (1987). Sixty two percent of the samples of fruit drinks examined are comparable to that of Paolo and Maurizio (1978). Table 3 shows the estimates of the doses of the metals, which may be derived from the ingestion of 1 L quantities of the fruit drinks. The estimated dose was found to be generally high for the eight metals studied. The estimated doses derived from the ingestion of 1 L quantities of the fruit drink follows the order Fe>Cu > Pb > Zn > Ni > Cr > Mn > Cd (Table 3). The estimated doses reported herein in this study are higher than estimated doses previous reported for fruit drinks (Onianwa et al., 1999).

Table 3:	Estimated dose of heavy metals from 1 L volume of fruit drink

Overall, the study shows that the levels of the eight heavy metals studied are generally above safe limits and except for iron, zinc and manganese compared well with levels in similar foods from the parts of the world. The data reported herein will be valuable in complementing available food composition data and estimating dietary intakes of heavy metals in Nigeria.