Levels Of Polycyclic Aromatic Hydrocarbon In Fresh Water Fish Dried Under Different Drying Regimes
Preservation of fish by drying over different types of heat regimes have been known. However, there has not been a comprehensive comparison in terms of the possible contamination associated with these drying regimes. This work was set to evaluate the levels of PAHs that are likely to accumulate in the bodies of fresh water fishes dried under heat from charcoal, sun (sun drying), electric oven and polythene augmented drying regimes (burning of used cellophone materials). The levels of sixteen PAHs were determined in fish samples harvested from Otuocha River in Anambra State, Nigeria. The fish samples were dried, pulverized and subjected to soxhlet extraction using n-hexane at 600c for 8hrs. The water content of the eluants were further removed with florisil clean-up before Gas chromatographic – mass spectrometric analysis. Results obtained showed that sun-dried fish had PAHs concentration to be 35.7+0.2µg/g; oven dried gave 47.7+ 0.2µg/g and charcoal dried 79.53+ 0.2µg/g, while drying with firewood resulted in 188.1+ 0.2µg/g. Charcoal drying augmented with polythene resulted into PAHs level of 166.2+ 0.1µg/g while fish dried under heat generated from burning firewood and polythene material resulted into PAHs concentration of 696.3+0.2µg/g. Preliminary analysis of the fresh water samples and the undried fish samples (control) revealed that the fresh water contained total PAHs level of 2.86+ 0.1µg/ml, while the fresh fish 4.97+ 0.2µg/g. The concentration of PAHs in all the dried fish under different drying agents were significantly higher than the control. The result is more worrisome in that even the fishes dried under the sun have PAHs significantly higher than that of the control (p<0.05). It is apparent that the increase in PAHs must have come from the environmental PAHs (exposure) under which the fishes were dried (under sun). For the other drying regimes, in which the levels of PAHs were significantly higher than that of sun-dried, it can be concluded that the excessive PAHs in the body of the dried fish were from the “burning” or drying agents. More significantly are the observed very high increase in PAHs when drying was augmented with polythene, an agent known to be a high source of PAHs when incinerated. Consumers of dried fish should therefore beware of the dried fish they purchase from the local market.
Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds consisting of two or more fused benzene rings (linear, cluster or angular arrangement), or compounds made up of carbon and hydrogen atoms grouped into rings containing five or six carbon atoms. They are called “PAH derivatives” when an alkyl or other radical is introduced to the ring, and heterocyclic aromatic compounds (HACs) when one carbon atom in a ring is replaced by a nitrogen, oxygen or sulphur atoms. PAHs originate mainly from anthropogenic processes particularly from incomplete combustion of organic fuels. PAHs are distributed widely in the atmosphere.
Natural processes, such as volcanic eruptions and forest fires, also contribute to an ambient existence of PAHs (Suchanova et al., 2008). PAHs can be present in both particulate and gaseous phases, depending on their volatility. Low molecular weight PAHs (LMW PAHs) that have two or three aromatic rings (molecular weight from 152 to 178g/mol) are emitted in the gaseous phase, while high molecular weight PAHs (HMW PAHs), molecular weight ranging from 228 to 278g/mol, with five or more rings, are emitted in the particulate phase, (ATSDR, 1995).
In the atmosphere, PAHs can undergo photo-degradation and react with other pollutants, such as sulfur dioxide, nitrogen oxides, and ozone. Due to widespread sources and persistent characteristics, PAHs disperse through atmospheric transport and exist almost everywhere. There are hundreds of PAH compounds in the environment but in practice PAH analysis is restricted to the determination of six (6) to sixteen (16) compounds. Human beings are exposed to PAH mixtures in gaseous or particulate phases in ambient air.
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The emphasis in this work is to determine the level of polycyclic aromatic hydrocarbons (PAHs) in fresh water fish dried under different drying agents. After the drying an average 78% body weight of the fishes were lost as water during the various regimes used in drying the fish samples.
PAHs were detected in the river water sample from Otuocha in Anambra State. The concentration of these PAHs is well above the US EPA maximum contaminant level (0.1-0.4 µg/ml) in water and appeared consistently throughout the period of the work indicating that the source of contamination was the water or sediment. The increased total PAHs content of the fresh fish sample (the control) could have been due to bioaccumulation in the fishes from the river. This level is below the maximum permissible level of 10µg/kg for total PAHs, but should be checked immediately since it could also rise to dangerous proportions and affect the health of the fishes and its consumers. The review of Katarina, (2011) reports that the concentration of PAHs found in fish and shellfish are expected to be much higher than in the environment from which they were taken thus confirming the above difference in total PAH concentration. Chrysene detected in the fresh fish but not in the river suggest there could be another source or that the fishes could have migrated from any nearby water body containing chrysene.
The Sun and Oven drying methods are the two non-smoking regimes used in this work. The total concentration in the sun dried fish sample was higher than that of the fresh fish sample (positive control) thus suggesting that the difference in PAH concentration could have come from the environment where the fishes were sundried. The oven dried fish samples had more PAHs than the fresh fish sample (control) possibly due to the water lost during the use of the oven which could have concentrated the PAHs in the fish relative to the weight (dry weight). Therefore since more intense heat was involved in the oven, more PAHs were present. This confirms the work of Lu et al., (2009) which reported that PAH emissions increased with increasing temperature from 200 to 7000c. The above two (2) regimes has more total PAHs concentrations than the control (fresh fish) which is in line with the work of Agerstad and Skog (2005) which reported that cooking and food processing at high temperature have been shown to generate various kinds of genotoxic substances, or cooking toxicants, including PAHs. Naphthalene and Benzo(a)pyrene detected in the sundried fish but was absent in the control sample could have come from the air where the fishes were sundried. This confirms that certain PAHs especially the low molecular weight PAHs are air-borne and that PAHs can be present in both particulate and gaseous phases, depending on their volatility.
The charcoal and firewood are the most ancient and prevalent methods of both cooking and drying foods in the African traditional setting. They involve the use of smoke from the charcoal and firewood to cook and dry the foods. In this work the charcoal and firewood are from the local hardwood called oil bean tree (Pentaclethra macrophylla). Pentaclethra macrophylla wood is a multipurpose tree from Africa with potential for agroforestry in the tropics. It is highly suitable for fuel wood and charcoal making (Ladipo et al., 1993). The total PAHs concentration from the
charcoal dried fish samples are much lower than that of the firewood dried fish samples. Thus suggesting that the smoke from the firewood has much more PAH components than that of charcoal. This confirms the report of Peter et al., (2003) that plants can absorb PAHs through their roots and translocate them to other plant parts. These are released onto food as they are burnt in the fire. The charcoal having undergone burning may have lost most of the PAHs originally in it, thus the difference in PAH concentration between the two methods. From the result two (2) PAH components were detected from the charcoal dried fish sample whereas seven (7) were detected from the firewood dried sample. This could only be from the wood smoke which has more PAH component than the smoke from charcoal. To further confirm this the work of Silva et al., (2011) showed that smoked fish samples processed by charcoal gave the lowest level of Total PAHs, followed by firewood method, while the sawdust method gave the highest level of total PAHs in the smoked fishes.
The act of augmenting fire is an age long habit in Africa and is seen in the use of various chaffs (e.g Palm kernel chaffs, coconut and rice huscs and so on) and other light materials (paper, sawdust, cellophone and plastics) to ignite fire especially during rainy seasons when wood or charcoal is wet or damp. The use of 20g of polythene material (pure water sachets) to augment the charcoal and firewood used in drying the fish samples in this work significantly increased the total PAH concentrations and the Total carcinogenic PAH concentrations. These significant increases could only be due to the augmentations with polythene materials during the drying regimes. There were not only increases in the individual PAHs as a result of the augmentation with polythene but the introduction of other PAHs onto the fish samples which could only have come from the polythene materials. The effect of augmentation as seen from the results is to generally increase the concentrations of Total PAHs in the fish sample. Some of the PAHs increased or introduced by argumentation with polythene (or tire and plastics) are classified by US EPA as probable human carcinogens (Benzoanthracene, Benzo(a)pyrene, Benzo(k)fluoranthene, ideno(1,2,3-cd)pyrene). This unwholesome practice is widespread as it is not only limited to fishes but can also be seen practiced by food vendors who use polythene and so on to augment firewood or charcoal while roasting corn, yams, plantain or meat (suya) that we consume daily. Added to the above route of exposure which is by ingestion are other routes such as inhalation and dermal contacts which some workers (mechanics, printers, carpenters, farmers, roofers, aluminum workers and so on) are daily exposed to. These long term (chronic) exposure to PAHs may lead to decreased immune function, skin inflammations, cataracts, kidney and liver damage, breathing problems and lung function abnormalities in these individuals. Though the human body (liver, kidney and lungs) by metabolism renders PAHs more water soluble and removes them via the bile and urine, accumulation of PAHs in the body (adipose tissue) could lead to biological effective dose that could cause pathogenic changes (carcinogenicity, genotoxicity and so on) in the individuals.
Based on the results from the different drying regimes used in this study, the safest method of drying fish is the Oven method. But due to cost and maintenance, the Oven may not be affordable for the average African home. Thus the charcoal method because it is next in safety is recommended and moreso it is cheap and affordable. The act of augmentation of charcoal or firewood smoke with polythene or plastic materials should be discouraged out rightly since from the results obtained in this work, these PAHs could build-up to very dangerous proportions (above the maximum permissible level of 10 and 1µg/kg for total PAHS and BaP) in the human body.
Polycyclic aromatic hydrocarbon (PAH) components detected in Otuocha river, though of low concentration, indicate a regular source of pollution entering into the river which if not stopped immediately could increase to dangerous proportions especially in the fishes and this could affect the people consuming these fishes from the river.
For the drying regimes, in which the levels of PAHs were significantly higher than that of sun-dried, it can be concluded that the excessive PAHs in the body of the dried fish were from the “burning” or drying agents. More significantly are the observed very high increase in PAHs when drying was augmented with polythene, an agent known to be a high source of PAHs when incinerated. These proportions may not only lead to various forms of cancerous growths but could affect the eyes (irritation and photosensitivity), respiratory system (Bronchitis), Gastrointestinal system (Leukoplakia), Hematopoietic system (Leukemia) and hematuria in the Genitourinary system. Consumers of dried fish should therefore beware of the dried fish they purchase from the local market.
Further research is indeed needful regarding:
- The mutagenic and carcinogenic effects from chronic exposure to PAHs and metabolites.
- Proper classification of the PAH compounds which are pathogenic and those which are not.
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