Heavy Metal Pollution of Fish and Fish Oils from some Coastal and Inland Waters of Ghana

Abstract

While fish and fish oil promote good health, increasing environmental pollution may introduce heavy metals into the fish which may render them injurious to health. Nine commonly consumed fish samples in Ghana, five from marine sources and four from freshwater sources were analyzed for their heavy metal contents. The heavy metals are Cadmium (Cd), Lead (Pb), Mercury (Hg), Arsenic (As) and Selenium (Se). The fish samples are Herring (Sardinella species), Redfish (Red mullet), Mackerel species, Tuna species and Anchovies all from coastal waters and Tilapia (Oreochromis niloticus'). Blolo (Chrvsichthvs nigrodiaitatus). Catfish (Heteroblancus species) and One- mouth- thousand (Serrathrissa leonensis) from fresh waters. Oil extracted from four fish samples were also analysed for their heavy metal contents. The fishes were selected from four environmental zones designated heavy industrial (James Town - Accra and Tema), light industrial (Apam and Elmina), river/lake (Weija and Kpong) and mining environment (Obuasi and Dunkwa). For each environmental zone, two locations were chosen based on industrial and/or fishing activities in the area. The analysis was done on the head, bone, flesh, whole fish and scales for those who have it in order to ascertain the distribution of the metal in the fish body. The metal contents were analyzed with Atomic Absorption Spectrophotometer (AAS) generally the bone had the highest content of the heavy metals. It was followed by the head, the scale, and then the flesh. The total metal levels in the whole fish was higher than that in the flesh alone. Analysis of variance showed significant difference (p= 0.03) in the levels of each heavy metal in the fish parts. There was a significant correlation (r=0.67 and p=0.01), between the Cadmium levels in the flesh and bone. The rest of the metals did not show any significant correlation in their distribution in the flesh and the bone. Mercury levels occurred as the highest heavy metal in all parts of the fish followed by Arsenic and Lead whose levels were close. Cadmium levels were lowest in the fish tissues studied. The ranges of the metal in the body of all the fish samples are as follows; Mercury 25 - 300ug/g dried weight of fish, Lead 2.44 36.6ug/g, Arsenic 3.26 - 36.96ug/g and Cadmium 0.3 2.8ug/g. Selenium analyzed in some of the fishes had levels slightly higher than Arsenic and lead in the flesh. Selenium levels ranged between 8.0 – 70ug/g. The heavy metal contents of the fish oils were as follows; Cadmium ranged from 0.34ug/g in the Mackerel oil from Tema to 0.70ug/g in Herring oil from James Town. Lead was 6.12ug/g in Tuna from Tema to 35.56 ug/g in Mackerel, also from Tema. Mercury ranged from 25ug/g in Tuna and Tilapia from Tema and Weija respectively to 75ug/g in Herring from James Town. Arsenic ranged from traces in Tilapia and Tuna to 28.6ug/g in Mackerel from Tema. Water sources of the fish were also analyzed for their heavy metal contents. The coastal water samples had higher metal levels than the fresh water samples. For the coastal water samples heavy metal ranges were: Cd 0.6 - 0.13ppm, Pd 0.17 - 0.36ppm, Hg 8.87 - 10.8ppm, As <1.0 - 2.3ppm. For the fresh waters the metal ranges were: Cd 0.02 - 0.7ppm, Pb 0.08 - 0.12ppm, Hg 2.25 - 5.6ppm, and Arsenic; only traces. The heavy metal levels in the fishes caught from heavy industrial coastal waters were slightly higher than those from light industrial coastal waters but only Arsenic and Mercury showed a significant difference (p<0.05). The content of lead in Tilapia and Blolo from non-mining areas (RL) were significantly different (p<0.05) from those from the mining environment. Analysis of variance showed no significant deference (p>0.05) between the heavy metal levels in the oil, flesh and water except for Cadmium levels. There was no significant correlation (p>0.05) between the heavy metals in the flesh and water sample, water and oil and also the oil and flesh. Comparison of the levels of the metal in lOOg of flesh of each fish to safe margins established by FAOAVHO revealed that the levels in the fish were higher than the safe margins. The only exception is Cadmium, whose safe levels may be exceeded after an intake of lOOOg of the flesh of the fish. The research revealed that no matter the source of the fish the level of the heavy metal in the fish is high enough to warrant alarm and action to reduce the level of pollution in the waters and the fish.