Comparison of the metal concentrations in muscle and liver tissues of fishes from the Erren River, Southwestern Taiwan, after the restoration in 2000

Metal concentrations in the muscle and liver tissues of fishes from the Erren River in southwestern Taiwan were analyzed to evaluate the pollution status after the completion of the restoration plan in 2000. It was the first time the tissue concentrations of 4 important elements, i.e. Fe, Mn, As and Hg, were reported in fishes from this area. Samples were collected in January 2002 at the junction of the Erren River and the Sanyegong River, the most polluted section of the river. Five fish species, Megalops cyprinoids (Indo-Pacific tarpon), Chanos chanos (milkfish), Liza macrolepis (large-scaled mullet), Mugil cephalus (striped mullet) and Orechromis sp. (tilapia) were collected. A total of 91 fishes were dissected and the muscle and liver tissues taken for analysis of seven metals, Fe, Zn, Cu, Mn, As, Hg and Cd, on a wet weight basis (mg/kg). Among them, Fe and Zn were the highest, followed by Cu, Mn and As, while the Hg and Cd concentrations were the lowest. Except for As and Hg, which showed higher concentrations in the muscle tissues than in the livers, the remaining elements showed higher concentrations in livers. Significant species differences were found in all elements and tissues. The highest concentrations of Fe, Zn, Cu and Mn in muscles were found in tilapia (4.04), striped mullet (4.38), large-scaled mullet (0.20) and milkfish (0.534), respectively. The highest concentrations of As and Hg were found in striped mullet (1.59) and Indo-Pacific tarpon (0.081), respectively. The highest concentrations of Fe (3122), Hg (0.045) and Cd (0.123) were found in livers of large-scaled mullet, while striped mullet had the highest concentration of Zn (77.6), Cu (78.2) and As (2.39). The level of Mn in tilapia was 1.32 mg/kg. The Zn, Cu and Cd concentrations of the muscles and livers were mostly 7-50% lower than the levels reported on the same species of the same tissue before the restoration indicating the improvement on the metal pollution status. The heavy metal concentrations in this area were similar to various uncontaminated areas around Taiwan and all were within the food standard levels of the FDA and NHMRC.