Observations on metal concentrations in commercial landings of two species of tilapia (Oreochromis mossambicus and Oreochromis niloticus) from reservoirs in six river basins in Sri Lanka

Samples of the muscle of two species of tilapia (Oreochromis mossambicus and O. niloticus; 17-20 cm length) were obtained from at least one reservoir in each of the six river basins (Aruvi Aru, Kala Oya, Kirindi Oya, Ma Oya, Mahaweli, and Walawe Ganga catchments) in Sri Lanka. The metals Ca, Cu, Fe, K, Mg, Mn, Na, and Zn were consistently detected in the muscle tissue. Overall, there were few differences in the concentration of metals between the two species of fish, although there were also some statistically significant differences (p &lt; 0.05) in the concentrations of some metals in fish obtained from some of the reservoirs. Aruvi Aru stands out as a river basin in which the two fish species have significantly lower concentration of metals when compared to other river basins. The concentration of the metals studied were below WHO and FSANZ guideline values for fish, suggesting that the consumption of the metals found in tilapia from these reservoirs poses little risk to human health. <br /

A PRELIMINARY STUDY ON THE PRESENCE OF-HEAVY METALS IN AQUATIC PLANTS FROM A FRESHWATER WETLAND AT KELANIYA

Aquatic plants are known for uptake of heavy metals from water and sediments. Thisvery feature qualifies these plants as wastewater treatment agents. Capacity to absorb,heavy metals however, varies among plants. Three aquatic plants, Pistia stratiotes(floating), Limnocharis jlava (rooted) and Ipomoea aqualica (rooted plant with floatingrunners) from lriyawetiya wetland at Kelaniya were tested for the presence of copper,zinc, lead, nickel, cadmium, manganese, tin and chromium in the plant tissues.P. stratiotes, L. jlava and 1. aquatica plants were collected from the inlets, outlets and themiddle part of the wetland and above heavy metal concentrations in acid-digested rootand shoot samples were measured separately using atomic absorption spectrophotometer.Tin (Sn) is the heavy metal that was found in relatively large quantities in all threeplants, and Ipomoea aquatica recorded the highest content of Sn. Next highestoccurrence was observed with Cr and the contents were highest in the rooted plant, L.jlava, indicating that the sediment loads of Cr may be greater than the load in the watercolumn. All other heavy metals occur in relatively low concentrations in all three plantspecies, indicating partly the lower loading rates of these heavy metals in Iriyawetiyawetland.Occurrence of heavy metals in the roots was generally higher than that of the shoots.Greater Cr concentrations were recorded from roots of floating species, P. stratiotes andI. aquatica than the rooted species, L. flava.Except for cadmium (in P. slratioles) and manganese (in L. flava and 1. aquaticay;content of all the other heavy metals that occur in the plants that have been collectedfrom the inlets was greater than that of those collected from the outlet, indicating thewetlands' capacity to remove heavy metals from water and sediment through plantuptake.

Trace metal concentrations in Nile Tilapia (Oreochromis Niloticus) in three catchments, Sri Lanka

Samples of the muscle and liver of the Nile tilapia (Oreochromis niloticus) were obtained from a single reservoir in each of three Sri Lankan catchments (Kaudulla, Rajanganaya, and Udawalawe reservoirs in the Mahaweli, Kala Oya, and Walawe Ganga river basins, respectively) in 2002. The concentrations of 12 elements were consistently detected in the tilapia muscle and liver (Ca, Cd, Cu, Fe, Hg, K, Mg, Mn, Na, P, Sr and Zn). However, a three factorial principal components analysis suggested that there were no differences in the metal profiles (range of elements and concentration) of the fish obtained from any of the three reservoirs, although the chemistries of each tissue (muscle and liver) were different. Metal concentrations were below WHO and Food Standards Australia and New Zealand guideline values, and substantial quantities of tilapia would need to be consumed each week on a regular basis to exceed intake limits (e.g. more than 1.5 kg to exceed intake lits for Cu), suggesting consumption of tilapia from these reservoirs poses little risk to human health.<br /