Risk assessment of Butrinti lagoon: spatial and temporal distribution of heavy metals in different pools

Heavy metals enter in lagoons from pedo-geological background as well as from man-made sources through several pathways. Heavy metals released into the water are eventually accumulated in the sediments and in the lagoon’s aquatic organisms, especially in mussels, which act as recorders of heavy metals pollution event. This study aims to contribute in (i) quantifying the origin and degree of heavy metals pollution in the sediments, water lagoon and mussels, (ii) exploring the concentrations of heavy metals in mussels widely cultivated in this Lagoon. The water samples were taken at the surface and bottom of the lake between May 2010 and January 2011. The results showed that the concentrations of Cd (2.9 mg kg-1) were higher in soils formed over lime in the north of the Lagoon. Hg was nearly 234.89 μg kg-1, which is also considered of medium values for these types of soil. The maximum values of Cr content were 237.38 mg kg-1, or much higher than the average of soils over lime in Albania. The highest concentrations in sediment samples (mg kg-1) for Pb (346), Cd (4.14), Cr (171.9) and Hg (36.4) were found in the eastern and southern area of the Lagoon where there have been intensive agricultural activities. The results showed that the concentration (μg L-1) of Pb (10.78) at the lake bottom in May was higher than at the surface of water but it was generally low when compared to the WHO standard. On the other hand Cr was high with mean values of 56.6 μg L-1 at the bottom of the lake water in August. The data also indicated that mussels’samples which was collected in May in the southern area of the Lagoon showed higher levels (mg kg-1) of Pb (0.49) and Hg (0.14). However, the highest concentrations of Cd (0.36), Cr (0.50) were recorded in August. There is a correlation between the heavy metals and their sources. We hold that some precautions should be taken against the heavy metal pollution around Butrinti Lake considering the ecological, agricultural and economic importance of this area.