The ecological complexity of the Thai-Laos Mekong River: II. Metals and polyaromatic hydrocarbons (PAHs) monitoring, modelling and environmental fate

The Mekong is an essential source of water and protein for the denizens of Thai Laos countries. It is hypothesized that pollution may be adversely affecting the water and sediment quality, which threatens the short and long-term use of this major river system. This directly impacts on the health and population of the aquatic life and ultimately human health and the economy for both countries is affected. The quality of the river can be assessed from various chemical and physical parameters, such as PAHs and metals content of both the water and the sediment. The introduction of Environmental Quality Standards (EQS) allows comparison of the values obtained with the guidelines. Furthermore the modelling program EPISUITE was used to determine the environmental partitioning of pollutants within the different environmental compartments. Using the data produced for PAHs and metals the experimental model was compared to the default model. This involved experimentally measuring the log Koc forMekong sediments and from this determining the log Kow. High availability in sediment of pollutants may lead to greater biomagnification in bethnic fish, which may then be hazardous for human consumption even if it is safe for the species that is accumulating pollutants. The potential for this is shown by the calculated accumulation in biota Cbio values exceeding both the Chronic value (ChrV) and Lethal Concentration 50 (LC50) for fish in the Mekong River. When compared to the EQS guidelines the amount of some PAHs, cadmium and lead in sediment were above the lowest effect level but below the severe effect level.