Base-metals and organic content in stream sediments in the vicinity of a landfill

Landfill facilities are essential to modern societies as repositories for municipal solid wastes (MSW). However, irrespective of the regulations necessary to their construction there is always a certain risk of environmental impact. For this reason monitoring should be essential to their operation. In the present work, the environmental impact of such a landfill is studied, whose operation has been running for only 3 a. The approach used was to sample a series of stream sediments along two contaminated run-off water paths. These sediments were chemically analysed, and their mineralogy was also studied. Their most important feature is the existence of some contamination in Cu, Zn, and Pb above background levels in the first 200 m in the direction of water flow, whose concentration gradually decreases until background levels are reached. Although some artificial alloys and sulphides (sphalerite) were shown to be present, they could not account for the analysed concentrations, and cannot explain the negative gradient concentration by themselves. Sequential metal extraction methods together with solid phase extraction for the isolation of organic content, showed that metals adsorbed on the sediments are mostly associated with organic compounds. Although monocarboxylic organic acids were among the most important organic compounds present both in the contaminated waters and sediments, there is no clear correlation between these and base metal concentrations in the sediments. A stronger correlation exists if the total concentration of organic compounds is considered, which suggests that base metals can be easily partitioned into the sediments by the rapid adsorption onto their surfaces by organic compounds near the pollution source. The organic content identified decreases down stream as do base metal concentrations. This can be explained by the formation of complexes with organic acids as is extensively reported in natural and laboratory systems. The overall results point to the limited capacity for pollutant retention in this system, and suggest that in case of serious failure the contaminated plumes are likely to disperse rapidly into the environment.