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Over the past 120 years, urban growth has been reaching extremely high rates worldwide. Human interaction with the ecosystem includes consumptive and nonconsumptive activities. The external supply of organic matter causes one of the most severe impacts on coastal marine environments. Montevideo City is currently suffering from the same environmental problems as other capital cities in the world, and its adjacent coastal zone has been influenced by anthropogenic alterations during the past 150 years. By integrating abiotic and biotic data, and using different statistical and ecological approaches, the coastal area of Uruguay close to Montevideo City has been classified into four zones with different environmental quality and degree of anthropogenic perturbation. In this area, several environmental problems and their impacts on economic productivity, human, and ecosystem health are the outcome of political and socioeconomical factors. Therefore, governmental authorities need to follow the concept of sustainable use and development, to preserve and optimize the ecological quality of natural resources, and to ensure the availability of this coastal ecosystem to future generations. Solutions to the conflictive uses of environment should be laid down on a solid scientific base to establish priorities and make the best decisions for its management and conservation.

The Rio de la Plata drains waters of the second largest basin of South America. The coast of Uruguay is located in a high dynamic area, where the interactions between the Rio de la Plata and the Atlantic Ocean produce an important patterns of natural variability. Alongside this, the area is under growing local and regional human pressure. The Uruguayan coast is affected directly and indirectly by activities developed in the drainage basin. La Plata Basin is densely populated and heavily industrialized with significant pollution. The Parana and Uruguay Rivers and their tributaries contribute xenobiotics and nutrients, especially during the ENSO phases, when important discharges of freshwater affect the whole coast. Unsurprisingly, the most impacted region is near Montevideo, while, in general, the pollution and/or impact level in the small estuaries along the Rio de la Plata coastline is slightly lower. Although available environmental information in the Uruguayan coastal zone has improved during recent decades, it is still restricted to isolated areas and to some aspects of aquatic ecosystems only. The development and implementation of integrative baseline studies on these topics are highly relevant, in order to contribute to the conservation of these ecosystems in Uruguay.

As part of the first environmental assessment within Montevideo Harbour, in summer and winter of 1998, sediments samples were collected at eight locations to determine the spatial distribution of anthropogenic pollutants. Muddy sediments with high organic matter content dominate the study area. Heavy metal levels indicated that sediments were highly polluted with Zn (overall mean: 312±102 μg g−1 dry sediment), Pb (85±31), Cu (89±25), Cr (162±62), and Hg (0.63±0.3) and moderately with Ni (30±2) and Ag (1.2±0.4). Depending on location and season, aliphatic hydrocarbons reached from 21 to 120 μg g−1, while the unresolved complex mixture represented up to 76% of the total aliphatic fraction. Total PAH concentrations ranged from 1.56 to 90.44 μg g−1; except at one location, petroleum derivatives were identified as main local source. The results pointed out that almost all the harbour area presented some substances that can cause adverse biological effects, especially in the inner region where all metals are above PEL levels. Principal components analysis confirmed that the inner harbour region is most severely affected by the pollutants and it was possible to differentiate three regions according to their environmental quality. Keywords: Environmental assessment, PAHs, Heavy metals, Coastal contamination, Rı́o de la Plata estuary